Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1999-05-28
2001-02-06
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
Reexamination Certificate
active
06184561
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of Japanese Patent Application No. 10-149908, filed on May 29, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor pressure sensor having strain gauges provided on a diaphragm portion for detecting pressure applied thereto.
2. Description of the Related Art
A conventional semiconductor pressure sensor includes a sensor chip
10
shown in
FIG. 1
having a thin diaphragm portion
10
a
indicated by a dotted line in the figure. The diaphragm portion
10
a
has four piezo-resistance members (strain gauges)
1
a
to
1
d
made of an impurity diffusion layer thereon, two of which are center gauges
1
a
,
1
b
arranged at the central portion thereof and the other two of which are side gauges
1
c
,
1
d
arranged at the periphery thereof. The gauges
1
a
to
1
d
are electrically connected to form a bridge circuit as shown in
FIG. 2
so that an electrical signal is output from terminals O
A
, O
B
in accordance with pressure. To form this constitution, an aluminum (Al) wiring member is provided around the diaphragm portion
10
a
to be electrically connected to the strain gauges
1
a
to
1
d
, and the sensor output is taken out from a circuit portion not shown to which the wiring member
2
is connected.
As shown in
FIG. 3
, the sensor chip
10
is fixed to a glass base
11
by anode-bonding, and the glass base
11
is adhered to an inside wall of a casing
13
made of polybutylene terephthalate (PBT) or the like by silicone system adhesive
12
. Silicone gel
14
is coated on the surface of the sensor chip
10
. In this constitution, the casing
13
can produce thermal distortion that adversely and innegligibly affects the sensor chip
10
. Therefore, as shown in
FIG. 3
, a plate
15
made of
42
alloy is adhered to the lower surface of the glass base
11
by silicone system adhesive
16
to reduce the adverse effect of the thermal distortion of the casing
13
to the sensor chip
10
. However, it is found that the sensor output still varies as a result of thermal hysteresis.
SUMMARY OF THE INVENTION
The present invention has been made in view of the problem described above. An object of the present invention is to reduce variations of an output value from a semiconductor pressure sensor, caused by thermal hysteresis.
According to a first aspect of the present invention, a semiconductor pressure sensor has a stress balance film for balancing changes in stress of a plurality of resistive members, produced by a change in temperature. This is based on an analysis that variation in sensor output is caused by different changes in stress of the resistive members, which are produced by the change in temperature. According to the present invention described above, the variation of the sensor output can be reduced to approximately zero by the stress balance film for balancing the changes in stress of the resistive members.
The stress balance film may be integrally formed with a wiring member that is electrically connected to the resistive members and provided around a diaphragm portion on which the resistive members are disposed. The stress balance film may include a plurality of stress balance film portions disposed around the diaphragm portion.
According to a second aspect of the present invention, a semiconductor pressure sensor includes a wiring member electrically connected to a plurality of resistive members, and made of a material that exhibits a yield phenomenon at a temperature higher than an operational temperature range of the pressure sensor. This is based on an analysis that the changes in stress of the resistive members are produced by thermal hysteresis characteristics of the wiring member arranged around the resistive members.
When the wiring member is made of the material described above, the wiring member does not exhibit thermal hysteresis characteristics within the operational temperature range of the pressure sensor. As a result, the variation of the sensor output can be prevented.
REFERENCES:
patent: 5289721 (1994-03-01), Tanizawa et al.
patent: 5600074 (1997-02-01), Marek et al.
patent: 5844287 (1998-12-01), Hassan et al.
patent: 5880509 (1999-03-01), Watanabe et al.
patent: 5889311 (1999-03-01), Shinogi et al.
patent: 5986316 (1999-11-01), Toyoda et al.
patent: 6011273 (2000-01-01), Ichikawa et al.
patent: 6-112506 (1994-04-01), None
patent: 6-163939 (1994-06-01), None
patent: 2650455 (1997-05-01), None
patent: 10-170367 (1998-06-01), None
Suzuki Yasutoshi
Tanaka Hiroaki
Toyoda Inao
Clark Sheila V.
Denso Corporation
Pillsbury Madison & Sutro LLP
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