Epitaxial Polysilicon MEMS Temperature Sensor with 0.043 °C Resolution at 4-Hz Data Rate

This work discloses a temperature sensor based on a polysilicon microelectromechanical systems (MEMS) resonator. The system exploits the temperature drift of the resonance frequency of two modes of a single MEMS structure and associated analog and digital electronics. The temperature coefficient of the two modes is found to differ by about 2 ppm/°C, enough to enable the implementation of a relative counting technique to measure the relative temperature. The design uses phase-locked loops to compensate for the challenge posed by the similarity between resonance frequencies and temperature coefficients of the two modes, which, otherwise, would hinder the achievable resolution. The temperature readout is entirely digital, based on counters and a combinational logic that computes temperature in real time. The sensor achieves 0.043 °C resolution with a 4-Hz output data rate (ODR). Fabricated in epitaxial polysilicon, this implementation is compatible with on-chip temperature measurement of large-volume, polysilicon-based inertial sensors, as a substitute for (or additional aid of) onboard or on-application-specific integrated circuit (ASIC) temperature sensors. The latter may be affected by spatial and temporal temperature differences with respect to the MEMS substrate, as extensively proved in this work.