Pure SH SAW on single crystal KNbO/sub 3/ for liquid sensor applications

Abstract

This paper reports on the design, fabrication, and testing of a surface acoustic wave (SAW) delay line on single crystal KNbO/sub 3/ Euler angles (0/spl deg/,90/spl deg/, 0/spl deg/). This particular orientation of KNbO/sub 3/ is of symmetry Type 4, which is known to support an electromechanically active shear horizontal (SH) SAW mode, and has a very large electromechanical coupling coefficient of 53%. The SH-SAW mode is especially attractive for liquid sensing applications because the SAW is not significantly attenuated by the adjacent aqueous media, unlike that of a generalized SAW (GSAW), which contains particle displacement normal to the surface. 100 MHz SH-SAW delay line devices with 20% bandwidths were fabricated. Experimental results are reported relevant to liquid sensing applications, such as the electromechanical coupling coefficient, K/sup 2/, /spl Delta/f/f/sub 0/ versus temperature, and the attenuation effect on the magnitude of the transmission coefficient, |S/sub 21/|, with and without de-ionized (DI) water loaded surface. Results show a difference of only about 2 dB in |S/sub 21/| when the surface is loaded with DI water, thus verifying the suitability of the pure SH-SHAW mode on KNbO/sub 3/ for liquid sensor applications.