A surface acoustic wave (SAW) resonator with quality factors ( Q ) of 3526/10205 at the resonant/anti-resonant frequencies ( f _r / f _a ) has been fabricated on thick MOCVD grown (0002) AlN films (4 μ m) on Sapphire. The impact of device parameters on Q of resonators, including aspect ratio of length to width ( L/W ), number of interdigital transducers, and IDT metal thickness, has been investigated. The high Q is obtained due to the large L/W value of 12 which can enhance the acoustic energy superimposition of interdigital transducers, and the thick AlN film (4 μ m), which can reduce the negative impact of seed layer. Moreover, temperature coefficient of frequency (TCF) values of -46.52/-46.09 ppm/°C for f _r / f _a with temperatures ranging from -50 °C to 250 °C and a high Q of 4027 at 250 °C of the resonator have been demonstrated for temperature sensor application.

AlGaN/GaN E/D-mode GaN inverters are successfully fabricated on a 150-mm Si wafer. P-GaN gate technology is applied to be compatible with the commercial E-mode GaN power device technology platform and a systematic study of E/D-mode GaN inverters has been conducted with detail. The key electrical characters have been analyzed from room temperature (RT) to 200 °C. Small variations of the inverters are observed at different temperatures. The logic swing voltage of 2.91 V and 2.89 V are observed at RT and 200 °C at a supply voltage of 3 V. Correspondingly, low/high input noise margins of 0.78 V/1.67 V and 0.68 V/1.72 V are observed at RT and 200 °C. The inverters also demonstrate small rising edge time of the output signal. The results show great potential for GaN smart power integrated circuit (IC) application.

The impact of device parameters, including AlN film thickness (h_AlN), number of interdigital transducers (N_IDT), and acoustic propagation direction, on the performance of c-plane AlN/sapphire-based SAW temperature sensors with an acoustic wavelength (λ) of 8 μm, was investigated. The results showed that resonant frequency (f_r) decreased linearly, the quality factor (Q) decreased and the electromechanical coupling coefficient $\left(K_t^2\right)$ increased for all the sensors with temperature increasing from −50 to 250 °C. The temperature coefficients of frequency (TCFs) of sensors on AlN films with thicknesses of 0.8 and 1.2 μm were −65.57 and −62.49 ppm/°C, respectively, indicating that a reduction in h_AlN/λ favored the improvement of TCF. The acoustic propagation direction and N_IDT did not obviously impact the TCF of sensors, but they significantly influenced the Q and $K_t^2$ of the sensors. At all temperatures measured, sensors along the a-direction exhibited higher f_r, Q and $K_t^2$ than those along the m-direction, and sensors with N_IDT of 300 showed higher Q and $K_t^2$ values than those with N_IDT of 100 and 180. Moreover, the elastic stiffness of AlN was extracted by fitting coupling of modes (COM) model simulation to the experimental results of sensors along different directions considering Euler transformation of material parameter-tensors. The higher f_r of the sensor along the a-direction than that along the m-direction can be attributed to its larger elastic stiffness c₁₁, c₂₂, c₄₄, and c₅₅ values.