The characteristics of surface acoustic waves on AIN/LiNbO3 substrates

The characteristics of surface-acoustic-wave (SAW) devices on various substrates were measured by a network analyzer in the temperature range from 0 to 80 degreesC. Based on the structure of IDT/AlN/LiNbO3, it was revealed that the magnitude of the temperature coefficient of frequency (TCF) of a SAW on a LiNbO3 substrate was significantly decreased due to the thickness increase of AlN thin film deposited on the LiNbO3 substrate. The TCF of a SAW on an AlN/LiNbO3 device was measured to be about -51 ppm/degreesC at h/lambda = 0.1, where h is the thickness of the AlN film and lambda is the wavelength of the SAW. This indicates that the deposition of an AlN film on a LiNbO3 substrate could improve the temperature stability, as compared with that of a SAW on a LiNbO3 substrate (-73 ppm/degreesC). The SAW device on the ST-X quartz is shown to have a positive TCF as the AlN thin film is deposited on the surface of the ST-X quartz. In addition, the phase velocity (V-p) of the SAW on an AlN/LiNbO3 substrate was significantly increased by the increase of AlN thickness (h/lambda).