Semiconductor physical quantity sensor

Details Semiconductor physical quantity sensor Semiconductor physical quantity sensor

2001-03-09

2002-12-17

Moller, Richard A. (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

Reexamination Certificate

active

06494096

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon Japanese Patent Application Nos. 2000-79352 filed on Mar. 16, 2000, and 2000-382422 filed on Dec. 15, 2000, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to semiconductor physical quantity sensors for detecting a physical quantity such as acceleration or angular velocity, especially, to a capacitance-detecting type semiconductor physical quantity sensor.
2. Related Arts
A structure of a differential capacitance type semiconductor acceleration sensor of a prior art is shown in
FIG. 1. A
semiconductor layer of a supporting substrate
110
has a moving portion
201
and a fixed portion
301
separated from the moving portion
201
by a trench
140
formed by etching.
The moving portion
201
has suspension parts
202
fixed to the supporting substrate
110
, a weight portion
210
supported by the suspension parts
202
, and two sets of plural movable electrode members
240
connected to both sides of the weight portion
210
.
The fixed portion
301
has plural first fixed electrode members
310
and plural second fixed electrode members
320
. Each of the fixed electrode members
310
,
320
is engaging with each set of the movable electrode members
240
. Each of the movable electrode members
240
and the fixed electrode members
310
,
320
has a detection surface and a non-detection surface opposite to each other. The detection surface of each movable electrode member
240
confronts the detection surface of each fixed electrode member
310
at one side with a detection interval
400
interposed therebetween to make a first capacitance. The non-detection surface of each movable electrode member
240
confronts the non-detection surface of each fixed electrode member
310
at the opposite side with a non-detection interval
410
interposed therebetween. The detection interval
400
and the non-detection interval
410
are defined between movable electrode members
240
and the fixed electrode members
320
at the right side of the weight portion
210
similarly to the left side. A second capacitance is formed by the detection surface of each movable electrode member
240
and the detection surface of each fixed electrode member
320
.
When a physical quantity is applied to the sensor shown in
FIG. 1
, the weight portion
210
displaces in a displacement direction Y, whereby the detection intervals
40
change, for example, when the first capacitances increase, the second capacitances decrease, and vice versa. As a result, a differential capacitance between the first capacitance and the second capacitance changes by the applied physical quantity. The applied physical quantity is detected based on a change of the differential capacitance. Conventionally, the differential capacitance is detected as a voltage.
However, when an excessively large physical quantity is applied to the sensor, at least one of the movable electrode members
240
hits to at least one of the fixed electrode members
310
and
320
, then adhesion (sticking) occurs between at least one of the movable electrode members
240
and at least one of the fixed electrode members
310
and
320
due to an electrostatic attracting force. Consequently, the sensor doesn't work normally.
For the purpose to prevent the adhesion of the electrode members, protrusions are formed on the detection surface of at least one of the movable electrode member
240
and the fixed electrode members
310
,
320
. They reduce the electrostatic attracting force significantly. These protrusions are disclosed in JP-A-4-337468, 6-213924, 6-347474, 11-230985, 11-326365 and U.S. Pat. No. 5,542,295.
However, the protrusions in the prior arts don't work sufficiently due to the following reason.
As mentioned above, a change of the detection interval
400
between the movable electrode member
240
and the fixed electrode member
310
is opposite to that of the detection interval
400
between the movable electrode member
240
and the fixed electrode member
320
. As a result, the direction of the electrostatic attracting force applied to the movable electrode member
240
on the right side of the weight portion
210
is opposite to that of the electrostatic attracting force applied to the movable electrode member
240
on the left side of the weight portion
210
. This structure is referred to as a non-symmetrical structure in this application.
For example, in
FIG. 1
, the movable electrode members
240
on the left side of the axis Y
1
are attracted to an upper side of FIG.
1
. To the contrary, the movable electrode members
24
on the right side of the axis Y
1
are attracted to a lower side of FIG.
1
. In addition, a spring restoring force caused by the suspension parts
202
works to restore the movable electrode members
240
to the initial positions against the electrostatic attracting force on each side. As a result, the weight portion
210
vibrates in a direction of the axis Y
1
and rotates easily in directions indicated by curved arrows R as shown in FIG.
1
.
It may occur that the movable electrode members
240
and the fixed electrode members
310
or the movable electrode members
240
and the fixed electrode members
320
adhere each other in the non-detection interval
410
when the excessively large physical quantity is applied to the sensor, although the non-detection interval
410
is larger than the detection interval
400
.
SUMMARY OF THE INVENTION
This invention has been conceived in view of the background as described above and an object of the invention is to prevent an adhesion of a movable electrode to a fixed electrode due to an electrostatic attracting force even in a non-detection interval interposed therebetween when the non-detection interval is larger than a detection interval interposed between the movable electrode and an opposite fixed electrode.
According to the present invention, the sensor has a supporting substrate, a movable portion separated from a fixed portion by a trench. The movable portion has a weight portion, and movable electrodes formed on both sides of the weight portion in a displacement direction, and the movable portion is suspended above the supporting substrate. The fixed portion has first and second fixed electrodes each engaging with each of the movable electrodes for forming capacitors.
Each of the first and second fixed electrode is disposed in parallel with the movable electrodes so that the side faces thereof determine specific intervals, a detection interval and a non-detection interval larger than the detection interval, with the side faces of adjoining two of the movable electrodes. Protrusions are formed, for example, on both side faces of the first fixed electrode opposing to the side faces of the adjoining two of the movable electrodes.
According to the present invention, these protrusions prevent the adjoining two of the movable electrodes from adhering to the first fixed electrode at both of the side faces of the first fixed electrode when an excessively large physical quantity is applied to the sensor. The protrusions may be formed on the side faces of the movable electrodes facing the side faces of the first fixed electrode.
Preferably, the protrusions on the both side faces of the first fixed electrode are formed in the same size and the same shape. It may allow stable forming of the protrusions. More preferably, the protrusions on the both sides are disposed symmetrically with respect to a longitudinal direction of the first fixed electrode.


REFERENCES:
patent: 5542295 (1996-08-01), Howe et al.
patent: 6065341 (2000-05-01), Ishio et al.
patent: 6105428 (2000-08-01), Schmiesing et al.
patent: 6151966 (2000-11-01), Sakai et al.
patent: 4-337468 (1992-11-01), None
patent: 11-344507 (1999-12-01), None

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