High sensitivity, GHz operating SAW pressure sensor structures manufactured by micromachining and nano-processing of GaN/Si

Two different novel SAW type pressure sensing structures were manufactured using micromachining and nanolihographic processes: SAW supported on a GaN/Si (1.2 µm/ 10 µm) membrane for the first type structure and SAW supported on a 1.2 µm thin GaN membrane for the second type. The two resonance peaks observed for both structures were identified, using wave shape simulations, as Rayleigh mode and symmetric Lamb mode, respectively. The resonance frequency shift vs. pressure (measured in the 1–5 Bar range), as well as the pressure sensitivity and its sign have been analyzed for both structures and both peaks. High absolute values of the sensitivity (in the range 346…2680 kHz/Bar) and of the pressure coefficient of frequency (in the range 66…278 ppm/Bar) have been obtained. It was demonstrated that the second type structures and the Lamb mode are more pressure sensitive.