Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-11-25
2001-09-18
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000, C310S367000, C310S368000
Reexamination Certificate
active
06291926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a piezoelectric resonator, a manufacturing method thereof, and a method of adjusting a resonance frequency of such a resonator. More particularly, the present invention relates to a piezoelectric resonator vibrating in a square vibration mode and provided in a ladder type filter, an oscillator, a filter, a discriminator, or other suitable electronic component, and a method of manufacturing and adjusting a resonance frequency of such a resonator.
2. Description of Related Art
A conventional piezoelectric resonator adapted to vibrate in a square vibration mode is shown in FIG.
11
.
The electrode structure of the piezoelectric resonator
51
includes a partial electrode
53
provided on a center area of one major surface of a piezoelectric substrate
52
having a square shape, and an electrode
54
provided on an entire surface of the other major surface of the piezoelectric substrate
52
.
The resonance of such a piezoelectric resonator
51
is defined by the resonance frequency thereof. Moreover, the attenuation property when being used for a ladder filter or other similar electronic component is determined by the electrostatic capacitance of the piezoelectric resonator disposed therein.
Therefore, when manufacturing a piezoelectric resonator, the electrostatic capacitance or the value of the resonance frequency must be controlled.
Conventionally, the piezoelectric resonator has been manufactured as shown in
FIGS. 12A
to
12
G.
First, electrically-conductive pastes, such as silver paste is coated almost entirely on the two major surfaces of a piezoelectric mother substrate
55
. The silver paste is baked to thereby form electrodes
56
and
57
(FIGS.
12
A and
12
B).
Subsequently, a DC voltage is applied between the first and second major surfaces of the piezoelectric mother substrate
55
via the electrodes
56
and
57
located on the first and second major surfaces of the piezoelectric mother substrate
55
. As a result, a polarization process is achieved so as to apply and define a predetermined piezoelectric characteristic of the piezoelectric mother substrate
55
(FIG.
12
C).
After this, pattern printing of resist ink
58
is performed on the electrode
56
at the first major surface of the piezoelectric mother substrate
55
to provide a partial electrode pattern, and printing of resist ink
58
is performed on substantially the entire surface of electrode
57
on the second major surface of the piezoelectric mother substrate
55
to provide a partial electrode pattern (FIG.
12
D).
Then, the piezoelectric mother substrate
55
, which was printed with the resist ink
58
, is soaked in etching liquid so as to remove via etching the electrode portion exposed from the resist ink
58
(FIG.
12
E).
If the resist ink is removed, the pattern of the electrode
56
will be formed on the first major surface of the piezoelectric mother substrate
55
so as to define a partial electrode pattern, and the electrode
58
will remain over almost the entire second major surface of the piezoelectric mother substrate
55
(FIG.
12
F).
Since the electrostatic capacitance of the piezoelectric resonator
51
is determined by the area of the partial electrode
53
, the partial electrode
53
of the piezoelectric resonator
51
is designed so that the electrode area thereof provides a desired electrostatic capacitance.
Therefore, in the above process, resist ink
58
must be printed on the electrodes
56
with high pattern accuracy and the electrodes
56
must be accurately patterned via etching so that the area of the electrode pattern (the partial electrodes) is formed precisely according to design for providing an exact desired electrostatic capacitance (FIG.
12
D).
Further, if the piezoelectric mother substrate
55
is cut so that each electrode
56
on the first major surface is centered, the partial electrodes
53
are formed on the first major surface at the center of each piezoelectric substrate
52
that is cut, and the surface electrode
54
is formed on the entire second major surface.
As a result, many piezoelectric resonators
51
adapted to vibrate in the square vibration mode as shown in
FIG. 11
are manufactured simultaneously.
After manufacturing the piezoelectric resonator
51
as described above, the resonance frequency of the piezoelectric resonator
51
is measured and adjusted in the following way so that a desired resonance frequency can be obtained.
When the resonance frequency is too high, as shown in
FIG. 13
, the resonance frequency of the piezoelectric resonator
51
is decreased by grinding the periphery of piezoelectric resonator
51
so as to form a plurality of grooves or cuts
59
in the resonator
51
.
Conversely, when a resonance frequency is too low, as shown in
FIG. 14
, the resonance frequency of the piezoelectric resonator
51
is increased by grinding and chamfering the corners of the piezoelectric resonator.
However, since for the above-mentioned piezoelectric resonator, the area of the partial electrode, i.e., the electrostatic capacitance of the piezoelectric resonator, is determined by pattern printing of the resist ink, in order to manufacture many varieties of piezoelectric resonators having different electrostatic capacitances, it is necessary to separately manufacture every piezoelectric resonator for which a different electrostatic capacitance is required.
Moreover, for the piezoelectric resonator manufactured as mentioned above, the periphery of the partial electrode spreads and blurs because of the resist ink bleeding at the time of pattern printing. The partial electrodes change the shape thereof due to distortions in the printing pattern of resist ink which causes degradation of the electric characteristics of the piezoelectric resonator.
Furthermore, because the partial electrode was formed by etching an electrode, using resist ink as an etching mask, the etching liquid corrodes the piezoelectric substrate and as a result, the electrical properties of the piezoelectric resonator are degraded.
Furthermore, even when the electrostatic capacitance of such a piezoelectric resonator is formed such that it deviates from designed specifications, it is difficult to finely tune the electrostatic capacitance later.
Moreover, in order to adjust the resonance frequency of the piezoelectric resonator, the periphery and especially the comers of the piezoelectric resonator must be grinded or cut off which makes the tuning of the resonance frequency difficult and labor-intensive.
Moreover, using the conventional manufacturing method, in order to form a partial electrode and a whole-surface electrode on both major surfaces of a piezoelectric resonator, many difficult processes are required, production time is long, and cost is very high.
Furthermore, after forming many partial electrodes on a large piezoelectric substrate (piezoelectric mother substrate), since the piezoelectric substrate was made by cutting every area including the partial electrode, the electric characteristics of the piezoelectric substrate degrade when the cut position deviated.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide a piezoelectric resonator which does not experience degradation of its electrical characteristics during its manufacturing and also facilitate a manufacturing process and a resonance frequency adjustment process of such an improved piezoelectric resonator.
A preferred embodiment of the present invention provides a piezoelectric resonator vibrating in a square vibration mode, including a piezoelectric substrate having a first major surface and a second major surface, electrodes provided on the first major surface and the second major surface of the piezoelectric substrate, and a groove provided on at least one of the first major surface and the second major surface of the piezoelectric substrate, the groove dividing at least one of the electrodes into a plurality of areas.
In the above
Budd Mark O.
Keating & Bennett, LL
Murata Manufacturing Co. Ltd
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