Loss Reduction of Longitudinal-Type Leaky Surface Acoustic Wave by Reverse Proton Exchange

Abstract

The longitudinal-type leaky surface acoustic wave (LLSAW) is one of the SAW modes that is advantageous for application to high-frequency SAW devices. However, the LLSAW has huge inherent attenuation. In this study, to reduce the attenuation of the LLSAW, we proposed a layered structure of air, a bulk LiNbO3 (LN) layer, and an elastically softened LN substrate. When the layered structure was applied to X–36°Y LN with a large coupling factor K2 for the LLSAW, the calculated attenuation for the metallized surface decreased at a certain depth of the bulk layer. To realize such a layered structure, a reverse proton exchange (RPE) process was applied to X–36°Y LN, and the propagation and resonance properties of the LLSAW were evaluated. A “good region” existed on the RPE wafer, in which the value of K2 for the Rayleigh wave was recovered to approximately 80% of that of the virgin wafer. In comparison with the virgin wafer, the propagation loss for the free surface of the good region on the RPE wafer was decreased threefold, the insertion loss was decreased drastically, and the resonance properties were improved markedly.