SSBW to PSAW conversion in SAW devices using heavy mechanical loading

The development of efficient computation tools based on mixed analytical and numerical calculation approaches allows precise descriptions and characterizations of surface acoustic waves (SAW) propagation, taking into account realistic electrical and mechanical boundary conditions. As an example, suppression of the leaky SAW, also called pseudo SAW (PSAW), attenuation has been predicted using such tools allowing to explain experimental occurrences for SAW devices on YX cut lithium niobate and lithium tantalate with thick aluminum strip gratings (6% < h/lambda < 10%). In this work, such a theoretical model is used to analyze the evolution of surface waves on standard YX lithium tantalate cuts versus aluminum strip height. It is shown that the surface skimming bulk wave (SSBW), which accompanies the pseudo SAW on such crystal orientations, may be trapped by the grating, exhibiting then a second pseudo SAW behavior when close to the Bragg condition. A device has been designed and fabricated to check these theoretical predictions. The experimental evidence of the existence of the phenomenon allows one to discuss its consequences on more classical devices built on (Y+36 degrees,X) LiTaO3 substrates.