Leaky-SAW properties on reverse-proton-exchanged LiNbO3

A proton-exchanged layer with an elastically soft property can be buried into a substrate by a reverse proton exchange (RPE) process. It is expected that the RPE layer with a property similar to that of bulk LiNbO₃ (LN) will prevent the degradation of the coupling factor and that the buried PE layer will reduce the leaky SAW (LSAW) attenuation. In this study, first, a layered structure of air/bulk LN/softened LN was assumed for the rotated Y-X LN and the LSAW attenuation was calculated. The rotation angle from the Y-axis giving zero attenuation shifted from 64deg toward 5deg for a metallized surface. The range of rotation angles at which the LSAW phase velocity exceeds that of a fast shear bulk wave was markedly expanded for a free surface, and the attenuation vanished at these boundaries. Next, the LSAW propagation loss PL was measured on 41deg Y-X LN. The PL for the metallized surface was decreased by carrying out the RPE process from 0.036 dB/lambda of a virgin sample to 0.015 dB/lambda. The decrease of the PL for the free surface was also observed.