Graphene, one of the recently discovered carbon nanostructures, has shown good piezoresistive properties. One of the most important areas of research for graphene sheets, in terms of basic science and application in strain or stress sensors, is the measurement of gauge factors. The gauge factors of various layers of graphene sheets are measured based on the equivalent stress beam. The measurement is carried out using a beam-bending method to detect the change in resistance of graphene sheets in different bending states. The gauge factor ranges from 10 to 15, depending on the number of layers in the graphene sheet. These results reveal the piezoresistance effect of single- and multi-layer graphene sheets, which will be of benefit in the fabrication of microsensors. The resistance of graphene sheets decreases as temperature increases from 20°C to 60°C, and the gauge factor is not very sensitive to changes in environmental temperature.
Presented in this paper is the investigation on sensitivity of micromachined condenser microphone. The sound-sensitive diaphragm of the microphone is formed by surface micromachined thin-film that is normally initially stressed due to the deposition process of the thin-film. Three varieties of diaphragm constructions, conventional flat diaphragm (FD), corrugated diaphragm (CD) and deep cavity-shaped diaphragm (DCD), are involved into the study. Both analysis and finite element model (FEM) are used for comparison of the mechanical sensitivity of the different kinds of diaphragm. Reasonable initial stress range of poly crystalline silicon thin films is assumed for the microphones. The DCD shows a much higher mechanical sensitivity compared to the other two kinds of diaphragm for the assumed film-stress range. A fabrication technology of low tensile-stress poly-silicon film is also provided and proposed for the high sensitivity microphone with the DCD.
Anisotropic etching of silicon creates different convex- corner undercutting contours in different varieties of etchant. This difference in undercutting configuration is investigated by analyses of the undercutting formation in detail. Based on Wulff-Jaccodine rules and some experimental results, theoretical analyses are given to clarify the reasons of different undercutting configuration caused by different etchant and the rationality of a certain plane occupying the undercutting position for a certain etchant. Furthermore, the investigation is lead to the convex-corner undercutting under maskless etching, i.e., during the etching mask on the structure removed. Experimental results show that the convex-corner undercutting under maskless etching is far different from that of conventional masked etching. The geometrical evolution of the undercutting is studied both experimentally and analytically. The compensation criteria for maskless etching are discovered and the corresponding compensation schemes are provided.
Described in this paper are a novel composite beam-mass structure and a micro gyroscope based on the structure. The composite beam consists of two sections: a section of vertical beam with a cross-section vertical to the wafer surface and a section of horizontal beam near the wafer surface. As the two sections have two orthogonal compliant directions, the structure has two orthogonal vibration modes: a vertical vibration mode decided by the horizontal beam and a lateral vibration mode decided by the vertical beam. Therefore, a vibratory gyroscope can be developed by this composite beam structure with a mass attached. As the composite beam is a multilevel structure that can hardly be fabricated by a conventional anisotropic etching technology, a novel 'maskless etching' technology for <100> vertical steps has been developed for the structure. Piezoresistive bridges on the surfaces of the horizontal and the vertical beams are used to monitor the driving vibration and to sense the output signal. Testing shows that the sensitivity from the piezoresistive bridge is 0.22 (mu) V/(degrees/sec) under a 6V AC driving with a DC bias. The special advantage of the sensor is the ability of working in an atmospheric environment.
Proceedings Volume Editor (2)
This will count as one of your downloads.
You will have access to both the presentation and article (if available).
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.