Semiconductor physical quantity sensor

Details Semiconductor physical quantity sensor Semiconductor physical quantity sensor

2000-07-26

2002-09-17

Williams, Hezron (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

C073S514240, C073S514320

Reexamination Certificate

active

06450031

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application is based upon Japanese Patent Application Nos. Hei. 11-210805 filed on Jul. 26, 1999, and Hei. 11-212734 filed on Jul. 27, 1999, 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, and particularly to a capacitance-detecting type semiconductor physical quantity sensor, wherein a moving electrode part and a fixed electrode part facing this moving electrode part are formed by forming trenches in a semiconductor layer of a supporting substrate consisting of a semiconductor and an applied physical quantity is detected on the basis of variation in a capacitance between these moving and fixed electrode parts.
2. Related Art
Semiconductor acceleration sensors include those of a differential capacitance type. The construction of a differential capacitance type semiconductor acceleration sensor of related art is shown in
FIG. 17. A
vertical sectional view on the line XVIII—XVIII in
FIG. 17
is shown in FIG.
18
. In
FIG. 18
, a semiconductor substrate
102
is fixed to a package plate
100
with an adhesive
101
, and a semiconductor thin film
104
is disposed on an insulating film
103
on the semiconductor substrate
102
. Through holes
105
,
106
are formed in the semiconductor substrate
102
and the insulating film
103
respectively. The semiconductor thin film
104
is patterned to form as separate sections a moving electrode bridge structure
107
, a first fixed electrode cantilever bridge structure
108
and a second fixed electrode cantilever bridge structure
109
, shown in FIG.
17
. The moving electrode bridge structure
107
has anchoring parts
110
, suspension parts
111
, a weight part
112
and comb-shaped moving electrodes
113
. The first fixed electrode cantilever bridge structure
108
has an anchoring part
114
and a fixed electrode
115
. Similarly, the second fixed electrode cantilever bridge structure
109
has an anchoring part
116
and a fixed electrode
117
. The moving electrodes
113
and the fixed electrodes
115
,
117
face each other, and when acceleration is applied in the X-direction in
FIG. 17
, the weight part
112
displaces and a difference in capacitance between the moving electrodes
113
and the fixed electrodes
115
,
117
changes, and by extracting this change in difference in capacitance as a voltage change it is possible to detect the acceleration.
However, when the temperature at which the sensor is being used changes, due to differences in the coefficients of thermal expansivity of the different parts of the sensor, that is, differences in coefficient of thermal expansivity between the package plate
100
, the adhesive
101
, the semiconductor substrate
102
, the insulating film
103
and the semiconductor thin film
104
, warp occurs in the semiconductor substrate
102
. Because of this warp, as shown in
FIGS. 19
,
20
A and
20
B, the fixed electrode
117
(
115
) deforms, and the spacing d between the fixed electrode
117
(
115
) and the moving electrode
113
ceases to keep a constant value, as shown in
FIG. 20B
(d
1
≠d
2
). As a result, there has been the problem that the temperature characteristic of the sensor is poor.
Also, another semiconductor acceleration sensor of the capacitance-detecting type which has been proposed is shown in
FIGS. 35 and 36
. Here,
FIG. 35
is a plan view and
FIG. 36
a sectional view on the line XXXVI—XXXVI in FIG.
35
. This sensor is formed by applying micro-machining using semiconductor manufacturing technology to a semiconductor substrate having an insulating layer J
3
between a first semiconductor layer J
1
and a second semiconductor layer J
2
.
In this semiconductor acceleration sensor, by forming trenches in the second semiconductor layer J
2
of the semiconductor substrate, a moving electrode part J
6
wherein a weight part J
4
is integrated with projecting parts J
5
is formed and comb-shaped fixed electrode parts J
7
, J
8
facing the projecting parts J
5
are formed. Here, the first semiconductor layer J
1
and the insulating layer J
3
constitute a supporting substrate, and an opening J
9
open at the second semiconductor layer J
2
side is formed in this supporting substrate. In the example shown in the drawings, the opening J
9
is so formed as to pass right through the supporting substrate from the second semiconductor layer J
2
side to the opposite side.
The moving electrode part J
6
is elastically supported at both ends on the edge of the opening in the supporting substrate, and displaces over the opening J
9
in the arrow X direction of
FIG. 35
in correspondence with an applied acceleration. The fixed electrode parts J
7
, J
8
are made up of facing electrodes J
7
a,
J
8
a
facing the projecting parts J
5
of the moving electrode part J
6
over the opening J
9
and interconnection parts J
7
b,
J
8
b
fixed to the edge of the opening in the supporting substrate and supporting the facing electrodes J
7
a,
J
8
a.
Thus this related art semiconductor acceleration sensor is of a construction having at least one moving electrode part J
6
and two fixed electrode parts, a first fixed electrode part J
7
and a second fixed electrode part J
8
, provided on opposite sides of the moving electrode part J
6
.
Here, the capacitance between the facing electrode J
7
a
of the first fixed electrode part J
7
and the respective projecting part J
5
of the moving electrode part J
6
will be called the first detection capacitance CS
1
and the capacitance between the facing electrode J
8
a
of the fixed electrode part J
8
and the respective projecting part J
5
will be called the second detection capacitance CS
2
. In the drawings, the capacitances are shown with capacitor symbols. In correspondence with the displacement of the moving electrode part J
6
caused by an applied acceleration, the detection capacitances CS
1
, CS
2
change, and by detecting (differentially detecting) this as a difference of the detection capacitances CS
1
and CS
2
, it is possible to detect the applied acceleration.
However, in studies carried out by the present inventors into the related art semiconductor acceleration sensor described above, the problem has arisen that manufacturing process error of the sensor causes the output error of the sensor, or offset, to be large. Next, a study carried out by the present inventors into this offset problem will be discussed on the basis of the related art sensor illustrated in
FIGS. 35 and 36
.
FIG. 24A
shows a detection circuit of a differential capacitance type semiconductor acceleration sensor. CP
1
, CP
2
and CP
3
denote parasitic capacitances.
Here, in this related art sensor, CP
1
is the capacitance between the interconnection part J
7
b
of the first fixed electrode part J
7
and the supporting substrate, CP
2
is the capacitance between the interconnection part J
8
b
of the fixed electrode part J
8
and the supporting substrate, and CP
3
is the capacitance between interconnection parts J
6
b
of the moving electrode part J
6
and the supporting substrate. Also, J
10
denotes a switched capacitor circuit (SC circuit); this SC circuit J
10
has a capacitor J
11
of capacitance Cf, a switch J
12
and a differential amplifier circuit J
13
and converts an inputted capacitance difference into a voltage.
An example of a timing chart of the circuit shown in
FIG. 24A
is shown in FIG.
24
B. In this related art sensor, for example a carrier wave
1
(frequency 100 kHz, amplitude 0 to 5V) is inputted through a fixed electrode pad J
7
c
and a carrier wave
2
(frequency 100 kHz, amplitude 0 to 5V) out of phase with a carrier wave
1
by 180° is inputted through a fixed electrode pad J
8
c,
and the switch J
12
of the SC circuit J
10
is opened and closed with the timing shown in the Figure. An applied acceleration is then outputted as a voltage value Vo as shown by the following express

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