Novel concept design for complementary metal oxide semiconductor capacitive Z-direction accelerometer

The purpose of this study is to provide a novel concept design for complementary metal oxide semiconductor (CMOS) capacitive Z-direction accelerometers. In this design, capacitance-sensing parallel plates and thin single-metal-layer springs are fabricated by chemical plasma etching. This plasma etching process utilizes a rough vacuum to shorten the mean free path of the reactive gases and increase lateral etching and undercut. Moreover, the thin single-metal-layer springs have the characteristic of a lower spring constant to increase the displacement of the proof mass. Thus, the sensitivity can be further improved. This study has established a post-CMOS chemical plasma etching process to release the accelerometer using sensing electrodes of the capacitance-sensing parallel plates. The Z-direction accelerometer has been fabricated by the standard CMOS 0.35mm two-polycrystalline silicon four-metal (2P4M) process and a post-CMOS process of chemical plasma etching. The measurement results indicate that the sensitivity of the accelerometer is about 0.8 mV/g and the total noise floor is 4.2μV/√Hz.