Characterization of Acoustic Losses in Interdigitated VHF to mmWave Piezoelectric M/NEMS Resonators

This work reports on a technology-agnostic and frequency-independent methodology combining a-priori modeling, Finite Element Analysis (FEA), and experimental results for the characterization of acoustic losses in interdigitated piezoelectric micro- and nano-electromechanical (M/NEMS) resonators. The proposed approach models the mechanical quality factor (Qm) and its dependency on piezoelectric (Qpiezo) and metal (Qmetal) acoustic losses, as a function of the mode of vibration dispersion characteristics. The model is finally experimentally validated by exploiting the intrinsic on-chip multifrequency manufacturability of interdigitated devices.A broad range of available resonator technologies, frequencies, and piezoelectric materials are investigated for this purpose, including bulk X-cut Lithium Niobate (XLN) leaky surface acoustic wave resonators operating at Ultra High Frequency (UHF), thin film XLN Lamb Wave resonators spanning between Very High Frequency (VHF) and the Ku band, and Aluminum Nitride (AlN) and scandium-doped AlN (ScAlN) cross-sectional lamé mode resonators ranging from the Ku to Ka band (mmWave).

I. Introduction

Microacoustic piezoelectric resonators have been pivotal components for the implementation of modern Radio Frequency (RF) communication paradigms [1]. However, research continues to explore the capabilities of micro- and nanoelectromechanical systems (M/NEMS) for cutting-edge applications, particularly within the 5G FR-2 (mmWave) and anticipated FR-3 (X to K_u) bands [2]. In fact, as frequency increases, acoustic losses become more pronounced, hindering the implementation of microacoustic filters beyond 5 GHz. This challenge persists across all proposed technologies, either based on nano-scaled fundamental modes or overtones, and piezoelectric materials [3].