Development of high frequency ZnO/SiO2/Si Love mode surface acoustic wave devices

The development of a ZnO/SiO2/Si based high frequency Love mode surface acoustic wave (LM-SAW) device operating at 1.5 GHz is reported. The growth of ZnO films on SiO2/(1 0 0)Si substrates using pulsed laser deposition has been developed and optimized to obtain efficient Love mode acoustic wave propagation in ZnO. Strain in the ZnO film is measured to be as high as 2.3% and was found to be a function of the SiO2 thickness. The effects of strain on the frequency response of the LM-SAW devices was studied and characterized for the first time. The highly strained film generated two surface acoustic wave velocities, where the higher velocity is believed to propagate in the less strained top layer of the film, and the lower velocity in the highly strained region of the film interface with the SiO2. Corresponding to these phase velocities, multiple non-harmonic frequencies of operation for the Love wave device are observed. Annealing the film at 500 °C in air for 45 min reduced the strain to 2%. Reducing the thickness of the SiO2 layer to 500 Å resulted in reducing the strain substantially to 0.56%, and the devices yielded a phase velocity of 4814.4 m/s in the ZnO guiding layer.