Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-03-28
2002-04-23
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S326000, C310S365000
Reexamination Certificate
active
06376970
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric resonator supporting structure and a piezoelectric component including the same, and more particularly to a piezoelectric resonator supporting structure for supporting a piezoelectric resonator on a supporting member, such as a base, via a fixing member.
2. Description of the Related Art
FIG. 21
illustrates an example of a piezoelectric resonator relating to a background of the invention and to which the present invention is applied.
FIG. 22
is a plan view showing a state in which insulating films are formed on a substrate of the piezoelectric resonator. The piezoelectric resonator
10
shown in
FIG. 21
includes a rectangular parallelopiped substrate
12
which is 4 mm long, 1 mm wide, and 1 mm high. The substrate
12
includes twenty piezoelectric layers
14
that are stacked on each other and formed of, for example, piezoelectric ceramic material. These piezoelectric layers
14
have the same dimensions. As indicated by the arrows in
FIG. 21
, the piezoelectric layers
14
are polarized in a longitudinal direction of the substrate
12
such that the polarization directions of adjacent piezoelectric layers
14
are opposite to each other. The piezoelectric layers
14
at both ends of the substrate
12
are not polarized.
Internal electrodes
16
are disposed between piezoelectric layers
14
of the substrate
12
, extend perpendicular to the longitudinal direction of the substrate
12
and are separated from each other in the longitudinal direction of the substrate
12
. The internal electrodes
16
are arranged to cover the entire main surfaces of the piezoelectric layers
14
. Therefore, the internal electrodes
16
are exposed at four side surfaces of the substrate
12
.
A groove
17
is formed in a center portion, in a widthwise direction of the substrate
12
, of one of the side surfaces of the substrate
12
. At one of the portions, in the widthwise direction of the substrate
12
, of the one side surface of the substrate
12
where the groove
17
is not formed, ends of alternate internal electrodes
16
are disposed so as to be covered with insulating films
18
. Ends of other alternate internal electrodes
16
are disposed at the other of the portions, in the widthwise direction of the substrate
12
, of the one side surface of the substrate
12
where the groove
17
is not formed.
At the one portion of the one side surface of the substrate
12
, an external electrode
22
is disposed on, for example, the insulating films
18
provided on the alternate electrodes
16
so as to be connected to the alternate electrodes
16
provided on the other portion. At the other portion of the one side surface of the substrate
12
, an external electrode
24
is disposed on, for example, the insulating films
20
provided on the alternate electrodes
16
so as to be connected to the alternate electrodes
16
provided on the one portion.
In the piezoelectric resonator
10
shown in
FIG. 21
, the external electrodes
22
and
24
are used as input/output electrodes. Since electric fields are applied between the internal electrodes
16
of adjacent layers when a signal is applied to the external electrodes
22
and
24
, the piezoelectric layers
14
, excluding those at both ends of the substrate
12
, become piezoelectrically active. In this case, electrical fields opposite in direction are applied to the piezoelectric layers
14
of the substrate
12
that are polarized in opposite directions. Therefore, the piezoelectric layers
14
as a whole tend to expand and contract in the same direction. In other words, when alternating current electric fields in the longitudinal direction of the substrate
12
are applied to the individual piezoelectric layers
14
by the internal electrodes
16
and the internal electrodes
16
connected to the external electrodes
22
and
24
, so that a driving force that expands and contracts the individual piezoelectric layers
14
is generated thereat, the entire piezoelectric resonator
10
is excited with a fundamental vibration of a longitudinal vibration, with the center portions, in the longitudinal direction of the substrate
12
, of the substrate
12
acting as nodes.
A description will now be provided of a conventional piezoelectric component in which the piezoelectric resonator
10
shown in
FIG. 21
is mounted via fixing members on a base which defines a supporting member.
FIG. 23
illustrates a state before the piezoelectric resonator of the conventional piezoelectric component is fixed.
FIG. 24
illustrates a state after the piezoelectric resonator of the piezoelectric component has been fixed. The piezoelectric component
1
shown in
FIGS. 23 and 24
includes a base
2
defining a supporting member. Two pattern electrodes
3
are provided on the base
2
. Fixing members
4
made of a urethane-type electrically conductive material, that is, a urethane-type synthetic resin containing 85 wt % of Ag are provided on respective center portions, in the longitudinal direction of the external electrodes
22
and
24
, of the external electrodes
22
and
24
. The fixing members
4
are bonded to the two pattern electrodes
3
on the base
2
via an electrically conductive paste
5
made of an epoxy-type electrically conductive material, that is, an epoxy-type synthetic resin containing Ag. This causes the external electrodes
22
and
24
of the piezoelectric resonator
10
to be electrically coupled to the respective pattern electrodes
3
on the base
2
, through the respective fixing members
4
, whereby the piezoelectric resonator
10
is fixed to the base
2
through the fixing members
4
.
In this case, the larger dimension W
1
of the upper portion of each fixing member
4
of the piezoelectric resonator
10
is in the longitudinal direction thereof, the easier it is for vibration to be transmitted. The dimension W
1
is in the range of from 1.0 mm to 1.4 mm.
The relationship between the transmission of vibration and dimension W
2
of the lower portion of each fixing member
4
of the piezoelectric resonator
10
in the longitudinal direction thereof is small, but with regard to the strength with which the base
2
and the fixing members
4
are grounded, it is, for example, set equal to or greater than 0.5 mm.
Although the amount of vibration transmitted varies with the hardness of the fixing members
4
and the amount of Ag contained in the fixing members
4
, it can be reduced by a certain amount even in a direction of thickness of the fixing members
4
by thickness t
1
of the fixing members
4
. The larger the value of thickness t
1
, the smaller the amount of vibration transmitted. The thickness t
1
has an upper limit due to the height of the piezoelectric components produced. It is within a range of, for example, from 130 &mgr;m to 170 &mgr;m.
Although thickness t
2
(shown in
FIG. 23
) prior to bonding with the electrically conductive paste
5
is not directly related to the transmission of vibration, when the electrically conductive paste
5
is thick, the fillet size with respect to the fixing members
4
becomes large, thereby increasing the amount of vibration transmitted. On the other hand, when it is thin, the strength with which the fixing members
4
is grounded is reduced. Therefore, the thickness t
2
is in a range of from 35 &mgr;m to 55 &mgr;m.
The piezoelectric component
1
shown in
FIGS. 23 and 24
possess the impedance characteristics and the phase characteristics illustrated in FIG.
25
and the filter characteristics illustrated in FIG.
26
.
However, in the above-described conventional piezoelectric component
1
, when the dimension W
1
of the upper portion of each fixing member
4
is made smaller in order to restrict the transmission of vibration, the dimension W
2
of the lower portion of the fixing members
4
inevitably becomes small, so that sufficient supporting strength cannot be obtained. On the other hand, in order to make the dimension W
2
of the lower portion of the fixing members
4
Kosugi Yuji
Kubo Takeshi
Kusabiraki Shigemasa
Yamazaki Takeshi
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