Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-08-24
2001-10-02
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S348000
Reexamination Certificate
active
06297581
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric element for use in an oscillator and a filter that vibrates in a longitudinal vibration mode, and an electronic component using the piezoelectric element.
2. Description of the Related Art
In a well-known piezoelectric element vibrated in a longitudinal vibration mode, as disclosed in Japanese Unexamined Patent Publication No.
2-224515
, an input electrode and an output electrode, which are separated by a linear groove extending in the longitudinal direction of the piezoelectric element, are provided on one major surface of a piezoelectric substrate, and a common electrode is disposed on the other major surface of the piezoelectric substrate. The input and output electrodes each include a support section made of conductive rubber which functions as an electrical contact for making an electrical connection with an outer conductor.
In the above-described piezoelectric element including the fixed support section, however, the longitudinal vibration is sometimes hindered due to the particular dimensions and material of the support section which deteriorates the resonance properties of the piezoelectric element.
As a result of various studies of this problem, it has been found that the thickness, length, and elastic coefficient (Young's modulus) of the support section are closely related to a resonance resistance and that resonance resistance is a cause of deterioration of resonant properties.
SUMMARY OF THE INVENTION
To overcome the problems described above, the preferred embodiments of the present invention provide a piezoelectric element that prevents interference with longitudinal vibration and eliminates deterioration of the resonance properties.
The preferred embodiments of the present invention also provide a electronic component having excellent electrical characteristics and including a piezoelectric element that prevents interference with longitudinal vibration and eliminates deterioration of the resonance properties.
According to a preferred embodiment of the present invention, there is provided a piezoelectric element vibrating in a longitudinal vibration mode and including a piezoelectric substrate; a pair of external electrodes provided on front and back major surfaces of the piezoelectric substrate, respectively; and a conductive support section disposed on one of the pair of external electrodes and located at a nodal portion of the piezoelectric substrate; wherein the piezoelectric element satisfies the following condition: T1/T<0.5 where T represents a thickness of the piezoelectric element and T1 represents a thickness of the support section.
According to another preferred embodiment of the present invention, there is provided a piezoelectric element vibrating in a longitudinal vibration mode and including a piezoelectric substrate; a pair of external electrodes respectively provided on front and back major surfaces of the piezoelectric substrate; and a conductive support section disposed on one of the pair of external electrodes and located at a nodal portion of the piezoelectric substrate; wherein the piezoelectric element satisfies the following condition: L1/L<0.2 where L represents the length of the piezoelectric element and L1 represents the length of the support section.
According to a further preferred embodiment of the present invention, there is provided a piezoelectric element vibrating in a longitudinal vibration mode and including a piezoelectric substrate; a pair of external electrodes respectively provided on front and back major surfaces of the piezoelectric substrate; and a conductive support section disposed on one of the pair of external electrodes and located at a nodal portion of the piezoelectric substrate; wherein the piezoelectric element satisfies the following conditions: T1/T<0.5 and L1/L<0.2 where T represents a thickness of the piezoelectric element, T1 represents a thickness of the support section, L represents a length of the piezoelectric element, and L1 represents a length of the support section.
The above-mentioned features and relationships set forth in the conditions provide a significant reduction in resonance resistance, prevent interference with the longitudinal vibration, and provide a piezoelectric element having excellent resonance performance and electrical properties which are hardly affected by the problems described with relation to the prior art devices and disadvantages.
When the piezoelectric element is fixedly connected to an outer conductor (e.g., a pattern electrode of a mounting substrate), the support section functions as a spacer which defines a vibration space between the piezoelectric element and the outer conductor, and functions as a conductive member for electrically connecting the electrode of the piezoelectric element and the outer conductor. In this case, it is preferable to set the thickness T1 and the length L1 of the support section as large as possible in order to enhance stability of the piezoelectric element and to prevent vibration failure and insulation failure. Since the thickness T1 and the length L1 are limited as mentioned above, however, it is preferable that the thickness T1 and the length L1 be as large as possible as long as they do not interfere with the vibration characteristics.
In addition to the dimensions of the support section, a material which is used to form the support section and a Young's modulus of such material has a great influence on the resonance resistance. Therefore, it is preferable to make the support section of a material having a Young's modulus of about 10
9
N/m
2
or more. The support section made of such a material having a high Young's modulus vibrates according to the vibration of the piezoelectric element and does not suppress the longitudinal vibration of the piezoelectric element, whereby the resonance resistance is significantly reduced.
A electronic component is provided by mounting the piezoelectric element according to preferred embodiments described above on a pattern electrode disposed on an upper surface of an insulating mounting substrate. That is, a major surface of the piezoelectric element where the support section is fixed is disposed opposite to the surface of the mounting substrate having pattern electrodes disposed thereon, the support section is fixedly connected to one pattern electrode of the mounting substrate, and an electrode on the other major surface of the piezoelectric element is connected to another pattern electrode of the mounting substrate via a conductive wire. A cap may be fixedly bonded to the mounting substrate so that the cap covers the piezoelectric element.
In such an electronic component, it is preferable to make the mounting substrate of a material having a Young's modulus of about 10
11
N/m
2
or less. That is, when the Young's modulus of the mounting substrate is preferably about 10
11
N/m
2
or less, the vibration of the piezoelectric element is transmitted to the mounting substrate via the support section, while a vibration-absorbing effect of the mounting substrate makes it difficult to return a reflected wave to the piezoelectric element. As a result, a piezoelectric component having excellent properties is achieved.
Further objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the attached drawings.
REFERENCES:
patent: 4454444 (1984-06-01), Fujiwara et al.
patent: 4455502 (1984-06-01), Nakatani
patent: 4455503 (1984-06-01), Nakatani
patent: 5859488 (1999-01-01), Okeshi et al.
patent: 5973442 (1999-10-01), Irie
patent: 6005330 (1999-12-01), Okeshi et al.
patent: 2-224515 (1990-09-01), None
Tietz et al., Non-Destructive Testing of Green Ceramic Materials, NDT.net, vol. 3, No. 11 (Nov. 1998).
Dougherty Thomas M.
Murata Manufacturing Co. Ltd.
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