This PDF file contains the front matter associated with SPIE Proceedings Volume 9185, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

A remarkable feature of the modern integrated circuit is its ability to operate in a stable fashion, with almost perfect reliability. Recently developed classes of electronic materials create an opportunity to engineer the opposite outcome, in the form of devices that dissolve completely in water, with harmless end products. The enabled applications range from ‘green’ consumer electronics to bio-resorbable medical implants—none of which would be possible with technologies that exist today. This talk summarizes recent work on this physically ‘transient’ type of electronics, from basic advances in materials chemistry, to fundamental studies of dissolution reactions, to engineering development of complete sets of device components, sensors, and integrated systems. An ‘electroceutical’ bacteriocide designed for treatment of surgical site infections provides an application example.

Recent studies of poly(3-hexylthiophene) solutions demonstrate that „sample history” (solution preparation, storage conditions) affects the aggregation process(es) and, consequently, electrical properties. In this paper, we demonstrate the evolution of UV-Vis spectra and the formation of additional red-shifted peaks which visualize the aggregation of p3ht chains. We report comparative study of p3ht based organic field effect transistors fabricated by spin coating using fresh and aged (for 6 months) chloroform solutions with anisole addition. Three order of magnitude improvement in the oFET charge carrier mobility is exhibited. These results provide new insight into p3ht crystallization process(es) and nanofiber-based oFETs.

Organic electronics hold the promise of enabling the field of flexible electronics. Several novel organic transistor concepts based on the technology of molecular doping are presented that open new directions to improve the performance of OFETs. The realization of doped organic transistors as well as organic junction field-effect transistors is demonstrated. Furthermore, vertical transistor concepts with channel lengths in the sub-micrometer regime are discussed.

This presentation focuses on recent development of key technologies for printed LSIs which can provide future low-cost platforms for RFID tags, AD converters, data processors, and sensing circuitries. Such prospect bears increasing reality because of recent research innovations in the field of material chemistry, charge transport physics, and solution processes of printable organic semiconductors. Achieving band transport in state-of-the-art printable organic semiconductors, carrier mobility is elevated above 15 cm2/Vs, so that reasonable speed in moderately integrated logic circuits can be available. With excellent chemical and thermal stability for such compounds, we are developing simple integrated devices based on CMOS using p-type and n-type printed organic FETs. Particularly important are new processing technologies for continuous growth of inch-size organic single-crystalline semiconductor “wafers” from solution and for lithographical patterning of semiconductors and metal electrodes. Successful rectification and identification are demonstrated at 13.56 MHz with printed organic CMOS circuits for the first time.

Thin-film transistors (TFTs) of a metal oxide semiconductor typically are transparent and have high mobility to be paid attention for back plane of displays. One of the most actively studied fabrication methods of metal oxide semiconductors is the solution processing (sol-gel) method, owing to its low-cost, simple and fast steps that ensure good product uniformity, and applicability to roll-to-roll processing. Our study focused on probing the electronic properties of solution-processed metal oxide TFTs. We have calculated the density of state (DOS) with monochromatic photonic capacitance-voltage (MPCV) measurements. Improvements in device are proved by electronic and photo-electronic methods.

We report the characteristics of ferroelectric field effect transistor (FeFET) nonvolatile flash memory devices using aligned P(VDF-TrFE) electrospun nanofibers as the dielectric layer. These FeFET devices showed reliable memory behaviors and memory window proportional to the quantity of aligned nanofibers containing the ferroelectric β-phase crystalline domain. Moreover, the FeFET devices using nanofibers exhibited the long-term stability in the data retention larger than 10₄ s with the ON/OFF ratio of ~10³, and the multiple switching operation stability up to 100 cycles.

Terahertz electromodulation spectroscopy is a novel tool for studying charge carrier transport in polycrys­talline thin films. The technique selectively probes the high-frequency response of mobile carriers and is insensitive to scattering at grain boundaries as well as to trapping processes. In thin films of pentacene we find a hole mobility of 21 cm² /Vs, which exceeds the largest previously reported values obtained in poly­ crystalline pentacene. Additionally, the data provide an upper limit of the hole conductivity effective mass of m_h ≈ 0.8 m_e.

