On-chip environmental sensors for bias drift compensation

This paper reports on the simulation, design and functional verification of high resolution on-chip environmental sensors in a 0.18 pm CMOS process. The environmental sensors include n-type piezoresistive stress sensors with measured 0.9 kPa normal stress resolution, p-type piezoresistive stress sensors with 4.5 kPa normal stress resolution and Proportional to Absolute Temperature (PTAT) sensors with 6.5 mK resolution. The full accelerometer system on chip integrates a CMOS-MEMS accelerometer array, a pre-amplifier and the sensors. Finite element analysis provides an estimate of the required temperature and stress resolution for stabilizing the accelerometer scale factor up to 1 ppm, which informs the required noise floor for the environmental sensors. Test results from the designed sensors match the expected resolution closely.