Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2002-05-30
2003-11-18
Noori, Max (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06647795
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates by reference Japanese patent application no. 2001-166350, which was filed on Jun. 1, 2001.
BACKGROUND OF THE INVENTION
This invention relates to a capacitive physical load sensor and a capacitive physical load detection system.
An example of a capacitive physical load detection system having a conventional capacitive physical load sensor will first be described by referring to FIG.
14
through FIG.
18
. As shown in
FIG. 14
, the conventional capacitive pressure detection system
1
includes a capacitive pressure sensor
10
and capacitive detection circuits
64
. The capacitive pressure sensor
10
includes a pressure sensitive capacitor
20
with pressure capacitance C
X
and a reference capacitor
30
with reference capacitance C
R
. The pressure sensitive capacitor
20
is connected to input
60
of a detection voltage V
X
. Reference capacitor
30
is connected to input
62
of a reference voltage V
R
. Pressure sensitive capacitor
20
and reference capacitor
30
are connected to the capacitance detection circuits
64
. The capacitance detection circuits
64
are connected to an output
78
of a voltage V
OUT
.
The capacitive pressure sensor
10
is manufactured by forming a diaphragm on a silicon substrate. More specifically, the capacitive pressure sensor
10
includes a silicon substrate
80
, a diaphragm
84
, which is formed across a gap
82
from the silicon substrate
80
, and a retaining part
86
for the diaphragm
84
, which is formed around the diaphragm
84
, as shown in
FIGS. 16
to
18
.
Formed on a top surface of the silicon substrate
80
is a pressure sensitive capacitor lower electrode
22
b
and reference capacitor lower electrode
32
b
. The pressure sensitive capacitor lower electrode
22
b
is connected to a pressure sensitive capacitor lower electrode pad
26
b
through a pressure sensitive capacitor lower electrode lead
24
b
(see FIG.
15
and FIG.
16
), and the reference capacitor lower electrode
32
b
is connected to a reference capacitor lower electrode pad
36
b
through a reference capacitor lower electrode lead
34
b
(see FIG.
15
and FIG.
16
). The surface of the silicon substrate
80
is covered by a substrate protective layer
88
(see FIG.
16
through FIG.
18
).
The diaphragm
84
includes a semiconductor film
92
, which consists of a poly silicon film, and a protective film
96
, which consists of a silicon nitride film. A pressure sensitive capacitor upper electrode
22
a
and a reference capacitor upper electrode
32
a
are formed on top of the semiconductor film
92
. The pressure sensitive capacitor upper electrode
22
a
is connected to a pressure sensitive capacitor upper electrode pad
26
a
through a pressure sensitive capacitor upper electrode lead
24
a
(see FIG.
15
and FIG.
17
), and the reference capacitor upper electrode
32
a
is connected to a reference capacitor upper electrode pad
36
a
through a reference capacitor upper electrode lead
34
a
(see FIG.
15
and FIG.
17
).
A pressure capacitor
20
shown in
FIG. 14
includes the pressure sensitive capacitor upper electrode
22
a
and the pressure sensitive capacitor lower electrode
22
b
shown in FIG.
16
through FIG.
18
. The reference capacitor
30
shown in
FIG. 13
includes the reference capacitor upper electrode
32
a
and reference capacitor lower electrode
32
b
shown in
FIGS. 16
to
18
.
When pressure is applied to the diaphragm
84
, the gap
82
acts as a pressure reference chamber that is sealed in a vacuum, and the diaphragm
84
stretches and changes shape in proportion to the applied pressure, as shown in
FIGS. 16
to
18
. When the shape of the diaphragm
84
changes, the distance between the upper electrode
22
a
and the lower electrode
22
b
changes. When the distance between the two electrodes changes, the capacitance between the two electrodes also changes. The circuits shown in
FIG. 14
detect a difference between a change in the pressure sensitive capacitance C
X
of the pressure sensitive capacitor
20
and the reference capacitance C
R
of the reference capacitor
30
and convert the results into an output voltage V
OUT
using the capacitance detection circuits
64
in order to detect the magnitude of the pressure being applied on the diaphragm
84
.
The reference capacitor
30
makes up for changes in capacitance due to changes in temperature in the environment in which the sensor
10
is placed. As a result, the output voltage V
OUT
of the sensor
10
is independent of temperature and dependent only on pressure.
In the conventional capacitive pressure sensor
1
, which was described above, the output voltage V
OUT
is proportional to the applied pressure, until the applied pressure reaches a value P
A
, as shown in a graph in FIG.
19
. Once the applied pressure reaches the value P
A
, the diaphragm
84
, shown in FIG.
16
through
FIG. 18
, comes into contact with the silicon substrate
80
, starting at the center, where the diaphragm
84
deforms the most. Beyond this point, the output voltage V
OUT
gradually becomes saturated and is no longer proportional to the applied pressure. When the applied pressure reaches a value P
B
, the center part of the diaphragm
84
comes into complete contact with the silicon substrate
80
. As a result, the output voltage V
OUT
is completely saturated with respect to the applied pressure and can no longer represent the applied pressure.
When the diaphragm
84
is thicker, or the diameter of the diaphragm
84
is smaller, the shape of the diaphragm
84
would not change as much with respect to the applied pressure, and it would be possible detect a wider range of pressure levels. However, when the diaphragm
84
is thicker, or the diameter of the diaphragm
84
is smaller, sensor sensitivity suffers. That is, the resolution in detectable pressure is smaller.
An ideal pressure sensor is able to detect a wide range of physical loads (pressure, acceleration, vibration, sound pressure) and offer a high level of sensitivity to detect minute changes in the physical loads across their entire ranges. However, it is difficult to produce such a sensor. On the other hand, a normal application for a capacitive pressure sensor would require a measurement range over which the measurement results must be highly precise, as well as a range over which lower sensitivity is acceptable. In many cases, a lower detectible resolution would be acceptable when the magnitude of the physical load to be measured is large.
Therefore, it is the goal of this invention to provide a capacitive pressure sensor capable of both detecting small changes in pressure across a range over which a high sensitivity is required and of detecting a wide range of pressure levels across a range over which high sensitivity is not required.
SUMMARY OF THE INVENTION
This invention is essentially a capacitive physical load sensor including a substrate having a fixed electrode and a diaphragm having a movable electrode. The diaphragm is located across a gap from the substrate. A retaining part for the diaphragm is formed around the diaphragm a protruding part extends from a surface of the substrate or from a surface of the diaphragm into the gap.
The protruding part may be one of a plurality of protruding parts, and surfaces of the protruding parts support the diaphragm when certain physical loads are applied to the diaphragm, respectively.
In a further aspect, the invention may include a correction circuit for correcting a load detection value outputted by the diaphragm, so that the sensor correction circuit issues an output value that changes in a manner that is substantially proportional to changes in the physical load applied to the diaphragm.
REFERENCES:
patent: 4204244 (1980-05-01), Ho
patent: 4380041 (1983-04-01), Ho
patent: 4838088 (1989-06-01), Murakami
patent: 4852443 (1989-08-01), Duncan et al.
patent: 4933807 (1990-06-01), Duncan
patent: 5321989 (1994-06-01), Zimmer et al.
patent: 6148674 (2000-11-01), Park et al.
Funabashi Hirofumi
Ishio Seiichiro
Ohta Norikazu
Shimaoka Keiichi
Suzuki Yasutoshi
Denso Corporation
Noori Max
Posz & Bethards, PLC
LandOfFree
Capacitive physical load sensor and detection system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Capacitive physical load sensor and detection system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Capacitive physical load sensor and detection system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3173916