Use of heavy dielectric materials in solidly mounted A1 mode resonators based on lithium niobate

Abstract

This paper discusses the applicability of dielectric materials with high acoustic impedance Z a for use in A1 Lamb mode solidly mounted resonator (SMR) with large electromechanical coupling coefficient k 2 . The study first shows that the use of metal as a reflector creates parasitic capacitance C p, which reduces k 2 significantly. Then, A1 Lamb mode SMRs are designed using HfN, HfO2, WN, WO3 etc., and achievable performances are compared. When either HfN, HfO2, WN, or WO3 is employed, relative large k 2 up to 25% is achievable. For further k 2 enhancement, a hybrid reflector configuration is also examined, wherein HfN is applied only to the top high Z a layer and W is applied to the others. The result indicates that C p caused by the W layers is still significant, and k 2 becomes worse in total.