Temperature stable LiNbO3 surface acoustic wave device with diode sputtered amorphous TeO2 over-layer

Amorphous TeO2 thin film, sputtered in the O2+Ar(25%+75%) gas environment using a metallic tellurium target, has been identified as an attractive negative temperature coefficient of delay (TCD) material that can yield a temperature stable device when combined with a surface acoustic wave (SAW) device based on positive TCD material such as LiNbO3. The influence of amorphous TeO2 over-layer on the SAW propagation characteristics (velocity and temperature coefficient of delay) of the SAW filters (36 and 70 MHz) based on 128 deg. rotated Y-cut X-propagating lithium niobate (128 deg. Y-X LiNbO3) single crystal has been studied. It is found that 0.042 λ thick TeO2 over-layer on a prefabricated SAW device operating at 36 MHz centre frequency, reduces the TCD of the device from 76 ppm deg. C-1 to almost zero (∼1.4 ppm deg. C-1) without deteriorating its efficiency and could be considered as a suitable alternative for temperature stable devices in comparison to conventional SiO2 over-layer