The Characterization of Surface Acoustic Wave Modes on Rotated Y-Cut Quartz (ST-X Quartz) with Different AlN Film Thickness

Abstract

The Y-rotated, X-propagating (ST-X) cut of quartz is used extensively for the development of surface acoustic wave (SAW) devices. Besides the commonly used generalized SAW (GSAW) mode, this crystal cut also supports a pseudo-SAW (PSAW) mode and a high velocity pseudo-SAW (HVPSAW) mode. AlN thin films are an attractive material that have some excellent characteristics, such as high surface acoustic wave (SAW) velocity, piezoelectricity, high-temperature stability, and stable chemical properties. In this paper, the AlN films with different thickness were successfully sputtered on ST-X quartz to study the SAW modes. The X-ray diffraction (XRD) pattern exhibited the AlN films were c-axis-oriented hexagonal structures. The result exhibited that the added AlN layer can effectively enhance the acoustic velocities. As the ratio (film-thickness/acoustic-wavelength) increased, the velocities of GSAW and PSAW were all increased but the HPSAW velocity maintained the same value.