Piezoelectric vibrator, filter using the same and its adjusting method
First Claim
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1. A piezoelectric vibrator comprising:
- a piezoelectric plate, having a polarization that points in a direction of a thickness of the piezoelectric plate, the piezoelectric plate having a first face and a second face;
a first electrode for covering the first face;
a second electrode for covering the second face;
a first dielectric film for covering the first electrode; and
a second dielectric film for covering the second electrode,wherein the piezoelectric plate employs a thickness longitudinal vibration as a principal vibration,the first dielectric film and the second dielectric film have substantially a same thickness, a substantially same area, and a substantially same geometric shape,a ratio of a sum of a thickness (ts) of the first dielectric film and the second dielectric film to the thickness (tp) of the piezoelectric plate is provided in a range such that an electromechanical coupling factor is substantially constant,wherein the range of the ratio (ts/tp) is between 0.7 and 2.0, inclusively.
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Abstract
A piezoelectric vibrator has a laminated structure where silicon oxide films having substantially the same thickness are disposed at both faces of piezoelectric plate as dielectric films. Using the structure discussed above, because dielectric films are formed at the both faces of the piezoelectric plate a difference of internal stress, which is caused by a difference of stress relaxation in a long term and affects the piezoelectric plate or the dielectric film, becomes small. Therefore, a warp can be considerably small. As a result, a change, which is caused by the warp of the piezoelectric vibrator, in a resonance frequency of the piezoelectric vibrator can be small.
50 Citations
12 Claims
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1. A piezoelectric vibrator comprising:
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a piezoelectric plate, having a polarization that points in a direction of a thickness of the piezoelectric plate, the piezoelectric plate having a first face and a second face; a first electrode for covering the first face; a second electrode for covering the second face; a first dielectric film for covering the first electrode; and a second dielectric film for covering the second electrode, wherein the piezoelectric plate employs a thickness longitudinal vibration as a principal vibration, the first dielectric film and the second dielectric film have substantially a same thickness, a substantially same area, and a substantially same geometric shape, a ratio of a sum of a thickness (ts) of the first dielectric film and the second dielectric film to the thickness (tp) of the piezoelectric plate is provided in a range such that an electromechanical coupling factor is substantially constant, wherein the range of the ratio (ts/tp) is between 0.7 and 2.0, inclusively. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A piezoelectric filter comprising:
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a piezoelectric vibrator including; a piezoelectric plate, having a polarization that points in a direction of a thickness of the piezoelectric plate, the piezoelectric plate having a first face and a second face; a first electrode for covering the first face; a second electrode for covering the second face; a first dielectric film for covering the first electrode; and a second dielectric film for covering the second electrode, wherein the piezoelectric plate employs a thickness longitudinal vibration as a principal vibration, the first dielectric film and the second dielectric film have substantially a same thickness, a substantially same area, and a substantially same geometric shape, a ratio of a sum of a thickness (ts) of the first dielectric film and the second dielectric film to the thickness (tp) of the piezoelectric plate is provided in a range such that an electromechanical coupling factor is substantially constant, wherein the range of the ratio (ts/tp) is between 0.7 and 2.0, inclusive. - View Dependent Claims (9, 10, 11)
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12. A method of adjusting a piezoelectric vibrator, the piezoelectric vibrator comprising:
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a piezoelectric plate, having a polarization that points in a direction of a thickness of the piezoelectric plate, the piezoelectric plate having a first face and a second face; a first electrode for covering the first face; a second electrode for covering the second face; a first dielectric film for covering the first electrode; and a second dielectric film for covering the second electrode; the method comprising; providing a ratio of a sum of a thickness (ts) of the first dielectric film and the second dielectric film to the thickness (tp) of the piezoelectric plate in a range such that an electromechanical coupling factor is substantially constant; and adjusting a resonance frequency of the piezoelectric vibrator by changing at least one of the first dielectric film and the second dielectric film, wherein the piezoelectric plate employs a thickness longitudinal vibration as a principal vibration, the first dielectric film and the second dielectric film have substantially a same thickness, a substantially same area, and a substantially same geometric shape, wherein the range of the ratio (ts/tp) is between 0.7 and 2.0, inclusive.
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Specification