Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-01-23
2003-12-30
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S365000, C310S364000
Reexamination Certificate
active
06670739
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave (SAW) apparatus having a SAW device that includes a piezoelectric substrate having pyroelectric properties and which is housed in a package. More particularly, the present invention relates to an edge-reflection-type SAW apparatus having a mechanism for preventing deterioration in performance or electrode damage due to a pyroelectric effect.
2. Description of the Related Art
When a surface acoustic wave (SAW) apparatus including a piezoelectric substrate having pyroelectric properties experiences a rapid change in temperature, a charge caused by the pyroelectric effect is generated on the piezoelectric substrate. This might result in discharging between a plurality of electrodes disposed on the piezoelectric substrate, causing damage to the electrodes. If the piezoelectric substrate is made of a piezo-ceramic, the piezoelectricity of the piezoelectric substrate is significantly reduced.
In order to solve the foregoing problems caused by the pyroelectric effect, a variety of proposals have been made. A SAW apparatus
101
shown in
FIG. 4
is disclosed in Japanese Utility Model Publication No. 2-15388. In this apparatus
101
, an interdigital transducer (IDT)
103
, and reflectors
104
and
105
are disposed on the top of a piezoelectric substrate
102
. A short-circuited electrode
106
having a rectangular band shape is disposed on the top of piezoelectric substrate
102
along its outer periphery. The technique described in this publication prevents dust that is scattered during manufacturing from adhering to electrodes such as the IDT
103
because of static electricity or pyroelectric charge generated during the heating step when a SAW device
101
is bonded to a package.
A SAW device
111
shown in
FIG. 5
is disclosed in Japanese Unexamined Patent Application Publication No. 56-16312. A piezoelectric substrate
112
is polarized in the direction indicated by an arrow P. IDTs
113
and
114
are disposed on the top of the piezoelectric substrate
112
. In order to prevent deterioration in piezoelectricity due to the pyroelectric effect in the case where the piezoelectric substrate
112
is made of a piezo-ceramic, conductive members
115
and
116
are disposed on ends
112
a
and
112
b
of the piezoelectric substrate
112
, respectively, so as to extend perpendicular to the polarization direction. The conductive members
115
and
116
are electrically connected to a lead
117
. Japanese Unexamined Patent Application Publication No. 56-37723 also discloses a SAW device having the same construction as in Japanese Unexamined Patent Application Publication No. 56-16312.
However, there are problems associated with the above-described techniques of the related art.
The SAW apparatus disclosed in Japanese Utility Model Publication No. 2-15388 requires the band-shaped short-circuited electrode
106
disposed around the periphery of the piezoelectric substrate
112
. Therefore, the SAW apparatus of this type cannot be implemented as, for example, an edge-reflection-type SAW apparatus
121
shown in
FIG. 6
which uses a Shear Horizontal (“SH”) surface acoustic wave. The edge-reflection-type SAW apparatus
121
requires electrode fingers along facing ends
122
a
and
122
b
of a piezoelectric substrate
122
or in the vicinity of the ends
122
a
and
122
b.
Therefore, the short-circuited electrode described in Japanese Utility Model Publication No. 2-15388 cannot be located along the outer periphery of the piezoelectric substrate
122
.
The SAW apparatus disclosed in Japanese Unexamined Patent Application Publication No. 56-16312 or No. 56-37723 requires the steps of, first, forming an electrode on the top of a mother piezoelectric substrate, cutting the piezoelectric substrate
112
therefrom by dicing, and then forming the conductive members
115
and
116
on the edges
112
a
and
122
b
of the piezoelectric substrate
112
. Therefore, an additional manufacturing step is necessary, thereby increasing the cost, time and difficulty of manufacturing.
SUMMARY OF THE INVENTION
In order to overcome the above-described problems with the related art, preferred embodiments of the present invention provide an edge-reflection-type SAW apparatus that eliminates the adverse effects of a pyroelectric charge due to a rapid change in temperature without requiring any additional manufacturing step.
According to a preferred embodiment of the present invention, a SAW apparatus includes a piezoelectric substrate having pyroelectric properties and having first and second main surfaces opposing each other, first and second sides opposing each other, and first and second ends opposing each other, at least one IDT disposed on the first main surface of the piezoelectric substrate for propagating surface acoustic waves in the direction that is substantially perpendicular to the first and second sides, the surface acoustic waves being reflected by the first and second sides, a SAW device disposed on the first main surface of the piezoelectric substrate, the SAW device including a first pyroelectric charge cancellation electrode in the vicinity of an edge defined by the first end and the first main surface, and a second pyroelectric charge cancellation electrode in the vicinity of an edge defined by the second end and the first main surface, and a package which houses the SAW device and which includes a plurality of electrodes which are electrically connected to the SAW device. The first and second pyroelectric charge cancellation electrodes are electrically connected via the electrodes on the package rather than directly on the piezoelectric substrate.
The first and second pyroelectric charge cancellation electrodes are not located on the first and second sides of the piezoelectric substrate, respectively, but in the vicinity of the edge defined by each of the first and second ends and the first main surface. The first and second pyroelectric charge cancellation electrodes are located in a region other than in or around the SAW propagation pass, and therefore, the performance of the SAW apparatus is not influenced by the pyroelectric charge cancellation electrodes. Since the first and second pyroelectric charge cancellation electrodes are electrically connected via the electrodes on the package, the pyroelectric charges having opposite polarities which are generated at both ends in the polarization direction are cancelled. Therefore, if temperature rapidly changes, pyroelectric charges do not damage the electrodes or deteriorate the performance of the SAW device on the piezoelectric substrate.
According to another preferred embodiment of the present invention, the SAW device is disposed on the piezoelectric substrate, and has a plurality of electrode patterns connected to the at least one IDT, the plurality of electrode patterns are electrically connected to the plurality of electrodes on the package, and the first and second pyroelectric charge cancellation electrodes are electrically connected to different electrodes of the electrodes on the package via different electrode patterns of the electrode patterns on the piezoelectric substrate, the different electrodes on the package being electrically connected within the package. The first and second pyroelectric charge cancellation electrodes are electrically connected to different electrodes on the package via the electrode patterns which are used to electrically connect the IDTs to the electrodes on the package. Therefore, there is no need for any additional electrically connecting member, such as a bonding wire, for electrically connecting the first and second pyroelectric charge cancellation electrodes to the electrodes on the package.
The first and second pyroelectric charge cancellation electrodes may be arranged along the edge defined by each of the first and second ends and the first main surface. Alternatively, the first and second pyroelectric charge cancellation electrodes may be separated from the edges.
In another preferred
Horiuchi Hideya
Ikeura Mamoru
Kadota Michio
Aguirrechea J.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Tamai Karl
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