| 摘要 |
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 Ca3Ga2Ge4O14 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: La3-xSrxTa0.5+0.5xGa5.5-0.5xO14. The composition ratio of Sr is preferably in the range of 0 <CUSTOM-CHARACTER FILE="US06400061-20020604-P00900.TIF" ALT="custom character" HE="20" WI="20" ID="CUSTOM-CHARACTER-00001"/>x<=0.15, and more preferably in the range of 0.07 <CUSTOM-CHARACTER FILE="US06400061-20020604-P00900.TIF" ALT="custom character" HE="20" WI="20" ID="CUSTOM-CHARACTER-00002"/>x<=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 (phi, theta, psi), adequate characteristics can be obtained by selecting these angles.
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