Tdk Corporation

Tdk Corpoartion

Hiroki Morikoshi

Kenji Inoue

Katsuo Sato

Katsumi Kawasaki

Kiyoshi Uchida

Jun Sato

Tsuguo Fukuda

Surface acoustic wave device and piezoelectric substrate used therefor

The surface acoustic wave device comprises a piezoelectric substrate ( ) and a pair of interdigitated electrodes ( ) provided on one main surface of the piezoelectric substrate ( ). As the material of the piezoelectric substrate ( ), a single crystal belonging to the point group having a crystal structure of Ca Ga Ge O type, containing Ca, Nb, Ga, Si and O as main components, and being represented by the chemical formula Ca NbGa Si O is used. The cut angle of the substrate ( ) and the propagation direction can be selected as appropriate to thereby realize the substrate ( ) which has a large electromechanical coupling coefficient that is effective to achieve a wider passband and a low SAW velocity that is effective to reduce the size of a surface acoustic wave device.

Piezoelectric substrate for surface acoustic wave device, and surface acoustic wave device

A surface acoustic wave device includes a substrate and an inter-digital electrode on a surface of the substrate, wherein the substrate is formed by cutting out of a single crystal represented by a chemical formula, La&agr;Ta&bgr;Ga&ggr;O&dgr;(2.9&lE;&agr;&lE;3.1, 0.48&lE;&bgr;&lE;0.52, 5.4&lE;&ggr;&lE;5.6 and 8&lE;&dgr;&lE;14); a cut angle of the substrate cut out of the single crystal and a direction of propagation of surface acoustic waves on the substrate represented in terms of Euler's angles (&phgr;, &thgr;, &psgr;), &phgr;, &thgr; and &psgr; are found in one of a first area represented by &minus;5 degrees&lE;&phgr;&lE;&minus;5 degrees, 135 degrees&lE;&thgr;&lE;150 degrees and 20 degrees<&psgr;<25 degrees, and a second area represented by &minus;5 degrees&lE;&phgr;&lE;&minus;5 degrees, 135 degrees&lE;&thgr;&lE;150 degrees and &minus;25 degrees&lE;&psgr;&lE;&minus;20 degrees, respectively; and a normalized thickness h/&lgr; obtained by normalizing a thickness h of the inter-digital electrode finger with a wavelength of the surface acoustic wave exceeds 0.5% and is equal to or smaller than 4%. The thus constituted surface acoustic wave device enables miniaturization, band-widening and excellent selectivity, namely, superior temperature characteristics.

Surface acoustic wave device

The present invention provides a piezoelectric substrate for a surface acoustic wave device which has high electromechanical coupling coefficient and low SAW velocity, and a surface acoustic wave device using the same. The present invention applies a single crystal comprising belonging to a point group 32 and having Ca Ga Ge O type crystal structure. The basic component of the single crystal is comprised of La, Sr, Ta, Ga and O and is represented by the chemical formula: La Sr Ta Ga O . The composition ratio of Sr is preferably in the range of 0x&lE;0.15, and more preferably in the range of 0.07x&lE;0.08. The present invention also provides a surface acoustic wave device using that in which an interdigital finger electrode is formed in one main surface of the aforementioned piezoelectric substrate. When a cut angle of the substrate cut out of the single crystal and a propagation direction of surface acoustic waves are represented in terms of Euler angles (&phgr;, &thgr;, &psgr;), adequate characteristics can be obtained by selecting these angles.

Surface acoustic wave device and substrate thereof

A surface acoustic wave device has a piezoelectric substrate whose properties include electromechanical coupling coefficient advantageous to widening passband width and SAW velocity advantageous to achieving a compact surface acoustic wave device. The piezoelectric substrate is composed of the single crystal represented by chemical formula Sr,TaGa,Si,O,belonging to point group,For example, cut angle of the single crystal and propagation direction of the surface acoustic wave are in region,-,wherein said region,-,represented by Euler angles (&phgr;, &thgr;, &psgr;) satisfies &phgr;&equals;25&deg; &tilde;35&deg;, &thgr;&equals;20&deg; &tilde;90&deg;, &psgr;&equals;&minus;40&deg; &tilde;40&deg;. These angles may be in range 1-2, wherein said range 1-2 satisfies &phgr;&equals;25&deg; &tilde;35&deg;, &thgr;&equals;20&deg; &tilde;90&deg;, &psgr;&equals;&minus;25&deg; &tilde;25&deg;.

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Tokyo, Japan

Hiroki Morikoshi