This paper describes several approaches to understanding and improving the response of π-conjugated (semiconducting) polymers to tensile strain. Our principal goal was to establish the design criteria for introducing elasticity and ductility in conjugated (semiconducting) polymers through a rigorous analysis of the structural determinants of the mechanical properties of this type of material. We elucidated the details of the effect of the alkyl side chain length on the mechanical properties of regioregular polythiophene and used this analysis to select materials for stretching and transfer printing of organic solar cells to hemispherical substrates. This demonstration represents the first time that a conjugated polymer device has ever been stretched and conformally bonded to a complex 3D surface (i.e., other than a cone or cylinder, for which flexibility—as opposed to stretchability—is sufficient). We then further explored the details of the dependence of the mechanical properties on the side chain of a semiconducting polymer by synthesizing a series of hybrid materials (block and random copolymers) containing both short and long side chains. This analysis revealed the unusual semiconducting polymer, poly(3-heptylthiophene), as having an excellent combination of mechanical and electronic properties. In parallel, we explored a new method of producing “blocky” copolymers using a new procedure based on random segmentation of conjugated monomers. We found that introduction of structural randomness increased the elasticity without having detrimental effects on the photovoltaic performance. We also describe methods of synthesizing large volumes of conjugated polymers in environmentally benign ways that were amenable to manufacturing.

Molecularly hybridized materials composed of polymer semiconductors (PSCs) and single-walled carbon nanotubes (SWNTs) may provide a new platform to exploit an advantageous combination of semiconductors, which yields electrical properties that are not available in a single component system. In this talk, we demonstrate high-performance ink-jet printed hybrid transistors with an electrically engineered heterostructure by using specially designed PSCs and semiconducting SWNTs (sc-SWNTs) whose system achieved a high mobility of 0.23 cm²V^-1s^-1, no V_on shift, a low off-current, and good bias-stability. We also revealed that binding energy between PSCs and sc-SWNT was strongly affected by side-chain length of PSCs, leading to the formation of homogeneous nanohybrid film. Eventually, understanding of electrostatic interactions in the heterostructure and experimental results suggest criteria for the design of nanohybrid heterostructures. Acknowledgement. This work was supported by a grant (Code No. 2011-0031628) from the Center for Advanced Soft Electronics under the Global Frontier Research Program of the Ministry of Science, ICT and Future Planning, Korea. The authors acknowledge Prof. Kilwon Cho for collaboration on the analysis of x-ray diffraction.

The fabrication of stretchable devices has been explored via two approaches: wavy design of non-stretchable materials or elastomeric electronic materials. The first approach has been widely used, specifically led by Rogers group. The second approach requests stretchability of all the device components, hence there have been no reports on the fabrication of semiconducting polymer-based stretchable transistors due to the lack of stretchable active layer and dielectric. This presentation deals with the fabrication of an array of highly stretchable polymer transistors made entirely of stretchable components. The transistors were constructed of stretchable Au nanosheet electrodes, polyelectrolyte gel for the gate dielectric, metal nanowires for the circuit, and nanofibril-based stretchable channel materials. This talk will present the issues of the components regarding with the stretchability and mechanical performance.

Two types of printable conductor and a bilayer gate dielectric are evaluated for use in all-additive, inkjetprinted complementary OTFTs. The Ag nanoparticle ink based on nonpolar alkyl amine surfactant or stabilizer enables good charge injection into p-channel devices, but this ink also leaves residual stabilizer that modifies the transistor backchannel and shifts the turn-on voltage to negative values. The Ag ink based on polar solvent requires dopant modification to improve charge injection to p-channel devices, but this ink allows the OTFT turn-on voltage to be close to 0 V. The reverse trend is observed for n-channel OTFTs. For gate insulator, a bilayer dielectric is demonstrated that combines the advantages of two types of insulator materials, in which a fluoropolymer reduces dipolar disorder at the semiconductor-dielectric interface, while a high-k PVDF terpolymer dielectric facilitates high gate capacitance. The dielectric is incorporated into an inverter and a three-stage ring oscillator, and the resulting circuits were demonstrated to operate at a supply voltage as low as 2 V, with bias stress levels comparable to circuits with other types of dielectrics.

We discuss a non-vacuum low-cost reverse stamping method for the realization of circuits based on top-gate organic field-effect transistors (OFETs) with a bi-layer gate dielectric. This method allows for patterning of high-k inorganic dielectric films produced by atomic layer deposition and consequently of the bilayer gate dielectric layers used in our top-gate OFETs. We demonstrate the fabrication and operation of logic inverters and ring oscillators following this approach.

