Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-11-27
2004-04-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06717335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to composite vibration devices that support a variety of vibrating members, with little influence on the vibration characteristics of the vibrating members. More particularly, the present invention relates to composite vibration devices, in which piezoelectric elements, electrostrictive elements, or other suitable elements are used as vibrating members.
2. Description of the Related Art
Conventionally, piezoelectric vibrating components have been widely used in resonators, filters, and other electronic components. For example, piezoelectric resonators use various vibration modes to obtain target resonant frequencies. As these vibrating modes, a thickness longitudinal vibration, a thickness-shear vibration, a length vibration, a width vibration, an extension vibration, a bending vibration, and other modes are known.
In such piezoelectric resonators, the supporting structures thereof vary with the type of vibration modes. Energy-trap piezoelectric resonators using a thickness longitudinal vibration and a thickness-shear vibration can be mechanically supported at both ends thereof.
FIG. 34
shows an example of an energy-trap piezoelectric resonator using a thickness-shear vibration. In a piezoelectric resonator
201
, a resonant electrode
203
is provided on the top surface of a piezoelectric plate
202
having a strip-like configuration and a resonant electrode
204
is provided on the bottom surface thereof and is disposed opposite to the resonant electrode
203
. The resonant electrodes
203
and
204
are opposed to each other at the approximate center in the lengthwise direction of the piezoelectric strip
202
. The opposing portion thereof defines an energy-trap piezoelectric vibrating section. As a result, vibration is trapped in the piezoelectric vibrating section. Thus, the piezoelectric resonator
201
can be mechanically supported at its ends without influencing the vibration of the piezoelectric vibrating section.
In the energy-trap piezoelectric resonator
201
, however, although vibrating energy is trapped in the piezoelectric vibrating section, a vibration attenuating section requiring a relatively large space must be provided outside the piezoelectric vibrating section. Consequently, for example, the length of the piezoelectric resonator strip
201
using a thickness-shear mode must be increased.
On the other hand, in piezoelectric resonators using a length vibration, a width vibration, an extension vibration, and a bending vibration, it is not possible to produce an energy-trap piezoelectric vibrating section. Thus, in order to prevent any influence on the resonant characteristics, a metal spring terminal is utilized to allow the terminal to be in contact with a node of vibration of the piezoelectric resonator. This arrangement permits the formation of a supporting structure.
In Japanese Unexamined Patent Application Publication No. 10-270979, a bulk acoustic wave filter
211
is provided as shown in FIG.
35
. In the bulk acoustic wave filter
211
, a plurality of films is stacked on a substrate
212
. In other words, a piezoelectric layer
213
is provided in the multi-layered structure. On the top and bottom of the piezoelectric layer
213
, stacked electrodes
214
and
215
are provided to define a piezoelectric resonator. In addition, on the bottom of the piezoelectric resonator, films made of silicon, polysilicon, or other suitable material are provided to define an acoustic mirror
219
having a multi-layered structure composed of a top layer
216
, a middle layer
217
, and a bottom layer
218
. In this case, the acoustical impedance of the middle layer
217
is higher than the acoustical impedances of the top layer
216
and the bottom layer
218
. The acoustic mirror
219
blocks the propagation of vibration produced by the piezoelectric resonator to the substrate
212
.
In addition, an acoustic mirror
220
having the same structure is stacked on the upper portion of the piezoelectric resonator. A passivation film
221
is provided on the acoustic mirror
220
. The passivation film
221
is made of a protective material such as epoxy, SiO
2
, or other suitable material.
In such a conventional energy-trap piezoelectric resonator, a vibration attenuating section must be provided on the outside of the piezoelectric vibrating section. Thus, although the resonator can be mechanically supported with an adhesive, the size of the piezoelectric resonator
201
is increased.
Furthermore, non-energy-trap piezoelectric resonators using a length vibration mode and an extension vibration mode do not need a vibration attenuating section. However, the resonant characteristics of the piezoelectric resonator deteriorate when the resonator is fixed and supported with an adhesive, solder, or other fixing material. As a result, since the resonator must be supported by a spring terminal, the supporting structure is complicated and requires many components.
As described above, in the bulk acoustic wave filter disclosed in Japanese Unexamined Patent Application Publication No. 10-270979, the plurality of films is stacked on the substrate
212
to define the piezoelectric resonator and the acoustic mirror
219
acoustically isolates the piezoelectric resonator from the substrate. Thus, the piezoelectric resonator is acoustically isolated and supported by the acoustic mirror
219
having the multi-layer structure on the substrate
212
.
However, in the bulk acoustic wave filter
211
, on the substrate
212
, many layers must be stacked to form the multi-layer structure defining the bottom acoustic mirror
219
, the piezoelectric resonator, and the piezoelectric filter, and also, many layers must be stacked to define the top acoustic mirror
220
. Additionally, on the top portion of the filter, the passivation film
221
must be arranged. As a result, the structure of the filter is complicated, and the vibration mode of the piezoelectric resonator is restricted because the resonator is defined by the multi-layer structure.
As mentioned above, conventionally, when a vibration source such as a piezoelectric resonator is supported without deteriorating the vibration characteristics, there are restrictions on the vibration mode of the resonator, the component size increases, and the structure is complicated.
SUMMARY OF THE INVENTION
To overcome the above-described problems, preferred embodiments of the present invention provide a composite vibration device that is supported by a relatively simple structure using a vibrating member producing a variety of vibration modes, with little or no influence on the vibration characteristics of the vibrating member.
According to a first preferred embodiment of the present invention, a composite vibration device includes a vibrating member as a vibration producing source, the vibrating member being made of a material having a first acoustical impedance Z
1
, first and second reflecting layers connected to respective sides of the vibrating member, each of the layers being made of a material having a second acoustical impedance Z
2
which is lower than the first acoustical impedance Z
1
, and supporting members, each of which is made of a material having a third acoustical impedance Z
3
which is higher than the second acoustical impedance Z
2
, the supporting members being connected to sides of the reflecting layers opposing the sides thereof connected to the vibrating member, In this composite vibration device, vibrations propagated from the vibrating member to the reflecting layers are reflected at the interfaces between the reflecting layers and the supporting members.
According to another aspect of the present invention, a composite vibration device includes a vibrating member as a vibration producing source, the vibrating member being made of a material having a first acoustical impedance Z
1
, a reflecting layer connected to a side of the vibrating member, the reflecting layer being made of a material having a second acoustical empedance Z
2
which is lo
Inoue Jiro
Kaida Hiroaki
Mitani Akihiro
Nishimura Toshio
Addison Karen
Dougherty Thomas M.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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