IDT-Based mmWave Resonator with Large Impedance Ratio and over-100% Frequency Offset between Resonance and Anti-resonance

At mmWave, electromagnetic (EM) self-resonances induced by large capacitance and parasitic inductance increasingly distort the admittance of acoustic wave resonators and are usually treated as unwanted effects. This work instead exploits these EM resonances and proposes an on-chip IDT-based mmWave resonator implemented on thin-film LiNbO3, using a process compatible with Lamb-wave platforms. A multi-branch equivalent circuit captures both the intentional EM path and fixture-related parasitics, and circuit-level parametric sweeps map each admittance feature to its dominant reactive loop. A high-offset antiresonance is identified that is mainly controlled by busline inductance, IDT loading, and release gap, enabling lithographic and process-level tuning of frequency and impedance ratio. Measurements on 350 nm Y-128°-cut and 450 nm X-cut LiNbO3 demonstrate comparable multi-mode EM spectra with impedance ratios up to 68.2 dB and fractional frequency offset of 112%, indicating material versatility and suggesting strong potential for future hybrid EM–acoustic resonators and mmWave filters and oscillators.