| 摘要 |
PROBLEM TO BE SOLVED: To provide a crystal filter, which improves filter characteristics, at low cost. SOLUTION: In a piezoelectric filter element, with which a thin vibrating part and a thick annular surrounding part supporting the periphery of the vibrating part are integrally formed of a piezoelectric substrate, a full electrode is provided on one side of the vibrating part and a divided electrode is provided on the other side, the other divided electrode parallel connected with the divided electrode and an area provided with no full electrode on the surface of the vibrating part opposed with the gap of the other divided electrode are provided, prescribed bridging capacitance is generated between the divided electrodes by making the inter-electrode distance of the other divided electrode into prescribed interval, the bridging capacitance is set to a required value by setting the area within a required range, and the pole frequency of the piezoelectric filter is controlled to a required value.
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