Silicon resonant accelerometer with electronic compensation of input-output cross-talk

A resonant accelerometer manufactured in silicon bulk micromachining with electrothermal excitation and piezoresistive detection is presented. The structure is a seismic mass supported by two parallel flexure hinges as a doubly-sustained cantilever, with a resonating microbeam located between the hinges. The acceleration normal to the chip plane induces an axial stress in the microbeam and, in turn, a proportional change in the microbeam resonant frequency. Beam resonant frequency of around 70 kHz and acceleration sensitivity of 35 Hz/g over the range 0–3 kHz were measured on prototypes, in accordance with analytical calculations and simulations. The microbeam operates unsealed at atmospheric pressure, therefore a comparatively low quality factor results due to air damping. In this condition, the effect of the input-output cross-talk was found to be significant. The cross-talk is analyzed and modeled, and an electronic active compensation is proposed. The compensated sensor was inserted into a phase-locked loop oscillator and tested. Reported experimental results show that the sensor performs in excellent agreement with the theoretical predictions.