This PDF file contains the front matter associated with SPIE Proceedings Volume 8673, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Combining advanced sensor technologies, with optimised data acquisition and diagnostic and prognostic capability, structural health monitoring (SHM) systems provide real-time assessment of the integrity of bridges, buildings, aircraft, wind turbines, oil pipelines and ships, leading to improved safety and reliability and reduced inspection and maintenance costs. The implementation of power harvesting, using energy scavenged from ambient sources such as thermal gradients and sources of vibration in conjunction with wireless transmission enables truly autonomous systems, reducing the need for batteries and associated maintenance in often inaccessible locations, alongside bulky and expensive wiring looms. The design and implementation of such a system however presents numerous challenges. A suitable energy source or multiple sources capable of meeting the power requirements of the system, over the entire monitoring period, in a location close to the sensor must be identified. Efficient power management techniques must be used to condition the power and deliver it, as required, to enable appropriate measurements to be taken. Energy storage may be necessary, to match a continuously changing supply and demand for a range of different monitoring states including sleep, record and transmit. An appropriate monitoring technique, capable of detecting, locating and characterising damage and delivering reliable information, whilst minimising power consumption, must be selected. Finally a wireless protocol capable of transmitting the levels of information generated at the rate needed in the required operating environment must be chosen. This paper considers solutions to some of these challenges, and in particular examines SHM in the context of the aircraft environment.

Biological olfaction outperforms chemical instrumentation in specificity, response time, detection limit, coding capacity, time stability, robustness, size, power consumption, and portability. This biological function provides outstanding performance due, to a large extent, to the unique architecture of the olfactory pathway, which combines a high degree of redundancy, an efficient combinatorial coding along with unmatched chemical information processing mechanisms. The last decade has witnessed important advances in the understanding of the computational primitives underlying the functioning of the olfactory system. EU Funded Project NEUROCHEM (Bio-ICT-FET- 216916) has developed novel computing paradigms and biologically motivated artefacts for chemical sensing taking inspiration from the biological olfactory pathway. To demonstrate this approach, a biomimetic demonstrator has been built featuring a large scale sensor array (65K elements) in conducting polymer technology mimicking the olfactory receptor neuron layer, and abstracted biomimetic algorithms have been implemented in an embedded system that interfaces the chemical sensors. The embedded system integrates computational models of the main anatomic building blocks in the olfactory pathway: the olfactory bulb, and olfactory cortex in vertebrates (alternatively, antennal lobe and mushroom bodies in the insect). For implementation in the embedded processor an abstraction phase has been carried out in which their processing capabilities are captured by algorithmic solutions. Finally, the algorithmic models are tested with an odour robot with navigation capabilities in mixed chemical plumes

The objective of this work is to develop MEMS vibration energy harvesters for tire pressure monitoring systems (TPMS), they can be located on the rim or on the inner-liner of the car tire. Nowadays TPMS modules are powered by batteries with a limited lifetime. A large effort is ongoing to replace batteries with small and long lasting power sources like energy harvesters [1]. The operation principle of vibration harvesters is mechanical resonance of a seismic mass, where mechanical energy is converted into electrical energy. In general, vibration energy harvesters are of specific interest for machine environments where random noise or repetitive shock vibrations are present. In this work we present the results for MEMS based vibration energy harvesting for applying on the rim or inner-liner. The vibrations on the rim correspond to random noise. A vibration energy harvester can be described as an under damped mass-spring system acting like a mechanical band-pass filter, and will resonate at its natural frequency [2]. At 0.01 g²/Hz noise amplitude the average power can reach the level that is required to power a simple wireless sensor node, approximately 10 μW [3]. The dominant vibrations on the inner-liner consist mainly of repetitive high amplitude shocks. With a shock, the seismic mass is displaced, after which the mass will “ring-down” at its natural resonance frequency. During the ring-down period, part of the mechanical energy is harvested. On the inner-liner of the tire repetitive (one per rotation) high amplitude (few hundred g) shocks occur. The harvester enables an average power of a few tens of μW [4], sufficient to power a more sophisticated wireless sensor node that can measure additional tire-parameters besides pressure. In this work we characterized MEMS vibration energy harvesters for noise and shock excitation. We validated their potential for TPMS modules by measurements and simulation.

Present work shows recent progresses in thin film-based flexible and wearable thermoelectric generator (TEG), finalized to support energy scavenging and local storage for low consumption electronics in Ambient Assisted Living (AAL) applications and buildings integration. The proposed TEG is able to recover energy from heat dispersed into the environment converting a thermal gradient to an effective electrical energy available to power ultra-low consumption devices. A low cost fabrication process based on planar thin-film technology was optimized to scale down the TEG dimensions to micrometer range. The prototype integrates 2778 thermocouples of sputtered Sb₂Te₃ and Bi₂Te₃ thin films (1 μm thick) on an area of 25 cm². The electrical properties of thermoelectric materials were investigated by Van der Pauw measurements. Transfer Length Method (TLM) analysis was performed on three different multi-layer contact schemes in order to select the best solution to use for the definition of the contact pads realized on each section of the thermoelectric array configuration to allow electrical testing of single production areas. Kapton polyimide film was used as flexible substrate in order to add comfortable lightweight and better wearability to the device. The realized TEG is able to autonomously recover the thermal gradient useful to thermoelectric generation thanks to an appropriate package designed and optimized by a thermal analysis based on finite element method (FEM). The proposed package solution consists in coupling the module realized onto Kapton foil to a PDMS layer opportunely molded to thermally insulate TEG cold junctions and enhance the thermal gradient useful for the energy scavenging. Simulations results were compared to experimental tests performed by a thermal infrared camera, in order to evaluate the real performance of the designed package. First tests conducted on the realized TEG indicate that the prototype is able to recover about 5°C between hot and cold thermocouples junctions with a thermal difference of 17°C initially available between body skin and environment, generating about 2 V of open circuit output voltage.

This paper describes an approach for efficiently storing the energy harvested from a thermoelectric module for powering autonomous wireless sensor nodes for aeronautical health monitoring applications. A representative temperature difference was created across a thermo electric generator (TEG) by attaching a thermal mass and a cavity containing a phase change material to one side, and a heat source (to represent the aircraft fuselage) to the other. Batteries and supercapacitors are popular choices of storage device, but neither represents the ideal solution; supercapacitors have a lower energy density than batteries and batteries have lower power density than supercapacitors. When using only a battery for storage, the runtime of a typical sensor node is typically reduced by internal impedance, high resistance and other internal losses. Supercapacitors may overcome some of these problems, but generally do not provide sufficient long-term energy to allow advanced health monitoring applications to operate over extended periods. A hybrid energy storage unit can provide both energy and power density to the wireless sensor node simultaneously. Techniques such as acoustic-ultrasonic, acoustic-emission, strain, crack wire sensor and window wireless shading require storage approaches that can provide immediate energy on demand, usually in short, high intensity bursts, and that can be sustained over long periods of time. This application requirement is considered as a significant constraint when working with battery-only and supercapacitor-only solutions and they should be able to store up-to 40-50J of energy.

Recent developments on the use of the piezoelectric effect in ZnO nanorod-based p-n junctions for energy harvesting applications are presented. We describe a hybrid p-n nanostructured ZnO energy device combined with the semiconducting polymer poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) to produce a kinetic energy harvesting. The load resistance-dependent power output from this p-n junction device is compared with the more common ZnO-PMMA device, which we make from ZnO nanorods manufactured using an identical process. It is shown that the PMMA device generates an open-circuit voltage of 150mV with a maximum power of 0.24μW/cm² giving 0.03nJ of available energy when on a load resistance of 324 kΩ. The PEDOT:PSS device generates significantly more power, 28.9μW/cm², when it is matched to a 1.6 kΩ load resistance. The energy output of the PEDOT:PSS device is 2.22nJ. Our results demonstrate the importance of measuring energy delivery to an electrical load to fully understand the output capability of these devices. By analysis of the time-dependent output of the devices the energy can be calculated giving a reasonable estimation as to the available energy and power in any given system.

This article describes the research work related to the ceramic joint quality evaluation, the thermal-structural analysis of ceramic joining and ceramic bond design and implementation. The role of ceramic material in electronics industry and motivation for joining ceramics is described in the introduction. Important directions for future research are summarized, with emphasis on the statistical determination of poor joint, and how the modification of a joint technology and process setting affects results and parameters that have been achieved. Main requirements for evaluating quality of joints are described in this paper together with the results of simulations of real ceramic joint application which is ceramic pressure sensor. During manufacturing process of this pressure sensor is one of the most critical part cooling process which was subjected to detail analysis due to number of failures and parasitic deformations revealed after removing assembled and joint pressure sensor from the oven. Our experimental results were evaluated by using the t-test before and after process cooling modification to verify their correctness.

The impact of process parameters on final bonding layer quality was investigated for Transient Liquid Phase (TLP) wafer-level bonding based on the Cu-Sn system. Subjects of this investigation were bonding temperature profile, bonding time and contact pressure as well as the choice of metal deposition method and the ratio of deposited metal layer thicknesses. Typical failure modes in Inter-Metallic Compound (IMC) growth for the mentioned process and design parameters were identified and subjected to qualitative and quantitative analysis. The possibilities to avoid abovementioned failures are indicated based on experimental results.

The ongoing miniaturization of micro-opto-electro-mechanical-systems requires compact multifunctional packaging solutions like offered by the three-dimensional MID (molded interconnect device) technology which combines integrated electronic circuitry and mechanical support structures directly into one compact housing. Due to the inherently large thermal resistance of thermoplastic MID substrate materials, temperature-sensitive applications require carefully arranged thermal vias in order to reduce the thermal resistance of the packaging effectively. This paper presents the analysis and optimization of various laser-drilled thermal via design parameters of MIDs including hole diameter, pitch, plating thickness of the Cu/Ni/Au metallization layers as well as the void level of the filling material inside the vias.

In the last decade Micro-Electro-Mechanical Systems (MEMS) technology experienced a significant development in various fields of Information and Communication Technology (ICT). In particular MEMS for Radio Frequency (RF) applications have emerged as a remarkable solution in order to fabricate components with outstanding performances. The encapsulation of such devices is a relevant aspect to be addressed in order to enable wide exploitation of RF-MEMS technology in commercial applications. A MEMS package must not only protect fragile mechanical parts but also provide the interface to the next level of the packaging hierarchy in a cost effective technology. Additionally, in RF applications the electromagnetic impact of the package has to be carefully considered. Given such a scenario, the focus of this work is the characterization of a chip capping solution for RF-MEMS devices. Such solution uses a quartz cap having an epoxy-based dry film sealing ring. Relevant issues affecting RF-MEMS devices once packaged, e.g. the mechanical strain induced by the cap and the hermeticity of the sealing ring, are worth investigating. This work focuses on the study of induced strain, as a function of different bonding parameters. Dimensional features of the sealing ring (i.e. the width), and process parameters, like temperature and pressure, have been considered. The package characterization is performed by using basic test vehicles, such as strain gauges, designed to be integrated inside the internal cavity of the package itself. Polysilicon piezoresistors are used as strain gauges, whereas aluminum resistors are used as thermometers to assess the impact of temperature changes on strain measurements. Experimental data are reported including calibration of the sensors as well as environmental measurements with and without cap. In addition measurements of the shear stress of the proposed packaging solution are also reported.

Thin film sensor systems based on hydrogenated carbon have the advantage to combine two very important characteristics. They show a piezoresistive behaviour and also a tribological stability caused by a high hardness and wear resistance. Therefore they can be applied on the surface of machine parts or used for building up universal insertable sensor systems like sensory washers. A real challenge is the deposition of a whole sensory layer system on technical components like a spindle, which have a length of 480 mm and an outer diameter of about 90 mm. The functions of the layer system directly applied in the contact zone between spindle shaft and tool holder are the measurement of the clamping force of the tool holder, the imbalance of the used tool and the process forces during machining. For this application a self-contained thin film sensor system is investigated. Directly in the spindle shaft an insulating alumina layer is deposited in a thickness of about 4 μm followed by electrode structures out of 200 nm thin chromium coating. On top of this the piezoresistive hydrogenated carbon layer in a thickness of about 1 μm is deposited, covered by a wear resistant and insulating top coating. Therefore a silicon and oxygen modified carbon layer in a thickness of about 2 μm is used. The piezoresistive sensor layer and also the top layer are part of the diamond like carbon layer family [1,2,3,4]. Another very important application is the sensory washer. The thin film sensor system, consisting out of the piezoresistive sensor layer deposited directly on the washer surface, the electrode structures out of chromium for the local detection of the load distribution in the washer system and the insulating layer as top layer out of the silicon and oxygen modified carbon layer, has a thickness in the range of 9 μm. In the latest investigations this layer system is connected with a RFID-chip for contactless data transmission.

