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This paper reports the design and implementation of a two-axis capacitive-type accelerometer using well-known two poly-Si processes. The accelerometer design consists of a pendulum proof-mass (bulk Si), a gimbal-spring (poly-Si film), and vertical-comb sensing electrodes. This design has three merits: 1) pendulum proof-mass to produce torque by in-plane acceleration; 2) high-aspect-ratio-micromachined (HARM) gimbal-springs enable the detection of two-axis accelerations; and 3) vertical-combs of different vertical positions enable the differential sensing electrodes design to detect the angular motion. In short, this paper exploits the vertical-comb electrodes for differential capacitive sensing to detect the two-axis in-plane accelerations. Measurement results show that the sensitivities (nonlinearity) of etch direction are 17.87 mV/G (2.65%) of X-axis, and 16.54 mV/G (2.71%) of Y-axis in the excitation range of 0.6~2 G. Due to the HARM gimbal-spring design, the cross axis sensitivity introduced by the Z-axis excitation is less than 0.3% for both X-axis and Y-axis sensing. However, the cross-axis error between the X-axis and the Y-axis sensing elements still need to be improved.
Date of Publication: Dec. 2012