A semiconducting polymers with conjugated diketopyrrolopyrrole (DPP) unit was developed for high performance ambipolar organic field-effect transistors (OFETs). We report electrical characteristics of DPP OFETs in various ways which measured transistor and inverter performance with various bias conditions and self-assembled monolayers (SAMs) treatment. Ambipolar DPP conjugated polymer OFETs showed high hole and electron mobility of μh=0.57 cm2V-1s-1 and μe=0.51 cm2V-1s-1 with O2 plasma treatment and 1-decanethiol SAMs treatment, respectively with annealing at 100°C. Contact resistance effect on mobilities was investigated by measuring contact resistance during device operation through gated four-point probe (gFPP) and simultaneous contact resistance extraction model directly from current voltage characteristics.

An organic thin film transistor has been fabricated using evaporated Magnesium Phthalocyanine as active layer. Parylene film prepared by chemical vapour deposition has been used as the organic gate insulator. Annealing of the samples is performed at 120 °C for 3 hrs. At room temperature, these transistors exhibit the p-type conductivity with field-effect mobility ranging from 0.009 - 0.021 cm2/Vs and ( I on/I off) ratio ~10³. The effect of annealing on the transistor characteristics is discussed.

The OTFTs with both p type and n type channel layers were fabricated using the inverted-staggered (top contact) structure by thermal vapour deposition on Si/SiO₂ substrate. Pentacene and N,N’-Dioctyl- 3,4,9,10- perylenedicarboximide (PTCDI-C8) were used as channel layer for the fabrications of p type and n type OTFTs respectively. A comparative study on the degradation and density of states (DOS) of p type and n type organic semiconductors have been carried out. In order to compare the stability and degradation of pentacene and PTCDI-C8 OTFTs, the devices were exposed to air for 2 h before performing electrical measurements in air. The DOS measurements revealed that a level with defect density of 10²⁰ cm^-3 was formed only in PTCDI C8 layer on exposure to air. The oxygen adsorption into the PTCDI-C8 active layer can be attributed to the formation of this level at 0.15 eV above the LUMO level. The electrical charge transport is strongly affected by the oxygen traps and hence n type organic materials are less stable than p type organic materials.

Luminescent materials have been widely applied in chemo- and bio-sensing applications because these luminescent materials offer high signal-to-background ratio, superior sensitivity and broad dynamic ranges in various detections. Conventional luminogens suffer from aggregation-caused quenching (ACQ) effect due to strong π–π stacking interaction upon aggregate formation of the luminogens with analytes. Such ACQ effect limits the scope of practical sensing applications. Luminogens with aggregation-induced emission (AIE) characteristics enjoy high emission efficiency in solid or aggregated state while they are non-emissive in solution. AIE luminogens (AIEgens) tackle the lethal problem of ACQ materials in the sensing applications. Siloles and tetraphenylethene (TPE) are archetypal AIE cores and possess advantages of facile synthesis and readily functionalization. AIEgens have been utilized to develop various fluorescent chemosensors. For example, hyperbranched AIE polymers with different topologies can be worked as turn-off explosive sensor with high sensitivity. The explosive detections can be done in solid film, which facilitates practical usage. The AIEgens can also be used as sensors for volatile organic compounds and metal ions through alternating fluorescence on/off mechanisms. Besides chemosensor, the AIEgens have been applied in the fields of biology. Water-soluble AIEgens have been developed for quantifying nucleic acids and proteins. They can serve as bioprobes for real-time monitoring and studying the kinetic of protein conformational changes, making them promising for diagnostic and therapeutic applications. These demonstrations significantly expand the scope of analysis applications of AIEgens and offer new strategies to the design of new fluorescent chemo- and bio-sensors.

Integration of electronics into materials and objects that have not been functionalized with electronics before, open up extensive possibilities to support mankind. By adding intelligence and/or operating power to materials in close skin contact like clothing, furniture or bandages the health of people can be monitored or even improved. Foil based electronics are interesting components to be integrated as they are thin, large area and cost effective available components Our developed technology of printed electronic structures to which components are reliably bonded, fulfills the promise. We have integrated these components into textiles and built wearable encapsulated products with foil based electronics. Foil components with organic and inorganic LEDs are interconnected and laminated onto electronic textiles by using conductive adhesives to bond the contact pads of the component to conductive yarns in the textile. Modelling and reliability testing under dynamic circumstances provided important insights in order to optimise the technology. The design of the interconnection and choice of conductive adhesive / underfill and lamination contributed to the durability of the system. Transition zones from laminated foil to textile are engineered to withstand dynamic use. As an example of a product, we have realized an electronic wristband that is encapsulated in rubber and has a number of sensor functionalities integrated on stretchable electronic circuits based on Cu and Ag. The encapsulation with silicone or polyurethanes was performed such, that charging and sensor/skin contacts are possible while simultaneously protecting the electronics from mechanical and environmental stresses.

