Observation for nonlinear harmonic generation of bulk modes in SAW devices

摘要

Nonlinear generation of harmonics is measured at wafer level on Temperature Compensated Surface Acoustic Wave (TC-SAW) Resonators on lithium niobate. The obtained results are different from those published for resonators on lithium tantalate. For second harmonic, strong peaks looking like multiple resonant modes are found. The frequency difference between the successive peaks increases when the substrate thickness decreases. Results also show that the level of the signal depends on the roughness of the back side of the substrate. Due to these findings, it was assumed that this signal is due to nonlinear generation of a bulk mode. This assumption is confirmed experimentally by scanning the back side with an interferometer. Possible nonlinear mechanisms explaining these results are discussed.