Early Days of SH-type Surface Acoustic Wave Research

In this paper, we review the research on SH-type (leaky) surface acoustic wave (LSAW), mainly carried out on 36° rotated Y-cut X-propagated LiTaO3 (36YX-LTO) during the first ten years after 1977. We discuss in detail how SH-type LSAWs are related to surface skimming bulk waves (SSBWs) which were then newly discovered on quartz, LiTaO3 and LiNbO3. An emphasis is laid on which of these waves becomes the main propagation mode for signal transfer in practical device structures. Through the discussion, various characteristics of LSAWs and SSBWs such as excitation, propagation, effects of surface metallisation and grating structures are clarified both theoretically and experimentally. A couple of significant features are also discussed, which definitely separate SH-type LSAWs from conventional Rayleigh-type SAWs and often play a key role in practical device applications of SH-type LSAWs.