| 摘要 |
PROBLEM TO BE SOLVED: To provide a BAW (bulk acoustic wave) resonator which has a plurality of layers to increase the function of the resonator. SOLUTION: The BAW resonator includes a piezoelectric layer 102, a first electrode 104 on a front surface, a second electrode 106 on the opposite surface, a substrate 108, and an acoustic reflector 110 provided between the substrate 108 and the second electrode 106. The acoustic reflector 110 has a plurality of alternately-arranged layers made of a material having a high acoustic impedance and made of a material having a low acoustic impedance. The function of the acoustic reflector 110 is determined by the reflectivity of longitudinal wave and the reflectivity of traverse wave which exist in the BAW resonator 100 with a resonant frequency of the BAW resonator 100. The acoustic reflector 110 and layers 106a and 106b provided between the acoustic reflector 110 and the piezoelectric layer 102 are chosen so that transmittance of the longitudinal wave and transmittance of the traverse wave at the resonant frequencyare less than -10dB, referring to the number of these layers, the material and thickness thereof. COPYRIGHT: (C)2004,JPO
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