Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-10-05
2001-05-15
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S365000
Reexamination Certificate
active
06232699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an energy-trap piezoelectric resonator used as, for example, an oscillator or a band-pass filter, and more particularly, to an energy-trap piezoelectric resonator in which resonance electrodes disposed opposite to each other with a piezoelectric substrate located therebetween have improved shapes.
2. Description of the Related Art
Conventionally, an energy-trap piezoelectric resonator suitable for use in an oscillator operating in a MHz band uses a non-fundamental harmonic of a thickness extensional vibration mode. For example, Japanese Patent Application Laid-Open (kokai) No. 4-216208 discloses an energy-trap piezoelectric resonator as shown in FIG.
16
.
An energy-trap piezoelectric resonator
51
shown in
FIG. 16
uses a piezoelectric substrate
52
polarized in the thickness direction thereof. A resonance electrode
53
is disposed on the upper surface of the piezoelectric substrate
52
at the center thereof, while a resonance electrode
54
is disposed on the lower surface of the piezoelectric substrate
52
at the center thereof. The resonance electrodes
53
and
54
have circular shapes, are the same size, and are positioned opposite to each other with the piezoelectric substrate
52
disposed therebetween.
In the energy-trap piezoelectric resonator
51
, the portion of the piezoelectric substrate
52
where the resonance electrodes
53
and
54
overlap each other constitutes a vibration portion. Upon application of an AC voltage to the resonance electrodes
53
and
54
, thickness extensional vibration is generated in the resonator
51
. Further, partial electrodes
55
are provided in order to utilize a non-fundamental harmonic of the thickness extensional vibration while lowering the response to the fundamental wave of the thickness extensional vibration. The partial electrodes
55
are disposed on the upper and lower surfaces of the piezoelectric substrate
52
so as to extend along the center portions of the corresponding longitudinal edges. Due to the mechanical load and the piezoelectric short-circuit effect created by the partial electrodes
55
, vibration energy is attenuated, resulting in a decrease in the response to the fundamental wave of the thickness extensional vibration.
Meanwhile, Japanese Utility-Model Application Laid-Open (kokai) No. 5-25823 discloses a ceramic resonator as shown in
FIG. 17. A
ceramic resonator
61
of
FIG. 17
utilizes the fundamental harmonic of thickness extensional vibration and has a structure in which circular resonance electrodes
63
and
64
having the same dimension are respectively disposed on the opposite main surfaces of a rectangular piezoelectric substrate
62
. In the ceramic resonator, a circular resin layer
65
is disposed on the upper resonance electrode
63
such that the circular resin layer
65
has a diameter equal to or smaller than that of the resonance electrode
63
.
The resin layer
65
is provided to produce a damping effect by means of its mass load, thereby suppressing ripples within a band to be used.
As described above, in the conventional energy-trap piezoelectric resonators, the resonance electrodes disposed on the opposite main surfaces of the piezoelectric substrate are typically of identical shape and size, and are positioned so that the resonance electrodes are opposite to and overlap each other in their entirety with the piezoelectric substrate disposed therebetween.
In energy-trap piezoelectric resonators of the above-described types, since vibrations other than vibration to be used are considered spurious vibrations, suppression of such spurious vibrations is strongly demanded.
In the prior art technique disclosed in Japanese Patent Application Laid-Open No. 4-216208, a non-fundamental harmonic of thickness extensional vibration is used, and the above-described partial electrodes
55
are used in order to suppress the fundamental harmonic of the thickness extensional vibration which is an undesired, spurious vibration. However, when the size of the piezoelectric resonator
51
is reduced, there is insufficient space for providing the partial electrodes
55
. That is, use of the partial electrodes
55
makes miniaturization of the piezoelectric resonator difficult.
Further, in the energy-trap piezoelectric resonator disclosed in Japanese Utility-Model Application Laid-Open No. 5-25823, undesired vibrations are damped through attachment of a resin layer
65
. However, when the resin layer
65
is applied, the vibration to be used is damped as well. Although not disclosed in Japanese Utility-Model Application Laid-Open No. 5-25823, when a resonator that utilizes a non-fundamental harmonic of thickness extensional vibration is constructed through use of the piezoelectric resonator
61
, the harmonic of thickness extensional vibration is damped, causing it to be impossible to achieve good resonance characteristics.
In addition, in the case of the piezoelectric resonator
61
, since the resin layer
65
must be applied in order to suppress undesired, spurious vibrations, the manufacturing process becomes overly complex.
SUMMARY OF THE INVENTION
To overcome the above-described problems, preferred embodiments of the present invention provide an energy-trap piezoelectric resonator which does not require formation of the above-described partial electrodes or resin layer, which effectively suppresses undesired vibration, which effectively generates a desired vibration mode, and which facilitates miniaturization of the resonator and simplification of the manufacturing process therefor.
One preferred embodiment of the present invention provides an energy-trap piezoelectric resonator adapted to vibrate in a thickness extensional vibration mode, including a piezoelectric substrate polarized in the thickness direction thereof and having first and second main surfaces, a first resonance electrode disposed on a portion of the first main surface of the piezoelectric substrate, and a second resonance electrode disposed on a portion of the second main surface of the piezoelectric substrate, the second resonance electrode being arranged to face the first resonance electrode with the piezoelectric substrate disposed therebetween and having an external dimension that is smaller than that of the first resonance electrode.
In the piezoelectric resonator of preferred embodiments of the present invention, since the external dimension of the second resonance electrode is smaller than that of the first resonance electrode, the fundamental harmonic of thickness extensional vibration easily leaks from the vibration portion. That is, the trap effect for the fundamental harmonic of thickness extensional vibration is set to a low level. Therefore, undesired, spurious vibrations resulting from the fundamental harmonic of thickness extensional vibration can be suppressed effectively. Thus, there is provided an energy-trap piezoelectric resonator which utilizes a non-fundamental harmonic of thickness extensional vibration and has excellent resonance characteristics.
Preferably, in the above described energy-trap piezoelectric resonator, a third harmonic of thickness extensional vibration is used. In this case, there is provided an energy-trap piezoelectric resonator which has excellent resonance characteristics resulting from the third harmonic of thickness extensional vibration and which is suitable for use in a MHz band.
Further, whereas conventional energy-trap piezoelectric resonators require the formation of partial electrodes or the application of a resin layer on the resonance electrode in order to suppress undesired spurious vibrations, the energy-trap piezoelectric resonator of preferred embodiments of the present invention does not require any excess member or element such as partial electrodes or a resin layer applied on the resonance electrode. Therefore, material costs are greatly reduced and the manufacturing process is greatly simplified in the preferred embodiments of the present invention.
In addition, in the conventi
Budd Mark O.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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