Semiconducting cuprous (Cu₂O) and cupric oxide (CuO) have been subject to intense research efforts, mainly because of the materials' potential for photovoltaic applications and as doping material. In this work, the impact of hydrogen sulfide (H₂S) exposure on thin film samples of CuO and Cu₂O has been investigated, focusing on alterations in the optical properties. The materials composition was verified using Raman spectroscopy. The samples were exposed to well-defined dosages of H₂S and the transmission and reflection characteristics in the expanded UV/Vis regime (350-1100 nm) were recorded. Cu₂O films showed an explicit increase in transmissivity for the wavelength region l = 550-900 nm, besides a general decrease in reflectivity of all samples within the considered spectral range. Optical band gaps were determined using Tauc's plotting, revealing a shift in the slope of a² of CuO after gas exposure. The observed effects can be exploited as sensing effect, which was examined in a thin film total-internal-reflection (TIR) set-up to transiently monitor surface-gas interactions, yielding reproducible changes in response to 20 min exposure to5 ppm H₂S.

Nanocomposite films comprised of either Pt-Rh/ZrO₂ or Pt-Rh/HfO₂ materials were co-deposited using multiple e-beam evaporation sources onto langasite (La₃Ga₅SiO₁₄) substrates, both as blanket films and patterned interdigital transducer electrodes for surface acoustic wave (SAW) sensor devices. The films and devices were tested after different thermal treatments in a tube furnace up to 1200°C. X-ray diffraction and electron microscopy results indicate that Pt-Rh/HfO₂ films are stabilized by the formation of monoclinic HfO₂ precipitates after high temperature exposure, which act as pinning sites to retard grain growth and prevent agglomeration of the conductive cubic Pt-Rh phase. The Pt-Rh/ZrO₂ films were found to be slightly less stable, and contain both tetragonal and monoclinic ZrO₂ precipitates that also help prevent Pt-Rh agglomeration. Film conductivities were measured versus temperature for Pt-Rh/HfO₂ films on a variety of substrates, and it was concluded that La and/or Ga diffusion from the langasite substrate into the nanocomposite films is detrimental to film stability. An Al₂O₃ diffusion barrier grown on langasite using atomic layer deposition (ALD) was found to be effective in minimizing interdiffusion between the nanocomposite film and the langasite crystal.

Magnetoelectric (ME) thin film composites are attracting a continually increasing interest due to their unique features and potential applications in multifunctional microdevices and integrated units such as sensors, actuators and energy harvesting modules. By combining piezoelectric and highly magnetostrictive thin films, the potentialities of these materials increase. In this paper we report the fabrication of SmFe₂ and PZT thin films and the investigation of their properties. First of all, a ~ 400 nm thin SmFe film was deposited on top of Si/SiO₂ substrate by magnetron sputter deposition. Afterwards, a 140 nm Pt bottom electrode was sputtered on top of the SmFe film forming a bottom electrode. Spin coating was employed for the deposition of the 150 nm thin PZT layer. A PZT solution with 10 %Pb excess was utilized for this fabrication step. Finally, circular Pt top electrodes were sputtered as top electrodes. This paper focuses on the microstructure of the individual films characterized by X-Ray diffractometer (XRD) and scanning electron microscopy (SEM). A piezoelectric evaluation system, aixPES, with TF2000E analyzer component was used for the electric hysteresis measurements of PZT thin films and a vibrating sample magnetometer (VSM) was employed for the magnetic characterization of the SmFe. The developed thin films and the fabricated double layer SmFe-PZT exhibit both good ferromagnetic and piezoelectric responses which predict a promising ME composite structure. The quantitative chemical composition of the samples was confirmed by energy dispersive spectroscopy (EDX).

In the last 2 years, the field of micro-electro-mechanical systems tunable vertical cavity surface-emitting lasers (MEMS-VCSELs) has seen dramatic improvements in laser tuning range and tuning speed, along with expansion into unexplored wavelength bands, enabling new applications. This paper describes the design and performance of high-speed ultra-broad tuning range 1050nm and 1310nm MEMS-VCSELs for medical imaging and spectroscopy. Key results include achievement of the first MEMS-VCSELs at 1050nm and 1310nm, with 100nm tuning demonstrated at 1050nm and 150nm tuning at shown at 1310nm. The latter result represents the widest tuning range of any MEMS-VCSEL at any wavelength. Wide tuning range has been achieved in conjunction with high-speed wavelength scanning at rates beyond 1 MHz. These advances, coupled with recent demonstrations of very long MEMS-VCSEL dynamic coherence length, have enabled advancements in both swept source optical coherence tomography (SS-OCT) and gas spectroscopy. VCSEL-based SS-OCT at 1050nm has enabled human eye imaging from the anterior eye through retinal and choroid layers using a single instrument for the first time. VCSEL-based SS-OCT at 1310nm has enabled real-time 3-D SS-OCT imaging of large tissue volumes in endoscopic settings. The long coherence length of the VCSEL has also enabled, for the first time, meter-scale SS-OCT applicable to industrial metrology. With respect to gas spectroscopy, narrow dynamic line-width has allowed accurate high-speed measurement of multiple water vapor and HF absorption lines in the 1310nm wavelength range, useful in gas thermometry of dynamic combustion engines.

The fermentation process that turns must into wine is traditionally monitored manually by enologists, with little aid from automation tools so far. This supervision requires the enologist to follow a daily routine consisting of must sampling and subsequent analysis at least twice a day during the whole fermentation span and for every single fermentation tank, which is awkward and time-consuming, especially in regions like La Mancha (Spain), where production takes place at a massive scale. In order to contribute to the automation of both the fermentation and the maceration supervision, an optoelectronic system has been developed. It was devised to record both the refractive index n and the chromatic characteristics of the fermenting must. The former, closely related to the fermentation kinetics, is obtained through measurements of a laser beam displacement; whereas the latter, which is essential for the maceration, relies on absorbance measurements in the visible spectrum. Additionally, the system measures the temperature, necessary to reference the data to 20°C. It comprises a frame that holds a laser diode, a PSD (position sensitive detector), three LEDs, six photodiodes and a temperature sensor, plus some conditioning electronics and a data acquisition board. Several fermentations have been monitored off-line with the reported system, reaching a resolution of 0.00046 RIU (refractive index unit). Data show a slight increase in n during the last stage of the fermentation, which does not have a match in the density measurements and could therefore be used as an alert to automatically detect the fermentation end.

Recently, we have realized a new position sensing device for MOEMS mirrors applicable to arbitrary trajectories, which is based on the measurement of a reflected light beam with a quadrant diode. In this work we present the characteristics of this device, showing first experimental results obtained with a test set-up, but also theoretical considerations and optical ray-tracing simulations.

At the microscale, cantilever vibrations depend not only on the microstructure’s properties and geometry but also on the properties of the surrounding medium. In fact, when a microcantilever vibrates in a fluid, the fluid offers resistance to the motion of the beam. The study of the influence of the hydrodynamic force on the microcantilever’s vibrational spectrum can be used to either (1) optimize the use of microcantilevers for chemical detection in liquid media or (2) extract the mechanical properties of the fluid. The classical method for application (1) in gas is to operate the microcantilever in the dynamic transverse bending mode for chemical detection. However, the performance of microcantilevers excited in this standard out-of-plane dynamic mode drastically decreases in viscous liquid media. When immersed in liquids, in order to limit the decrease of both the resonant frequency and the quality factor, alternative vibration modes that primarily shear the fluid (rather than involving motion normal to the fluid/beam interface) have been studied and tested: these include in-plane vibration modes (lateral bending mode and elongation mode). For application (2), the classical method to measure the rheological properties of fluids is to use a rheometer. To overcome the limitations of this classical method, an alternative method based on the use of silicon microcantilevers is presented. The method, which is based on the use of analytical equations for the hydrodynamic force, permits the measurement of the complex shear modulus of viscoelastic fluids over a wide frequency range.

In-situ monitoring of the physical properties of liquids is of great interest in the automotive industry. For example, lubricants are subject to dilution with diesel fuel as a consequence of late-injection processes, which are necessary for regenerating diesel particulate filters. This dilution can be determined by tracking the viscosity and the density of the lubricant. Here we report the test of two in-plane movement based resonators to explore their capability to monitor oil dilution with diesel and biodiesel. One of the resonators is the commercially available millimeter-sized quartz tuning fork, working at 32.7 kHz. The second resonator is a state-of-the-art micron-sized AlN-based rectangular plate, actuated in the first extensional mode in the MHz range. Electrical impedance measurements were carried out to characterize the performance of the structures in various liquid media in a wide range of viscosities. These measurements were completed with the development of low-cost electronic circuits to track the resonance frequency and the quality factor automatically, these two parameters allow to obtain the viscosity of various fluids under investigation, as in the case of dilution of lubricant SAE 15W40 and biodiesel.

In this paper, a set of flexible aeroMEMS sensor arrays for flow measurements in boundary layers is presented. The sensor principle of these anemometers is based on convective heat transfer from a hot-film into the fluid. All sensors consist of a nickel sensing element and copper tracks. The functional layers are attached either on a ready-made polyimide foil or on a spin-on polyimide layer. These variants are necessary to meet the varying requirements of measurements in different environments. Spin-on technology enables the use of very thin PI layers, being ideal for measurements in transient flows. It is a unique characteristic of the presented arrays that their total thickness can be scaled from 5 to 52 μm. This is essential, because the maximum sensor thickness has to be adapted to the various thicknesses of the boundary layers in different flow experiments. With these sensors we meet the special requirements of a wide range of fluid mechanics. For less critical flow conditions with much thicker boundary layers, thicker sensors might be sufficient and cheaper, so that ready-made foils are perfect for these applications. Since the presented sensors are flexible, they can be attached on curved aerodynamic structures without any geometric mismatches. The entire development, starting from theoretical investigations is described. Further, the micro-fabrication is explained, including all typical processes e.g. photolithography, sputtering and wet-etching. The wet-etching of the sensing element is described precisely, because the resulting final dimensions are critical for the functional characteristics.

The analysis of fluid mixtures regarding their composition is still a major challenge, e.g. for Direct Methanol Fuel Cells (DMFC) to determine the concentration of methanol in water or for Selective Catalytic Reduction (SCR) to determine the amount of urea in water. A simple measurement method is realized with a microthermal sensor that introduces a short heat pulse into the fluid under test whilst the resulting temperature increase is measured reflecting thermal parameters of the fluid. For methanol in water this principle showed an almost linear dependence of the temperature increase on the methanol content for the concentration range 0 to 20 vol%. The sensitivity was determined to S = 0.12 K/vol% for methanol in water for a heat pulse of 0.5 s duration and a heater power of 60 mW. The accuracy achieved in single pulse measurements is approximately 2 %. By integrating additional temperature sensors in front and behind the microheater the flow rate of the liquid can also be determined using thermal anemometry. Because of the physical measurement principle to determine the chemical properties of the liquid the sensor promises better long-term stability than chemical principles. At the same time the low cost sensor construction and simple signal analysis make this principle promising for use in low cost mobile applications like DMFC power supplies for laptops.

The performance of thermal conductivity vacuum gauges can be improved by a well-designed geometry. The lower measurement range limit is determined by the size of the active sensing area and the thermal conduction heat losses through the supporting structures. The upper measurement range is limited by the distance between the heated element and the cold reference plane. Silicon based MEMS-technology gives the possibility to fabricate both sensing structures with suitable areas out of low thermal conductive materials and narrow gaps in order to extend the measurement range in both directions. In this work we present a MEMS-process to fabricate high thermal resistance sensor structures. The rectangular sensitive areas are anchored by four beams and are structured out of low thermal conductive PECVD-siliconnitride films with 1 µm in thickness. The metallic heating structure is completely embedded in the SiN-layer. Both sensitive area and its support beams were released from the silicon bulk material by anisotropic underetching. In this way a free-supporting structure with a gap of 150 μm to the silicon substrate was formed. The influence of the filament geometry and temperature was systematically investigated to determine the properties of the chips as thermal conductivity vacuum gauges. The temperature of the sensitive area was held constant by a self-balancing bridge circuit and the heating power was measured by a Δ-Σ-ADC. The average solid state thermal conductivity is in the order of 10⁶WK¹. The measuring range of the most sensitive structures covers 8 orders of magnitude from 10⁵ mbar to 1000mbar.

High precision microactuators have become key elements for many applications of MEMS, for example for positioning and handling systems as well as for microfluidic devices. Electromagnetic microactuators exhibit considerable benefits such as high forces, large deflections, low input impedances and thus, the involvement of only low voltages. Most of the magnetic microactuators developed so far are based on the variable reluctance principle and use soft magnetic materials. Since the driving force of such actuators is proportional to their volume, they require structures with rather great heights and aspect ratios. Therefore, the development of new photo resists, which allow UV exposure of thick layers of resist, has been essential for the advancement of variable reluctance microactuators. On the other hand, hard magnetic materials have the potential for larger forces and larger deflections. Accordingly, polymer magnets, in which micro particles of hard magnetic material are suspended in a polymer matrix, have been used to fabricate permanent magnet microactuators. In this paper we give an overview of sophisticated electromagnetic microactuators which have been developed in our laboratory in the framework of the Collaborative Research Center “Design and Manufacturing of Active Microsystems”. In particular, concept, fabrication and test of variable reluctance micro stepper motors, of permanent magnet synchronous micromotors and of microactuators based on the Lorentz force principle will be described. Special emphasis will be given to applications in lab-on-chip systems.

