Toward Interdigital Transducer-Based mmWave Acoustic: Mitigating Self-Resonances

Higher-order asymmetric Lamb wave mode resonators utilizing interdigital transducers (IDTs) and LiNbO₃ thin films show significant promise for miniaturized millimeter wave (mmWave) acoustic filters, thanks to their enhanced electromechanical coupling and increased phase velocities. However, achieving impedance matching in 50 Ω systems requires large static capacitance, coupled with significant self-inductance, which leads to multiple electromagnetic (EM) self-resonances. These self-resonances negatively impact the resonator’s performance, especially in higher-order modes. To overcome these challenges, a novel design approach is proposed that reduces self-inductance while maintaining the required static capacitance. The 3D model in EM software is developed to analyze the surface current distribution density and experimental validation on Y-128° cut LiNbO3 thin films demonstrates a significant improvement in self-resonant frequency (SRF) from 11.19 GHz to 22.07 GHz, enhancing the performance of A1 and A3 modes without compromising capacitance, providing a foundation for advancing IDTs applications in the mmWave frequency range.