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

Abstract

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 °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 °C- 1 within the temperature range from room temperature to 200 °C, and an average linear TCf of - 16 ppm °C- 1 between 200 and 600 °C, from the fundamental- mode resonance of AlScN/SiC circular diaphragm resonator with a thickness of 1.9 µm and diameter of 250 µm, 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.This work demonstrates aluminum scandium nitride on silicon carbide (AlScN/SiC) heterostructure thin film micromachined resonant transducers operating in a high- temperature environment up to 600 °C. Macroscopic and microscopic vibrations are investigated through a combination of laser interferometry techniques and Raman spectroscopy. The results provide insight for understanding the resonant characteristics and intrinsic material properties of AlScN/SiC at both device and crystal structure levels.