Analysis of XBAR resonance and higher order spurious modes

Abstract

A suspended 400nm thin mono-crystalline ZY cut Lithium Niobate (LN) membrane with narrow interdigital electrodes (IDEs) on top having a pitch of the order of few microns excites standing shear bulk acoustic wave resonance (XBAR) within the membrane through lateral field excitation. Recently the first XBAR was simulated and demonstrated experimentally with a resonance frequency of 4800MHz having high electromechanical coupling of about 25% and loaded quality factor at resonance close to 500.This device lays the path to production of RF filters for 5G applications close to 5GHz with low losses and large bandwidth. This work aims to study behavior of the A1 XBAR mode and its higher order lateral harmonics (A1-3, A1-5…) as a function of thickness, pitch and material properties. They are studied with respect to design parameters in order to eliminate spurious modes close to the intended filter band, increase electromechanical coupling and establish guidelines for resonator design.