Temperature dependence of torsional and flexural modes in 6H-SiC microdisk resonators

We report on the experimental calibration of the temperature coefficient of frequency (TCf) in single crystal 6H-silicon carbide (SiC) microdisk resonators based on a smartcut technology. We vary the temperature (T) from -32^oC to 125^oC while monitoring the undriven thermomechanical multimode resonances of the devices using sensitive optical motion detection. Both torsional mode and flexural mode resonances are carefully examined. We observe a salient difference in TCf values for the different modes on the same device: while the TCf of torsional mode is as small as -20ppm/K, the flexural mode TCf has opposite sign and is 76ppm/K. By carefully examining the TCf of the different resonant modes, we can gain insight into the temperature stability of the material and the structure, and engineer devices with desired TCf on different modes, on which certain modes can act as temperature sensor and facilitate the compensation mechanism for the temperature-insensitive modes to achieve highly stable output.