This paper reports on thermal design of a micro linear tristable actuator with an integrated sensor platform. On the basis of theoretic analysis and previous works, a novel design for the set-up of the one-axis actuator is proposed, in which electromagnetic driving is used, and the actuator will be hold only with permanent magnet forces on the end. It consists of a slider carrying the movable structure to which the actuated component is connected mechanically and electrically. Springs with low stiffness in the plane of actuation but high stiffness in all other directions connect the movable structure to the slider frame. Conducting paths are situated on the springs to provide electrical connectivity on the movable structure. For the contacting, power supply and signal read out of the two micro sensors on the sensor chip, six conducting paths which were led over the mechanical spring are necessary. They carry a current up to 100 mA. In order to confirm the thermal stability by working under strong current on micro spring, a thermal analysis is made. Though the thermal FEA of microstructures is a very challenging, the essential convection coefficient is calculated with help of a CFD-Simulation of a 2D finite element. A 3D finite element modeling is presented in brief theoretical analysis, modeling and simulation of temperature distribution were done for the realized micro actuator. Simulations of temperature distribution in the realized actuator were done taking into account the thermal-mechanical deformation and stress by working under named current. A thermal measurement results to underlay the FEM model are shown. The obtained simulation and experimental results are graphically presented, compared and analyzed. At the end a conclusion was made and an aspect of the further work is presented.

A thermal actuator based on two symmetrical V-shaped beam stacks (also called chevron-type) is presented. Each beam stack consists of 6 beams in parallel. The stacks are coupled facing each other and are slightly shifted along the mirror axis. Both stacks are connected to a lever beam. Due to the thermal expansion of the material, the tip of the lever moves up and downwards perpendicular to the mirror axis. The device is built up of galvanic deposited nickel. Finite element simulations were carried out for design considerations prior to the manufacturing of the device. The simulations were used to optimize the design regarding to the sensitivity and the maximum mechanical stress to be expected. The stress level needs to be lower than the yield strength of the material, to prevent plastic deformation and, therefore, irreversible tip defections. This also limits the overall sensitivity of the design. First results of the device with 400 µm long bent beams show a linear behavior and a sensitivity of 0.5 μm/K and expectable forces of 66 μN/K in a temperature range of -30°C up to +40°C.

The reduction of power consumption of sensors allows the local power supply or wireless sensor networks. This paper introduces the results of design and experiments on devices for harvesting energy from vibrations of machines. The main contribution of this research is the empirical evaluation of different technical solutions able to improve harvester performances and sensing system duty cycle. Satisfactory results have been achieved in lowering of resonance by levitating suspensions and in increasing of Q-factor by studying the air flows. Output power values of 10mW (5.7Hz, 1.4g) and 115mW (3.2Hz, 0.2g) were obtained for piezoelectric and inductive harvesters respectively.

Vertical silicon nanowire (SiNW) resonators are designed and fabricated in order to assess exposure to aerosol nanoparticles (NPs). To realize SiNW arrays, nanolithography and inductively coupled plasma (ICP) deep reactive ion etching (DRIE) at cryogenic temperature are utilized in a top-down fabrication of SiNW arrays which have high aspect ratios (i.e., up to 34). For nanolithography process, a resist film thickness of 350 nm is applied in a vacuum contact mode to serve as a mask. A pattern including various diameters and distances for creating pillars is used (i.e., 400 nm up to 5 μm). In dry etching process, the etch rate is set high of 1.5 μm/min to avoid underetching. The etch profiles of Si wires can be controlled aiming to have either perpendicularly, negatively or positively profiled sidewalls by adjusting the etching parameters (e.g., temperature and oxygen content). Moreover, to further miniaturize the wire, multiple sacrificial thermal oxidations and subsequent oxide stripping are used yielding SiNW arrays of 650 nm in diameter and 40 μm in length. In the resonant frequency test, a piezoelectric shear actuator is integrated with the SiNWs inside a scanning electron microscope (SEM) chamber. The observation of the SiNW deflections are performed and viewed from the topside of the SiNWs to reduce the measurement redundancy. Having a high deflection of ~10 μm during its resonant frequency of 452 kHz and a low mass of 31 pg, the proposed SiNW is potential for assisting the development of a portable aerosol resonant sensor.

In this study, an analogue Q-control circuit is presented, based on a digital feedback loop. In this approach, a self-actuated and self-sensing piezoelectric microstructure is used in combination with a lock-in amplifier to extract the Q-control feedback signal amplitude which is proportional to the piezoelectric current. In the next step, the DC-value supported by the lock-in amplifier is multiplied with a sine signal on a custom-designed analogue circuit board containing an analogue amplifier IC. This generated analogue feedback signal allows to drive a complete analogue feedback loop enabling faster response of the Q-control and further faster measurements can be performed. Using this Q-factor enhancement technique, the Q-factor was increased from 397 to about 5357 in air without driving the used Q-control approach to its limits. These promising results will push further activities in measuring the viscosity of liquids in the future.

The aim of this contribution is to report and discuss a preliminary study and rough optimization of a novel concept of MEMS device for vibration energy harvesting, based on a multi-modal dynamic behavior. The circular-shaped device features Four-Leaf Clover-like (FLC) double spring-mass cascaded systems, kept constrained to the surrounding frame by means of four straight beams. The combination of flexural bending behavior of the slender beams plus deformable parts of the petals enable to populate the desired vibration frequency range with a number of resonant modes, and improve the energy conversion capability of the micro-transducer. The harvester device, conceived for piezoelectric mechanical into electric energy conversion, is intended to sense environmental vibrations and, thereby, its geometry is optimized to have a large concentration of resonant modes in a frequency range below 5-10 kHz. The results of FEM (Finite Element Method) based analysis performed in ANSYS^TM Workbench are reported, both concerning modal and harmonic response, providing important indications related to the device geometry optimization. The analysis reported in this work is limited to the sole mechanical modeling of the proposed MEMS harvester device concept. Future developments of the study will encompass the inclusion of piezoelectric conversion in the FEM simulations, in order to have indications of the actual power levels achievable with the proposed harvester concept. Furthermore, the results of the FEM studies here discussed, will be validated against experimental data, as soon as the MEMS resonator specimens, currently under fabrication, are ready for testing.

It is well known that for precise biological cell injection the applied forces should be exactly controlled in any specific case. In this paper we present design, prototyping, calibration and testing of a microforce sensor, which fulfils the requirements for injection monitoring of biological cells. It is an axial all-silicon piezoresistive Micro Electro-Mechanical System (MEMS) device. The layout of the all-silicon force sensor is adapted for operation at partial dipping in biochemical solutions. A prototype of this sensor is investigated and its parameters are measured. To verify the applicability of the MEMS for bio-applications, it was used in force monitoring injection of Xenopus Oocyte cells. Force measurements during the injection process and interpretation of the force-penetration curve are presented and discussed. Thus, it has been experimentally proved that the developed all-silicon force sensor can be successfully applied for force monitoring in different bio-applications.

We present the development of a novel integrated device for airborne nanoparticle filtering with bioinspired nanoscale functionality. The underlying idea is to investigate the principle of adherent surfaces, e.g. pollen, as a biological model and transfer this functionality into a technology using functionalized microstructured surfaces offering an efficient filtering method for nanoscale airborne particles. We investigated the different pollen species for their structural and biochemical surface properties to achieve bioinspired surface functionality on silicon surfaces. Depending on surface morphology, the adhesive properties of the surfaces towards aerosol particles could be directly influenced.

Microbial Fuel Cells (MFCs) are energy sources which generate electrical charge thanks to bacteria metabolism. Although functionally similar to chemical fuel cells (both including reactants and two electrodes, and anode and cathode), they have substantial advantages, e.g. 1) operation at ambient temperature and pressure; 2) use of neutral electrolytes and avoidance of expensive catalysts (e.g. platinum); 3) operation using organic wastes. An MFC can be effectively used in environments where ubiquitous networking requires the wireless monitoring of energy sources. We then report on a simple monitoring system for MFC comprising an ultra-low-power Impulse-Radio Ultra-Wide-Band Transmitter (TX) operating in the low 0-960MHz band and a nanostructured piezoresistive pressure sensor connected to a discrete component digital read-out circuit. The sensor comprises an insulating matrix of polydimethylsiloxane and nanostructured multi-branched copper microparticles as conductive filler. Applied mechanical stress induces a sample deformation that modulates the mean distance between particles, i.e. the current flow. The read-out circuit encodes pressure as a pulse rate variation, with an absolute sensitivity to the generated MFC voltage. Pulses with variable repetition frequency can encode battery health: the pressure sensor can be directly connected to the cells membrane to read excessive pressure. A prototype system comprises two MFCs connected in series to power both the UWB transmitter which consumes 40μW and the read-out circuit. The two MFC generate an open circuit voltage of 1.0±0.1V. Each MFC prototype has a total volume of 0.34L and is formed by two circular Poly(methyl methacrylate) (PMMA) chambers (anode and cathode) separated by a cation exchange membrane. The paper reports on the prototype and measurements towards a final solution which embeds all functionalities within a MFC cell. Our solution is conceived to provide energy sources integrating energy management and health monitoring capabilities to sensor nodes which are not connected to the energy grid.

There are great efforts in developing effective composite structures for lightweight constructions for nearly every field of engineering. This concerns for example aeronautics and spacecrafts, but also automotive industry and energy harvesting applications. Modern concepts of lightweight components try to make use of structures with properties which can be adjusted in a controllable was. However, classic composite materials can only slightly adapt to varying environmental conditions because most materials, like carbon or glass-fiber composites show properties which are time-constant and not changeable. This contribution describes the development, the potential and the limitations of novel smart, self-controlling structures which can change their mechanical properties - e.g. their flexural stiffness - by more then one order of magnitude. These structures use a multi-layer approach with a 10-layer stack of 0.75 mm thick polycarbonate. The set-up is analytically described and its mechanical behavior is predicted by finite element analysis done with ABAQUS. The layers are braided together by an array of shape memory alloy (SMA) wires, which can be activated independently. Depending on the temperature applied by the electrical current flowing through the wires and the corresponding contraction the wires can tightly clamp the layers so that they cannot slide against each other due to friction forces. In this case the multilayer acts as rigid beam with high stiffness. If the friction-induced shear stress is smaller than a certain threshold, then the layers can slide over each other and the multilayer becomes compliant under bending load. The friction forces between the layers and, hence, the stiffness of the beam is controlled by the electrical current through the wires. The more separate parts of SMA wires the structure has the larger is the number of steps of stiffness changes of the flexural beam.

A miniaturised, piezoelectrically driven shaker system is presented which is suitable for MEMS characterisation in vacuum. It offers a broad frequency and amplitude range. The fully vacuum compatible shaker is constructed out of one single peace of aluminium with a piezo-stack-actuator working in-plane against four beam springs. It can easily be fabricated at low costs using a hand operated milling machine. The systems characteristics are easily tuned to different applications as the first resonance frequency is given by the stiffness of the beam springs and the mass of the moving shaker table. The utilised piezoelectric stack determines the maximum reachable amplitude for a given spring stiffness. Finite Element simulations have been carried out to design a at transfer characteristic of the shaker up to 10 kHz and amplitudes in the range from sub nanometres up to 1μm. The simulations were evaluated by laser vibrometer measurements of the shaker which also show a good linearity between electrical excitation signal and output deection amplitude. To account for other resonance frequencies introduced by a preexisting MEMS mounting device, the resulting vibration amplitude on the MEMS structure can be normalised by adjusting the electrical excitation amplitude with the help of a Polytec laser vibrometer.

