Fig. 1. (Color online) (a) Schematic picture of SAW resonators. (b) SEM image of IDT fingers.

Fig. 2. (Color online) (a) 2θ–ω XRD scan patterns of bulk GaN. XRD rocking curves of bulk GaN along (b) [0002]_GaN and (c) [ 101¯2]_GaN. (d) AFM image of bulk GaN in a range of 10 × 10µm².

Fig. 3. (Color online) Frequency response (a)S₁₁ and (b)S₂₁ of the resonator, respectively. (c) Magnitude and (d) phase of input admittance of the resonator versus frequency.

Fig. 4. (Color online) (a) Schematic diagram of the SAW wireless temperature sensor. (b) Setup of GaN-based SAW wireless temperature sensing system. (c) RF power distribution in the frequency domain received by the transceiver from the resonator at 120 °C. (d) Temperature dependency off_r of GaN-based SAW wireless sensor during heating and cooling, respectively. (e) Admittance magnitude |Y₁₁| of SAW sensors versus frequency with various temperatures from 23 to 100 °C.

Table 1. The performance of SAW resonators with different device parameters.