Double-layer Thin-film LiNbO3 Longitudinally Excited Shear Wave Resonators with Ultra-large Electromechanical Coupling Coefficient and Spurious-Free Performance

TL;DR

This paper introduces a double-layer thin-film LiNbO3 shear wave resonator with an ultra-high electromechanical coupling coefficient over 60%, no spurious modes, and tunable frequency, promising advancements in high-performance acoustic filters for mobile communications.

Contribution

It presents a novel double-layer thin-film LiNbO3 resonator with record-high coupling, tunable frequency, and no spurious modes, suitable for next-generation high-bandwidth filters.

Findings

Electromechanical coupling coefficient exceeds 60%.

Resonator frequency covers 1-10 GHz range.

No spurious modes observed in the design.

Abstract

This work proposes a double-layer thin-film lithium niobate (LiNbO3) longitudinally excited shear wave resonator with a theoretical electromechanical coupling coefficient exceeding 60%, RaR close to 28%, and no spurious modes. This ultra-large electromechanical coupling coefficient, which is close to the upper limit of LiNbO3, is much larger than all microwave acoustic resonators reported so far. Based on X-cut thin-film LiNbO3, when the film thickness is in the order of hundreds of nanometers, the frequency of the fundamental mode of the resonator can cover 1GHz to10GHz. The resonator design is convenient and flexible. The resonant frequency can be modulated monotonically by changing either the electrode or the thickness of the thin-film LiNbO3 without introducing additional spurious modes. This ideal resonator architecture is also applicable to LiTaO3. With the development of the new generation of mobile communications, this resonator is expected to become a key solution for future high-performance, ultra-wide-bandwidth acoustic filters.