The controlled deposition of materials by means of electron beam induced processing (EBIP) is a well-established patterning method, which allows for the fabrication of nanostructures with high spatial resolution in a highly precise and flexible manner. Applications range from the production of ultrathin coatings and nanoscaled conductivity probes to super sharp atomic force microscopy (AFM) tips, to name but a few. The latter are typically deposited at the very end of silicon or silicon-nitride tips, which are fabricated with MEMS technologies. EBIP therefore provides the unique ability to converge MEMS to NEMS in a highly controllable way, and thus represents an encouraging opportunity to refine or even develop further MEMS-based features with advanced functionality and applicability. In this paper, we will present and discuss exemplary application solutions, where we successfully applied EBIP to overcome dimensional and/or functional limitations. We therefore show the fabrication stability and accuracy of “T-like-shaped” AFM tips made from high density, diamond-like carbon (HDC/DLC) for the investigation of undercut structures on the base of CDR30-EBD tips. Such aggressive CD-AFM tip dimensions are mandatory to fulfill ITRS requirements for the inspection of sub-28nm nodes, but are unattainable with state-of-art Si-based MEMS technologies today. In addition to that, we demonstrate the ability of EBIP to realize field enhancement in sensor applications and the fabrication of cold field emitters (CFE). For example: applying the EBIP approach allows for the production of CFEs, which are characterized by considerably enhanced imaging resolution compared to standard thermal field emitters and stable operation properties at room temperature without the need for periodic cathode flashing – unlike typical CFEs. Based on these examples, we outline the strong capabilities of the EBIP approach to further downscale functional structures in order to meet future demands in the semiconductor industry, and demonstrate its promising potential for the development of advanced functionalities in the field of NEMS.

The implementation of innovative methods and concepts for microsurgery – especially in the context of endovascular and interventional treatment – require properly fitted and resized instruments. These surgical tools, such as micro-guiding systems, must be of the highest quality regarding reliability and accuracy while additional medical requirements for the application in the human body have to be fulfilled. In this paper an innovative hydrostatic microactuator system for controlling the rotational degree of freedom of microsurgery instruments is presented. From the possible hydrostatic motor designs, an annular gear motor in orbit setup has been chosen based on its suitability for micro manufacturing. The innovative actuator design includes a rotor-integrated control for connecting the actuator’s individual positive-displacement chambers. Firstly, a macro-model of the new actuator was fabricated and tested. The obtained test results have already confirmed the functionality and show the actuator’s exciting potential. Currently the macro-model is further resized and the micro fabrication process is being developed.

This paper presents a simple and quick method to integrate microlens with the microfluidics systems. The polystyrene (PS) based microlens is fabricated with the free surface thermal compression molding methods, a thin PS sheet with the microlens is bonded to a PMMA substrate which contains the laser ablated microchannels. The convex profiler of the microlens will give a magnified images of the microchannels for easier observation. Optical simulation software is being used for the design and simulation of the microlens to have optimal optical performance with the desired focal length. A microfluidic system with the integrated PS microlens is also fabricated for demonstration.

Ultrasensitive magnetic field sensors at low frequencies are necessary for several biomedical applications. Suitable devices can be achieved by using large area magnetic tunnel junction sensors combined with permanent magnets to stabilize the magnetic configuration of the free layer and improve linearity. However, further increase in sensitivity and consequently detectivity are achieved by incorporating also soft ferromagnetic flux guides. A detailed study of tunnel junction sensors with variable areas and aspect ratios is presented in this work. In addition, the effect in the sensors transfer curve, namely in their coercivity and sensitivity, as a consequence of the incorporation of permanent magnets and flux guides is also thoroughly discussed. Using sensors with a tunnel magnetoresistance of ~200 %, incorporating both permanent magnets and flux guides sensitivities of 220-260 %/mT were obtained for high aspect ratio sensors, increasing to values larger than ~2000%/mT for large areas and low aspect ratio sensors. Measured noise levels of the final device at 10 Hz yield 3.9×10^-17 V²/Hz, leading to an improved lowest detectable field of ~ 94 pT/ Hz^0.5.

In microchip capillary electrophoresis most frequently electrokinetic sample injection is utilized, which does not allow pressure driven sample handling and is sensitive for pressure drops due to different reservoir levels. For efficient field tests a multitude of samples have to be processed with the least amount of external equipment. We present the use of a hydrogel plug to separate the sample from clean buffer to enable independent sample change and buffer refreshment. In-situ polymerization of the gel does away with complex membrane fabrication techniques. The sample is electrokinetically injected through the gel and subsequently separated by a voltage between the second gel inlet and the buffer outlet. By blocking of disturbing flows by the gel barrier a well-defined ion plug is obtained. After each experiment, the sample and the separation channel can be flushed independently, allowing for a continuous operation mode in order to process multiple samples.

We present a new method for the direct injection of liquid sample into a capillary electrophoresis (CE) device. Instead of a double-T injection mechanism, a single inlet provided with a membrane filter is used. From a reservoir on top of this inlet, the liquid directly enters the separation channel through the membrane. The driving force is a short electrical pulse. This avoids an additional sample channel, so that the chip needs only three microfluidic connects and no mechanical sample pumping is demanded. The high injection reproducibility and the comparatively simple setup open up the way for mobile application of soil analysis.

This work aims at simulating and optimizing the magnetic field intensity in different electroplated copper micro-coil designs that can be integrated in a recently developed electromagnetic micro-pump. The results of this study will be used in fabricating new optimized micro-coil designs that may enhance the performance of the developed synchronous micro-pump (i.e., the maximum back pressures and flow rates). The synchronous micro-pump concept depends on managing the movement of two magnets in an annular fluidic channel. Magnet rotation is achieved by sequentially activating a set of planar micro-coils to repel or attract the first magnet (traveling magnet) through the channel, while the second one is anchored between the inlet and the outlet ports. At the end of each pumping cycle, the magnets exchange their anchored and traveling functions. To achieve the maximum back pressure and flow rate (highest performance) in such micro-pump, higher magnetic fields without exceeding the material temperature limitation are required. The stronger the magnetic fields that can be generated, the higher the hydraulic power that can the pump deliver. This study presents extensive numerical simulations using the commercial software package COMSOL and presents also optimizations for the effect of the main micro-coil parameters on the generated magnetic field: coil wire width and height, the coil turns offset distance, the effect of including an iron core inside the coil area, and the number of coil turns. The main analyzed results are: the normal magnetic flux contours at the top (upper) surface of the coil - where the permanent magnets rotate in the micro-pump channel -, the distribution of the magnetic field streams and the area averaging of the magnetic field intensity all over the micro-coil sector.

This paper deals with an energy harvesting system for avionics; it is an energy source for a unit which is used for wireless monitoring or autonomous control of a small aircraft engine. This paper is focused on development process of energy harvesting system from mechanical vibrations in the engine area. The used energy harvesting system consists of an electro-magnetic energy harvester, power management and energy storage element. The energy harvesting system with commercial power management circuits have to be tested and verified measured results are used for an optimal redesign of the electro-magnetic harvester. This developmental step is necessary for the development of the optimal vibration energy harvesting system.

Increasing demand in mobile, autonomous devices has made energy harvesting a particular point of interest. Systems that can be powered up by a few hundreds of microwatts could feature their own energy extraction module. Energy can be harvested from the environment close to the device. Particularly, the ambient mechanical vibrations conversion via piezoelectric transducers is one of the most investigated fields for energy harvesting. A technique for optimized energy harvesting using piezoelectric actuators called “Synchronized Switching Harvesting” is explored. Comparing to a typical full bridge rectifier, the proposed harvesting technique can highly improve harvesting efficiency, even in a significantly extended frequency window around the piezoelectric actuator’s resonance. In this paper, the concept of design, theoretical analysis, modeling, implementation and experimental results using CEDRAT's APA 400M-MD piezoelectric actuator are presented in detail. Moreover, we suggest design guidelines for optimum selection of the storage unit in direct relation to the characteristics of the random vibrations. From a practical aspect, the harvesting unit is based on dedicated electronics that continuously sense the charge level of the actuator’s piezoelectric element. When the charge is sensed, to come to a maximum, it is directed to speedily flow into a storage unit. Special care is taken so that electronics operate at low voltages consuming a very small amount of the energy stored. The final prototype developed includes the harvesting circuit implemented with miniaturized, low cost and low consumption electronics and a storage unit consisting of a super capacitors array, forming a truly self-powered system drawing energy from ambient random vibrations of a wide range of characteristics.

Piezoelectric materials are widely used in various applications including sensors, actuators, and energy harvesting devices. Energy harvesting devices can be used to power autonomous wireless sensors that are placed in remote or difficult to reach areas, where replacing a battery is not practical or feasible. In this paper the authors present work on the fabrication and design of a CMOS compatible Aluminium Nitride (AlN) piezoelectric based MEMS cantilever structure for harvesting vibrational energy. In order for AlN to be piezoelectric it needs to be highly structured in the c-axis (002) crystal orientation. The deposition of highly structured AlN and its polarity is dependent on the underlying films and their crystal orientation. XRD rocking curve results from this paper show a highly oriented (002) AlN film with a FWHM value of 2.1°. The MEMS cantilever structures were fabricated using standard MEMS fabrication techniques using SOI wafers. By optimising the AlN material deposition process and the stress values in the cantilever structures the authors were able obtain a power density of 2.55 mW/ cm³/g² for a single MEMS structure with 500 nm thick AlN. The cantilever structure had a resonant frequency of approximately 150 Hz. In this paper the authors also investigated methods to increase the bandwidth of the cantilever structures, by building an array of devices with slightly varying length masses.

Energy harvesting could provide power-autonomy to many important embedded sensing application areas. However, the available envelope often limits the power output, and also voltage levels. This paper presents the implementation of an enabling technology for space-restricted energy harvesting: Four highly efficient and fully autonomous power conditioning circuits are presented that are able to operate at deep-sub-milliwatt input power at less than 1 V_pk AC input, and provide a regulated output voltage. The four complete systems, implemented using discrete components, include the power converters, the corresponding ancillary circuits with sub-10 μW consumption, start-up circuit, and an ultra-lowpower shunt regulator with under-voltage lockout for the management of the accumulated energy. The systems differ in their power converter topology; all are boost rectifier variants that rectify and boost the generator’s output in a single stage, that are selected to enable direct comparison between polarity–dependent and –independent, as well as between full-wave and half-wave power converter systems. Experimental results are derived over a range of 200–1200 μW harvester output power, the system being powered solely by the harvester. Experimental results show overall conversion efficiency, accounting for the quiescent power consumption, as high as 82% at 650 μW input, which remains in the 65–70% range even at 200 μW input for the half-wave variant. Harvester utilisation of over 90% is demonstrated in the sub-milliwatt range using full-wave topologies. For the evaluated generator, the full-wave, polarity-dependent boost rectifier offers the best overall system effectiveness, achieving up to 73% of the maximum extractable power.

The design of a piezoelectric device aimed at harvesting the kinetic energy of random vibrations on a vehicle’s wheel is presented. The harvester is optimised for powering a Tire Pressure Monitoring System (TPMS). On-road experiments are performed in order to measure the frequencies and amplitudes of wheels’ vibrations. It is hence determined that the highest amplitudes occur in an unperiodic manner. Initial tests of the battery-less TPMS are performed in laboratory conditions where tuning and system set-up optimization is achieved. The energy obtained from the piezoelectric bimorph is managed by employing the control electronics which converts AC voltage to DC and conditions the output voltage to make it compatible with the load (i.e. sensor electronics and transmitter). The control electronics also manages the sleep/measure/transmit cycles so that the harvested energy is efficiently used. The system is finally tested in real on-road conditions successfully powering the pressure sensor and transmitting the data to a receiver in the car cockpit.

The human motion energy harvesting is under investigation. The aim of this investigation: to develop electromagnetic human motion energy harvester that will consist only from flat elements and is integrable into the apparel. Main parts of the developed human motion energy harvester are flat, spiral-shaped inductors. Voltage pulses in such flat inductors can be induced during the motion of a permanent magnet along it. Due to the flat structure, inductors can be completely integrated into the parts of the clothes and it is not necessary to keep empty place for the movement of the magnet, as in usual electromagnetic harvesters. The prototype of the clothing, jacket with integrated electromagnetic human motion energy harvester with flat inductors is tested. The theoretical model for the induction of the electromotive force due to the magnet’s movement is created for the basic shapes (round, rhombic, square) of the inductive elements and the results (shape of voltage pulse and generated energy) of the calculations are in a good qualitative and quantitative coincidence with an experimental research.

The aim of this paper is to examine the performances of thermoelectric generator based on microelectromechanical systems technology (MEMS) in wide range of operational conditions. The goal is to evaluate capability of this technology for a development of an independent energy source for aircraft applications. Complex overview of MEMS TEG properties obtained by computational modeling, simulations and experimental testing is utilized to define critical phenomena of MEMS TEG technology.

Greener, more power efficient technologies as well as cost reduction are driving forces in energy efficient systems. Energy autonomous wireless health monitoring systems can potentially reduce aircraft maintenance costs by requiring no conventional power supply or supervision and by providing information of the health of an aircraft without human interaction. Thermoelectric energy harvesting seems the best choice for aircraft related applications, since sufficient energy can be generated to power up a wireless sensor node. The general concept is based on an artificially enhanced temperature difference across a thermoelectric generator (TEG), which is created by attaching one side to the fuselage and the other side to a thermal mass, which, in this case, is a phase change material. In detail, two different geometries and three different container materials are evaluated. As input and output parameters, the temperature profiles as well as the voltage of the TEGs are given. The output power and the total energy are determined by connecting a load resistor in parallel. Furthermore, the power to weight ratio for each combination is provided according to theoretical considerations and experimental tests done in a climate chamber mimicking a real flight profile.

