| 摘要 |
PROBLEM TO BE SOLVED: To provide a thickness longitudinal piezoelectric resonator that can suitably be used for a serial arm resonator of a ladder type filter. SOLUTION: N-sets (N is a natural number being 3 to 5) of internal electrodes (e.g. 3 to 6) are placed in a piezoelectric body 2 of this resonator 1, and an electric field is applied alternately to piezoelectric layers among the internal electrodes 3-6 in the thickness direction in the thickness longitudinal piezoelectric resonator. In the case of N=3, a relation of 0.50<=(D1+D2)/2D<=1.00 holds, in the case of N=4, a relation of 0.50<=(D1+D2)/2D<=0.90 holds, and in the case of N=5, a relation of 0.50<=(D1+D2)/2D<=0.80 holds, where D is the thickness of the piezoelectric body between the internal electrodes adjacent in the thickness direction, and D1, D2 are the thickness of the 1st and 2nd piezoelectric layers, respectively, located outside the internal electrodes that are located at outermost positions in the thickness direction.
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