Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-11-12
2003-02-25
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S320000
Reexamination Certificate
active
06525449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thickness-extensional piezoelectric resonators which utilize harmonics in a thickness extensional vibration mode, and more particularly, to a thickness-extensional piezoelectric resonator which suppresses spurious resonances caused by a fundamental wave, via an improved electrode shape.
2. Description of the Related Art
As a MHz-band piezoelectric resonator used for generating a clock signal for a microcomputer, for example, a piezoelectric resonator utilizing a harmonic in a thickness-extensional vibration mode is known. Since such a piezoelectric resonator uses a harmonic in a thickness-extensional vibration, a response caused by the fundamental wave in the thickness-extensional vibration is a spurious resonance. Therefore, it is urgently needed to suppress a spurious resonance caused by the fundamental wave.
In Japanese Unexamined Patent Publication No. 4-216208, a piezoelectric resonator is disclosed which uses a third harmonic in the thickness-extensional vibration and which can suppress, via the use of floating electrodes, a spurious resonance caused by the fundamental wave.
FIG. 15
shows a structure of the piezoelectric resonator described in the above patent publication. In a piezoelectric resonator
61
, a vibration electrode
63
is located at the center of the first major surface of a rectangular piezoelectric substrate
62
and a vibration electrode
64
is provided at the center of the second major surface. The vibration electrodes
63
and
64
are opposed to each other with the piezoelectric substrate
62
located therebetween.
The vibration electrode
63
is connected to a terminal electrode
65
b
provided along an edge at a short side of the piezoelectric substrate
62
, through a lead electrode
65
a.
The vibration electrode
64
is electrically connected to a terminal electrode
66
b
provided along an edge at a short side, via a lead electrode
66
a
provided on the second major surface of the piezoelectric substrate
62
.
On the first major surface of the piezoelectric substrate
62
, floating electrodes
67
a
and
67
b
are provided along edges at a pair of long sides of the piezoelectric substrate
62
, and floating electrodes
67
c
and
67
d
are provided on the second major surface such that they are opposed to the floating electrodes
67
a
and
67
b
with the piezoelectric substrate
62
located therebetween.
In the piezoelectric resonator
61
, a portion where the vibration electrodes
63
and
64
are opposed to each other defines a vibration section, and the third harmonic of the thickness-extensional vibration is trapped in the vibration section. The fundamental wave is transferred from the vibration section to a surrounding area. Due to mechanical loads and piezoelectric short-circuit effects of the floating electrodes
67
a
to
67
d,
the portions where the floating electrodes
67
a
to
67
d
are located absorb the vibration energy of the fundamental wave, and an unwanted spurious resonance caused by the fundamental wave is suppressed.
Since the floating electrodes
67
a
to
67
d
need to be provided at both sides of the vibration section and extend in the short-side direction of the piezoelectric substrate
62
in the piezoelectric resonator
61
, however, the piezoelectric resonator
61
cannot be made compact due to the portions where the floating electrodes
67
a
to
67
d
are located. Since the areas of the floating electrodes
67
a
to
67
d
must be large in order to guide the fundamental wave to the portions where the floating electrodes
67
a
to
67
d
are located, it is very difficult to suppress a spurious resonance caused by the fundamental wave and to make the piezoelectric resonator
61
compact at the same time.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a thickness-extensional piezoelectric resonator utilizing a harmonic in a thickness-extensional vibration mode, which can effectively suppress an unwanted spurious resonance caused by the fundamental wave and which can also be made compact.
A preferred embodiment of the present invention provides a piezoelectric resonator utilizing a harmonic in a thickness-extensional vibration mode, including a piezoelectric substrate, first and second excitation electrodes provided partially on a first major surface and a second major surface of the piezoelectric substrate, respectively such that they are opposed to each other via the piezoelectric substrate, first and second lead electrodes connected to the first and second excitation electrodes and extending toward edges of the piezoelectric substrate, respectively, first and second terminal electrodes connected to the first and second lead electrodes and provided along edges of the piezoelectric substrate, respectively, and a spurious suppressing electrode section connected to a portion of at least one of the first and second lead electrodes.
Since the spurious suppressing electrode section is connected to a portion of at least one of the first and second lead electrodes, which are connected to the first and second excitation electrodes, in the thickness-extensional piezoelectric resonator according to one preferred embodiment of the present invention, the fundamental wave in the thickness-extensional vibration mode is effectively led towards ends of the piezoelectric substrate by the first and second lead electrodes. Therefore, by securing the thickness-extensional piezoelectric resonator with the use of the first and second terminal electrodes connected to the first and second lead electrodes, the led fundamental wave is effectively damped, and thereby a spurious resonance caused by the fundamental wave is suppressed. Consequently, a thickness-extensional piezoelectric resonator using a harmonic in the thickness-extensional vibration mode and having excellent resonance characteristics is provided.
In contrast to the conventional thickness-extensional piezoelectric resonator which is prevented from being made compact when the fundamental wave is suppressed by the floating electrodes since it is required in the conventional thickness-extensional piezoelectric resonator that the floating electrodes be provided at both sides of the vibration section in the short-side direction of the piezoelectric substrate, the piezoelectric resonator according to preferred embodiments of the present invention is not prevented from being made compact since the spurious suppressing electrode section is connected to a portion of the lead electrodes.
In the above described piezoelectric resonator, the spurious suppressing electrode section may be arranged to extend in a direction which intersects with the direction in which the lead electrodes extend, so as to increase the width of the lead electrodes.
In this case, since the spurious suppressing electrode section is arranged to extend in a direction which intersects with the direction in which the lead electrodes extend so as to increase the width of the lead electrodes, the spurious suppressing electrode section can be easily provided in a process in which the lead electrodes are provided. In addition, the spurious suppressing electrode section can be easily provided just by increasing the width of the lead electrodes when the lead electrodes are formed. Further, even though a spurious resonance caused by the fundamental wave is suppressed, the piezoelectric resonator can still be made compact.
In the above described piezoelectric resonator, the width dimension of a portion of the lead electrodes where the spurious suppressing electrode section is provided may be equal to or more than about a half of the width dimension of the excitation electrodes.
It is preferred that the width dimension of a portion of the lead electrodes where the spurious suppressing electrode section is provided be equal to or greater than the width dimension of the excitation electrodes.
The thickness-extensional piezoelectric resonator may be configure
Keating & Bennett LLP
Medley Peter
Murata Manufacturing Co. Ltd.
Ramirez Nestor
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