P1L-2 Reflection Properties of SH-Type SAW in Periodic Gold Grating on Langasite

The reflection properties of a pure shear-horizontal (SH)-type surface acoustic wave (SAW) in a periodic gold (Au) grating on rotated Y-cut 90deg X propagation langasite (LGS) with Euler angles of (0deg, thetas, 90deg) are investigated experimentally. The cut angle thetas of 0deg was chosen because a coupling factor of 1.0% and a zero temperature coefficient of delay can both be expected at around this cut angle. The reflection coefficient was directly measured using the electrode consisting of two probe interdigital transducers and a shorted grating with 60 metal strips. When the Au film thickness was 0.015 lambda and the metallization ratio eta was 0.43, the reflection coefficient was measured to be 0.73, which was larger than the similarly measured values for Rayleigh waves on Al/ST-X quartz of 0.62 and Al/LGS(0deg, 140deg, 25deg) of 0.41. By taking the measured propagation loss for SH-type SAW on Au/LGS(0deg, 0deg, 90deg) into consideration, a reflection coefficient close to 1.0 was obtained. Furthermore, the equivalent-circuit parameters for SH-type SAW on Au/LGS(0deg, 0deg, 90deg) were determined from the measured resonance characteristics of a normal-type IDT with 60 finger pairs, then the reflection coefficient was calculated using these parameters. The reflection coefficient predicted was 0.97 for the shorted grating with 60 metal strips on Au/LGS(0deg, 0deg, 90deg), and agreed with the result obtained by direct measurement. The number of strips on Au/LGS(0deg, 0deg, 90deg) required to obtain a reflection coefficient of 0.9 was predicted to be 20, which was one fourth that in the case of Al/ST-X quartz