Measurement of Saw Velocity by Focussing System Using Fresnel Phase Plate IDT

Abstract

A method of measuring the surface acoustic wave (SAW) velocity using an interdigital transducer (IDT) is presented. The system to measure the variation of the SAW velocity on a sample substrate has been constructed using the Fresnel Phase Plate type IDT (FPP-IDT). In the measurement system, the FPP-IDT is used to excite a focussing Leaky SAW(LSAW) on the surface of sample materials. The measurement of the LSAW velocity variation is achieved by recording the phase difference between the two output of the close IDT's. The system is applied to measure the LSAW velocity variation on a SAW device material. The measurement are made for anisotropic materials such as 128° rotated Y-cut LiNb0₃ and X-cut LiTa0₃ at a frequency of 45 MHz. The results of the initial experiments show that the FPP-IDT system is suitable for mapping the two dimensional variation of LSAW velocity on a SAW device wafer.