Metal working – Piezoelectric device making
Reexamination Certificate
1998-09-24
2001-05-01
Young, Lee (Department: 3729)
Metal working
Piezoelectric device making
C333S187000, C333S189000, C310S321000, C310S348000, C310S359000, C310S366000, C310S367000
Reexamination Certificate
active
06223406
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a piezoelectric resonator. More particularly, the present invention relates to a method of manufacturing a piezoelectric resonator which is provided in electronic components, such as an oscillator, a discriminator, and a filter, and which uses mechanical resonance of a piezoelectric body.
2. Description of the Related Art
FIG. 26
is a perspective view showing an example of a conventional piezoelectric resonator. A piezoelectric resonator
1
shown in
FIG. 26
includes a piezoelectric substrate
2
, for example, having a rectangular plate shape. The piezoelectric substrate
2
is polarized along the thickness direction thereof. Electrodes
3
are provided on both major surfaces of the piezoelectric substrate
2
. As a result of inputting a signal between these electrodes
3
, an electric field is applied along the thickness direction of the piezoelectric substrate
2
, causing the piezoelectric substrate
2
to vibrate along the length direction thereof.
The piezoelectric resonator shown in
FIG. 26
is an unstiffened type, in which the vibration direction is different from the electric-field direction and the polarization direction. An electro-mechanical coupling coefficient of a piezoelectric resonator of such an unstiffened resonator is lower than that of a stiffened piezoelectric resonator, in which the electric-field direction, the polarization direction, and the vibration direction coincide with each other. Therefore, in the unstiffened type piezoelectric resonator, the difference &Dgr;F between the resonance frequency and the anti-resonance frequency is relatively small. This causes a very small bandwidth when such an unstiffened piezoelectric resonator is used for a filter. Therefore, the degree of characteristic design freedom is small in such an unstiffened piezoelectric resonator and electronic components incorporating such a resonator.
Furthermore, in the piezoelectric resonator shown in
FIG. 26
, a primary resonance of a length mode is used. However, due to the structure of the resonator shown in
FIG. 26
, an odd-number multiple high-order mode, such as a third order mode or a fifth order mode, and a large spurious vibration of a width mode, are generated.
Japanese Patent Application No. 8-110475, filed by the applicant of the present invention, describes a piezoelectric resonator having a multilayered base structure having a longitudinal direction which is provided as a result of a plurality of piezoelectric layers and a plurality of electrodes being alternately stacked and laminated. The plurality of piezoelectric layers are polarized along the length direction of the base, and a fundamental vibration of a longitudinal vibration is excited. The piezoelectric resonator of such a multilayered structure is a stiffened type resonator, in which the polarization direction, the electric-field direction, and the vibration direction are the same. As a result, such a stiffened resonator has spurious emissions that are smaller than that of an unstifffened type resonator, and the difference &Dgr;F between the resonance frequency and the anti-resonance frequency is large in this stiffened type resonator.
Next, an example of a piezoelectric resonator having such a multilayered structure will be described in detail.
FIG. 1
is a perspective view showing an example of a conventional piezoelectric resonator having a multilayered structure, to provide a background against which-the present invention will be compared later.
FIG. 2
is a schematic view of the piezoelectric resonator.
FIG. 3
is a plan view of the essential portion of the piezoelectric resonator.
A piezoelectric resonator
10
in
FIG. 1
having such a multilayered structure includes a base
12
, for example, having a rectangular body. The base
12
includes a plurality of piezoelectric layers
12
a
, which are formed from, for example, a piezoelectric ceramic, and are multilayered. In the plurality of piezoelectric layers
12
a
in the intermediate portion along the length direction of the base
12
, a plurality of internal electrodes
14
are disposed on each of the two main surfaces so as to be perpendicular relative to the length direction of the base
12
. Therefore, a plurality of internal electrodes
14
are disposed and spaced apart in a direction that is perpendicular to the length direction of the base
12
and along the length direction of the base
12
. Also, the plurality of piezoelectric layers
12
a
in the intermediate portion along the length direction of the base
12
, as indicated by the arrows in
FIG. 2
, are polarized along the length direction of the base
12
so that adjacent piezoelectric layers are oppositely polarized relative to each other on both sides of the respective internal electrodes
14
. However, the piezoelectric layers
12
a
of both end portions along the length direction of the base
12
are not polarized. In this base
12
, the internal electrodes
14
are exposed at four side surfaces which are parallel to the length direction of the base
12
.
A groove
15
which extends along the length direction of the base
12
is formed on one side surface of the base
12
. The groove
15
is formed in the center in the width direction of the base
12
, dividing one side surface of the base
12
into two portions. Furthermore, as shown in
FIG. 2
, a first insulation film
16
and a second insulation film
18
are disposed on the side surfaces divided by the groove
15
. On one side divided by the groove
15
on the side surface of the base
12
, every alternate exposed portion of the internal electrodes
14
is covered by the first insulation film
16
. Also, on the other side divided by the groove
15
on the side surface of the base
12
, the exposed portions of the internal electrodes
14
that are not covered by the first insulation film
16
on one side of the groove
15
are covered by the second insulation film
18
.
Furthermore, at the portions where the first and second insulation films
16
and
18
of the base
12
are disposed, that is, on both sides of the groove
15
, two external electrodes
20
and
22
are disposed. Therefore, the internal electrodes
14
that are not covered by the first insulation film
16
are connected to the external electrode
20
, and the internal electrodes
14
that are not covered by the second insulation film
18
are connected to the external electrode
22
. That is, adjacent internal electrodes
14
are connected to the external electrode
20
and the external electrode
22
, respectively.
In this piezoelectric resonator
10
, the external electrodes
20
and
22
are used as input and output electrodes. In the intermediate portion along the length direction of the base
12
, since the section between adjacent internal electrodes
14
is polarized and an electric field is applied between the adjacent internal electrodes
14
, the section is piezoelectrically active. Since mutually opposite voltages are applied to the portions of the base
12
which are mutually oppositely polarized, the base
12
expands or contracts in the same direction as a whole. Therefore, in the entire piezoelectric resonator
10
, a fundamental vibration in a longitudinal vibration mode, in which the center portion along the length direction of the base
12
is a node, is excited. Both end portions along the length direction of the base
12
are not polarized, and an electric field is not applied thereto because no electrode is disposed at the end portions. Therefore, both end portions are piezoelectrically inactive.
In this piezoelectric resonator
10
, the polarization direction of the base
12
, the electric-field direction applied by the input signal, and the vibration direction of the base
12
are the same. That is, this piezoelectric resonator
10
is a stiffened piezoelectric resonator. This piezoelectric resonator
10
has an electro-mechanical coupling coefficient greater than that of an unstiffened type, such that the polarization direc
Kawai Yutaka
Kusabiraki Shigemasa
Takeshima Tetsuo
Yamazaki Takeshi
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Smith Sean
Young Lee
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