Effect of nonuniform piezoelectric films on monolithic surface acoustic wave devices

The effect of film thickness variation on the performance of ZnO on silicon surface acoustic wave delay lines is examined. The thickness variation obtained from a planar magnetron sputtering system with a 5-cm diameter erosion ring was measured and found to be in good agreement with the calculated thickness variation. This information, together with theoretical data on the dependence of surface acoustic wave velocity on ZnO film thickness, is used to predict phase distortions of 400° across 1-mm-wide, 2.5-cm-long delay lines. This high level of phase distortion was confirmed by experimental measurements with a laser probe.