Amplifiers – With semiconductor amplifying device – Including combined diverse-type semiconductor device
Reexamination Certificate
2003-05-09
2004-08-10
Le, Dinh T. (Department: 2816)
Amplifiers
With semiconductor amplifying device
Including combined diverse-type semiconductor device
C333S188000
Reexamination Certificate
active
06774729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to composite-material vibrating devices in which a plurality of material portions having different acoustic impedances are coupled, and more particularly relates to a composite-material vibrating device in which a plurality of material layers having different acoustic impedances are coupled to a vibrating member such as a piezoelectric element.
The present invention further relates to methods for fabricating a composite-material vibrating device in which a plurality of material portions having different acoustic impedances are coupled, and more particularly relates to a method for fabricating a composite-material vibrating device that is capable of reflecting vibrations that have propagated from a vibrating member at the interfaces between the other material portions to thereby confine the vibrations in a portion within the interfaces.
2. Description of the Related Art
Conventionally, a structure in which casing substrates are laminated on the upper and lower surfaces of a piezoelectric vibrating element has been widely used for piezoelectric resonator components for use as piezoelectric resonators or piezoelectric filters. In this case, a space for permitting vibration of the piezoelectric vibrating portion of the piezoelectric element must be formed in the laminate. Thus, examples of methods that have been available include a method in which a depression for forming a cavity is provided in a piezoelectric-element-side surface of a casing substrate to be laminated and a method in which a region corresponding to a cavity is provided in an adhesive-applied area for forming the cavity before a casing substrate is laminated on a piezoelectric element.
As described above, in the laminated piezoelectric resonator components of the related art, a cavity for permitting vibrations of the piezoelectric vibrating portion must be formed. This makes it difficult to achieve miniaturization and cost reduction.
Meanwhile, Japanese Unexamined Patent Application Publication No. 10-270979 discloses a bulk acoustic wave filter having a laminated structure without a cavity. As shown in
FIG. 13
, in a bulk acoustic wave filter
211
, a piezoelectric filter is configured by providing a large number of films on a substrate
212
.
That is, in this laminated structure, a piezoelectric layer
213
is formed and electrodes
214
and
215
are provided on the upper and lower surfaces of the piezoelectric layer
213
to provide a piezoelectric resonator.
Layers made of silicon, polysilicon, or other suitable material are provided on the lower surface of the piezoelectric resonator to provide an acoustic mirror
219
having a laminated structure that includes a top layer
216
, a middle layer
217
, and a bottom layer
218
. Also, an acoustic mirror
220
having a similar laminated structure is provided on the upper surface of the piezoelectric resonator and a passivation layer
221
is formed on the acoustic mirror
220
as a protection layer.
In the acoustic mirror
219
, the acoustic impedance of the middle layer
217
is higher than the acoustic impedance of the top layer
216
and the bottom layer
218
. In the acoustic mirror
220
, similarly, the acoustic impedance of the middle layer higher than the acoustic impedance of the top and bottom layers.
In the bulk acoustic wave filter
211
, the provision of the acoustic mirrors
219
and
220
on the piezoelectric resonator portion allows vibrations that have propagated from the piezoelectric resonator to be reflected back toward the piezoelectric resonator. Thus, this structure can be mechanically supported using the substrate
212
without affecting the resonance characteristics of the piezoelectric resonator portion.
The bulk acoustic wave filter
211
shown in
FIG. 13
is configured such that the acoustic mirrors
219
and
220
reflect vibrations that have propagated from the piezoelectric resonator. In each of the acoustic mirrors
219
and
220
, the top and bottom layers are provided on the corresponding upper and lower surfaces of the middle layer and the acoustic impedance of the middle layer is higher than the acoustic impedance of the top and bottom layers. Thus, a large number of material layers must be provided for the acoustic mirrors
219
and
220
. Thus, while no cavity needs to be formed, a large number of material layers must be provided in the bulk acoustic wave filters
211
, which makes it difficult to achieve a compact, particularly, low profile structure. The fabrication process is also complicated.
In addition, in the bulk acoustic wave filter
211
, lateral vibrations in the piezoelectric resonator propagate and the vibrations that have alternately propagated are damped at side portions of the piezoelectric resonator. Thus, the side portions of the piezoelectric resonator portion are fixed, which poses a problem in that resonance characteristics of the piezoelectric resonator are deteriorated by the holding structures.
SUMMARY OF THE INVENTION
To overcome the shortcomings and problems of the related art described above, preferred embodiments of the present invention provide a composite-material vibrating device that is inexpensive, compact, and particularly suitable for a low profile application and that can be supported with little or no influence on vibration characteristics of a vibrating member using a relatively simple structure.
A composite-material vibrating device according to a preferred embodiment of the present invention includes a vibrating member that is made of material having a first acoustic impedance Z
1
and that defines a vibration generating source, and at least three reflective layers that are coupled to corresponding outer surfaces located in at least three directions of the vibrating member and that are made of material having a second acoustic impedance Z
2
that is smaller than the first acoustic impedance Z
1
. The composite-material vibrating device further includes holding members that are made of material that are coupled to surfaces opposite to the surfaces, coupled to the vibrating member, of the reflective layers and that are made of a material having a third acoustic impedance Z
3
that is greater than the second acoustic impedance Z
2
. Vibrations that have propagated from the vibrating member to the reflective layers are reflected at interfaces between the reflective layers and the corresponding holding members.
In preferred embodiments of the present invention, vibrations that have propagated from the vibrating member to the reflective layers are reflected at the interfaces between the reflective layers and the corresponding holding members. With this arrangement, vibrations of the vibrating member are securely confined in regions within the interfaces. Thus, the composite-material vibrating device of preferred embodiments of the present invention can be supported by the holding members without preventing the vibration of the vibrating member using a relatively simple structure. Thus, there is no need to form a cavity for permitting vibration of the vibrating member, which allows for significant reduction in the size and cost of the composite-material vibrating device. In addition, since the acoustic impedance Z
2
is preferably smaller than the acoustic impedances Z
1
and Z
3
to thereby reflect vibrations at the interfaces, the vibration mode of the vibrating member used is not particularly limited. Thus, it is possible to easily provide composite-material vibrating devices utilizing various vibration modes. Preferably, the vibrating member has a substantially rectangular parallelepiped or substantially cubic shape and the reflective layers are provided on at least three outer surfaces of the vibrating member. Thus, the composite-material vibrating device can be supported using an outer surface, which is located in any one of the at least three directions, of the composite-material vibrating device.
Preferably, the ratio Z
2
/Z
1
of the second acoustic impedance Z
2
to the first acoustic impedance Z
Inoue Jiro
Kaida Hiroaki
Nishimura Toshio
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