Thin Film PZT Multimode Resonant MEMS Temperature Sensor

This digest paper reports on the experimental demonstration of an integrated multimode resonant MEMS temperature sensor by exploiting a thin film ceramic PZT multi-frequency piezoelectric micromachined ultrasonic transducers (pMUTs) in the MHz range. The three resonance modes examined (at 1.107, 3.620, 6.778MHz) all exhibit excellent linearity and responsivity to temperature variations in the range of 0 to 211 degrees C, with temperature coefficients of resonance frequency (TCf) at similar to -200 to -270ppm/degrees C for openloop measurement. We have demonstrated the temperature sensing with real-time tracking of the resonance frequency using a phase-locked loop. We also build a self-sustaining MEMS oscillator and study the closed-loop TCf which is smaller than the open-loop TCf. We compare the open-loop and closed-loop TCfs in both air and vacuum for different type of heaters and find that the TCf can be affected by heating method, pressure, and measurement scheme.