Self-balanced navigation-grade capacitive microaccelerometers using branched finger electrodes and their performance for varying sense voltage and pressure

Abstract

This paper presents a navigation-grade capacitive microaccelerometer, whose low-noise high-resolution detection capability is achieved by a new electrode design based on a high-amplitude anti-phase sense voltage. We reduce the mechanical noise of the microaccelerometer to the level of 5.5 mug/rootHz by increasing the proof-mass based on deep RIE process of an SOI wafer. We reduce the electrical noise as low as 0.6 mug/rootHz by using an anti-phase high-amplitude square-wave sense voltage of 19 V. The nonlinearity problem caused by the high-amplitude sense voltage is solved by a new electrode design of branched finger type. Combined use of the branched finger electrode and high-amplitude sense voltage generates self force-balancing effects, resulting in an 140% increase of the bandwidth from 726 Hz to 1734 Hz. For a fixed sense voltage of 10 V, the total noise is measured as 2.6 mug/rootHz at the air pressure of 3.9 torr, which is the 51% of the total noise of 5.1 mug/rootHz at the atmospheric pressure. From the excitation test using I g, 10 Hz sinusoidal acceleration, the signal-to-noise ratio of the fabricated microaccelerometer is measured as 105 dB, which is equivalent to the noise level of 5.7 mug/rootHz. The sensitivity and linearity of the branched finger capacitive microaccelerometer are measured as 0.638 V/g and 0.044%, respectively.