This paper describes a multi-source energy harvester IC for arrays of independent transducers, designed in a 0.32μm STMicroelectronics BCD technology, that can manage up to 5 AC-DC channels (e.g. piezoelectric transducers). The IC implements a boost converter based on synchronous electrical charge extraction. A single external inductor is time-shared among all transducers and access conflicts are handled by an arbiter circuit implemented as an asynchronous FSM. The designed converter is fully autonomous and suitable for battery-less operation. The circuit area is 4.6 mm² and has a power consumption of 175 nW/source at 2.5 V while efficiency ranges between 70% and over than 85%.

Current version of implantable cardioverter defibrillators (ICDs) and pacemakers consists of a battery-powered pulse generator connected onto the heart through electrical leads inserted through the veins. However, it is known that long-term lead failure may occur and cause a dysfunction of the device. When required, the removal of the failed leads is a complex procedure associated with a potential risk of mortality. As a consequence, the main players in the field of intracardiac implants prepare a next generation of devices: miniaturized and autonomous leadless implants, which could be directly placed inside the heart. In this paper, we discuss the frequency content of a heart vibration spectrum, and the dimensional restrictions in the case of a leadless pacemaker. In combination with the requirements in terms of useable energy, we will present a design study of a resonant piezoelectric scavenger aimed at powering such a device. In particular, we will show how the frequency-volume-energy requirement leads to new challenges in terms of power densities, which are to be addressed through implementation of innovative piezoelectric thick films fabrication processes. This paper also presents the simulation, fabrication and the testing of an ultralow frequency (15Hz) resonant piezoelectric energy harvester prototype. Using both harmonic (50mg) and real heart-induced vibrations, we obtained an output power of 60μW and 10μW respectively. Finally, we will place emphasis on the new constraint represented by the gravitational (orientation) sensitivity inherent to these ultra low frequency resonant energy harvesters.

A micro-power energy harvesting system based on core(crystalline Si)-shell(amorphous Si) nanowire solar cells together with a nanowire-modified CMOS sensing platform have been developed to be used in a dust-sized autonomous chemical sensor node. The mote (SiNAPS) is augmented by low-power electronics for power management and sensor interfacing, on a chip area of 0.25mm². Direct charging of the target battery (e.g., NiMH microbattery) is achieved with end-to-end efficiencies up to 90% at AM1.5 illumination and 80% under 100 times reduced intensity. This requires matching the voltages of the photovoltaic module and the battery circumventing maximum power point tracking. Single solar cells show efficiencies up to 10% under AM1.5 illumination and open circuit voltages, V_oc, of 450-500mV. To match the battery’s voltage the miniaturised solar cells (~1mm² area) are connected in series via wire bonding. The chemical sensor platform (mm² area) is set up to detect hydrogen gas concentration in the low ppm range and over a broad temperature range using a low power sensing interface circuit. Using Telran TZ1053 radio to send one sample measurement of both temperature and H₂ concentration every 15 seconds, the average and active power consumption for the SiNAPS mote are less than 350nW and 2.1 μW respectively. Low-power miniaturised chemical sensors of liquid analytes through microfluidic delivery to silicon nanowires are also presented. These components demonstrate the potential of further miniaturization and application of sensor nodes beyond the typical physical sensors, and are enabled by the nanowire materials platform.

This research work presents the design, fabrication and characterization of micromachined piezoelectric energy harvester stimulated by ambient random vibrations utilizing AlN as a piezoelectric material. The device design consists of a silicon cantilever beam on which AlN is sandwiched between two electrodes and a silicon seismic mass at the end of the cantilever beam. The generated electric power of the devices was experimentally measured at various acceleration levels. A maximum power of 34 μW was obtained at an acceleration value of 2g for the device which measures 5.6 x 5.6 mm². Various unpackaged devices were tested and assessed in terms of the generated power and resonant frequency at various acceleration values.

Commercial photovoltaic cells used in energy harvesting applications suffer from low power conversion efficiencies at low light intensities. Typical efficiencies are in the range of 2 to 5% at 100 Lux. This is because the cells are typically optimized and specified with respect to the AM 1.5 sun spectrum at 1000 W/m2 light intensity, which is far away from the required operating range. This paper infers design rules for photovoltaic cells with special attention to the low intensity range. It discusses the major parameters for the optimization of photovoltaic cell for different material classes like crystalline silicon, amorphous silicon and III-V materials. Measurement results for an optimized silicon cell with more than 15% efficiency at 100 Lux are presented.

The specific technical challenges associated with the design of an ambient energy powered electronic system currently requires thorough knowledge of the environment of deployment, energy harvester characteristics and power path management. In this work, a novel flexible model for ambient energy harvesters is presented that allows decoupling of the harvester’s physical principles and electrical behavior using a three dimensional function. The model can be adapted to all existing harvesters, resulting in a design methodology for generic ambient energy powered systems using the presented model. Concrete examples are included to demonstrate the versatility of the presented design in the development of electronic appliances on system level.

In MEMS (micro electromechanical system) devices, piezoelectric aluminum nitride (AlN) thin films are commonly used as functional material for sensing and actuating purposes. Additionally, AlN features excellent dielectric properties as well as a high chemical and thermal stability, making it also a good choice for passivation purposes for microelectronic devices. With those aspects and current trends towards minimization in mind, the dielectric reliability of thin AlN films is of utmost importance for the realization of advanced device concepts. In this study, we present results on the transversal dielectric strength of 100 nm AlN thin films deposited by dc magnetron sputtering. The dielectric strength was measured using a time-zero approach, where the film is stressed using a fast voltage ramp up to the point of breakdown. The measurements were performed using different contact pad sizes, different voltage ramping speeds and device temperatures, respectively. In order to achieve statistical significance, at least 12 measurements were performed for each environment parameter set and the results analyzed using the Weibull approach. The results show, that the breakdown field in positive direction rises with the pad size, as expected. Furthermore, lower breakdown fields with increasing temperatures up to 300°C are observed with the mean field to failure following an exponential law typical for temperature activated processes. The activation energy was determined to 27 meV, allowing an estimation of the breakdown field towards even higher temperatures. In negative field direction no breakdown occurred, which is attributed to the metal-insulator-semiconductor configuration of the sample and hence, the larger depletion layer forming in the silicon dominates the observed current behavior.

This work investigates the interfacial adhesion between the iron fillers and the silicone matrix in magneto-rheological elastomers at high deformations. Carbonyl iron powder, composed of mechanically soft spherical particles with a median size of 3.5 μm and a volume concentration of 3.5%, was mixed in a soft silicone matrix (Shore 00-20); the compound was then degassed and cured under temperature. The presence of a homogeneous magnetic field of 0.3 T during the curing process allowed the formation of particle chains. Tensile tests of these samples under scanning electron microscope showed interfacial slipping and debonding between the two phases. To improve interfacial adhesion, a silane primer was applied to the iron particles, following two different procedures, before the mixing and crosslinking process, thus giving two additional types of samples. In tensile testing lengthwise to the particle alignment, with engineering strains up to 150%, the structural responses of the different types of samples were compared. An enhanced adhesion of the iron fillers to the silicone matrix resulting in a reinforced matrix and increased tensile strength during the first loading path could be observed. Furthermore, scanning electron microscope images show that a more elaborated particle-matrix interface was obtained with the primer additive.

In this paper we report on the high temperature compatibility of various adhesion layers for plat inum (Pt ) thin films. We investigated different adhesion layers, such as titanium (Ti), tantalum (Ta), aluminium nitride (AlN), aluminium oxide (Al₂O₃) and titanium oxide (TiO₂). All films were deposited on SiO₂/Si substrate by using the sputter technique. After deposition the films were annealed in air at 800°C for different time lengths up to 16 h ours. After annealing, Al₂O₃ and TiO₂ showed a dense oxide layer between Pt and SiO₂/Si and they seem to be suitable as adhesion layers for Pt at high temperatures. AlN is not suitable as adhesion layer for Pt at high temperatures. Ti and Ta are also not suitable for high temperatures, diffusing strongly into Pt layers and leading to the format ion of oxide precipitates (TiO_x or TaO_x) in the Pt grain boundaries. In addition, the format ion of Pt-crystallites (hillocks) on the surface was common in all the films.

In this paper effect of the orientation of the main crystallographic axes on the piezoelectric anisotropy and hydrostatic parameters of 2–2 parallel-connected single crystal (SC) / auxetic polymer composites is analysed. SCs are chosen among the perovskite-type relaxor-ferroelectric solid solutions of (1 – x)Pb(Zn_1/3Nb_2/3)O_3–xPbTiO₃ and xPb(In_1/2Nb_1/2)O_3–yPb(Mg_1/3Nb_2/3)O₃–(1 – x – y)PbTiO₃. The SC layers in a composite sample are poled along the perovskite unit-cell [011] direction and characterised by mm2 symmetry. The orientation of the main crystallographic axes in the SC layer is observed to strongly influence the effective piezoelectric coefficients d^*_3j, g^*_3j, squared figured of merit d^*_3j g^*_3j, electromechanical coupling factors k^*_3j (j = 1, 2 and 3), and hydrostatic analogs of these parameters of the 2–2 composite. A comparison of values of d^*_3j g^*_3j was first carried out at d^*₃₁ ≠ d^*₃₂ in a wide range of orientations and volume-fraction. Large values of the effective parameters and inequalities | d^*₃₃ / d^*_3f | > 5 and | k^*₃₃ / k^*_3f | > 5 (f = 1 and 2) are achieved at specific orientations of the main crystallographic axes due to the anisotropy of elastic and piezoelectric properties of the SC component. The use of an auxetic polyethylene with a negative Poisson’s ratio leads to a significant increase in the hydrostatic parameters of the 2–2 composite. Particular advantages of the studied composites over the conventional ceramic / polymer composites are taken into account for transducer, hydroacoustic and energyharvesting applications.

Nanopillar-based structures hold promise as highly sensitive resonant mass sensors for a new generation of aerosol nanoparticle (NP) detecting devices because of their very small masses. In this work, the possible use of a silicon nanopillar (SiNPL) array as a nanoparticle sensor is investigated. The sensor structures are created and simulated using a finite element modeling (FEM) tool of COMSOL Multiphysics 4.3 to study the resonant characteristics and the sensitivity of the SiNPL for femtogram NP mass detection. Instead of using 2D plate models or simple single 3D cylindrical pillar models, FEM is performed with SiNPLs in 3D structures based on the real geometry of experimental SiNPL arrays employing a piezoelectric stack for resonant excitation. In order to achieve an optimal structure and investigate the etching effect on the fabricated resonators, SiNPLs with different designs of meshes, sidewall profiles, lengths, and diameters are simulated and analyzed. To validate the FEM results, fabricated SiNPLs with a high aspect ratio of ~60 are employed and characterized in resonant frequency measurements. SiNPLs are mounted onto a piezoactuator inside a scanning electron microscope (SEM) chamber which can excite SiNPLs into lateral vibration. The measured resonant frequencies of the SiNPLs with diameters about 650 nm and heights about 40 μm range from 434.63 kHz to 458.21 kHz, which agree well with those simulated by FEM. Furthermore, the deflection of a SiNPL can be enhanced by increasing the applied piezoactuator voltage. By depositing different NPs (i.e., carbon, TiO₂, SiO₂, Ag, and Au NPs) on the SiNPLs, the decrease of the resonant frequency is clearly shown confirming their potential to be used as airborne NP mass sensor with femtogram resolution level.

This study describes the design, simulation, and micro fabrication of a micro thermoelectric generator (μTEG) based on planar technology using constantan (CuNi) and copper (Cu) thermocouples deposited electrochemically (ECD) on silicon substrate. The present thin film technology can be manufactured into large area and also on flexible substrate with low cost of production and can be used to exploit waste heat from equipments or hot surfaces in general. In the current implementation, the silicon structure has been designed and optimized with analytical models and FE simulations in order to exploit the different thermal conductivity of silicon and air gaps to produce the maximum temperature difference on a planar surface. The results showed that a temperature difference of 10K across the structure creates a temperature difference of 5.3K on the thermocouples, thus providing an efficiency of thermal distribution up to 55%, depending on the heat convection at the surface. Efficiency of module has been experimentally tested under different working condition, showing the dependence of module output on the external heat exchange (natural and forced convection). Maximum generated potential at 6m/s airflow is 5.7V/m² K and thermoelectric efficiency is 1.9μW K^-2 m^-2.

