Impact of gamma irradiation on GaN/sapphire surface acoustic wave resonators

Space environments contain harsh conditions such as extreme temperature variations, high levels of radiation, and mechanical shocks. Resonator components made from quartz are susceptible to such environmental conditions so that complex packaging and shielding are typically required. As alternative to quartz, wide bandgap material platforms, such as gallium nitride (GaN), are being investigated due to their tolerance to harsh environments and high acoustic velocities. This paper presents the characterization of GaN/sapphire surface acoustic wave (SAW) resonators upon gamma irradiation. Microfabricated resonators were exposed to prolonged gamma ray radiation with (up to 850 krad) and the reflection characteristics (S₁₁) were obtained before irradiation, after irradiation, and after thermal annealing at 100°C. The measured frequency response of the irradiated GaN/sapphire structures showed negligible shift in the resonance frequency (229 MHz). However, a decrease in the resonance peak intensity with increasing irradiation levels is observed. The state of the crystalline structure before and after irradiation (100 krad) is examined using rocking curve X-ray diffraction (XRD) analysis.