Frequency-scalable fabrication process flow for lithium niobate based Lamb wave resonators

In this paper, we demonstrate the fabrication and characterization of lithium niobate (LN) based Lamb wave mode (S0 and SH0) resonators that address the stringent requirements of RF filtering for modern communication systems. The devices consist of a 400 nm-thick X-cut LN membrane anchored from two ends with interdigitated transducer (IDT) on the top. We present a frequency-scalable process flow using e-beam lithography for the fabrication of ultra-high frequency (10(8) to 10(9) Hz) devices. Our fabricated devices yield the highest reported electromechanical coupling (k(t)(2)) of 31% and 40% for S0 and SH0 modes, respectively, in X-cut LN. We also investigate the influence of IDT material and coverage on k(t)(2) and quality factor (Q) by fabricating identical devices with aluminum and platinum electrodes with electrode coverages ranging from 20% to 70%.