Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-02-09
2002-03-26
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S320000
Reexamination Certificate
active
06362561
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric vibration devices and to piezoelectric resonance components for use in piezoelectric resonators, piezoelectric filters, and other similar devices. More specifically, the present invention relates to a piezoelectric vibration device and a piezoelectric resonance component each having a beveled surface located near each end of a piezoelectric element.
2. Description of the Related Art
Energy-trapping piezoelectric devices have been widely used in resonators, band-pass filters, and other similar devices. An example of a piezoelectric device of this sort is disclosed in Japanese Unexamined Patent Publication No. 56-165413.
FIG. 7
of the present application shows a perspective view of a piezoelectric device described in the related art. A piezoelectric device
51
includes a piezoelectric substrate
52
. The piezoelectric substrate
52
is polarized along a direction indicated by an arrow P in
FIG. 7
, that is, in a direction parallel to the main surface of the substrate
52
. At the centers of the top surface and the bottom surface of the piezoelectric substrate
52
, vibration electrodes
53
and
54
are provided so as to oppose each other with the piezoelectric substrate
52
disposed therebetween. The vibration electrode
53
is electrically connected to a terminal electrode
55
located at one end of the piezoelectric substrate
52
. On the bottom surface of the piezoelectric substrate
52
, the vibrating electrode
54
is connected to a terminal electrode
56
located on the other end of the piezoelectric substrate
52
.
In the piezoelectric device
51
, at least one of four ridges at longitudinal ends of the piezoelectric substrate
52
is cut along a width direction of the piezoelectric substrate
52
. In other words, beveled surfaces
52
a
and
52
b
are formed at opposite ends of the substrate
52
.
In the piezoelectric device
51
, by properly setting dimensions of the beveled surfaces
52
a
and
52
b
, spurious responses generated due to a longitudinal mode may be suppressed.
Also, as disclosed in Japanese Unexamined Utility Model Publication No. 1-40920, a piezoelectric resonator that generates thickness shear vibration has beveled surfaces at both ends of a piezoelectric substrate. In this device, by forming a beveled surface at end of the piezoelectric substrate, energy trap efficiency is increased and filtering characteristics are improved. This publication also describes that spurious responses due to a contour mode may be suppressed, and it is easier to make the device compact.
As described in the above-mentioned related art, in an energy-trapping piezoelectric device which generates thickness shear vibration, it is known that by forming a beveled surface on a piezoelectric substrate, spurious responses due to a longitudinal mode or a contour mode may be suppressed, and energy trap efficiency may be increased.
However, in a conventional energy-trapping piezoelectric device having a beveled surfaces, a problem occurs in that by increasing energy trap efficiency, a response of a higher-order mode vibration which results in spurious responses is greatly increased.
When a thickness shear mode energy-trapping piezoelectric device is utilized as an oscillator, suppression of harmonics generated at frequencies of odd-number multiples of a fundamental vibration is absolutely necessary. When suppression of the harmonics is insufficient, oscillations are likely to occur at frequencies of odd-number multiples, such as three times, five times, and other multiples, of a transmission frequency.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide an energy-trapping piezoelectric vibration device arranged to generate a thickness shear mode and to effectively suppresses spurious responses due to a longitudinal direction mode and a contour mode and also effectively suppresses spurious responses due to higher-order modes, thus realizing improved resonance and filtering characteristics.
A preferred embodiment of the present invention provides a piezoelectric vibration device having a piezoelectric element including first and second longitudinally opposed ends, top and bottom surfaces provided between the first and second ends such that the top and bottom surfaces oppose each other, and beveled surfaces disposed at a vicinity of the first and second ends such that the thickness of the piezoelectric element gradually decreases towards the first and second ends, respectively, and first and second vibration electrodes disposed on the top surface and the bottom surface of the piezoelectric element, respectively, the first and second vibration electrodes located substantially at a middle portion of the piezoelectric element so as to oppose each other with the piezoelectric element disposed therebetween to define opposing portions which constitute a vibrator, wherein a roughness of the beveled surfaces is greater than a roughness of the surface of the piezoelectric element located at the opposing portions and beneath the first and second vibration electrodes.
Preferably, Ra
1
−Ra
2
>0.3 &mgr;m is satisfied where Ra
1
is the mean roughness of the center line according to Japanese Industrial Standard B0601 of the beveled surface, and Ra
2
is the mean roughness of the center line of the surface of the piezoelectric element located at the opposing portions and beneath the first and second vibration electrodes.
In the present invention, the beveled surfaces may be provided on the top surface only, or the bottom surface only, or on the top and bottom surfaces.
In another preferred embodiment of the present invention, there is provided a piezoelectric resonance component including a case substrate, a piezoelectric vibration device mounted on the case substrate, and a case member mounted on the case substrate so as to enclose the piezoelectric vibration device, wherein the piezoelectric vibration device includes a piezoelectric element including first and second longitudinally opposed ends, top and bottom surfaces provided between the first and second ends such that the top and bottom surfaces oppose each other, and beveled surfaces disposed at a vicinity of the first and second ends such that the thickness of the piezoelectric element gradually decreases towards the first and second ends, respectively; and first and second vibration electrodes disposed on the top surface and the bottom surface of the piezoelectric element, respectively, the first and second vibration electrodes located substantially at a middle portion of the piezoelectric element so as to oppose each other with the piezoelectric element disposed therebetween to define opposing portions which constitute a vibrator, and wherein a roughness of the beveled surfaces is greater than a roughness of a surface of the piezoelectric element located at the opposing portions and beneath the first and second vibration electrodes.
Preferably, the above described piezoelectric resonance component further includes a capacitor device mounted on the case substrate, wherein the piezoelectric vibration device is secured on the capacitor device and mounted on the case substrate via the capacitor device, and a built-in load capacitance type oscillator is configured by the above arrangement. Note that when a capacitor device is mounted on the case substrate and when the piezoelectric vibration device is secured on the capacitor device, a piezoelectric resonance component that oscillates positively at a desired frequency and is free from abnormal oscillations or other defects is obtained.
In preferred embodiments of the present invention, since a beveled surface is provided on a piezoelectric element having an energy-trapping piezoelectric vibrator, spurious responses due to a longitudinal mode or a contour mode are effectively suppressed. Further, since the surface roughness of the beveled surface is greater than the surface roughness of the surface of the piezoelectr
Kuroda Hideaki
Yoshida Ryuhei
Keming & Bennett, LLP
Medley Peter
Murata Manufacturing Co. LTD
Tamai Karl
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