High-resolution Capacitive Microaccelerometers using Branched finger Electrodes with High-Amplitude Sense Voltage

This paper presents a navigation garde 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$\mu\textrm{g}$/(equation omitted) by increasing the proof-mass based on deep RIE process of an SOI wafer. We reduce the electrical noise as low as 0.6$\mu\textrm{g}$/(equation omitted) by using an anti-phase high-amplitude square-wave sense voltage of 19V. 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㎐ to 1,734㎐. For a fixed sense voltage of 10V, the total noise is measured as 2.6$\mu\textrm{g}$/(equation omitted) at the air pressure of 3.9torr, which is the 51％ of the total noise of 5.1$\mu\textrm{g}$/(equation omitted) at the atmospheric pressure. From the excitation test using 1g, 10㎐ sinusoidal acceleration, the signal-to-noise ratio of the fabricated microaccelerometer is measured as 105㏈, which is equivalent to the noise level of 5.7$\mu\textrm{g}$/(equation omitted). The sensitivity and linearity of the branched finger capacitive microaccelerometer are measured as 0.638V/g and 0.044％, respectively.

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