Thin-Film Piezoelectric Resonators and Filters at mm-Wave

This talk presents our recent work using transferred lithium niobate (LN), along with sputtered scandium aluminium nitride (ScAlN) thin-films for demonstrating low-loss and compact acoustic resonators and filters at mm-wave bands. More specifically, 110nm thick single-crystal 128° Y-cut LN thin-films with opposite polarizations are transferred to sapphire substrates with intermediate amorphous silicon (a-Si) sacrificial layer. Based on the novel platforms, thickness shear mode piezoelectric resonators are fabricated for mm-wave operation. The measured compact acoustic resonators show high electromechanical coupling (k2) of 7.55% and quality factor (Q) of 222, leading to a figure of merit (FoM, Q·k2) of 16.8 at 50.07GHz, 50-times higher than the state-of-the-art (SoA) at 50GHz. Consequently, compact acoustic filters are built with electrically coupled resonators, showing low insertion loss (IL) of 1.29dB, and fractional bandwidth (FBW) of 20.1% at 21.2GHz, doubling the operating frequency of SoA acoustic filters while keeping low-loss and wideband performance. Advances in delivering ScAlN resonators using sputtered films will be discussed. Further development of recent 50GHz acoustic filter will be discussed, pointing out the future opportunities for frequency scaling acoustic technology.