Monolithically Integrated High-Resolution and Large-Range MEMS Triaxial Force Sensor with Sub-Millimeter Proximity Sensing

This paper presents a monolithically integrated piezoresistive MEMS triaxial force sensor composed of a force-sensing unit and an on-chip signal processing circuit. An integration process of SOI-CMOS and MEMS was developed on an SOI wafer. The integrated triaxial force sensor can reduce noise voltage to less than$6 \mu ~\mathrm{V}$at a 400 Hz output sampling rate, and force sensitivities of 21.81$\text{mV} / \mathrm{N}, 18.31 \text{mV} / \mathrm{N}$, and$22.11 \text{mV} / \mathrm{N}$along X, Y and Z axes, respectively, with an Fz sensing range of 7 N were obtained. A minimum detectable force of the sensor of 0.27 mN and a force resolution of 0.004% full scale (F.S.) was achieved. Based on the photoelectric effect of semiconductors, the integrated sensor can also realize proximity detection with a minimum distance of 1 mm.