A High Performance Accelerometer With A Newly Developed Silicon Bulk Micromachining Technology

In this thesis, a high-performance in-plane-sensitive sidewall-piezoresistive accelerometer with self-test function is proposed and developed. A set of new silicon bulk micromachining process is developed to fabricate the proposed device. With the developed fabrication technique, conventional silicon wafer can be used instead of expensive SOI wafer.Previous works have been studied and summarized. A novel design is then proposed for this high performance accelerometer. The proposed accelerometer consists of 2 rightabout in-plane deflected cantilevers, and the etched trench is serving as overange stop. This design improves the sensitivity by putting the piezoresistor on the surface of the vertical sidewall of the cantilevers. Also by laying out integrated actuator on the vertical sidewall, we realize electrostatic self-test function of the accelerometer. Specifications such as sensitivity, damping ratio and self-test force, etc, are designed with analysis. The designed sensitivity is almost doubled compared with conventional design.The successful fabrication of the device is attributed to the newly developed bulk micromachining technique, which includes deep-trench sidewall diffusion and vertical isolation bar. By using the technique, conventional silicon wafer can be used instead of expensive SOI wafer, with extra advantages such as single-wafer-process, high yield, integration compatibility with IC, etc.Based on testing results, the performance of the device agrees well with design. 7.02mV peak output is obtained for self-testing when the AC actuating frequency is tuned to the resonant frequency of the device. The sensitivity is also tested as0.972uV/3.3V/g.This novel silicon bulk micromachining technology can be widely used as a standard process in MEMS to fabricate various micro sensors and micro actuators.