Loss reduction of leaky surface acoustic wave by loading with high-velocity thin film

Abstract

The propagation properties of a leaky surface acoustic wave (LSAW) on rotated Y-cut X-propagating lithium niobate (YX-LN) substrates loaded with an aluminum nitride (AlN) thin film with a higher phase velocity than that of the substrate were investigated theoretically and experimentally. From the theoretical calculation, it was found that the minimum attenuation can be obtained at a certain thickness of the AlN thin film for a cut angle ranging from 0 to 60° because the cut angle giving the minimum attenuation shifts toward a smaller cut angle as the film thickness is increased. The propagation properties of an LSAW on several rotated YX-LN substrates were measured by using an interdigital transducer (IDT) pair with a wavelength λ of 8 µm, and the predicted shifts of the minimum attenuation toward a smaller cut angle were demonstrated experimentally. For 0° and 10°YX-LN samples, the measured insertion loss and propagation loss were markedly reduced by loading with the AlN thin film. A larger electromechanical coupling factor (16.9%) than that at the cut angle giving zero attenuation without a film and a propagation loss less of 0.02 dB/λ were obtained simultaneously at a film thickness of 0.125 λ for the 10°YX-LN sample.

Propagation characteristics of longitudinal-type leaky surface acoustic wave on layered structure consisting of ScxAl1−xN film/LiNbO3substrate

“…K 2 in these structures decreased with increasing ScAlN film thickness, similarly to in a polycrystal AlN film=LN structure. [5][6][7] From these results, the piezoelectricity of the ScAlN films in these structures may not contribute to the LLSAW propagation. Thus, the polarity direction of the ScAlN films did not affect the LLSAW characteristics.…”

“…Our group demonstrated theoretically and experimentally that the attenuation of LLSAWs can be reduced by growing higher-velocity films, such as a polycrystal AlN film, on a piezoelectric single-crystal substrate. [5][6][7] The attenuation of LLSAWs was decreased from 0.28 dB=λ for an X-36°Y LN sample to 0.03 dB=λ by loading polycrystal AlN films. 6) However, decreases in K 2 were also observed in these SAW devices.…”

High-performance surface acoustic wave devices using composite substrate structures

“…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.…”

“…When an amorphous AlN thin film is deposited on the substrate, the cut angle having zero attenuation shifts from 41°to the negative direction and reaches 0°(Y-cut), at which LN or LT possesses a larger K 2 . 81) However, in the case of the above methods, a large attenuation still remains at cut angles other than those in the range of the cut angle with zero attenuation, and K 2 is reduced because the loading material has a low piezoelectricity or no piezoelectricity. To prevent the decrease in K 2 , we proposed the reduction of LSAW attenuation by combining a bulk LN layer and an elastically softened support substrate and realized such a structure by forming a reverseproton-exchanged (RPE) layer.…”

High coupling and highly stable leaky surface acoustic waves on LiTaO3 thin plate bonded to quartz substrate

“…[24][25][26] In addition, to obtain a substrate structure with a large K 2 , the propagation properties of LSAWs and LLSAWs on a LiNbO 3 (LN) or LT thin plate bonded to a high-velocity substrate were investigated theoretically and experimentally. 27) In that study, K 2 larger than that of a single LT substrate was obtained theoretically when 36°Y-cut X-propagating LT (36°YX-LT)= AT-cut 90°X-propagating quartz (AT90°X-quartz) for an LSAW and X-cut 31°Y-propagating LT (X31°Y-LT)=AT-cut 45°X-propagating quartz (AT45°X-quartz) for an LLSAW were employed.…”