Improvements in the temperature stability of an IDT/ZnO/fused-quartz thin film SAW device with ZnO over-layer

Zinc oxide thin film SAW filters in the frequency range (38 to 64 MHz) have been fabricated on a fused quartz substrate. SAW propagation characteristics including electromechanical coupling coefficient (K²), SAW phase velocity (ν), insertion loss, and temperature coefficient of delay (TCD) have been measured. The measured SAW velocity and the negative TCD are in agreement with theoretical calculations, but a significant deviation is observed in the measured coupling coefficient values. Temperature stability is achieved using a ZnO over-layer. Changes in SAW and TCD characteristics of the modified ZnO/TDT/ZnO/fused quartz structure have been investigated as a function of ZnO over-layer thickness. A 5.4 μm thick ZnO over-layer is found to reduce the negative TCD of an IDT/ZnO/fused quartz layered structure to almost zero (-3 ppm/°C) and a coupling coefficient, K²=1.1% and insertion loss, IL=27 dB were measured.