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

• GaN based SAW temperature sensor was designed, manufactured and characterized.
• The SAW structures have been obtained using advanced nano-lithographic techniques in order to increase the resonance frequency beyond 5 GHz and to improve their sensitivity.
• A single resonator structure was used for temperature determinations and it was demonstrated that the performances of this structure in terms of sensitivity and losses are very good.
• The temperature where the TCF for GaN vanishes was determined.

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 200 nm) and resonance frequencies higher than 5 GHz 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 300 kHz/°C, (corresponding to values higher than 50 ppm/°C) have been obtained.