Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-05-19
2001-11-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S320000, C310S340000, C310S348000
Reexamination Certificate
active
06313569
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric devices used as piezoelectric resonators and piezoelectric filters and to methods for manufacturing the same. In particular, the present invention relates to a piezoelectric device including a piezoelectric substrate having outer coating substrates secured on two surfaces thereof via adhesive layers, the piezoelectric substrate including an energy-trap-type piezoelectric vibration unit. The present invention also relates to a method for manufacturing such a piezoelectric device.
2. Description of the Related Art
In an energy-trap-type piezoelectric device, a piezoelectric vibration unit is provided partially on a piezoelectric substrate. The piezoelectric vibration unit must be sealed in a manner such that the piezoelectric vibration unit is not prevented from vibrating.
A piezoelectric device of the energy-trap-type described above is disclosed in Japanese Unexamined Patent Application Publication No. 8-335844. The piezoelectric device is described below with reference to
FIGS. 4 and 5
.
A piezoelectric device
51
shown in
FIG. 4
includes a piezoelectric substrate
52
laminated with outer coating substrates
53
and
54
on the upper and lower surfaces thereof. A layered body defined by the piezoelectric substrate
52
and the outer coating substrates
53
and
54
is provided with external electrodes
55
,
56
, and
57
.
As shown in
FIG. 5
, the piezoelectric substrate
52
includes driving electrodes provided partially on the upper and lower surfaces of the piezoelectric substrate
52
, which define piezoelectric vibration units
52
a
and
52
b
. The outer coating substrates
53
and
54
are bonded to the piezoelectric substrate
52
via adhesive layers which have through-holes to provide spaces for the vibration of the piezoelectric vibration units
52
a
and
52
b.
In the piezoelectric device
51
, the adhesive layers include first layers
58
and
59
which are located adjacent to the outer coating substrates
53
and
54
, respectively, and second layers
60
and
61
which are disposed adjacent to the piezoelectric substrate
52
. The first layers
58
and
59
include a soft adhesive having a Shore D hardness of not more than 60, and the second layers
60
and
61
include a hard adhesive having a Shore D hardness of at least 60. The first layers
58
and
59
are provided with through-holes
58
a
and
58
b
and through-holes
59
a
and
59
b
, respectively. The second layers
60
and
61
are provided with through-holes
60
a
and through-holes
61
a
, respectively.
An excellent damping effect and a space for vibration are provided by the first soft adhesive layers
58
and
59
and the second hard adhesive layers
60
and
61
laminated in the piezoelectric device
51
, respectively. However, when the outer coating substrates
53
and
54
expand or contract, for example, by heating when mounting on a printed circuit board, the stress produced by the expansion or contraction is absorbed by the first layers
58
and
59
, thereby suppressing variation in the frequency characteristics of the device after soldering and when kept in a humid environment.
The cut-away through-holes
58
b
and
59
b
are provided at the periphery of the first layers
58
and
59
for preventing the external electrodes
55
,
56
, and
57
from breaking. There is a risk of breakage of the external electrodes
55
,
56
, and
57
in that, when applying the first soft adhesive layers
58
and
59
to the outer coating substrate
53
and
54
, the adhesive tends to flow out from the periphery of the outer coating substrate
53
and
54
to the side edge portions of the layered body due to its relative softness, and the flow of adhesive to the side edges portions of the layered body prevents the external electrodes
55
,
56
, and
57
from being properly formed by thin-film deposition or by coating and curing a conductive paste.
In the first step of manufacturing the piezoelectric device
51
, the first layer
58
of a soft adhesive is provided on a surface of the planar outer coating substrate
53
, and the first layer
59
of the soft adhesive is provided on a surface of the planar outer coating substrate
54
. The viscosity of an adhesive having a Shore D hardness of not more than 60 is generally not more than 1.5×10
5
mPas at 25° C. Therefore, in spite of being provided with the cut-away through-holes
58
b
and
59
b
, there is a risk of the adhesive flowing into the cut-away through-holes
58
b
and
59
b
, and flowing out of the periphery on which the external electrodes
55
,
56
, and
57
are provided, thereby causing a risk of breakage.
The above-described problem is eliminated when an adhesive having a Shore D harness of not more than 60 and having a viscosity before curing of at least approximately 3.0×10
5
mPas at 25° C. is used, however, such an adhesive is difficult to produce.
When manufacturing the piezoelectric device
51
, the second layers
60
and
61
of a hard adhesive are provided on the first layers
58
and
59
. In this case, recesses are provided in the second layers
60
and
61
in the layered body by the cut-away through-holes
58
b
and
59
b
of the first layers
58
and
59
disposed under the second layers
60
and
61
. Specifically, the thickness of the adhesive varies between a region at the periphery of the layered body on which the external electrodes
55
,
56
, and
57
are provided and the remaining region on which the external electrodes
55
,
56
, and
57
are not provided, which produces gaps at the periphery of the layered body, thereby causing a risk of breakage of the external electrodes
55
,
56
, and
57
.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a reliable piezoelectric device and a method for manufacturing the same, in which a space for vibration of the piezoelectric vibration unit is provided, the stress produced by a variation in temperature during reflow soldering or other suitable methods is suppressed, the frequency characteristics are not altered, and the risk of breakage of external electrodes caused by adhesive layers is greatly reduced.
According to a preferred embodiment of the present invention, a piezoelectric device includes a piezoelectric substrate provided with driving electrodes on the major surfaces thereof and opposing each other, outer coating substrates, each of which is laminated on the major surfaces of the piezoelectric substrate, adhesive layers to bond the piezoelectric substrate and the outer coating substrates to each other at the major surfaces of the piezoelectric substrate, and a plurality of external electrodes provided on lateral side surfaces of a layered body including the piezoelectric substrate, the outer coating substrates, and the adhesive layers. Each of the adhesive layers includes a first layer of an adhesive having a Shore D hardness after curing of not more than approximately 60 which is arranged such that the first layer is not exposed in a region of the lateral side surfaces of the layered body having the plurality of external electrodes provided thereon, a second layer of an adhesive having a Shore D hardness after curing of at least approximately 60, and a third layer of an adhesive having a Shore D hardness after curing of at least approximately 60, and having a viscosity before curing of at least approximately 3.0×10
5
mPas at a temperature of 25° C. The third layer is disposed between the periphery of the first layer and the region of the lateral side surfaces of the layered body which is provided with the plurality of external electrodes thereon. The second layer is laminated on the first layer and the third layer.
According to a preferred embodiment of the present invention, the first layer and the third layer of each of the adhesive layers are disposed adjacent to the outer coating substrate and the second layer of each of the adhesive layers is disposed adjacent th
Fujii Syuji
Sawai Kunio
Yonemura Motohide
Dougherty Thomas M.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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