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

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In this paper, first, the surface acoustic wave (SAW) propagation mode and a method of analyzing the propagation property are introduced briefly. Then, typical composite substrate structures that have been developed to obtain high-performance SAW devices are reviewed. Furthermore, the recent results obtained by the author and research colleagues on the propagation and resonance properties of leaky SAW (LSAW) and longitudinal-type LSAW on dissimilar-material bonded structures comprising a LiTaO3 (LT) or LiNbO3 thin plate with a thickness of less than 1 λ (λː wavelength) and a quartz substrate are described. The control of attenuation and the cause of large coupling factor of LSAWs by utilizing layered structures were also discussed. For the bonded 4 inch wafer of 36°YX-LT/AT90°X-quartz with a thin-plate thickness of 0.3 λ, an admittance ratio of 81 dB, a fractional bandwidth of 4.2%, and resonance and antiresonance factors of approximately 1500 with markedly improved properties compared with a single 36°YX-LT substrate were obtained experimentally at 2.2 GHz.

Section: Control Of Lsaw Properties Using Layered Structuresmentioning

confidence: 99%

High-performance surface acoustic wave devices using composite substrate structures

Kakio

2021

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“…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.…”

Section: Introductionmentioning

confidence: 97%

Propagation characteristics of longitudinal-type leaky surface acoustic wave on layered structure consisting of Sc_xAl₁₋_xN film/LiNbO₃substrate

Suzuki¹,

Gomi²,

Kakio³

2018

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A longitudinal-type leaky surface acoustic wave (LLSAW) has a high phase velocity. Therefore, LLSAW devices are suitable for applications to high-frequency filters. However, the attenuation of LLSAWs is higher than that of other SAW modes. This higher attenuation of LLSAWs, which causes a low Q factor, can be reduced by growing a higher-velocity film on a piezoelectric substrate. On the other hand, K2 in the layered structure decreases because of the small piezoelectricity in high-velocity films. In this study, LLSAW propagation characteristics on a layered structure consisting of high-piezoelectric ScAlN film/X-cut 36°Y-propagation LiNbO3 were investigated. When a or ScAlN film was loaded, the reduction of the attenuation was observed, but K2 for this layered structure is lower than that of LiNbO3. On the other hand, K2 for Sc0.4Al0.6N film/LN is higher than that of LiNbO3.

“…Because of the above reasons, substrate structures that reduce attenuation by combining various materials have been proposed and studied. [1][2][3][4][5][6][7][8] Our research group reported that the resonance Q factor of LLSAWs increased because the energy leakage in the depth direction of the structure significantly decreased when an LT or LN thin plate with a small thickness of one SAW wavelength or less was bonded to a quartz support substrate with a higher phase velocity than the thin plate (LT/quartz or LN/quartz). The electromechanical coupling factor K 2 for this bonded structure increased 2-3 times that for a single substrate owing to a strong concentration effect of particle displacement on the surface.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of leaky surface acoustic wave harmonics excitation using bonded dissimilar-material structures

Asakawa

Suzuki

Kakio

et al. 2021

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The enhancement of high-order surface acoustic wave (SAW) harmonics by increasing the metallization ratio was theoretically and experimentally investigated in high-performance bonded dissimilar-material structures. The simulation using a finite element method for 36°Y-cut X-propagating LiTaO3 (36°YX-LT)/AT-cut 90°X-propagating quartz (AT90°X-quartz) and 27°YX-LiNbO3/AT90°X-quartz was performed by setting the metallization ratio of the interdigital transducer to a/p = 0.8 (a: electrode width, p: pitch), and the LT and LN thin-plate thicknesses to h/λ = 0.05 (λ: wavelength) and 0.1, respectively. The fractional bandwidths for 36°YX-LT/AT90°X-quartz and 27°YX-LN/AT90°X-quartz were obtained to be 1.6% and 4.0%, respectively, which were larger than those for single LT and LN. For a leaky SAW (LSAW) resonator with a/p = 0.8 fabricated on 36°YX-LT/AT0°X-quartz, the resonance properties and temperature coefficient of frequency of LSAW fundamental waves and harmonics were measured. The measured fractional bandwidth increased from 0.8% to 1.4% for single LT.