GaN/Si based single SAW resonator temperature sensor operating in the GHz frequency range

Abstract

The paper presents the manufacturing and characterization of GaN based SAW (surface acoustic wave) type temperature sensors. In contrast with most SAW sensor structures, manufactured on classical piezoelectric materials where delay lines or two port resonators have been used, in this paper, the resonance frequency shift vs. temperature for a single resonator structure was used for temperature measurements. It is demonstrated that the single resonator SAW structures ensure better performances in terms of sensitivity and losses compared with two port resonator structures. The sensor structure was manufactured using deep submicron e-beam nano-lithographic process on GaN/Si (finger width and interdigit spacing of 200nm) and resonance frequencies higher than 5GHz have been obtained at room temperature. The high resonance frequency ensures an increase of the sensitivity of the sensor structure. The sensor was characterized by “on wafer” resonance frequency shift and sensitivity measurements in the 23–150°C temperature range using S11 reflection parameter. The resonance frequency shift vs. temperature and the sensitivity for the sensor structures assembled on a special ceramic carrier, were measured, in a cryostat, in the −268–+150°C temperature range. Sensitivities higher than 300kHz/°C, (corresponding to values higher than 50ppm/°C) have been obtained.