A Near Zero TCF Acoustic Resonator with High Electromechanical Coupling of 13.5% at 3.5 GHz

In this paper, the design, implementation, and measurements of a near-zero temperature coefficient of frequency (TCF) acoustic resonator are demonstrated. The acoustic resonator is based on laterally vibrating Lamb-waves in a bimorph composed of Lithium Niobate and Silicon Dioxide. The resonator is optimized for the A3 mode by adjusting the thickness of different materials in the bimorph to maximize the coupling and minimize the TCF simultaneously. The optimization resulted in ultra-low TCF of −1.1 ppm/°C, a high electromechanical coupling of 13.5%, and a good quality factor of 500 at 3.5 GHz. The achieved specifications are adequate for 5G sub-6 GHz frequency bands n77 and n78.