We present an organic X-ray detector with an active layer deposited from a novel semiconducting ink formulation. The precursor ink consists of blended poly(3-hexylthiophene-2,5-diyl) (P3HT), phenyl-C61-butyric acid methyl ester (PCBM) and the organometallic nanostructure copper(II) 2,2'-bipyridine (Cu(II)BPY). The use of ligands like 2,2' byripidine with cationic species such as Cu(II) improves their solubility in organic solvents. The purpose of the organometallic complex Cu(II)BPY is twofold: to achieve a homogeneous semiconducting ink with P3HT:PCBM blends and to enhance the X-ray interaction with the organic layer through the Cu(II) cation. Our X-ray displays consist of several pixels, each with vertical structures comprising a bendable PET/ITO substrate with a spin-coated semiconducting ink of P3HT:PCBM:Cu(II)BPY (60 nm), followed by thermal evaporation of Al (100 nm) contacts. To the best of our knowledge, this is the first example where an organic X-ray detector includes the organometallic complex Cu(II)BPY in P3HT:PCBM blends, and the electrical characterization of the detector is carried out by impedance spectroscopy (IS). In order to test the devices, each pixel is exposed to X-ray energies ranging from 0 keV to 35 keV and characterized by impedance spectroscopy (IS). Impedance spectra were recorded at frequencies between 20 Hz and 20 kHz and at a modulating signal of 50 mV. Analysis of IS measurements revealed a linear dependence between impedance and X-ray energy. IS analysis is more sensitive compared with standard photocurrent-voltage characteristics.

Electrolyte-gated organic field-effect transistors (EGOFETs) used as transducers and amplifiers in potentiometric sensors have recently attracted a significant amount of scientific interest. For that reason, the fundamental prerequisites to achieve a proper potentiometric signal amplification and transduction are examined. First, polarizable as well as non-polarizable semiconductor- and gate-electrolyte- interface combinations are investigated by normal pulse voltammetry. The results of these measurements are correlated with the corresponding transistor characteristics, clarifying the functional principle of EGOFETs and the requirements for high signal amplification. In addition to a good electrical performance, the EGOFET-transducers should also be compatible with the targeted sensing application. Accordingly, the influence of different gate materials and electrolytes on the sensing abilities, are discussed. Even though all physical requirements are met, EGOFETs typically exhibit irreversible degradation, if the gate potential exceeds a certain level. For that reason, EGOFETs have to be operated using a constant source-drain operation mode which is presented by means of an H⁺ (pH) sensitive ion-sensor.

Electrochemical reduction and oxidation of PEDOT:PSS are used to modulate the channel current in organic electrochemical transistors (OECTs). In addition to changing PEDOT conductivity over more than 4 orders of magnitude, these redox reactions cause a shift in the PEDOT:PSS absorption spectrum. In this work we have used this shift in the absorption spectrum to make spatially and temporally resolved measurements of the redox state of PEDOT:PSS. By applying these measurements to the PEDOT:PSS in an OECT channel, we have shown that the redox state of the PEDOT:PSS is not constant along the channel during transistor operation. Furthermore, we have shown that the time constant of the optical transition is significantly larger near the transistor source than it is near the transistor drain. These results are not considered in existing models of the OECT transient response, and they may lead to a better understanding of geometry-performance relationships in OECTs.

Interface formation between organic semiconductors and substrates or electrodes is of great interest to develop functional devices. In this paper we discuss on the interface formation between the organic semiconductor pentacene and silver as the top electrode. Pentacene is commonly used as active layer in organic field-effect transistors (OFETs). It is known that in OFEts significant percentage of the drain current is realized at organic layer thickness below 5 nm. Therefore, understanding the monolayer regime is vital to identify the physics and chemistry of the organic semiconductor. We report Raman spectroscopy measurements of 1.5 nm pentacene films deposited under high vacuum conditions onto Au or SiO₂ and covered by silver contacts. In order to achieve a detailed molecular identity upon metal evaporation, Raman spectra at each evaporation stage was recorded. Analysis proved that a bare 1.5 nm pentacene film on smooth Au substrates reflects significant enhancement of the Raman signal. Silver contact of about 1 nm thickness promotes enhancement of the Raman internal vibrational modes along the activation of normally infrared-active modes, and the enhancement factors are estimated to be close to 100. The Raman spectroscopy measurements indicate absence of metallorganic pentacene-Ag complexes regardless of the substrate.