Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
2000-02-08
2001-07-24
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C257S254000, C073S780000
Reexamination Certificate
active
06265238
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic capacitive sensor and a method for producing the same sensor.
2. Description of the Related Art
Progress is rapidly being made in silicon micromachining technology in which various types of miniature parts are produced by using a very-high-precision etching method for single-crystal silicon and a polysilicon-deposition method, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD). As a consequence, various types of miniature parts, such as electrostatic capacitive sensors for detecting, for example, acceleration and angular velocity, have been developed.
The principle of the capacitive sensor will now be explained with reference to FIG.
5
A. The capacitive sensor is constructed of a sensing unit
1
and a CV conversion circuit
2
for converting capacitance into voltage.
The sensing unit
1
is formed of a movable electrode
3
and a stationary electrode
4
, both of which are flat-plate type and placed parallel to each other with their surfaces opposedly facing. When acceleration is applied perpendicular to the surface of the movable electrode
3
, the electrode
3
is displaced in a direction indicated by the arrow D
1
shown in
FIG. 5A
to change the distance L
1
between the movable electrode
3
and the stationary electrode
4
. Accordingly, the capacitance between the two electrodes
3
and
4
is changed in proportion to the reciprocal of the distance L
1
therebetween. In contrast, upon application of acceleration parallel to the surface of the movable electrode
3
, the electrode
3
is displaced in a direction indicated by the arrow D
2
shown in
FIG. 5A
to vary the opposing area of the electrodes
3
and
4
. Consequently, the capacitance between the electrodes
3
and
4
is changed in proportion to the opposing area.
As the CV conversion circuit
2
, a capacitance detecting circuit using what is referred to as a “diode bridge” is generally employed. The input terminals of the conversion circuit
2
are electrically connected to the movable electrode
3
and the stationary electrode
4
, respectively, via individual lead lines
5
. As a consequence, a change in the capacitance between the electrodes
3
and
4
is converted into a voltage by the CV conversion circuit
2
, thereby detecting the acceleration.
In the principle explained above, the sensing unit
1
has been provided by way of example only, and it is not restricted to the above-described type. For example, the sensing unit
1
may be formed, as illustrated in
FIG. 5B
, of a movable electrode
3
and a pair of stationary electrodes
4
A and
4
B. In this case, the electrodes
4
A and
4
B are disposed parallel to each other with their surfaces opposedly facing. Further, the movable electrode
3
is located parallel to and between the stationary electrodes
4
A and
4
B in such a manner that the top and bottom surfaces of the electrode
3
opposedly face the electrodes
4
A and
4
B. The input terminals of the CV conversion circuit
2
are electrically connected to the movable electrode
3
and the stationary electrodes
4
A and
4
B, respectively, via individual lead lines
5
. Upon application of acceleration perpendicular to the surface of the movable electrode
3
, the electrode
3
is displaced in a direction indicated by the arrow D
1
shown in
FIG. 5B
to change the distance L
2
between the movable electrode
3
and the stationary electrode
4
A and the distance L
3
between the electrodes
3
and
4
B. Accordingly, changes in the capacitance between the movable electrode
3
and the stationary electrode
4
A and the capacitance between the electrodes
3
and
4
B are converted into a differential voltage by the CV conversion circuit
2
, thereby detecting the acceleration. It should be noted that an explanation of the structure of the differential-voltage-type sensor will be omitted in a specific example of the capacitive sensor to be described below.
A typical known type of electrostatic capacitive sensor will now be explained more specifically with reference to
FIGS. 6A and 6B
.
The capacitive sensor is constructed of a support base
6
, a sensing unit
7
, and a CV conversion circuit
8
. The support base
6
is formed in the shape of a quadrilateral plate and made of, for example, electrically insulating glass. A rectangular recessed portion (opening)
9
is formed substantially at the center of the surface of the support base
6
, while another rectangular recessed portion (opening)
10
is provided in the vicinity of one edge of the base
6
. The recessed portions
9
and
10
are disposed parallel to each other.
The sensing unit
7
is formed of a stationary electrode
11
and a movable electrode
12
, both of which exhibit electrical conductivity. The sensing unit
7
is produced by using single-crystal silicon doped with impurity ions, such as phosphorus, boron, or antimony. The stationary electrode
11
, being formed in the shape of a rectangular plate, is provided projecting from a longitudinal edge of the recessed portion
9
on the opposite side thereof, away from the other recessed portion
10
formed in the support base
6
.
The movable electrode
12
is integrally constructed of a pair of support portions
13
, a mass portion
14
, and a pair of interconnecting portions
15
for connecting the mass portion
14
to the respective support portions
13
.
The pair of support portions
13
are formed in the shape of a quadrangular prism and project from the respective end edges of the recessed portion
9
. The support portions
13
are disposed with their major side faces opposedly facing each other. The height of the support portions
13
is the same as the stationary electrode
11
.
The mass portion
14
is formed in the shape of a rectangular prism and is interposed between the opposing side faces of the support portions
13
. The mass portion
14
is disposed parallel to the stationary electrode
11
with a predetermined spacing in such a manner that one longitudinal face of the mass portion
14
opposedly faces one longitudinal face of the stationary electrode
11
. The height of the mass portion
14
is the same as the stationary electrode
11
.
The interconnecting portions
15
are formed in the shape of a thin rectangular plate and each connect the end face of the mass portion
14
to the opposing face of the support portion
13
. The interconnecting portion
15
is identical to the mass portion
14
in height and perpendicularly provided at the center of the end face of the mass portion
14
. With this arrangement, the mass portion
14
is held by the interconnecting portions
15
in such a manner that it floats over the recessed portion
9
. The interconnecting portions
15
are formed thin in a direction perpendicular to the longitudinal face of the mass portion
14
so that they can be easily deformed in a bending manner in the same direction. Thus, when acceleration is applied perpendicular to the longitudinal faces of the mass portion
14
, the interconnecting portions
15
are deformed in a bending manner in the direction in which acceleration is applied, thereby changing the distance between the mass portion
14
and the stationary electrode
11
.
The CV conversion circuit
8
is formed at the center of the bottom surface of a single-crystal-silicon block
16
. The block
16
is located on the recessed portion
10
in such a manner that the peripheral edge on the bottom surface of the block
16
is disposed around the recessed portion
10
. Accordingly, the CV conversion circuit
8
is held at the center of the recessed portion
10
without directly contacting the insulating substrate
6
. The height of the block
16
is the same as the stationary electrode
11
. The input terminals of the CV conversion circuit
8
are electrically connected to the stationary electrode
11
and the movable electrode
12
, respectively, via individual lead lines
17
formed on the top surface of the support base
6
and the bottom surface of the block
16
.
Kobayashi Shinji
Yaji Kaneo
Lee Calvin
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Smith Matthew
LandOfFree
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