Design, fabrication and test of a bulk SiC MEMS accelerometer

The application of micro accelerometer in extremely high temperature environment has become an urgent problem to be solved. However, current microelectromechanical system (MEMS) Si-based accelerometer cannot adapt to higher temperatures than 500 °C. Because of its excellent properties in high temperature environments, silicon carbide (SiC) shows promising potential in development of high temperature MEMS sensors, and it is a good alternative to Si for developing accelerometers. Due to the difficulty of bulk-SiC fabrication process and the complex structure of MEMS accelerometers, there are few studies on bulk SiC accelerometers and few test data of the performance. In this study, in order to solve the problem of fabrication, a MEMS accelerometer based on bulk SiC processing technology is designed, and fabricated. The sensor is fabricated using a 4H-SiC wafer and adopts the classic elastic beam-proof mass structure. The top surface of the wafer is a doped N-type SiC epitaxial layer that is used as piezoresistive material to develop sensitive resistance. Ultra-thin (20 μm) elastic beams obtained using dry etching form the sensitive mechanical structure to realize a high-sensitivity output in low/medium-g-value environments. The static flip and dynamic vibration experiments show that the final sensor can test low/medium-g-value acceleration signals precisely. Finally, the dynamic sensitivity obtained is 0.21 mV/g under 5 V input voltage and the linearity is 99.8%. This work has potential value for promoting the practical application of fabrication of bulk micromachined SiC in accelerometer, and the test data can provide guidance for future design of bulk SiC piezoresistive sensors.