Ultralow-Noise Readout for an MEMS Epitaxial Polysilicon Temperature Sensor

This work discloses the development of an ultralow-noise readout for a polysilicon-microelectromechanical system (MEMS)-based temperature sensor. The system relies on a multimode resonator realized in a conventional epitaxial polysilicon process and exploits the slightly different temperature dependence of the resonance frequency of a flexural mode and a torsional mode. Instead of using the consolidated relative counting method, widely discussed in the literature, the system uses a single free-running counter and retrieves the temperature information after a discrete-time derivative operation. This enables shaping of quantization and phase noise at high frequency, which is then filtered by a second-order low-pass filter. The residual experimental white noise floor is measured as about $0.001~^{\circ } $ C/ $\sqrt {\text {Hz}}$ , representing a 30-fold improvement with respect to previous work.