Vacuum packaged low-power resonant MEMS strain gauge

This paper describes a technical approach toward the realization of a low-power temperature-compensated micromachined resonant strain sensor. The sensor design is based on two identical and orthogonally-oriented resonators where the differential frequency is utilized to provide an output proportional to the applied strain with temperature compensation achieved to first order. Interface circuits comprising of two front-end oscillators, a mixer, and low-pass filter are designed and fabricated in a standard 0.35 µm CMOS process. The characterized devices demonstrate a scale factor of 2.8 Hz/ µε over a strain range of 1000 µε with excellent linearity over the measurement range. The compensated frequency drift due to temperature is reduced to 4% of the uncompensated value through this scheme. The total continuous power consumption of the strain sensor is 3 µW from a 1.2 V supply. This low power implementation is essential to enable battery-powered or energy harvesting enabled monitoring applications