Sezawa Propagation Mode in GaN on Si Surface Acoustic Wave Type Temperature Sensor Structures Operating at GHz Frequencies

This letter investigates the applicability of Sezawa propagation mode for various GaN/Si surface acoustic wave (SAW) temperature sensor structures. First, different acoustic propagation modes in GaN on Si single SAW resonators, operating at GHz frequencies, were evaluated. The variation of the phase velocity versus the normalized thickness of the GaN layer is analyzed experimentally for different propagation modes, on the SAW structures manufactured using e-beam lithography. The different acoustic modes were also identified using finite-element method calculations. The effective coupling coefficients for the Sezawa mode are determined and show larger values than those obtained for the Rayleigh mode. The sensitivities obtained for the temperature sensor structures are 1.8 times higher for Sezawa than for the fundamental Rayleigh mode.