Wafer-level hermetic packaged microaccelerometer with fully differential BiCMOS interface circuit

This paper presents a microaccelerometer with wafer-level packaged MEMS sensing element with fully differential, continuous-time BiCMOS interface circuit. The MEMS sensing element is fabricated on a (1 1 1)-oriented SOI wafer by using the sacrificial bulk micromachining (SBM) process. To protect the silicon structure of the sensing element and to enhance the reliability, a wafer level hermetic packaging process is achieved, using silicon–glass anodic bonding. The fabricated sensing element gives the improved noise performance and low bias instability by the inherent high-aspect-ratio, large sacrificial gap and footing-free advantages of the SBM process. The interface circuit is fabricated using a 0.8 μm Polarfab BiCMOS process. The continuous-time, fully-differential transconductance input amplifier and the chopper-stabilization architecture is adopted to reduce low-frequency noise. The fabricated microaccelerometer has a total noise equivalent acceleration of 0.23 μg/(Hz) 1/2, bias instability of 490 μg, input range of ±10 g, and output non-linearity of ±0.5% FSO.