Anomalous elastic properties of RF-sputtered amorphous TeO2+x thin film for temperature-stable SAW device applications

The anomalous elastic properties of TeO_2+x thin films deposited by rf diode sputtering on substrates at room temperature have been studied. The deposited films are amorphous, and IR spectroscopy reveals the formation of Te-O bond. X-ray photoelectron spectroscopy confirms the variation in the stoichiometry of TeO_2+x film from x = 0 to 1 with an increase in the oxygen percentage in processing gas composition. The elastic parameters of the films in comparison to the reported values for TeO_2+x single crystal are found to be low. However, the temperature coefficients of elastic parameters of all deposited films exhibit anomalous behavior showing positive values for TC(C₁₁) in the range (32.0 to 600.0) x 10^-40 C^-1 and TC(C¹¹) = (35.0 to 645.5) x 10^-4degC^-1 against the negative values TC(Cn) = -2.7 x 10^-4degC^-1 and TC(C₁₁) = -0.73 x 10^-4degC^-1 reported for TeO₂ single crystal. The variation in the elastic parameters and their temperature coefficients is correlated with the change in the three-dimensional network of Te-O bonding. The anomalous elastic properties of the TeO_2+x films grown in 100% O₂ are useful for potential application in the design of temperature stable surface acoustic wave devices.