| 摘要 |
A surface acoustic wave apparatus which is small in size, exhibits a favorable selectivity or temperature characteristics and has a wide pass band. The apparatus has interdigital electrodes on the surface of a substrate of a single crystal of langasite represented by the chemical formula: La3Ga5SiO14 and belonging to point group 32. In the substrate, when the angle of cutting from the single crystal of langasite and the direction of propagation of surface acoustic wave are expressed by Euler's angles ( phi , theta , psi ), the values of phi , theta and psi lie in the regions of phi of -5 to 5 degrees, theta of 136 to 146 degrees and psi of 21 to 30 degrees, respectively. The relationship between psi (unit: degree) representing the direction of propagation of surface acoustic wave and the normalized film thickness h/ lambda (unit: percent) of the thickness h of the interdigital electrodes normalized by the wavelength lambda of the surface acoustic wave is as follows: -3.79 (h/ lambda ) + 23.86 </= psi </= -5.08 (h/ lambda ) + 26.96 when psi </= 25.5 degrees, and 4.39 (h/ lambda ) + 24.30 </= psi </= 3.54 (h/ lambda ) + 27.17 when psi > 25.5 degrees.
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