AlScN-on-SiC Thin Film Micromachined Resonant Transducers Operating in High-Temperature Environment up to 600 °C

The experimental demonstration of aluminum scandium nitride (AlScN)-on-cubic silicon carbide (SiC) heterostructure thin film micromachined resonant transducers operating in a high-temperature environment up to 600 degrees C is reported. Macroscopic and microscopic vibrations are investigated through a combination of ultrasensitive laser interferometry techniques and Raman spectroscopy. An average linear temperature coefficient of resonance frequency (TCf) of <1 ppm degrees C-1 within the temperature range from room temperature to 200 degrees C, and an average linear TCf of -16 ppm degrees C-1 between 200 and 600 degrees C, from the fundamental-mode resonance of AlScN/SiC circular diaphragm resonator with a thickness of 1.9 mu m and diameter of 250 mu m, is obtained. Higher-order modes exhibit much larger TCf, which make them strong candidates as high-temperature-tolerant temperature sensors or ultraviolet detectors. Raman spectroscopy indicates that the turning points of the peak positions of the longitudinal optical phonon modes of both 3C-SiC and AlScN occur in almost the same temperature region where the turnover point of TCf is observed, suggesting that the microscopic vibrations in the crystal lattice and the macroscopic oscillation of the diaphragm are naturally mediated by the residual strain inside the materials at varying temperature.

Automated summary

This study demonstrates the experimental performance of aluminum scandium nitride (AlScN)-on-cubic silicon carbide (SiC) heterostructure thin film micromachined resonant transducers at high temperatures up to 600 degrees C. The investigation of macroscopic and microscopic vibrations using ultrasensitive laser interferometry and Raman spectroscopy reveals the temperature coefficients of resonance frequency and the potential applications of higher-order modes as high-temperature-tolerant sensors or detectors. The correlation between the phonon modes and temperature variation suggests the role of residual strain in mediating the vibrations in the crystal lattice and the diaphragm.