Lame mode quartz crystal resonator

Details Lame mode quartz crystal resonator Lame mode quartz crystal resonator

2001-04-18

2003-04-08

Budd, Mark O. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S366000, C310S367000

Reexamination Certificate

active

06545394

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a Lame mode quartz crystal resonator including a quartz crystal obtained by cutting out a blank quartz crystal along particular planes, and more particularly to a Lame mode quartz crystal resonator most suitable as a reference signal source for use in portable instruments such as IC cards strongly required to be miniaturized, to operate with high accuracy and to be manufactured inexpensively.
BACKGROUND OF THE INVENTION
An outline of Lame mode quartz crystal reson Resonators and Devices” which is a thesis written b application in the Transaction of “the Institute of Communication Engineers”, vol. J82-C-I, No. 12 (December 1999), pages 667 to 682.
FIG. 7
illustrates well-known cutting directions of a quartz crystal structure of a Lame mode quartz crystal resonator with respect to the coordinate system o-xyz of the crystal structure. In the drawing, axes x′, y′, z′ and z″ are coordinate axes after the coordinate system has been rotated (crystal axes after being cut). The cutting directions are obtained by rotating a Y-plate quartz crystal through an angle of &phgr;
y
about the x-axis and then rotating the Y-plate quartz crystal through an angle of &thgr;
y
about the new axis y′ corresponding to the y-axis produced by the rotation about the x-axis.
FIG. 8
illustrates a relation between the cut angles &phgr;
y
and &thgr;
y
of the quartz crystal for the Lame mode quartz crystal resonator of the prior art, giving a zero temperature coefficient. As shown in the curve
102
, the cutting angle &thgr;
y
of the Lame mode quartz crystal resonator of the prior art exists within 30° to 60°.
FIG. 9
illustrates the relation between the cutting angle &thgr;
y
and the second order temperature coefficient &bgr; with the cutting angle &thgr;
y
being within the range in FIG.
8
. As shown in the curve
103
in
FIG. 9
, when the cutting angle &thgr;
y
is 45°, the second order temperature coefficient &bgr; is −5.4×10
−8
/° C.
2
whose absolute value is very large. As the cutting angle &thgr;
y
varies from 45°, the absolute value of the second order temperature coefficient &bgr; becomes smaller as shown in the curve
103
in FIG.
9
. At the cutting angle &thgr;
y
of 30° or 60°, &bgr; becomes −4.5×10
−8
/° C.
2
.
FIG. 20
illustrates a Lame mode quartz crystal resonator using the quartz crystal
200
of the prior art described above, which includes a vibrating portion
207
, supporting frames
201
and
213
and a mounting portion
202
. Disposed on the vibrating portion
207
are electrodes
208
,
209
and
210
, which have electrode terminals
211
and
212
at the mounting portions
202
. (Also disposed on the rear side of the vibrating portion are electrodes, which are not visible in
FIG. 20.
) Among these electrodes, two electrodes adjacent each other on the same side or two electrodes positioned aligned on front and rear sides form the different polarity. Moreover, the vibrating portion
207
is connected through connecting portions
203
and
206
to the supporting frames
213
and
201
and connected through connecting portions
204
and
205
to the supporting frames
213
and
201
and the mounting portion
202
.
With this arrangement, however, as such a quartz crystal has the very large second order temperature coefficient &bgr; described above, it would be impossible to obtain a Lame mode quartz crystal resonator having less frequency change over a wide temperature range. Accordingly, there has been a remaining problem to be solved to realize a Lame mode quartz crystal resonator having a smaller second order temperature coefficient &bgr;.
Moreover, as the Lame mode quartz crystal resonator of the prior art includes the vibrating portion connected through the connecting portions at its four ends to the supporting frames and the mounting portion described above, the vibrating portion suffers from increased energy losses upon vibrating, as a result of which its series resistance R
1
increases and quality factor Q decreases as remaining problems to be solved. Consequently, it has been expected to provide a novel Lame mode quartz crystal resonator minimizing the energy losses at a vibrating portion.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved Lame mode quartz crystal resonator which eliminates all the disadvantages of the prior art described above and which has small second order temperature coefficient &bgr; and is adapted to minimize energy losses at its vibrating portion leading to lower series resistance R
1
higher quality factor Q.
In order to accomplish this object, the Lame mode quartz crystal resonator vibrating in two vibrations in different phases according to the invention is formed of an X-plate quartz crystal obtained in a manner that a blank X-plate quartz crystal having a coordinate system consisting of x, y and z axes is rotated through 36.5° to 47° about its y-axis and further rotated through 65° to 85° about a new x′-axis corresponding to said x-axis produced by said rotation about said y-axis, and the thus rotated blank X-plate quartz crystal is then cut out along planes parallel to x-y, y-z and z-x planes of the original coordinate system, respectively.
In another aspect of the invention, the Lame mode quartz crystal resonator vibrating in overtone mode includes a vibrating portion, a supporting frame and a mounting portion formed integrally, and the vibrating portion is connected through two connecting portions to the supporting frame and the mounting portion.
In this manner, the invention provides the Lame mode quartz crystal resonator using the quartz crystal cut in a novel fashion exhibits a small second order temperature coefficient &bgr;, and owing to the two connecting portions for connecting the vibrating portion and supporting frame, a micro-miniature Lame mode quartz crystal resonator can be obtained which has less vibrational energy losses at the vibrating portion and a smaller series resistance R
1
.
The overtone Lame mode quartz crystal resonator having the quartz crystal cut in the novel manner has following significant effects.
(1) With the overtone Lame mode quartz crystal resonator according to the invention, the second order temperature coefficient &bgr; is −1×10
−8
/° C.
2
whose absolute value is very small. Therefore, the invention can provide a Lame mode quartz crystal resonator whose frequency change is minimized over a wide temperature range.
(2) According to the invention, two connecting portions are provided for connecting the vibrating portion and the support frame, thereby minimizing the vibrational energy losses, as a result of which a Lame mode quartz crystal resonator having a lower series resistance Q
1
and a high quality factor Q can be obtained.
(3) According to the invention it is possible to form integrally the vibrating portion, the supporting frame, the mounting portion and the connecting portions so that a quartz crystal resonator can be realized which is miniaturized, inexpensive and beneficial to mass production because a number of resonators on a quartz crystal wafer can be simultaneously treated in a batch.
(4) The invention can produce the quartz crystal resonator formed integrally by the chemical etching process so that a Lame mode quartz crystal resonator can be realized which is superior in shock resistance.
The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.


REFERENCES:
patent: 4178566 (1979-12-01), Kawashima
patent: 4450378 (1984-05-01), Hermann et al.
patent: 4486682 (1984-12-01), Nakazawa et al.
patent: 4503353 (1985-03-01), Hermann et al.
patent: 4772130 (1988-09-01), Ueda et al.
patent: 5274297 (1993-12-01), Hermann et al.
patent: 10-327038 (1998-12-01), None
Handbook of Piezoelectric Crystals, pp 9-24 J. Buchanan, Dec. 1954.*
Kawashima, H.; Kanie, H; Yamagata, S.; “Quartz Microresonator Temperature Sensors Using Lamé-Made” E

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