Piezoelectric resonator

Details Piezoelectric resonator Piezoelectric resonator

1998-11-12

2001-08-14

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S366000, C310S326000

Reexamination Certificate

active

06274964

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric resonator adapted to generate a third harmonic wave of a thickness extensional vibration mode, and more particularly, relates to a piezoelectric resonator in which the use of a floating electrode makes it possible to suppress the fundamental harmonic wave.
2. Description of the Related Art
In piezoelectric resonators adapted to vibrate in a thickness extensional vibration mode, a variety of piezoelectric resonators utilizing harmonics thereof have been proposed in order to cope with piezoelectric resonators of higher frequencies.
For example, in Japanese Unexamined Patent Publication No. 9-181556, a piezoelectric transducer adapted to generate a third harmonic wave of a thickness extensional vibration mode is disclosed.
FIG. 11
is a top plan view of the piezoelectric transducer described in JP 9-181556. In the piezoelectric transducer
51
, a vibration electrode
53
extending to the center from the end portion
52
a
of a piezoelectric substrate
52
is disposed on a first major surface of the strip-shaped piezoelectric substrate
52
. On a second major surface of the piezoelectric substrate
52
, a vibration electrode
54
extending to the center from the end portion
52
b
is disposed. The vibration electrodes
53
and
54
are arranged in the middle area of the piezoelectric substrate so as to oppose each other via the piezoelectric substrate
52
. The portion where the vibration electrodes
53
and
54
oppose each other constitutes a vibrating portion and the application of an alternating voltage between the vibration electrodes
53
and
54
causes the vibrating portion to vibrate in a thickness extensional vibration mode.
Because the third harmonic wave of a thickness extensional vibration mode is utilized, it is necessary to suppress the fundamental wave as an unwanted spurious component. So, damping layers
55
and
56
are disposed on the first major surface of the piezoelectric substrate
52
. Then, the damping layers
55
and
56
are disposed between the above-mentioned vibrating portion and the end portion
52
a
and between the vibrating portion and the end portion
52
b
, respectively.
Also, a pair of damping layers with the vibrating portion arranged between them are disposed on the second major surface of the piezoelectric substrate
52
. Each of the damping layers on the second major surface is arranged to face the damping layers
55
and
56
disposed on the first major surface, respectively.
The damping layers
55
and
56
, and the damping layers disposed on the second major surface are made up of, for example, thermosetting epoxy resins, phenolic resins, solder, and others. It is claimed in JP 9-181556 that in the piezoelectric transducer
51
, the vibration of a third harmonic wave can be distributed in the area between the damping layer
55
and the damping layer
56
, and the fundamental wave can be effectively suppressed at the damping layers
55
and
56
, and others.
On the other hand, in Japanese Unexamined Patent Publication No. 4-216208, a piezoelectric resonator adapted to generate a third harmonic wave of a thickness extensional vibration mode in which the use of a floating electrode makes it possible to suppress spurious components caused by the fundamental wave is disclosed. The piezoelectric resonator described in JP 4-216208 is shown in FIG.
12
. In the piezoelectric resonator
61
, a vibration electrode
63
is disposed in the middle of the first major surface of a rectangular piezoelectric substrate
62
and a vibration electrode
64
is located in the middle of the second major surface. The vibration electrodes
63
and
64
oppose each other via the piezoelectric substrate
62
located therebetween.
In addition, the vibration electrode
63
is connected to the lead-out electrode
65
disposed along the edge on the short side of the piezoelectric substrate
62
, and the vibration electrode
64
is electrically connected to the lead-out electrode
66
disposed along the edge of the short side on the second major surface of the piezoelectric substrate
62
.
On the other hand, a pair of floating electrodes
67
a
and
67
b
are disposed along the long-side edges on the first major surface of the piezoelectric substrate
62
. Also, on the second major surface of the piezoelectric substrate
62
, floating electrodes
67
c
and
67
d
are disposed so as to oppose the floating electrodes
67
a
and
67
b
via the piezoelectric substrate
62
disposed therebetween.
In the piezoelectric resonator
61
, the portion where the vibration electrodes
63
and
64
oppose each other constitutes a vibrating portion, and a third harmonic wave of a thickness extensional vibration mode is trapped in the vibrating portion. Also, the fundamental wave is propagated outwardly from the vibrating portion located in the center, but because of the mechanical load of the floating electrodes
67
a
through
67
d
and the piezoelectric short-circuit effect, the vibration energy of the fundamental wave is absorbed by the portions in which the floating electrodes
67
a
through
67
d
are disposed, and accordingly, the suppression of unwanted spurious components caused by the fundamental wave is supposedly achieved.
Further, in Japanese Unexamined Patent Publication No. 9-139651, a harmonic quartz oscillator provided to suppress the fundamental wave by using floating electrodes is disclosed. The quartz oscillator of JP 9-139651 is explained with reference to FIG.
13
.
The quartz oscillator
71
is composed of a rectangular quartz crystal
72
. An excitation electrode
73
is disposed in the middle of the first major surface of the quartz crystal
72
. Another excitation electrode is disposed in the middle of the second major surface of the quartz crystal
72
. The excitation electrode disposed on the second major surface is arranged to oppose the excitation electrode
73
disposed on the first major surface. The excitation electrode
73
is connected to the lead-out electrode
74
disposed around the end portion
72
a
on the short side of the quartz crystal
72
. The lead-out electrode
74
is disposed around the end portion
72
a
so as to extend over the end surface and the first and second major surfaces.
Also, the other excitation electrode disposed in the middle of the second major surface of the quartz crystal
72
is electrically connected to the lead-out electrode
75
disposed at the other end portion
72
b
of the quartz crystal
72
. The lead-out electrode
75
is disposed at the end portion
72
b
so as to extend over the end surface and the first and second major surfaces.
Accordingly, the application of an alternate voltage to the lead-out electrodes
74
and
75
produces harmonic waves of a thickness extension mode. In addition, fundamental wave suppressing electrodes
76
and
77
are disposed along the edge of the long sides of the quartz crystal
72
. The fundamental wave suppressing electrodes
76
and
77
are disposed along the edge of the long sides on the first and second major surfaces of the quartz crystal
72
.
That is, the mechanical damping of only the fundamental wave leaked out of the vibrating portion by the fundamental wave suppressing electrodes
76
and
77
suppresses the fundamental wave.
However, in the above-mentioned piezoelectric resonator making use of a harmonic wave of a thickness extension mode, spurious components caused by the fundamental wave are suppressed only to a certain level, but the fundamental wave can not be fully suppressed.
SUMMARY OF THE INVENTION
In order to solve the problems described above, preferred embodiments of the present invention provide a piezoelectric resonator adapted to generate a third harmonic wave of a thickness extensional vibration mode and effectively suppress a fundamental wave as a spurious component.
A preferred embodiment of the present invention provides a piezoelectric resonator adapted to generate a third harmonic wave of a thickness extensional vibration mode including a pi

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