Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-11-03
2001-10-09
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000, C310S368000
Reexamination Certificate
active
06300708
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric resonator and a method of manufacturing thereof, in which the piezoelectric resonator is adapted to be vibrated in a square type vibration mode for use in an oscillator, a filter, a discriminator, a ladder type filter, or other apparatuses.
2. Background of the Related Art
Referring to
FIG. 14
, a structure of a conventional piezoelectric resonator
51
is shown. The piezoelectric resonator
51
is adapted to be vibrated in a square type vibration mode. The piezoelectric resonator
51
includes a piezoelectric substrate
52
having a square shape and first and second flat main surfaces. A partial electrode
53
is disposed on the center of the first main surface of the piezoelectric substrate
52
and a whole-surface electrode
54
is disposed on the second main surface so as to cover an entire surface thereof.
The piezoelectric resonator
51
is characterized by its resonant frequency. Moreover, the piezoelectric resonator
51
has a damping property so that if the resonator
51
is used in a ladder filter, or other similar apparatus, the resonator
51
is characterized by its electrostatic capacitance. Therefore, when manufacturing the piezoelectric resonator
51
, controlling the value of the resonant frequency or the electrostatic capacitance is essential. The electrostatic capacitance is controlled by adjusting the area of the partial electrode
53
.
However, in the conventional piezoelectric resonator
51
, it is necessary to provide electrically conductive paste on both main surfaces of the piezoelectric substrate
52
to define the electrodes. One of the electrodes is then patterned via etching to define the partial electrode
53
. However, the outline of the partial electrode
53
becomes faded by bleeding and blurring of the resist ink that is used for the etching process. Further, the partial electrode
53
may become deformed by the distortion in the printed pattern of the resist ink. These manufacturing problems degrade the electrical properties of the piezoelectric resonator
51
. Additionally, because the partial electrode
53
is defined by an etching process with the resist ink acting as the etching mask, the etching liquid corrodes the piezoelectric substrate
52
. This may also degrade the electrical properties of the piezoelectric resonator
51
.
One way to overcome the above-mentioned problems is by making a piezoelectric resonator
61
as shown in FIG.
15
. The piezoelectric resonator
61
is made by dividing an electrode into partial electrode
63
a
for input-output, and defining other partial electrodes
63
b
(electrodes in which an electrical signal is not transmitted) by cutting grooves
64
in the piezoelectric substrate
62
. This method does not require that etching be performed on the electrodes disposed on the main surfaces.
So by making a piezoelectric resonator as shown in
FIG. 15
, the above-mentioned problems caused by the etching process are overcome. Further, in the piezoelectric resonator
61
, a space B, which is equal to the distance between the center lines of the grooves, is defined so that the desired electrostatic capacitance and a mechanical coupling coefficient is obtained. Moreover, a length L of one edge of the piezoelectric resonator
61
is defined so that the desired resonant frequency is obtained. Finally, to prevent the variation of the resonator characteristics which occurs in every piezoelectric resonator, the width and depth of the grooves are set at appropriate fixed values.
Note that when defining the grooves
64
to have a fixed depth in the piezoelectric resonator
61
, the piezoelectric resonator
61
is first placed on a fixed board. The resonator
61
is then cut by horizontally moving a precise cutting apparatus, such as a cutting saw, to define the grooves
64
. Referring to
FIG. 16
, the depth D of the groove
64
is equal to the difference between the total thickness T and the remaining thickness N of the piezoelectric resonator
61
. Note that the depth D is equal to the distance from the surface of fixed board to the lowest point in the groove
64
.
However, a significant drawback of the piezoelectric resonator
61
is that it is difficult and complicated to make. It is especially difficult to detect the position of the surface of the piezoelectric resonator
61
(the thickness of the piezoelectric substrate
62
) every single time to define the groove
64
in the piezoelectric resonator
61
, especially in a mass-production environment. Note that the variation in thickness of the piezoelectric substrate
62
can be comparatively large.
This drawback is illustrated in
FIGS. 17A
,
17
B and
17
C. If the thickness T
1
of the piezoelectric resonator
61
is as small as shown in
FIG. 17A
, the depth D
1
of the groove
64
of the piezoelectric resonator
61
becomes shallow, or if the thickness T
2
of the piezoelectric resonator
61
is thick as shown in
FIG. 17B
, the depth D
2
of the groove
64
of the piezoelectric resonator
61
becomes deep. Also, as shown in
FIG. 17C
, the thickness variation of the groove
64
that is cut into the piezoelectric substrate
61
is large when the piezoelectric substrate
62
has a curvature.
Therefore, in the above-described method, after the manufacture of a piezoelectric resonator, an additional step of resonance tuning is required. This results in increased difficulty, time and cost of manufacture and affects the resonance characteristics of the resonator.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide a piezoelectric resonator and a method of manufacturing a piezoelectric resonator, where variations in the resonant frequency caused by a manufacturing process are greatly reduced while preventing any increase in cost or difficulty of the resonator manufacturing process.
According to a preferred embodiment of the present invention, a piezoelectric resonator constructed to be vibrated in a square type vibration mode includes a piezoelectric substrate having a first main surface and a second main surface, electrodes disposed on the first main surface and the second main surface, grooves provided in the first main surface of the piezoelectric substrate such that one of the grooves divides at least one of the electrodes so as to define a plurality of divided electrodes, and one of the plurality of divided electrodes defines an input/output electrode, and a maximum distance between outer edges of two of the grooves disposed opposite to each other across the input/output electrode is about 0.5 to about 0.55 times the length of one side edge of the piezoelectric substrate.
The input/output electrode preferably has a substantially circular shape and is constructed so that the maximum distance defined above is substantially equal to the sum of the diameter of the input/output electrode and two times the width of the groove.
Thus, it was discovered that the relationship between the ratio of the maximum distance between the outer edges of two of the grooves disposed opposite to each other across the input/output electrode to the length of the edge of a piezoelectric substrate, a resonance frequency, the depth of the groove provided in the piezoelectric resonator, and the width of the groove, is such that the dependency of the resonance frequency on the depth of the groove is minimal when the ratio of the maximum distance between the outer edges of the two of the grooves disposed opposite to each other across the input/output electrode to the length of the edge of a piezoelectric substrate is within a range of about 0.5 to about 0.55 and the width of the groove is constant.
In another preferred embodiment of the present invention, a method of manufacturing a piezoelectric resonator constructed to be vibrated in a square type vibration mode includes the steps of providing a piezoelectric mother substrate having first and second main surfaces, forming electrodes on substantially an entire area of th
Budd Mark O.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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