Optimal cut of lithium niobate with suppressed Rayleigh-type mode for application in resonator SAW filters

Results of resonators constructed on rotated YX lithium niobate (LiNbO3), to provide minimum coupling of the spurious Rayleigh-type mode are reported. The resonator employs non-leaky waves which result when the metal grating's electrodes are sufficiently heavy to suppress attenuation of leaky waves. The coupling of two SAW modes propagating in rotated YX cuts was estimated as function of cut angle and electrode thickness, with Al or Cu as electrode material. The optimal orientation, 19 degrees YX for Al grating or 20 degrees YX for Cu grating, is compared with previously reported 15 degrees YX cut. If the electrode thickness is optimized to suppress the spurious mode, in 15 degrees YX the coupling of this mode grows fast with variation of frequency or electrode thickness because of close proximity between the velocities of two modes. In 19 degrees YX cut the resonance of the spurious mode is located in the middle of the interval between the resonance and anti-resonance of non-leaky SAW mode. The spurious mode is made less sensitive to variations of frequency or metal thickness and provides better performance of resonator filters. This conclusion is confirmed experimentally.