Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-03-28
2001-04-10
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S367000, C333S187000
Reexamination Certificate
active
06215228
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stacked piezoelectric resonator and more particularly, the invention relates to, for example, a stacked piezoelectric resonator including a base having piezoelectric layers and internal electrodes and that is constructed to vibrate in a longitudinal vibration mode, a characteristics-adjusting method therefor, and a ladder-type filter including such a resonator.
2. Description of the Related Art
A conventional stacked piezoelectric resonator of the above-mentioned type related to the present invention is disclosed in, for example, Japanese Unexamined Patent Publication No. 104330.
FIG. 10
is a view of a conventional stacked piezoelectric resonator
1
which includes a base
2
having a rectangular-parallelepiped shape. The base
2
is formed by stacking multiple piezoelectric layers
3
and multiple internal electrodes
4
. Stacked surfaces of the piezoelectric layers
3
and the internal A electrodes
4
are arranged perpendicular to a length direction of the base
2
. On a peripheral surface of one of two sides of the base
2
, exposed portions of the internal electrodes
4
are covered alternately by insulators
5
a
. On a peripheral surface in the other one of the two sides of the base
2
, exposed portions of the internal electrodes
4
which are not covered by the insulators
5
a
are alternately covered by insulators
5
b
. In addition, external electrodes
6
a
and
6
b
are provided on one of the two sides and the other one of the two sides of the base
2
. Since the insulators
5
a
and
5
b
are provided on the two sides, the internal electrodes
4
arranged to be adjacent to each other are connected alternately to the external electrodes
6
a
and
6
b
. In such a conventional stacked piezoelectric resonator
1
, the piezoelectric layers
3
arranged to be adjacent to each other are polarized in opposite directions relative to each other in the length direction of the base
2
, as indicated by arrows in FIG.
10
.
To manufacture the stacked piezoelectric resonator
1
, a mother substrate
7
shown in
FIG. 11
is prepared. The mother substrate
7
is formed by stacking the multiple piezoelectric layers
3
and the multiple internal electrodes
4
. As indicated by dotted lines in
FIG. 11
, the mother substrate
7
is cut perpendicular to the stacked surfaces. The mother substrate
7
is thus cut, thereby forming the base
2
. Also, the insulators
5
a
and
5
b
are disposed on opposite peripheral surfaces of the base
2
, and the stacked piezoelectric resonator
1
is completed by burning processing performed after materials for the external electrodes are coated on the base
2
.
In the conventional stacked piezoelectric resonator
1
, in response to input of signals to the external electrodes
6
a
and
6
b
that define input/output terminals, electrical fields opposing each other are generated between the internal electrodes
4
. Also, since the adjacent piezoelectric layers
3
are polarized so as to oppose each other, the entire base
2
vibrates in a longitudinal vibration mode according to the electrical fields applied thereto. The stacked piezoelectric resonator
1
thus manufactured can be used as a piezoelectric resonator.
A ladder-type filter is constructed by connecting multiple stacked piezoelectric resonators in series and/or in parallel. In such a ladder-type filter, the amount of attenuation can be adjusted according to adjustment of the capacitance ratio of stacked piezoelectric resonators to be connected in series and stacked piezoelectric resonators to be connected in parallel. For this reason, in the ladder-type filter, the stacked piezoelectric resonators to be connected in parallel have a capacitance that is larger than capacitance of the stacked piezoelectric resonators to be connected in series in order to obtain desired characteristics. The capacitance of the stacked piezoelectric resonators must be adjusted to adjust characteristics of the ladder-type filter. The capacitance of the stacked piezoelectric resonators can be adjusted by, for example, a method for varying the number of the internal electrodes provided in the base, changing distances between the internal electrodes, or permittivity of the piezoelectric layers themselves.
However, there are cases where implementation of the adjustment as described above requires design modification for the mother substrate. Also, even when the capacitance of the stacked piezoelectric resonators is adjusted, there are cases where outer dimensions cannot be changed because of restrictions in construction.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a stacked piezoelectric resonator arranged to achieve desired capacitance and a characteristics-adjusting method therefor without modifying the design and outline dimensions of a mother substrate therefor.
According to a preferred embodiment of the present invention, a stacked piezoelectric resonator includes a base on which multiple piezoelectric layers and multiple internal electrodes are stacked in a length direction thereof, and external electrodes connected to the internal electrodes. The stacked surfaces of the piezoelectric layers and the internal electrodes are arranged so as not to be perpendicular to the length direction of the base.
Also, according to another preferred embodiment of the present invention, a ladder-type filter wherein multiple piezoelectric layers are connected in a ladder arrangement so as to provide serial and parallel connections, and a stacked piezoelectric resonator as described above is included at least as a piezoelectric resonator for parallel connection.
Furthermore, according to another preferred embodiment of the present invention, a characteristics-adjusting method for a stacked piezoelectric resonator including a base on which multiple piezoelectric layers and multiple internal electrodes are stacked in a length direction and two external electrodes connected to the piezoelectric layers, the method including a step for adjusting an angle so that each of the stacked surfaces of the piezoelectric layers and the internal electrodes are not perpendicular to the length direction of the base.
In the above case, the mother substrate on which the piezoelectric layers and internal electrodes are stacked is cut at an angle so as not to be perpendicular to each of the stacked surfaces of the piezoelectric layers and the internal electrodes. This allows adjustment of the angle between the length direction of the base and each of the stacked surfaces.
As described above, in the arrangement such that the stacked surfaces of the piezoelectric layers and the internal electrodes are not perpendicular to the length direction of the base, by changing the angle between each of the stacked surfaces and the base, an opposing area of each of the internal electrode can be varied. Thereby, the capacitance of the stacked piezoelectric resonator can also be varied. The angle between each of the stacked surfaces and the length direction of the base can be varied by changing angles at which the mother substrate on which the piezoelectric layers and the internal electrodes are stacked is cut. This does not require modifications, for example, a design modification of the mother substrate as is required in the prior art. Therefore, use of the stacked piezoelectric resonator adjusted for its capacitance allows adjustment of the amount of attenuation of the ladder-type filter.
The above-described and other elements, characteristics, features and advantages of the present invention will be more readily apparent from a detailed description below with reference to the accompanying drawings.
REFERENCES:
patent: 5900790 (1999-05-01), Unami
patent: 6054793 (2000-04-01), Kawai
Addison Karen
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Ramirez Nestor
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