Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-05-12
2001-04-10
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S320000, C310S348000
Reexamination Certificate
active
06215229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chip-type piezoelectric resonator including a capacitor and to a method for adjusting the resonance frequency of the chip-type piezoelectric resonator. More particularly, the present invention relates to a chip-type piezoelectric resonator including a capacitor having a piezoelectric element disposed between dielectric substrates, as well as, to a method for adjusting the resonance frequency thereof.
2. Description of Related Art
A conventional chip-type piezoelectric resonator including a capacitor is shown in
FIGS. 7A and 7B
.
As shown in
FIG. 7A
, in a chip-type piezoelectric resonator
51
, a first sealing substrate
53
made of an insulating ceramic is laminated on the lower surface of a plate-like piezoelectric element
52
, while a second sealing substrate
54
made of a dielectric ceramic is laminated on the upper surface of the piezoelectric element
52
.
The piezoelectric element
52
includes a plate-like piezoelectric substrate
52
a
which is polarized in a thickness direction. As shown in
FIG. 7B
, a first excitation electrode
52
b
is disposed on the upper surface of the piezoelectric substrate
52
a
and a second excitation electrode
52
c
is disposed on the lower surface of the piezoelectric substrate
52
a
, such that the electrode
52
b
and the electrode
52
c
face each other with the piezoelectric substrate
52
a
disposed therebetween.
The excitation electrodes
52
b
and
52
c
are connected with lead electrodes
52
d
and
52
e
, respectively. The lead electrode
52
d
is disposed on the upper surface of the piezoelectric substrate
52
a
so as to extend to a peripheral edge thereof, while the lead electrode
52
e
is disposed on the lower surface of the piezoelectric substrate
52
a
so as to extend to another peripheral edge thereof opposite to the peripheral edge to which the lead electrode
52
d
extends.
A cavity
53
a
is formed in the inner surface of the sealing substrate
53
, and a cavity
54
a
is formed in the inner surface of the sealing substrate
54
.
The piezoelectric element
52
is laminated with the first and second sealing substrates
53
and
54
via an unillustrated adhesive layer, to thereby provide a monolithic structure. External electrodes
57
,
58
and
59
are disposed on the outer surface of the resulting laminate. The external electrode
57
is connected to the lead electrode
52
d
to thereby establish electrical connection with the exitation electrode
52
b
, while the external electrode
59
is connected to the lead electrode
52
e
to thereby establish electrical connection with the excitation electrode
52
c.
The external electrode
58
is connected to ground. Thus, the resonator is connected between the external electrodes
57
and
59
and electrostatic capacitance is provided between the ground and the external electrodes
57
and
59
. Since the sealing substrate
54
is made of a dielectric ceramic, the above-described electrostatic capacitance is substantially defined by the sealing substrate
54
between the external electrode
58
and the external electrodes
57
and
59
.
In the chip-type resonator
51
shown in
FIGS. 7A and 7B
, once the sealing substrates
53
and
54
have been bonded to the piezoelectric element
52
, the surfaces other than side surfaces, i.e., the upper and the lower surfaces of the piezoelectric element
52
, are sealed by the sealing substrates
53
and
54
. Therefore, the resonance frequency must be adjusted prior to bonding of the piezoelectric element
52
to the sealing substrates
53
and
54
.
However, even after the bonding step of the piezoelectric element
52
and the sealing substrates
53
and
54
, the adjusted frequency tends to vary, due to factors occurring in subsequent manufacturing and processing steps. Thus, even if the resonance frequency is controlled with high precision during the step of producing the piezoelectric element
52
, the production of a chip-type piezoelectric resonator
51
having high precision in terms of achieving a desired frequency is very difficult. Therefore, the percent ratio of non-defective chip-type piezoelectric resonators
51
is disadvantageously low.
When an external electrode portion of the sealing substrate
54
made of a dielectric ceramic is partially removed after production of the chip-type piezoelectric resonator
51
, the electrostatic capacitance changes significantly, so that fine adjustment of the resonance frequency is very difficult.
In addition, since the shapes of the external electrodes as viewed from the upper-surface side is identical to those as viewed from the lower-surface side, automated recognition of the top and reverse sides of the resonator has been difficult.
Another conventional chip-type piezoelectric resonator including a capacitor is shown in
FIGS. 8A and 8B
.
A chip-type piezoelectric resonator
61
has a package structure including a dielectric substrate
62
and a downwardly-opening cap
63
.
As shown in
FIGS. 8A and 8B
, external electrodes
64
,
65
and
66
are disposed on the dielectric substrate
62
such that the electrodes extend from the upper surface of the substrate to the lower surface thereof via two side surfaces. A piezoelectric element
69
is bonded to the external electrodes
64
and
66
via conductive adhesive layers
67
and
68
. The piezoelectric element
69
is made of a plate-like piezoelectric substrate
69
a
. A first excitation electrode
69
b
is disposed on the upper surface of the piezoelectric substrate
69
a
, and a second excitation electrode
69
c
is disposed on the lower surface thereof.
The first excitation electrode
69
b
is connected to a lead electrode
69
d
. The lead electrode
69
d
is arranged on the piezoelectric substrate
69
a
so as to extend to a peripheral edge thereof and further to extend to the lower surface of the piezoelectric substrate
69
a
via the side surface. The lead electrode
69
d
is bonded to the conductive adhesive layer
68
at a portion at which the lead electrode
69
d
reaches the lower surface of the piezoelectric substrate
69
a.
The second excitation electrode
69
c
is connected to a lead electrode
69
e
, which is bonded to the conductive adhesive layer
67
.
The cap
63
, having an opening
63
a
which covers the above-described piezoelectric element
69
, is bonded onto the upper surface of the dielectric substrate
62
via an insulating adhesive which is not shown in
FIGS. 8A and 8B
.
In the chip-type piezoelectric resonator
61
, resonance portions having first and second excitation electrodes
69
b
and
69
c
, respectively, are connected between external electrodes
64
and
66
. The external electrode
65
is connected to ground. Thus, electrostatic capacitance attributed to the dielectric substrate
62
is provided between the external electrode
65
and each of the external electrodes
64
and
66
.
In the chip-type piezoelectric resonator
61
shown in
FIGS. 8A and 8B
, the resonance frequency can be adjusted, prior to bonding of the cap
63
to the dielectric substrate
62
, in a state in which the piezoelectric element
69
has been bonded to the dielectric substrate
62
. However, when only the excitation electrode on one surface of the piezoelectric element
69
is machined so as to adjust the resonance frequency, the symmetry between the excitation electrodes
69
b
and
69
c
is lost. Thus, spurious vibrations attributed to asymmetry of the excitation electrodes
69
b
and
69
c
increases, therefore disadvantageously deteriorating the characteristics of the resonator.
Alternatively, the resonance frequency can be adjusted by modifying the shape of the external electrodes
64
,
65
and
66
at the lower surface of the dielectric substrate
62
. However, the lower surface of the dielectric substrate
62
is a surface for mounting, and such modification of the external electrodes
64
,
65
and
66
causes variation of mounting conditions among individual chip-type piezoelectric resonators
61
.
SUMMARY OF T
Kuroda Hideaki
Wajima Masaya
Yoshida Ryuhei
Dougherty Thomas M.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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