Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-03-17
2001-05-22
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000, C310S320000
Reexamination Certificate
active
06236140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric vibration device utilizing a thickness-shear vibration available for communication devices or the like. In giving particulars, the present invention relates to a piezoelectric vibration device which can restrain influences by a spurious vibration or an unnecessary vibration of the general non-harmonic overtone mode, and enhance guarantee attenuation characteristics.
2. Description of the Prior Art
Referring to
FIGS. 31 and 32
, prior art is described as below.
FIG. 31
is a diagram of an electrode structure and a vibrational energy distribution of spurious vibration of non-harmonic overtone mode, generally referred to as a (3,1,3) mode, seen from a bottom surface of a conventional piezoelectric vibration device.
FIG. 32
is a sectional view along line S—S in
FIG. 31 and a
diagram of the vibrational energy distribution of spurious vibration of a principal vibration mode (substantial line) and the (3,1,3) mode. Each symbol of (3,1,3) designates an order of overtone in a Y′-axis (thickness) direction, an order of overtone in an X′-axis direction, and an order of overtone in a Z′-axis direction. As shown in
FIG. 31
, the (3,1,3) mode is a mode of the spurious vibration having three vibration crests (troughs) arranged in parallel to the Z′-axis direction.
As a quartz plate
90
, an AT cut quartz plate is employed. A principal plane of the quartz plate
90
is provided with an input electrode
191
, an output electrode
192
, outgoing electrodes
191
a
,
192
a
for leading the input electrode
191
and the output electrode
192
to peripheral portion of the quartz plate
90
, and the other principal plane of the quartz plate
90
is provided with a common electrode
193
, and an outgoing electrode
193
a for leading the common electrode
193
to the peripheral portion of the quartz plate
90
. Each electrode is formed by means of thin film forming means using vacuum evaporation method or the like. Though it is not shown, the input and output electrodes
191
,
192
are respectively connected to an input terminal and an output terminal, the common electrode
193
is hermetically confined in a state of being connected to a grounding terminal.
In the piezoelectric vibration device having such a structure, the input and output electrodes
191
,
192
formed oppositely each other in a state wherein the quartz plate
90
intervenes therebetween and the common electrode
193
are designated as resonant areas, a symmetrical mode (fs) and oblique symmetrical mode vibration (fa) are confined by the electrodes, they are acoustically coupled thereby forming a multiple mode principal vibration with the result that the piezoelectric vibration device having pass band characteristics as a predetermined filter is designed.
Moreover, in the prior art, as high-frequency type or three-order overtone type electrode materials, aluminium is generally employed.
As mentioned above, the piezoelectric vibration device is designed so that, as well as the principal vibration, a higher-order non-harmonic overtone mode such as the spurious vibration of the (3,1,3) mode is confined by the electrodes, thus exciting them simultaneously. Furthermore, as well: as such a mode, there are various spurious vibrations such as one referred as to a (3,3,1) mode having three crests (or troughs) of vibration arranged in parallel in the X-axis direction, or a vibration mode having three crests (or troughs) of vibration respectively in the axis direction. These spurious vibrations wherein energy is confined under exciting electrodes, thus exciting the vibration as a standing wave relatively strongly, have problems wherein spurious vibrations affect the principal vibration, the spurious vibrations disorders the pass band characteristics, and the guarantee attenuation characteristics in portions outside of the pass band are not obtained enough. In case of employing aluminium as the electrode material in the same way as prior art, it is easy to oxidize aluminium, thus resulting in bad yield and productivity. In addition, in case that aluminium oxide is formed by oxidizing aluminium, a conductive resistance to a conductive adhesive is greater so that the guarantee attenuation characteristics are inferior.
SUMMARY OF THE INVENTION
In order to solve the problems, an object of the present invention is to provide a piezoelectric vibration device for restraining the spurious vibration mode generated near the principal vibration (what is called “frequency”), making the pass band characteristics more excellent and wider, and enhancing the guarantee attenuation characteristics in the portions outside of the pass band.
In order to achieve the object of the present invention, a piezoelectric vibration device utilizing a thickness-shear vibration having a resonant area formed by an input electrode, an output electrode and a common electrode, the piezoelectric vibration device comprises a quartz plate having a pair of principal planes, the input electrode and the output electrode disposed on a principal plane of the quartz plate, the input electrode and the output electrode formed close to each other at a regular interval, and the common electrode disposed on the other principal plane of the quartz plate, corresponding to the input electrode and the output electrode, wherein either a weight reducing portion or a weight adding portion is partially disposed on at least one of each peripheral zone of the input electrode, the output electrode and the common electrode.
In a three-pole-type piezoelectric vibration device utilizing a thickness-shear vibration having a resonant area formed by an input electrode, an output electrode, a grounding electrode and a common electrode, the piezoelectric vibration device comprising a quartz plate having a pair of principal planes, the input electrode and the output electrode disposed on a principal plane of the quartz plate, the grounding electrode interposed between the electrodes, in which the input electrode, the output electrode and the grounding electrode are formed close to each other at regular intervals, and the common electrode disposed on the other principal plane of the quartz plate, corresponding to the input electrode, the output electrode, and the grounding electrode, and in a four-pole-type piezoelectric vibration device utilizing a thickness-shear vibration having resonant areas formed by two pairs of input and output electrodes and common electrodes, the piezoelectric vibration device comprising a quartz plate having a pair of principal planes, the two pairs of input and output electrodes respectively including an input electrode and an output electrode, disposed on a principal plane of the quartz plate in parallel, in which the input electrode and the output electrode are formed close to each other at a regular interval, and the common electrodes disposed on the other principal plane of the quartz plate, corresponding to the respective pairs of input and output electrodes, the weight reducing portion or the weight adding portion is applicable.
Preferably, either the weight reducing portion or the weight adding portion is disposed on a portion where a vibrational energy of a spurious vibration generated in excitation of the piezoelectric vibration device is relatively greater than that of a principal vibration.
In addition, the piezoelectric vibration device comprises a quartz plate having a pair of principal planes, a rectangular input electrode and a rectangular output electrode disposed on a principal plane of the quartz plate, the input electrode and the output electrode formed close to each other at a regular interval, a rectangular common electrode disposed on the other principal plane of the quartz plate, corresponding to the input electrode and the output electrode, and a resonant area formed by the input electrode, the output electrode and the common electrode, in which the piezoelectric vibration device utilizing a thickness-shear vibration includes an
Arent Fox Kintner & Plotkin & Kahn, PLLC
Budd Mark O.
Daishinku Corporation
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