This work presents mathematical modelling of unimorph and bimorph AlN piezoelectric micromachined harvesters utilizing an energetic electron source - amenable to powering miniaturized devices such as MEMS(micro electro mechanical system) sensors. Tritiated silicon, as the energetic electron source, is appropriately aligned under a cantilever structure such that the emitted electrons are trapped by the collecting surface of the cantilever, thereby rendering it negatively charged while the electron emitting surface becomes positively charged. As a result, the attractive electric force causes the cantilever to bend towards the electron emitting surface until it makes contact and is discharged, and thus the cantilever snaps back. The resulting energy from the piezoelectric capacitor is rectified to provide electrical power to MEMS devices. Detailed electromechanical analysis and modelling of unimorph and series and parallel bimorph architectures are presented. Very good agreement between the results of the analytical model and the available experimental findings is demonstrated, thus providing assurance for the optimization study of tritiated silicon radioisotope excited piezoelectric energy harvesters.

The market for mobile devices like tablets, laptops or mobile phones is increasing rapidly. Device housings get thinner and energy efficiency is more and more important. Micro-Electro-Mechanical-System (MEMS) loudspeakers, fabricated in complementary metal oxide semiconductor (CMOS) compatible technology merge energy efficient driving technology with cost economical fabrication processes. In most cases, the fabrication of such devices within the design process is a lengthy and costly task. Therefore, the need for computer modeling tools capable of precisely simulating the multi-field interactions is increasing. The accurate modeling of such MEMS devices results in a system of coupled partial differential equations (PDEs) describing the interaction between the electric, mechanical and acoustic field. For the efficient and accurate solution we apply the Finite Element (FE) method. Thereby, we fully take the nonlinear effects into account: electrostatic force, charged moving body (loaded membrane) in an electric field, geometric nonlinearities and mechanical contact during the snap-in case between loaded membrane and stator. To efficiently handle the coupling between the mechanical and acoustic fields, we apply Mortar FE techniques, which allow different grid sizes along the coupling interface. Furthermore, we present a recently developed PML (Perfectly Matched Layer) technique, which allows limiting the acoustic computational domain even in the near field without getting spurious reflections. For computations towards the acoustic far field we us a Kirchhoff Helmholtz integral (e.g, to compute the directivity pattern). We will present simulations of a MEMS speaker system based on a single sided driving mechanism as well as an outlook on MEMS speakers using double stator systems (pull-pull-system), and discuss their efficiency (SPL) and quality (THD) towards the generated acoustic sound.

The study of damping in MEMS (micro electro-mechanical systems) is crucial for dynamic response prediction and functional parameters estimation as switch and release time, resonance and quality factor. Geometrical features (borders, perforations, anchors, etc.) complicate the airflow and impose to validate the results calculated or simulated with models. Fluid damping is the dominant dissipation source, accompanied by structural dissipations, thermo-elastic damping, anchor losses, surface effects and electric losses. In literature, the damping coefficient of MEMS is generally derived from the peaks of the structural frequency response function (FRF) by the half power method. Despite the wide usage of this approach, it is affected by two main drawbacks: highly precise and automated detection instruments are needed, and it is applicable only in resonance conditions. The method presented here is based on the measurement of damping from the hysteresis cycle of the actuation force; it applies in the time domain and works at any frequency and vibration amplitude. The effectiveness of this methodology on MEMS is proved by comparing the damping results with those provided at resonance conditions by the half power method. The samples, designed by the authors, are gold microplates with square holes and elastic springs. The measurements are conducted by the laser vibrometer Polytech MSA500. The comparison shows very good agreement with the damping coefficients calculated with the traditional approach (differences within 2% at resonance).

Mechanical parameters, especially mechanical stress of membranes used in silicon microphones strongly depend on the manufacturing process. As a result, deviations during this process can result in sensitivity variations of the microphone. Therefore, the stress should be well controlled within a certain tensile level. This paper describes a method to test devices electrically using the MEMS related pull-in phenomenon with respect to the mechanical compliance of microphone membranes. Using this method, out of specification chips can be detected at an early stage within the manufacturing process instead of determination at a system functionality test after packaging. Therefore, the adequacy for the intended use of the pull-in voltage and its dependency on varying tensile stress due to manufacturing tolerance is evaluated.

Incorporating resistive strain-sensing elements into MEMS devices is a long-standing approach for electronic detection of the device deformation. As the need for more sensitivity trends the device dimensions downwards, the size of the strain-sensor may become comparable to the device size, which can have significant impact on the mechanical behaviour of the device. To study this effect, we modelled a submicron-thickness silicon nitride AFM cantilever with strain-sensing element. Using finite element analysis, we calculated the strain in the sensor elements for a deflected cantilever. The sensor element contributes to a local stiffening effect in the device structure which lowers the strain in the sensor. By varying the sensor geometry, we investigated the degree to which this effect impacts the strain. Minimizing the sensor size increases the strain, but the reduction in sensor cross-sectional area increases the resistance and expected sensor noise. The optimal sensor geometry must therefore account for this effect. We used our analysis to optimize geometric variations of nanogranular tunnelling resistor (NTR) strain sensors arranged in a Wheatstone bridge on a silicon nitride AFM cantilever. We varied the dimensions of each sensor element to maintain a constant cross-sectional area but maximize the strain in the sensor element. Through this approach, we expect a 45% increase in strain in the sensor and corresponding 20% increase in the Wheatstone bridge signal. Our results provide an important consideration in the design geometry of resistive strainsensing elements in MEMS devices.

Magnetic shape memory alloy (MSMA) is a relatively new kind of smart material. Upon application of a large magnetic field, it exhibits actuation strains up to 10% similar to thermal shape memory alloy (SMA) but shows significantly reduced response time in the millisecond range. Currently, application is restricted by the brittleness of the single crystal material, its nonlinear behaviour and the difficulty to generate and apply a magnetic field around 0.6T in order to exploit the full actuation potential. The focus of this work is on the design of miniaturized magnetic circuits for bulk MSMAs. Various circuit designs are compared such as toroidal and series-parallel shapes. Equivalent circuit as well as finite element simulation is used to increase the magnetic field in a characteristic air gap where the smart material is placed. A symmetrical toroid coil layout with the MSMA element at the center that allows easy integration of the actuator in various applications is described. Static characterization results of this actuator are provided. Using the described magnetic circuit and 5M - MSMA rods with dimensions of 20x2.5x1mm³, a peak displacement of 0.8mm and a blocked force of 4.5N was obtained. Further design guidelines for such miniaturized actuators are given.

The motion of the seismic mass that is induced by thermal noise limits the resolution of typical micromachined vibration sensors. Its value can be adjusted by the size of the proof mass which is also a quantity for the inertial actuation input. Owing to a novel transduction concept, micro-opto-electro-mechanical vibration sensors featuring approximately twice as much mass per chip area are feasible, while decreasing the technological efforts during fabrication. The essence of the devised sensor principle is the modulation of the intensity of a light flux propagating perpendicularly through a pair of micromachined apertures. One aperture is fixed to the encapsulation and the second one is deffected by inertial forces. Earlier attempts have employed opto-electrical transmitters and receivers operating at a wavelength where silicon is intransparent. Thus, openings in the silicon mass were necessary. The presented evaluation technique utilizes the transparency of silicon in the infrared region at wavelengths well above 1.1 μm. In contrast to the previously used optoelectronic components, an InGaAs LED and an InGaAs pin-diode were integrated. This all enables of thin-film metal apertures deposited on top of the silicon seismic mass instead of etched silicon windows. Beside the increase in mass, this approach offers larger scope for design and implies a reduced damping coefficient yielding an improved quality factor. A structure for the proof of concept was fabricated and characterized together with a sensor based on the preceding principle. The results are in good agreement with the predicted behavior and the parameters tested by FEM analysis considering the fabrication related underetching as well.

The authors propose an analysis of a model solar element based on the principle of a resonance system facilitating the transformation of the external form of incident energy into electrical energy. A similar principle provides the basis for harvesters designed to operate at lower frequencies, Jirků T., Fiala P. and Kluge M.,2010, Wen J.L., Wen Z., Wong P.K., 2000. In these harvesters, the efficiency of the energy form transformation can be controlled from the frequency spectrum of an external source (the Sun).

The focus of this study is biomimetic concept development for a MEMS sensor array for navigation and water detection. The MEMS sensor array is inspired by abstractions of the respective biological functions: polarized skylight-based navigation sensors in honeybees (Apis mellifera) and the ability of African elephants (Loxodonta africana) to detect water. The focus lies on how to navigate to and how to detect water sources in desert-like or remote areas. The goal is to develop a sensor that can provide both, navigation clues and help in detecting nearby water sources. We basically use the information provided by the natural polarization pattern produced by the sunbeams scattered within the atmosphere combined with the capability of the honeybee’s compound eye to extrapolate the navigation information. The detection device uses light beam reactive MEMS, which are capable to detect the skylight polarization based on the Rayleigh sky model. For water detection we present various possible approaches to realize the sensor. In the first approach, polarization is used: moisture saturated areas near ground have a small but distinctively different effect on scattering and polarizing light than less moist ones. Modified skylight polarization sensors (Karman, Diah and Gebeshuber, 2012) are used to visualize this small change in scattering. The second approach is inspired by the ability of elephants to detect infrasound produced by underground water reservoirs, and shall be used to determine the location of underground rivers and visualize their exact routes.

For several applications, micro cells with a uniform temperature profile and at least one optical port are required. One example for those cells is the physics package of a chip-scale-atomic-clock. It is necessary that the micro chambers are heated homogeneously to 353 K using a low energy consumption heater. In this work transparent heating structures are investigated to achieve this goal. First an analytical approach is used to describe the behavior of thermal energy dissipation of the heating structures. Then different approaches of possible heater structures are simulated to find the optimal basic configuration. Furthermore, this configuration is optimized to obtain a uniform temperature distribution in the whole cell.

To miniaturize piezoresistive barometric pressure sensors we have developed a package using flip-chip bonding. However, in a standard flip-chip package the different coefficients of thermal expansion (CTE) of chip and substrate and strong mechanical coupling by the solder bumps would lead to stress in the sensor chip which is not acceptable for piezoresistive pressure sensors. To overcome this problem we have developed a new ultra low stress flip-chip packaging technology. In this new packaging technology for pressure sensors first an under bump metallization (UBM) is patterned on the sensor wafer. As the next step solder bumps are deposited. After wafer-dicing the chips are flip-chip bonded on copper springs within a ceramic cavity. As sources of residual stress we identified the copper springs, the UBM and the solder bumps on the sensor chip. Different CTEs of the silicon chip and the UBM/solder lead to creep strain in the aluminum metallization between UBM and chip. As a consequence a temperature hysteresis can be measured.

We present a novel design of a resonant magnetic field sensor with capacitive read-out permitting wafer level production. The device consists of a single-crystal silicon cantilever manufactured from the device layer of an SOI wafer. Cantilevers represent a very simple structure with respect to manufacturing and function. On the top of the structure, a gold lead carries AC currents that generate alternating Lorentz forces in an external magnetic field. The free end oscillation of the actuated cantilever depends on the eigenfrequencies of the structure. Particularly, the specific design of a U-shaped structure provides a larger force-to-stiffness-ratio than standard cantilevers. The electrodes for detecting cantilever deflections are separately fabricated on a Pyrex glass-wafer. They form the counterpart to the lead on the freely vibrating planar structure. Both wafers are mounted on top of each other. A custom SU-8 bonding process on wafer level creates a gap which defines the equilibrium distance between sensing electrodes and the vibrating structure. Additionally to the capacitive read-out, the cantilever oscillation was simultaneously measured with laser Doppler vibrometry through proper windows in the SOI handle wafer. Advantages and disadvantages of the asynchronous capacitive measurement configuration are discussed quantitatively and presented by a comprehensive experimental characterization of the device under test.

We present a silicon (Si) based infrared (IR) absorption sensor which is suitable for integration into a miniaturized sensor system. The sensor is designed to operate in the wavelength region around λ=5 μm. We particularly discuss the design, the modeling and the optical characterization of the used materials. The sensor operates as a singlemode Si waveguide (WG) on low refractive index Si₃N₄ membrane. The single-mode requirement for the WG is needed to avoid losses due to imperfections on the WG walls causing redistribution of the carried energy among the different modes. The waveguide interacts with the sample by means of the evanescent field which extends into the sample. This sensor configuration is not only compatible to the Si technology, but can also be realized on a single chip. In addition, the principle of operation is not limited to a single wavelength: by changing the waveguide dimensions, it can be applied to a broad spectral range. Thus, by its dimensions, performance and Si-compatibility, the sensor is expected to overcome previously published device concepts. The single-mode requirements lead to WG dimensions of 2 μm width x 600 nm height for an operation at λ=5 μm, which are verified by 3D simulations. For those parameters, the WG will support one transverse electric (TE) mode and one transverse magnetic (TM) mode. Efficient guidance is only obtained for the fundamental TE and TM modes. As an example, it is shown that mode TE1 is a non-guided mode. The experimentally obtained WG dimensions are 605 nm height and 2 μm width. In our paper we discuss issues with the design, the material characterization and first experimental results obtained with the recently fabricated prototypes.

