A single mass two-axis capacitive MEMS accelerometer with force rebalance

This paper presents a single mass 2-axis MEMS capacitive accelerometer with a unique force rebalance method achieved with the readout circuit developed for the simultaneous 2-axis acceleration sensing. Using a single mass structure with extra fingers for reading multiple axes allows better sensor performances when compared to multi-axis accelerometers with individual proof masses occupying the same die area. Test results show 274 mV/g scale factor for x-axis, and 280 mV/g scale factor for y-axis, while the cross-axis sensitivity for x-axis is calculated as 3.4 mV/g (% 1.26), and the cross-axis sensitivity for y-axis is -3.9 mV/g (% 1.4). Additionally, the bias instability values are measured as 22 μg and 23 μg, and the velocity random walk values are determined as 9.8μg/ √Hz and 9.9 μg/ √Hz for x and y axes, respectively. This sensing and readout approach can easily be adapted to achieve a high performance single mass 3-axis accelerometer in a small die area.