The Study of Phononic Crystal Reflectors and Transverse‐Mode Suppression in LiNbO 3 /Quartz LSAW Resonators

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This work reports a leaky surface acoustic wave (LSAW) resonator fabricated on a 36°YX LiNbO 3 thin film bonded to an AT90°X quartz substrate, in which phononic crystals (PnCs) are introduced as equivalent reflector to replace conventional electrode gratings. By tailoring the geometric parameters of the PnC structure, its band dispersion characteristics are engineered to provide strong reflection for Love‐mode acoustic waves. Finite‐element simulations reveal a Love‐mode bandgap spanning approximately 391–468 MHz for the phononic crystal with a period of 5.5 µm. Prototype devices are fabricated to validate the proposed design. To suppress transverse spurious modes, two interdigital transducer (IDT) configurations—hammer‐shaped and rhombus‐shaped—are investigated. Experimental results demonstrate that the rhombus‐shaped IDT, when combined with PnC reflectors, achieves effective transverse‐mode suppression. Compared with conventional electrode‐grating‐based resonators, the presented PnC‐based resonator—which achieved a Bode‐ Q max of 3843 and a FoM of 850 at 436.1 MHz—enables a substantial reduction in reflector dimensions, exhibits an enhanced effective electromechanical coupling coefficient ( k 2 eff ), and provides stronger suppression of Rayleigh‐type surface acoustic waves (RSAWs), with an improvement of approximately 3.76 dB. In addition, PnC reflectors effectively mitigate in‐band spurious responses, highlighting their potential for high‐performance and miniaturized SAW devices.