High-temperature characterization of bimorph X-cut lithium niobate piezoelectric micromachined ultrasonic transducers up to 1000 °C

We characterize a 20-μm-thick bimorph X-cut lithium niobate (LN) piezoelectric micromachined ultrasonic transducer from room temperature to 1000 °C using an open-air measurement platform built around a fully packaged device—gold wire bonds on a ceramic printed circuit board. The platform sustains continuous operation at 800 °C, confirmed by frequency-response measurements at the start and end of a 1-h dwell. A sodium-silicate bondline that fills coefficient-of-thermal-expansion-driven substrate cracks as they form is central to sustained operation above 500 °C. The flexural resonance shifts downward with increasing temperature up to the onset of substrate cracking, and a coherent simple-harmonic-oscillator/modified Butterworth–Van Dyke fit extracts a temperature-dependent effective stiffness for LN up to ∼400 °C; above the 500–600 °C cracking onset, the resonance evolves non-monotonically as crack formation and bondline stabilization successively modify the modal boundary conditions. The measurement terminates near 1000 °C as the gold electrodes dewet and diffuse approaching their melting point (∼1064 °C), rather than at any LN material limit, indicating that packaging and metallization—not the piezoelectric film—set the practical ceiling for these devices. The platform is reusable for high-operating-temperature microelectromechanical systems beyond this device.