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

Abstract

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 thin film of dielectric such as tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2). Rotated Y-cut X-propagating lithium niobate (LiNbO3) is used for the substrate. For a certain range of the rotation angle, the attenuation of the LSAW can be suppressed by choosing the appropriate material and thickness for the film. For the free surface of 64° Y−X LiNbO3 with Ta2O5 film, and the metallized surface of 41° Y−X LiNbO3 with SiO2 film, the measured propagation losses decreased approximately to one-fourth to half of that of the sample without the thin film. It is shown that, even if the propagation path is a free surface, the particle displacement distribution in the LSAW is concentrated near the substrate surface by the loading with the thin film, as for the metallized surface. This result suggests that the bulk wave radiation in the LSAW excitation can be suppressed. The bulk wave radiation loss for the 41° Y−X LiNbO3 with the Ta2O5 film decreased approximately to one-sixth of that of the sample without the thin film.

Pseudo surface acoustic wave dual delay line on 41°YX LiNbO3 for liquid sensors

“…For thickness above this value, insertion loss was nearly constant and equal to about 14 dB. This effect is caused by an additional guiding introduced by the SiO 2 layer [8]. The insignificant change of insertion loss was observed for metallized surface by the loading with SiO 2 film.…”

“…It is seen that the insertion loss is reduced to about 14 dB for metallized delay lines. This phenomenon can be explained [8] by the fact that the bulk wave is not radiated if the propagation path is shorted electrically by a thin metal film. The influence of deposition SiO 2 layer and its thickness on the response of delay line was experimentally investigated.…”

“…The response of PSAW sensor against liquid conductivity (σ): (1) differential insertion loss ( IL) and (2) frequency shift ( f) due to phase change. be explained by a small PSAW penetration depth caused by metallization [8]. To diminish this effect, Al was deposited on the 2 m SiO 2 layer, and final insertion loss of about 17 dB was achieved (Fig.…”

High-performance surface acoustic wave devices using composite substrate structures

“…5) The author and co-workers clarified theoretically that this phenomenon is due to a shifted cut angle having zero attenuation to a negative direction upon introducing the SiO 2 thin film. 80) Moreover, we clarified theoretically and experimentally that such a shift of the cut angle with zero attenuation is also realized by introducing an amorphous thin film, such as Ta 2 O 5 or AlN, or forming a proton-exchanged (PE) layer on the LN or LT substrate, and the attenuation can be reduced within a certain range of cut angles while the phase velocity remains above that of the bulk wave. [80][81][82][83] As an example, the control of attenuation by forming the PE layer is described below.…”

Effect of interfacial damping on high-frequency surface wave resonance on a nanostrip-bonded substrate

“…When they are very close, SAW is generated efficiently and less energy dissipates into the bulk, so that the attenuation of SAW is suppressed. 26 Similarly, it is important to study the relative displacement between the strips and substrate in the SAW resonance mode, which will be helpful to illustrate the attenuation behavior at the SAW resonance. Although we cannot obtain the exact displacements in the strip and substrate in the modal analysis, it is useful to calculate their ratio to illustrate the essence.…”