Pressure sensor

Details Pressure sensor Pressure sensor

2002-08-09

2003-07-15

Oen, William (Department: 2855)

Measuring and testing

Fluid pressure gauge

With pressure and/or temperature compensation

C374S143000

Reexamination Certificate

active

06591683

ABSTRACT:

TECHNICAL FIELD
This invention relates to a pressure sensor which measures pressure. More particularly, this invention relates to a pressure sensor which measures calories deprived from a heating element included in a thermal pressure detector or a section heated by the heating element by a diaphragm which is arranged to be opposite to and spaced from the heating element or the heated section by a fixed distance, by using the thermal pressure detector.
BACKGROUND ART
A pressure sensor which measures the flexible quantity of a diaphragm using an almost univocal functional relationship held between the pressure of a measurement target fluid and the flexible quantity of the diaphragm on a cylinder which diaphragm receives pressure from the measurement target fluid and using a distortion gauge which is formed on the diaphragm by a film formation technique, a photo-engraving technique or the like, and which sensor thereby obtains the pressure of the fluid proportional to the flexible quantity of the diaphragm, is widely utilized for the detection of the quantity of the intake air of an internal combustion engine, that of the oil pressure of a vehicle brake or the like.
FIG. 5
is a cross-sectional view of a conventional pressure sensor which is disclosed by, for example, Japanese Utility Model Application Laid-Open No. S61-137242 (microfilm of Japanese Utility Model Application No. S60-19572).
In
FIG. 5
, a reference symbol
101
denotes a metallic cylinder,
102
denotes a semiconductor monocrystalline plate which is provided. with a distortion gauge
103
and the semiconductor monocrystalline plate consists of, for example, a silicon substrate. For the pressure sensor in which the semiconductor monocrystalline plate
102
is bonded to the metallic cylinder
101
shown in
FIG. 5
, the metallic cylinder
101
and the semiconductor monocrystalline plate
102
differ in material and a distortion, therefore, tends to occur to the semiconductor monocrystalline plate
102
which constitutes a diaphragm due to the difference in the coefficient of linear expansion between the cylinder
101
and the plate
102
at a time when temperature change. This causes a measurement error. In addition, since the pressure of a measurement target fluid is directly applied to the semiconductor monocrystalline plate
102
, it is necessary to secure sufficiently high bonding strength between the metallic cylinder
101
and the semiconductor monocrystalline plate
102
.
In
FIG. 6
, a reference symbol
104
denotes a metallic cylinder which consists of a cut-off pipe such as a stainless pipe. A metallic thin film
105
which is welded to the cylinder
104
is formed out of a thin plate of a rolled material and it has a uniform film thickness and a flat surface because of the rolled material. The material of the metallic thin film
105
is the same as that of the cylinder
104
. In addition, a silicon oxide thin film
106
which functions as an insulating film, is formed on the upper surface of the metallic thin film
105
. A plasma CVD method is used to form the silicon oxide thin film
106
. A silicon thin film which constitutes a distortion gauge
107
is then formed on the silicon oxide thin film by the plasma CVD method. This silicon thin film is etched to partially leave the silicon thin film and remove the other sections as shown in
FIG. 6
, and the distortion gauge
107
is formed out of the silicon thin film which is thus left. Furthermore, metal such as gold is deposited on the distortion gauge
107
to thereby form an electrode. A lead wire is bonded to this electrode by ultrasonic bonding. The electrode and the lead wire are appropriately connected to each other, whereby a circuit can be formed.
Each of the conventional pressure sensors shown in
FIGS. 5 and 6
uses the distortion gauge. The diaphragm is distorted by the pressure of the measurement target fluid applied to the diaphragm and each of these pressure sensors measures the, distortion by the distortion gauge provided on the diaphragm. Besides these pressure sensors, a pressure sensor which detects the flexure of a diaphragm as a capacitance change is also used.
FIG.
7
(
a
) is a cross-sectional view and FIG.
7
(
b
) and FIG.
7
(
c
) are top views of a conventional pressure sensor of a capacitance detection type disclosed in, for example, Japanese Patent Application Laid-Open No. S60-56233.
In FIG.
7
(
a
), reference symbol
108
denotes a substrate which has an electrode
109
provided in the central portion of an upper surface thereof, an electrode
110
for correction concentric to the both and provided on an edge section thereof and a hole
111
provided in between the electrode
109
and the correction electrode
110
. Reference symbol
112
denotes a diaphragm on one surface of which an electrode
113
is provided at a position opposite to the electrode
109
. Reference symbol
114
denotes gap adjustment glass beads which are interposed between the substrate
108
and the diaphragm
112
so as to form a gap
115
between the electrodes
109
and
113
. In this pressure sensor, when pressure P is applied to the diaphragm
112
, the gap
115
in the central section becomes smaller and static capacitance increases between the electrodes
109
and
113
. The pressure sensor is intended to measure the pressure using an almost univocal functional relationship held between this capacitance change and the pressure of a measurement target fluid.
According to the conventional pressure sensor which is constituted as explained above, when the distortion gauge formed on the silicon substrate is used, it is impossible to secure sufficient bonding strength between the cylinder and the silicon substrate on which the distortion gauge is formed. It is, therefore, impossible to directly apply the pressure of the measurement target fluid to the silicon substrate and to measure the pressure of the measurement target fluid. Accordingly, it is required to cause pressure to be acted on a buffer in a different chamber using the diaphragm which is deformed by the measurement target fluid and to measure the pressure of the buffer using the distortion gauge provided on the silicon substrate.
Further, when the distortion gauge of the silicon thin film provided on the metallic diaphragm is used, it is not easy to directly manufacture silicon thin film distortion gauges on the metallic diaphragmwhich receives the pressure in block in large quantities. This is because an apparatus for the silicon substrate (for silicon process) cannot be used as a diversion.
Moreover, according to the capacitance detection type pressure sensor, it is necessary to form an insulating layer on the metallic diaphragm and to then form a capacitance detection electrode using the photo-engraving technique or the like. As can be seen, when the metallic diaphragm is used, it is conventionally necessary to subject the metallic diaphragm to film formation processing, photo-engraving processing and the like. However, a film formation apparatus and a photo-engraving apparatus conventionally used for a silicon substrate cannot be used to carry out these processing. Besides, when the silicon substrate is used, the structure of the pressure sensor is complicated, making it disadvantageously impossible to manufacture a highly reliable, inexpensive pressure sensor.
This invention has been achieved solve the above-explained conventional disadvantages. It is an object of this invention to provide a simple thermal pressure sensor. The thermal pressure sensor thermally detects the displacement quantity of a diaphragm which receives pressure and measures a change in calorie following the deformation of the diaphragm and deprived of from the heating element of a detector or a section heated by the heating element which is away from the diaphragm by a fixed distance.
According to this invention, it is possible to manufacture measurement target elements on a silicon substrate in block in large quantities using a manufacturing technique and a manufacturing apparatus which are conventionally adapte

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