Effect of a thin-film phase-transition material on surface acoustic wave propagation

The electrical conductivity of a material adjacent to the surface of a piezoelectric may influence the energy loss and/or phase velocity of a propagating surface acoustic wave (SAW). Several transitionmetal oxides and sulfides exhibit a semiconductor-to-metal phase transition, and these materials may be useful in creating programmable SAW deviees. This work reports an investigation of the effect of a thin film of vanadium dioxide (VO2) on SAW propagation on LiNbO3. V02 has a reversible firstorder temperature-induced phase transition at a temperature of 67°C which produces a factor of 10³ change in conductivity as well as a substantial change in other physical characteristics such as refractive index. In thin films of VO2, temperature hysteresis in the phase transition allows bistable switching of SAW propagation characteristics. The interaction was investigated by depositing VO2 on a SAW deviee. Properties of the material such as resistivity ratio, temperature hysteresis, change in refractive index, and switching sensitivity are discussed.