Transverse Modes In Temperature Compensated Surface Acoustic Wave Devices

This paper discusses behavior of transverse modes in temperature compensated (TC) surface acoustic wave (SAW) devices employing the SiO2/128 degrees rotated Y-cut LiNbO3 (128-LN) structure. The Rayleigh SAW on the structure often exhibits anomalous behaviors such as rapid variation of the anisotropy factor 7 with the electrode and SiO2 thicknesses and the piston mode operation without use of phase shifters. They are mainly caused by the coupling of the main mode (Rayleigh SAW) with the shear horizontal (SH) SAW. Note that even when SH-like spurious resonances are completely suppressed, the coupling still remains. First, it is shown how the coupling influences lateral SAW propagation in the structure. Its impact to transverse modes properties is also discussed. Finally, it is shown that the two SAW coupling enables the piston mode operation without giving phase shifters.