Piezoresistors have been used widely for various microsensors, such as accelerometers and pressure sensors. Conventionally, piezoresistive sensors are fabricated by placing the piezoresistors on the region where largest strain would occur. In order to satisfy the measurement sensitivity as well as the fabrication processes, the substrate underneath the microstructures are usually removed through the back-sided etching. Hence, the fabrication processes are complex and time-consuming. To solve this problem, this article intends to propose an alternative design for piezoresistive sensors. The approach is to form the piezoresistors behind the boundary of the microstructure by diffusion. Therefore, this piezoresistive sensor is compatible with front-side etch process and without depositing an additional polysilicon layer. The proposed design also provides the capability of integrating with various microactuators. In application of the proposed design, a micromachined cantilever was used to provide the strain field to the piezoresistive sensor. The feasibility of the sensor was verified by both simulation and experiment. According to the results predicted by the finite element analysis, the stress at the proposed sensing region is approximate one order of magnitude smaller than that at the end of the microstructure. In other words, a reasonable signal is still available at this region. During the experiment, silicon dioxide microcantilevers were fabricated, and piezoresistors were formed by diffusing n+ on silicon substrate. An experimental setup containing a micropositioner and a piezoelectric shaker was constructed. The output of piezoresistors was then measured when microcantilevers bending or vibrating.

Date Published: 31 August 1999
PDF: 8 pages
Proc. SPIE 3876, Micromachined Devices and Components V, (31 August 1999); doi: 10.1117/12.360500

Published in SPIE Proceedings Vol. 3876:
Micromachined Devices and Components V
Patrick J. French; Eric Peeters, Editor(s)