Micromachined Thin Film Ceramic PZT Multimode Resonant Temperature Sensor

Micromachined thin-film lead zirconate titanate (PZT) retains exceptional piezoelectric and energy-harvesting capabilities, thus offering an excellent platform for enabling efficient piezoelectric microsystems on chip. Here, we design and fabricate thin-film ceramic PZT piezoelectric microelectromechanical systems (MEMS) operating on flexural-mode resonances, by using wafer bonding and chemical mechanical polishing (CMP) techniques. We describe the experimental demonstration of an integrated multimode resonant PZT MEMS temperature sensor. The three resonance modes examined (at 1.1, 3.6, and 6.8 MHz) all exhibit excellent linearity and responsivity to temperature variations in the range of 25 degrees C to 211 degrees C, with temperature coefficients of resonance frequency (TCf) at -200 ppm/degrees C to -270 ppm/degrees C for open-loop measurement. We have demonstrated dual-mode temperature sensing with real-time tracking of the resonance frequency using a phase-locked loop (PLL). We have also built a self-sustaining MEMS oscillator and studied the closed-loop TCf. We compare the open-loop and closed-loop TCfs in both air and vacuum and find that the TCf can be affected by heating method, pressure, and measurement scheme. The results extend the understanding of temperature effects on the resonance frequency of PZT MEMS, demonstrate real-time temperature sensing, and pave the way for enabling multifunctional PZT microsystems on chip.