Near-Zero Drift and High Electromechanical Coupling Acoustic Resonators at > 3.5 GHz

In this article, near-zero drift and high electromechanical coupling acoustic resonators have been designed and demonstrated. The acoustic resonator is based on Lamb acoustic waves in a bimorph composed of lithium niobate on silicon dioxide. Our approach breaks through a performance boundary in conventional Lamb-wave resonators by introducing the bimorph while operating at higher order resonant modes. This enables the resonator to achieve frequency scalability, a low-temperature coefficient of frequency, and high electromechanical coupling altogether. The electromechanical coupling and temperature coefficient of the resonator were analytically optimized for the A
₃
mode through adjusting the thicknesses of different materials in the bimorph. Resonators with different dimensions and stack thickness were fabricated and measured, resulting in a temperature coefficient of frequency ranging from -17.6 to -1.1 ppm/°C, high electromechanical coupling ranging from 13.4% to 18%, and quality factors up to 800 at 3.5 GHz. The achieved specifications are adequate for fifth-generation (5G) sub-6-GHz frequency bands n77 and n78.