It is challenging to provide contact measurements of travel in mm-range with nm/sub-nm resolution. It is even more complex to perform such measurements in static regime. In order to respond to the need for a simple, reliable and costeffective tool for contact travel measurements in mm-range with nm/sub-nm resolution, test MEMS sensor with sidewall embedded piezoresistors have been developed. The sensor comprises of two outer members having thickness of 270μm and two symmetrical sets of in-plane compliant elements: differential springs and displacement detection cantilevers, having thickness of 12μm. The MEMS devices have been bonded directly on low-noise amplifier PCB. For detailed characterization of the sensors in mm-travel range, two different experimental setups have been used. Measurements of 0.6 mm travel range at 1nm resolution have been demonstrated experimentally.

Bad indoor environment is often the reason for health impairment of people who spend most of their time indoors. Modern buildings are almost air tight and air exchange is too low. This problem often occurs in retrofitted buildings. A long time result can be mold formation in buildings. To get early information about bad indoor climate or mold formation, sensor systems which detect volatile organic compounds (VOC) are needed. The biggest challenge in measuring VOC gases in this scenario are the small concentrations. We present a miniaturized preconcentrating gas sensor system with two chambers for measuring organic gases. Preconcentration is realized with a thermoelectric element to activate sampling and desorption process in one chamber, delivering temperature gradients to a highly porous surface. The second chamber consists of a gas detecting element to indicate the preconcentrated VOC. By driving a temperature cycle with longtime cooling and fast heating the gas is preconcentrated and then desorbed quickly. Furthermore an electronic circuit board has been developed to control the complete system. The result is a complete sensor system with mechanical setup, electronic control, measurement, analyzation and peripheral communication. Measurements regarding temperature behavior of the system are performed, as measurements with VOC.

This paper reports on the modeling and experimental investigation of optical excitation of silicon cantilevers. In this work, the silicon cantilevers fabricated have dimensions with width of 15 μm, thickness of 0.26 μm, and variable length from 50 to 120 μm. In order to investigate the effect of the laser modulation frequency and position on the temperature at the anchor edge and displacements at the tip of cantilevers, a transient thermal ANSYS simulation and a steady-state static thermal mechanical ANSYS simulation were undertaken using a structure consisting of silicon device layer, SiO₂ sacrificial layer and silicon substrate. The dynamic properties of silicon cantilevers were undertaken by a series of experiments. The period optical driving signal with controlled modulation amplitude was provided by a 405 nm diode laser with a 2.9 μW/μm₂ laser power and variable frequencies. The laser spot was located through the longitude direction of silicon cantilevers. In factor, simulation results well matched with experimental observation, including: 1) for untreated silicon cantilevers, the maximum of displacement is observed when the laser beam was located half a diameter way from the anchor on the silicon suspended cantilever side; 2) for the both cantilevers, maximum displacement occurs when the optical actuation frequency is equal to the resonant frequency of cantilevers. Understanding the optical excitation on silicon cantilevers, as waveguides, can potentially increase sensing detection sensitivity (ratio of transmission to cantilever deflection).

The development of low-cost and low-power MEMS-based cantilever sensors for possible application in hand-held airborne ultrafine particle monitors is described in this work. The proposed resonant sensors are realized by silicon bulk micromachining technology with electrothermal excitation, piezoresistive frequency readout, and electrostatic particle collection elements integrated and constructed in the same sensor fabrication process step of boron diffusion. Built-in heating resistor and full Wheatstone bridge are set close to the cantilever clamp end for effective excitation and sensing, respectively, of beam deflection. Meanwhile, the particle collection electrode is located at the cantilever free end. A 300 μm-thick, phosphorus-doped silicon bulk wafer is used instead of silicon-on-insulator (SOI) as the starting material for the sensors to reduce the fabrication costs. To etch and release the cantilevers from the substrate, inductively coupled plasma (ICP) cryogenic dry etching is utilized. By controlling the etching parameters (e.g., temperature, oxygen content, and duration), cantilever structures with thicknesses down to 10 - 20 μm are yielded. In the sensor characterization, the heating resistor is heated and generating thermal waves which induce thermal expansion and further cause mechanical bending strain in the out-of-plane direction. A resonant frequency of 114.08 ± 0.04 kHz and a quality factor of 1302 ± 267 are measured in air for a fabricated rectangular cantilever (500x100x13.5 μm3). Owing to its low power consumption of a few milliwatts, this electrothermal cantilever is suitable for replacing the current external piezoelectric stack actuator in the next generation of the miniaturized cantilever-based nanoparticle detector (CANTOR).

A 5 MHz, 16-element phased array concave ultrasonic probe for non-destructive testing has been designed, fabricated and tested. To improve the probes performance its curvature, as opposed to present solutions, was not obtained by adding a corresponding delay wedge, but rather by manufacturing the functional elements (i.e. active material, matching layer) with a curvature. The piezoelectric material used here was a 1-3 composite material made of PZT. The finished probe was tested on a steel half circle with the corresponding radius (100 mm) and on the Olympus PAUT test piece. Good results could be obtained. Three transverse holes with a diameter of 1 mm and a distance of 5 mm to one another could be detected and resolved.

Design, simulation, fabrication, and characterization of novel MEMS pressure sensors with new back-side-direct-exposure packaging concept are presented. The sensor design is optimized for harsh environments e.g. space, military, offshore and medical applications. Unbreakable connection between the active side of the Si-sensor and the protecting glass capping was realized by anodic bonding using a thin layer of metal. To avoid signal corruption of the measured pressure caused by an encapsulation system, the media has direct contact to the backside of the Si membrane and can deflect it.

Crickets use highly sensitive mechanoreceptor hairs to detect approaching spiders. The high sensitivity of these hairs enables perceiving tiny air-movements which are only just distinguishable from noise. This forms our source of inspiration to design sensitive arrays made of artificial hair sensors for flow pattern observation i.e. Flow camera. The realization of such high-sensitive hair sensor requires designs with low thermo-mechanical noise to match the detection-limit of crickets’ hairs. Here we investigate the damping factor in our artificial hair-sensor using different models as it is the source of the thermo-mechanical noise in MEMS structures. The results show that the damping factor estimated in air is in the range of 10^-12 N.m/rad.s^-1 which translates into a 52 μm/s threshold flow velocity.

The developed direct converting X-ray line detectors offer a number of advantages in comparison to other X-ray sensor concepts. Direct converting X-ray detectors are based on absorption of X-rays in semiconductor material, which leads to a generation of charge carriers. By applying high bias voltage charge carriers can be separated and with this the arising current pulse can be assessed by suitable readout integrated circuits (ICs) subsequently. The X-ray absorber itself is implemented as a diode based on GaAs to use it in the reverse direction. It exhibits low dark currents and can therefore be used at room temperatures. The GaAs absorber has a structured top electrode designed on variable bonding and high breakdown voltages. The implemented GaAs absorber exhibits a pixel size of 100 μm while the readout IC features fast dead-time-free readout, energy discrimination by two individually adjustable thresholds with 20 bit deep counters and radiation-hard design on chip level. These properties guarantee the application as fast and thus sensitive line detector for imaging processes. Another advantage of the imaging line detector is the cascadability of several sensor modules with 1024 pixels each. This property ensures that the 102.4 mm long sensor modules can be concatenated virtually with arbitrary length gaplessly. The readout ICs hitting radiation dose can be further minimized by implementing constructive steps to ensure longer lifetime of the sensor module. Furthermore, first results using the introduced sensor module for solid state X-ray detection are discussed.

The interaction of the radiation pressure with micro-mechanical oscillators is earning a growing interest for its wide-range applications (including high sensitivity measurements of force and position) and for fundamental research (entanglement, ponderomotive squeezing, quantum non-demolition measurements). In this contribution we describe the fabrication of a family of opto-mechanical devices specifically designed to ease the detection of ponderomotive squeezing and of entanglement between macroscopic objects and light. These phenomena are not easily observed, due to the overwhelming effects of classical noise sources of thermal origin with respect to the weak quantum fluctuations of the radiation pressure. Therefore, a low thermal noise background is required, together with a weak interaction between the micro-mirror and this background (i.e. high mechanical quality factors). The device should also be capable to manage a relatively large amount of dissipated power at cryogenic temperatures, as the use of a laser with power up to a ten of mW can be useful to enhance radiation pressure effects. In the development of our opto-mechanical devices, we are exploring an approach focused on relatively thick silicon oscillators with high reflectivity coating. The relatively high mass is compensated by the capability to manage high power at low temperatures, owing to a favourable geometric factor (thicker connectors) and the excellent thermal conductivity of silicon crystals at cryogenic temperature. We have measured at cryogenic temperatures mechanical quality factors up to 10⁵ in a micro-oscillator designed to reduce as much as possible the strain in the coating layer and the consequent energy dissipation. This design improves an approach applied in micro-mirror and micro-cantilevers, where the coated surface is reduced as much as possible to improve the quality factor. The deposition of the highly reflective coating layer has been carefully integrated in the micromachining process to preserve its low optical losses: an optical finesse of F = 6×10⁴ has been measured in a Fabry-Perot cavity with the micro-resonator used as end mirror.

Measurement of the 1/f noise of MEMS devices with sidewall embedded piezoresistors, prototyped for the current study, are described in the present paper. A modified sample conditioning and pre-amplification setup was employed and the complete arrangement was kept at 30°C. The 1/f and the 1/Δf noise signals are fully correlated as the underlying mechanism is the same for both phenomena. The bias voltage of each resistor ranges from zero to V_pp and the device currents contain 1/f noise due to the DC bias in conjunction with conductivity fluctuations. Accordingly, the AC bias results in 1/Δf noise centred about the frequency of the sinusoidal. The spectrally resolved analysis of the 1/f and down-converted 1/Δf noise signals was then established with two instances of a digital lock-in amplifier capable of mHz operation. As both lock-in amplifiers have been locked to a common reference signal, the spectral analyser keeps any correlation between the two channels. Measurements of the current noise were done over the frequency range 0.0625 Hz to 2.048 kHz and measurement resolution of about 10^-18 V²/Hz is determined by the selected correlator averaging period in conjunction with the total noise of the instrumentation channels. For a direct comparison with metal-film resistor technology, sidewall piezoresistors have been replaced by 1 kΩ metal-film resistors for dedicated measurements. The crossover of the 1/f noise of a full bridge of piezoresistors and their thermal noise will appear below 10 Hz for a bias voltage smaller than 1V. This is, to our best knowledge, among the best 1/f noise performances for piezoresistors.

We present the design and implementation of a MEMS pressure sensor with an operation potential under harsh conditions at high temperatures (T = 300 – 800°C). The sensor consists of a circular HEMT (C-HEMT) integrated on a circular AlGaN/GaN membrane. In order to realize MEMS for extreme conditions using AlGaN/GaN material system, two key issues should be solved: (a) realization of MEMS structures by etching of the substrate material and (b) formation of metallic contacts (both ohmic and Schottky) to be able to withstand high thermal loads. In this design concept the piezoresistive and piezoelectric effect of AlGaN/GaN heterostructure is used to sense the pressure under static and/or dynamic conditions. The backside bulk micromachining of our SiC wafer in the first experiment started with FS-laser ablation down to ~200 -270μm deep holes of 500μm in diameter. Because no additional intermediate layer can stop the ablation process, the number of laser pulses has to be optimized in order to reach the required ablation depth. 2D structural-mechanical and piezoelectric analyses were performed to verify the mechanical and piezoelectric response of the circular membrane pressure sensor to static pressure load (in the range between 20 and 100kPa). We suggested that suppressing the residual stress in the membrane can improve the sensor response. The parameters of the same devices previously fabricated on bulk substrates and/or membranes were compared. The maxima of drain currents of our C-HEMT devices on SiC exhibit more than four times higher values compared to those measured on silicon substrates.

This article describes the application of a microelectromechanical system (MEMS) with a beam-shaped cantilever and an integrated piezo-resistive measuring bridge. This device is used for a quick inline control of building panels, which consist of different materials (e.g. metals, polymers and elastomers). The micro sensing device distinguishes itself by a comparatively very low probing force (<100 μN), a high natural frequency (<2.7 kHz) and a very small mass (≈ 0.1 mg). Measuring speeds up to approx. 10 mm/s can be realized. In addition, this sensor comes with a typical resolution in vertical displacement of 2 nm (due to noise floor Δf = 1,6 kHz).

