Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2001-07-03
2003-01-21
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S862381
Reexamination Certificate
active
06508126
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dynamic quantity sensor that detects a dynamic quantity such as acceleration based on a change in capacitance between a comb-shaped movable electrode and a comb-shaped fixed electrode.
2. Description of the Related Art
FIGS. 1 and 2
show this kind of dynamic quantity sensor. The dynamic quantity sensor is manufactured by performing well-known semiconductor manufacture techniques to a lamination substrate
10
such as a SOI (Silicon On Insulator) substrate that is composed of a first semiconductor substrate
11
, a second semiconductor substrate
12
laminated with the first semiconductor substrate
11
with an insulating layer
13
interposed therebetween.
A groove
14
is formed in the second semiconductor layer
12
, and an opening portion
13
a
is formed in the first semiconductor layer
11
and the insulation film
13
. Accordingly, the first semiconductor layer
11
forms a frame-shaped base portion, and the second semiconductor layer
12
forms a beam structure.
The beam structure formed by the second semiconductor layer
12
is composed of a weight portion
210
, which is supported by the base portion through beam portions
22
so that it can be displaced in a predetermined direction (direction Y indicated by an arrow in FIG.
1
), and comb-shaped movable electrodes
240
protruding from the weight portion
210
, and comb-shaped fixed electrodes
310
,
320
protruding from the base portion
11
to face respective side faces of the comb-shaped movable electrodes
240
while defining a specific interval therebetween.
When a dynamic quantity is applied to the sensor, the weight portion
210
is displaced in the direction Y due to elastic forces of the beam portions
22
so as to change a capacitance in detection interval
40
defined between the movable electrodes
240
and the fixed electrodes
310
,
320
, and the dynamic quantity can be detected based on the change in capacitance in the detection interval
40
.
SUMMARY OF THE INVENTION
An object of the present invention is to improve characteristics of a dynamic quantity sensor that has a pole-shaped movable electrode and a pole-shaped fixed electrode and detects a dynamic quantity based on a change in capacitance between the movable electrode and the fixed electrode.
According to a first aspect of the present invention, in a dynamic quantity sensor having a movable electrode and a fixed electrode defining a detection interval therebetween, at least one of the movable electrode and the fixed electrode has a tapered plane shape with a width that decreases from a root portion toward a tip portion of the one of the movable electrode and the fixed electrode. Accordingly, the one of the movable electrode and the fixed electrode can have an improved rigidity. Therefore, sticking caused by bending of the electrode can be prevented.
According to a second aspect of the present invention, a dynamic quantity is detected based on a change in capacitance of a detection interval between a fixed electrode and a movable electrode while applying, to the fixed electrode and the movable electrode, carrier wave signals having a carrier wave frequency. The carrier wave frequency is shifted from 1
(n: positive integer) of a natural frequency of the fixed electrode when the fixed electrode performs flexural vibration. Preferably, the carrier wave frequency is shifted from 1
(n: positive integer) of a natural frequency of the movable electrode when the movable electrode performs flexural vibration.
When the carrier wave frequency is shifted from 1
of the natural frequencies of the fixed electrode and the movable electrodes, the fixed electrode and the movable electrode can be prevented from resonating to perform the flexural vibration due to the carrier wave signals, resulting in improved accuracy of sensor output.
According to a third aspect of the present invention, a carrier wave frequency of carrier wave signals applied for performing self-diagnosis of a dynamic quantity sensor is shifted from. 1
(n: positive integer) of a natural frequency of a fixed electrode when the fixed electrode performs the flexural vibration. Preferably, the carrier wave frequency in the self-diagnosis is shifted from 1
of a natural frequency of a movable electrode. Accordingly, the fixed electrode and the movable electrode are prevented from resonating to perform the flexural vibration in the self-diagnosis.
According to a fourth aspect of the present invention, at least one of a movable electrode and a fixed electrode has a root portion and a tip portion in a protruding direction thereof, the root portion having a rigidity larger than that of the tip portion. In this case, the one of the movable electrode and the fixed electrode can have an increased strength. Further, because the rigidity of the root portion is larger than that of the tip portion in the electrode, a natural frequency of the electrode can be easily made larger than a carrier wave frequency of carrier wave signals used for a normal operation or self-diagnosis of the sensor.
REFERENCES:
patent: 5747690 (1998-05-01), Park et al.
patent: 6122964 (2000-09-01), Mohaupt et al.
patent: 6151966 (2000-11-01), Sakai et al.
patent: 6276207 (2001-06-01), Sakai et al.
patent: 6308567 (2001-10-01), Higuchi et al.
patent: 6450029 (2002-09-01), Sakai et al.
U.S. patent application Ser. No. 09/667,800, Sakai et al., filed Sep. 22, 2000.
U.S. patent application Ser. No. 09/438,293, Sakai et al., filed Nov. 12, 1999.
U.S. patent application Ser. No. 09/458,954, Higuchi et al., filed Dec. 10, 1999.
Aoyama Seiki
Funato Hirotsugu
Sakai Minekazu
Denso Corporation
Law Offices of David G. Posz
Moller Richard A.
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