A calibration technique for measuring MEM's strain sensor performance is presented. For resistance based sensors, calibration entails determining a relationship between change in resistance of the sensor and strain (the gauge factor). A modification to the standard calibration method employed for metal foil, resistance strain gauges is presented. The approach entails constructing two nearly identical test specimens: a specimen with the MEM's sensor mounted with adhesive and a specimen with a strain gauge on silicon mounted with adhesive. Data from the strain gauge specimen provide the basis for evaluating the strain at the sensor. Test data are presented which show that strain at the wafer is 52% to 55% of the strain applied to the specimen. A theoretical basis for this strain transfer relationship is presented. Finally, a dimensionless geometry factor, based on shear lag theory, is derived. As the sensor cross section (width and length) and thickness changes, the strain transfer between the specimen and sensor vary linearly with the geometry factor. This result emphasizes the importance in considering the overall sensor geometry when employing semiconductor strain gauges.
Bibliographical noteFunding Information:
Manuscript received May 7, 2002; revised March 14, 2003. This work was supported by the U.S. Naval Research Laboratory (NRL) under Contract N00014-94-C-2231. Subject Editor W. N. Sharpe, Jr. C. Hautamaki, J. Zhou, and S. C. Mantell are with the Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455 USA (e-mail: email@example.com). L. Cao is with the Department of Mechanical Engineering, Iowa State University, Ames, IA 50011 USA. T. S. Kim is with the Microsystem Research Center, Korean Institute of Science and Technology (KIST), Seoul 136-791, Korea. Digital Object Identifier 10.1109/JMEMS.2003.817887 Fig. 1. (a) SEM of the patterned polysilicon in a monofilament sensor. (b) Schematic top view of a monofilament sensor.
- Gauge factor
- Sensor geometry