Advances in the miniaturization of semiconductor devices have been made possible by new methods of microfabrication techniques . These advances have stimulated the birth of Micro Electro Mechanical Systems (MEMS) technology which enable the fabrication of a wide variety of sensing and actuating devices of microscopic dimensions . Of particular interest are thermal microactuators which provide large deflections and are compatible with existing IC technologies. In MEMS technology, a well controlled etching process is critical for the fabrication of structures with specific geometry and properties. Increasing demand for intricate semiconductor devices has fueled and motivated researches to develop high precision micromachining techniques . Inductively coupled plasma- Reactive ion etching (ICP-RIE) is capable of producing features with high aspect ratio as high as 90:1. Taking advantage of the notching effect when making a structure from silicon on insulator (SOI), structure release without the use of HF acid has been demonstrated. We report on the development of a self-aligned single-mask process for the fabrication of released and movable MEMS devices. ICP-RIE was used to realize the structures directly out of single crystal silicon. Applying side wall passivation, controlling the ratio of ion flux and radical flux, smooth etching profile can be obtained with high aspect ratio. No wet etching process is required to release the structures as is the case with SOI wafers. This approach overcomes the stiction limitation associated with wet etching and yields good thickness uniformity over the entire structure. Electrothermal microactuators with integrated microgrippers were designed, fabricated and characterized. harvesters.

Nickel is often used in the micro fabrication because of its fatigue resistance and its mechanical properties. It is used for instance for thermal actuators, micro-grippers, or RF-switches. The defined electrodeposition of the nickel matrix is crucial for the properties and functionality of the thermal actuators. Micro galvanic processes are the basis of this electrodeposition, and require knowledge of the electrochemical fundamentals as well as numerical electrochemical process simulation for adjustment. Especially realization of high aspect ratios requires the use of sophisticated plating techniques such as pulse reverse deposition. The pulse plating process was adjusted by using the results of electrochemical numerical simulation routines, visualizing the (local) potential field and the current field line distribution as a function of the applied electrochemical parameters. Compact, completely void free structures could be obtained applying the developed pulse plating process to the structured wafers. The electrodeposited material has been nickel for stability and hardness reasons. MEMS structures were designed to convert the thermal expansion of the material into an in-plane defection. A custom made measurement setup, consisting of a sealable chamber, a Peltier element with a temperature control unit, and an optical microscope is used to measure these defections at different temperatures. Additional, finite element simulations are carried out to determine the thermal expansion coefficient of the plated Nickel.

A pre-bond cleaning process was developed utilizing a unique, radially uniform, large area proximity type Megasonic transducer. In prior work this new cleaning method was investigated for PRE (particle removal efficiency) as well as particle neutrality. These tests yielded higher values than those achieved with the processes of record. Subsequently, this process was integrated into an industrial volume low temperature fusion bonding process and enabled higher bonding yields. In the above process flow the process fluid was dispensed to fill the gap between the Megasonic transducer surface and the substrate using an atmospheric free flow stream applied to the substrate. Current work describes development, testing and operational verification of a process fluid management device used in conjunction with the wide area proximity Megasonic transducer. The goals of this development were reduction of process fluid amount required, increase the operating substrate rotation speed, and provide better control of process fluid parameters. The design criteria and process flow as well as test results demonstrating the benefits of the new system are presented.

This work presents polymeric microsensors for the monitoring of alcohol contents in aqueous solutions. The inexpensive sensor device is partially built by polymers. The housing consists of (100) Si substrate, whereas the sensitive material is poly(N-isopropylacrylamide) (PNIPAAm). The acquisition of the sensor data is realized by a non-contact light barrier. The output answer of this light barrier is strong linear. The continuous sensor signal observed by the light barrier is the deflection of an elastic membrane, which is caused by the swelling or deswelling of the stimuli-responsive hydrogel. To achieve an electronic adjustment of the sensor’s measurement range we use a controlled double-sensitivity of hydrogel. By controlling the temperature of the temperature-responsive hydrogel PNIPAAm the phase transition concentration is precisely adjustable to the required value. The electrothermic control interface is based on a Peltier element. The response time of the sensors is in the lower minute range and therefore fast enough for the most of applications. The average sensor resolution for measurements of ethanol is ca. 23mV/wt.-%. The shift of measurable concentration range approximately amounts to 5.6 wt.-% ethanol per 5°C. Further improvements are possible.

Artificial compound eye cameras are a prominent approach of next generation wafer level cameras for consumer electronics due to their lower z-height compared to conventional single aperture objectives. In order to address low cost and high volume markets, their fabrication is based on a wafer level UV-replication process. The image quality of compound eye cameras can be increased significantly by the use of refractive freeform arrays (RFFA) instead of conventional microlens arrays. Therefore, we present the fabrication of a RFFA wafer level molding tool by a step and repeat process for the first time. The surface qualities of the fabricated structures were characterized with a white light interferometer.

Advances in micro and nano fabrication technologies for MEMS require high-level measurement techniques with regard to sampling and sensitivity. For this purpose at the Institute of Microtechnology (IMT) highly sensitive piezoresistive 3D force sensors based on SU-8 polymer have been developed. In this paper we present an improved micro fabrication process for a double-sided micro structured design. The sensors are produced by multilayer processing techniques such as UV lithography and coating methods. The double-sided micro structured design demands a photoresist application method which simultaneously features a top side structuring and a casting from a mold. We use a new micro molding process to meet the demands. The micro fabrication technology is described, focusing on the development of the molding structure for shaping of the bottom side and a capable release process for the detachment of the molded structures. The fabrication process of the SU-8 mold layer is optimized to fabricate molding structures with heights from a few μm up to 350 μm. Therefore different SU-8 formulations, namely with classification numbers 5, 25, 50, and 100, have been used. The fundamental limitations for the mold design result from the lithography process, which defines the smallest lateral resolution, and from the characteristics of a molding process, e. g. the impossibility to realize an undercut. To allow for reliable release, the molding structures have to be coated with a sacrificial layer. A silicon nitride is deposited onto the substrate with an accompanying monitoring of the deposition temperature during the PECVD process.

This paper presents the design and fabrication of a 2nd order L/S band filter used as a test vehicle for the development of a fabrication technology for cavity microwave filters based on micromachining in order to preliminary explore all the technological constraints on a simpler structure. The multilayered 2nd order pseudo-elliptic L/S band filter is based on λ/4 TEM mode resonators which are patterned on a dielectric layer. For convenience 500 μm thick Si wafers have been used even if this limits the simulated Q factor of the 2nd order L/S band filter to about 200. The test structures presented here amount to the more sophisticated 4th order filters in an extended technological concept (i.e. 1500 μm thick Si wafer and two additional modules) but still based on similar resonating elements aiming to replace the existing bulky metallic waveguide filters installed in many satellite transceivers. A five mask fabrication process is employed for the realization of the elements of said filter which is based on three modules. Module A and B are fabricated on the same wafer while module C which served as ground is fabricated on a separate wafer. A 2 μm high sealing ring is etched on the back of module A and B by DRIE (Deep Reactive Ion Etching) while cavities and TSVs (Through Silicon Vias) are etched by TMAH (TetraMethylAmmonium Hydroxide). The surface mounting compatibility of the filter is obtained by adopting vertical via holes to connect the external feeding lines (e.g. microstrip or coplanar) with the filter resonators. Such a transition separates the input/output from the filter input/output coupling mechanism. The final wafers are diced and specimens are vertically stacked and bonded through thermocompression bonding. The overall filter dimensions are 48x20x1.5 mm³.

In this work, we study the modes of vibration for two different families of aluminium nitride-actuated piezoelectric microstructures: contour modes and flexure-actuated modes. For the contour modes, the structure vibrates at frequencies determined by its edge dimensions whereas for the flexure-actuated modes a suspended structure is displaced by the lateral bending of the flexures. We combine electrical and optical techniques to fully characterize the vibrating modes of these types of in-plane MEMS structures. An electronic speckle pattern interferometry technique is used for a full 3D detection of the movement of the structures. Quality factors as high as 5000 and motional resistance as low as 4 KOhm were obtained for in-plane modes in air and a quality factor as high as 300 was obtained for an in-plane structure with water on the top surface. This work shows the great flexibility in the selection of resonant modes in piezoelectric resonators and actuators, implemented by a proper design of the electrode layout geometry.

In this work, the fabrication process of piezoelectric AlN cantilevers is presented. The cantilevers were electrically characterized in a vacuum chamber offering the possibility to close-loop control the back pressure from atmospheric conditions down to 5x10^-3 mbar. The quality factor (Q factor) is an important figure of merit to evaluate the performance of micro-resonators. In particular, two different modes were detected and analyzed. The first bending mode detected at 19.5 kHz has a quality factor of 470 at atmospheric pressure which increases continuously to 985 at 1x10^-1 mbar. The corresponding resonant frequency shifted from 19.500 kHz at atmospheric pressure to 19.573 kHz at 5 mbar. Below this pressure level, the resonance frequency stays unaffected within the measurement accuracy. The second bending mode detected at 117.264 kHz exhibits a quality factor of about 570 at atmospheric pressure increasing continuously to 1275 at 1x10^-1 mbar. In agreement with the other resonant frequency under investigation the corresponding resonant frequency decreased from 117.264 kHz at atmospheric pressure to 117.630 kHz at 5 mbar.

During the last decades in the theory of machining nonmetallic materials some serious advances have been achieved in the field of applying fundamental scientific approaches to the grinding and polishing technologies for high-quality precision surfaces of electronic components, optical systems, and decorative articles made of natural and synthetic stone [1–9]. These achievements include a cluster model of material removal in polishing dielectric workpieces [1–3, 6–7] and a physical-statistical model of formation of debris (wear) particles and removal thereof from a workpiece surface [8–10]. The aforesaid models made it possible to calculate, without recourse to Preston’s linear law, the removal rate in polishing nonmetallic materials and the wear intensity for bound-abrasive tools. Equally important for the investigation of the workpiece surface generation mechanism and formation of debris particles are the kinetic functions of surface roughness and reflectance of glass and quartz workpiece surfaces, which have been established directly in the course of polishing. During the in situ inspection of a workpiece surface by laser ellipsometry [11] and reflectometry [12] it was found out that the periodic change of the light reflection coefficient of a workpiece surface being polished is attributed to the formation of fragments of a deposit consisting of work material particles (debris particles) and tool wear particles [13, 14]. The subsequent studies of the mechanism of interaction between the debris particles and wear particles in the tool–workpiece contact zone, which were carried out based on classical concepts [15, 16], yielded some unexpected results. It was demonstrated that electrically charged debris and wear particles, which are located in the coolant-filled gap between a tool and a workpiece, move by closed circular trajectories enclosed in spheres measuring less than one fifth of the gap thickness. This implies that the probability of the debris and wear particles reaching the tool and workpiece surfaces and, especially, getting localized on the surfaces is extremely low, which contradicts the results of experimental examination of these surfaces. Based on the quantum-mechanical description of the process of scattering of the debris and wear particles that are as small as 3–4 nm in the tool–workpiece contact zone, the mechanism of formation of a workpiece microrelief and the mechanism of formation of a debris-particle deposit on the tool surface were clarified [17–21]. However, the mechanism of formation of the deposit fragments and their discrete arrangement on the workpiece surface in the process of polishing with a bound-abrasive tool has not been studied yet.

A closed loop circuit capable of tracking resonant frequencies for MEMS-based piezoresistive cantilever resonators is developed in this work. The proposed closed-loop system is mainly based on a phase locked loop (PLL) circuit. In order to lock onto the resonant frequency of the resonator, an actuation signal generated from a voltage-controlled oscillator (VCO) is locked to the phase of the input reference signal of the cantilever sensor. In addition to the PLL component, an instrumentation amplifier and an active low pass filter (LPF) are connected to the system for gaining the amplitude and reducing the noise of the cantilever output signals. The LPF can transform a rectangular signal into a sinusoidal signal with voltage amplitudes ranging from 5 to 10 V which are sufficient for a piezoactuator input (i.e., maintaining a large output signal of the cantilever sensor). To demonstrate the functionality of the system, a self-sensing silicon cantilever resonator with a built-in piezoresistive Wheatstone bridge is fabricated and integrated with the circuit. A piezoactuator is utilized for actuating the cantilever into resonance. Implementation of this closed loop system is used to track the resonant frequency of a silicon cantilever-based sensor resonating at 9.4 kHz under a cross-sensitivity test of ambient temperature. The changes of the resonant frequency are interpreted using a frequency counter connected to the system. From the experimental results, the temperature sensitivity and coefficient of the employed sensor are 0.3 Hz/°C and 32.8 ppm/°C, respectively. The frequency stability of the system can reach up to 0.08 Hz. The development of this system will enable real-time nanoparticle monitoring systems and provide a miniaturization of the instrumentation modules for cantilever-based nanoparticle detectors.

This paper deals with the simulation of membrane actuators based on thick film piezoelectric ceramics with interdigitated electrodes using the finite element method. A modified piezoelectric coupling matrix is introduced to account for the piezoelectric non-linearity due to poling and actuation at high electric fields. Electrodes were fabricated on top of 250 μm thick PZT substrates which were characterized. The experimental data verified the simulation results and proved the necessity of the modified coupling matrix.