Suppression of bulk wave radiation from leaky surface acoustic waves by loading with thin dielectric films

The bulk wave, which is radiated into the substrate from the leaky surface acoustic wave (LSAW), can be suppressed by loading the substrate with a thi n film of dielectric such as tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2). Rotated Y-cut X-propagating lithium niobate (LiNbO3) is used for t he substrate. For a certain range of the rotation angle, the attenuation of the LSAW can be suppressed by choosing the appropriate material and thickn ess for the film. For the free surface of 64 degrees Y-X LiNbO3 with Ta2O5 film, and the metallized surface of 41 degrees Y-X LiNbO3 with SiO2 film, t he measured propagation losses decreased approximately to one-fourth to hal f of that of the sample without the thin film. It is shown that, even if th e propagation path is a free surface, the particle displacement distributio n in the LSAW is concentrated near the substrate surface by the loading wit h the thin film, as for the metallized surface. This result suggests that t he bulk wave radiation in the LSAW excitation can be suppressed. The bulk w ave radiation loss for the 41 degrees Y-X LiNbO3 with the Ta2O5 film decrea sed approximately to one-sixth of that of the sample without the thin film. (C) 2000 American Institute of Physics. [S0021-8979(00)05103-3].