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

This paper discusses the applicability of dielectric materials with high acoustic impedance Z (a) for use in A(1) 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, A(1) 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.