Pressure sensor with a thermal pressure detecting element

Details Pressure sensor with a thermal pressure detecting element Pressure sensor with a thermal pressure detecting element

2000-08-24

2002-05-28

Oen, William (Department: 2855)

Measuring and testing

Fluid pressure gauge

With pressure and/or temperature compensation

Reexamination Certificate

active

06393919

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a pressure sensor for measuring pressure, and particularly to a pressure sensor for measuring, by using a thermal pressure detecting element, heat quantities deprived by means of a pressure receiving diaphragm which is disposed as to oppose a heating element included in the thermal pressure detecting element or a portion heated by the heating element with being remote therefrom by a specified distance.
BACKGROUND ART
A pressure sensor wherein a deflection value of a diaphragm is measured based on a substantially non-ambiguous functional relationship that is satisfied between a pressure of a measuring fluid and a deflection value of the diaphragm formed on a cylindrical body which receives pressure of the fluid with the use of a strain gage formed onto the diaphragm through film forming techniques or photolithographic techniques for obtaining the pressure of the fluid proportional to the deflection value of this diaphragm is widely applied for detecting an amount of absorbed air of an internal combustion engine or for detecting a hydraulic pressure of a brake of a vehicle.
FIG. 22
is a sectional view of a conventional pressure sensor as disclosed, for instance, in Japanese Unexamined Utility Model Publication No. 137242/1986 (microfilm of Japanese Utility Model Application No. 19572/1985).
In
FIG. 22
, numeral
101
denotes a metallic cylindrical body, numeral
102
a semiconductor single crystalline plate including a strain gage
103
, wherein the semiconductor single crystalline plate comprises, for instance, a silicon substrate. In the arrangement of
FIG. 22
wherein the semiconductor single crystalline plate
102
is adhered to the metallic cylindrical body
101
, the difference in materials between the metallic cylindrical body
101
and the semiconductor single crystalline plate
102
resulted in the fact that strain was apt to occur in the semiconductor single crystalline plate
102
forming the diaphragm owing to difference in coefficients of linear expansion at the time of temperature variations, thereby causing measuring errors. Further, since a pressure of the measuring fluid is directly applied to the semiconductor single crystalline plate
102
, a sufficiently strong bonding strength was required between the metallic cylindrical body
101
and the semiconductor single crystalline plate
102
.
In
FIG. 23
, numeral
104
denotes a metallic cylindrical body comprising, for instance, a cut pipe material which might be a stainless steel pipe. A metallic thin film
105
welded to the cylindrical body
104
is formed of a thin plate of rolled material, and owing to the fact that this is a rolled material, it is formed to assume a uniform film thickness as well as a smooth surface. The metallic thin film
105
is formed of a material that is identical to that of the cylindrical body
104
. A silicon oxide thin film
106
that functions as an insulating film is formed on an upper surface of the metallic thin film
105
. Plasma CVD methods are employed for forming the silicon oxide thin film
106
. Then, a silicon thin film forming a strain gage
107
is formed onto the silicon oxide thin film through plasma CVD methods. Etching of the silicon thin film is performed to remove portions other than partial portions of the silicon thin film as shown in
FIG. 23
, and the strain gage
107
is formed by the remaining silicon thin film. Further, an circuit might be arranged by forming an electrode by performing vapor deposition of metal such as gold on to the strain gage
107
, attaching a lead wire to the electrode by means of ultrasonic bonding, and suitably connecting the electrode and the lead wire.
The conventional pressure sensor as shown in FIG.
22
and
FIG. 23
is a pressure sensor employing a strain gage wherein the diaphragm is strained through pressure of measuring fluid applied to the diaphragm and the strain is measured by the strain gage on the diaphragm. There is also employed a pressure sensor for detecting a deflection of a diaphragm as a change in capacity.
FIG. 24
is a sectional view (a) and top views (b), (c) of a conventional pressure sensor of capacity detecting type as disclosed, for instance, in Japanese Unexamined Patent Publication No. 56233/1985.
In the drawings, numeral
108
denotes a base having an electrode
109
in a central portion on its upper surface and a correction electrode
110
at its peripheral edge portion, both in a concentric manner, while a through hole
111
is formed in a clearance formed between these electrodes. Numeral
112
denotes a diaphragm having an electrode
113
on its surface as to oppose the electrode
109
. Numeral
114
denotes glass beads for gap adjustment interposed between the substrate
108
and the diaphragm
112
for forming a gap
115
between the electrodes
109
,
113
. The pressure sensor is so arranged that the gap
115
in the central portion becomes smaller when pressure P is applied onto the diaphragm
112
whereby capacitance between the electrodes
109
,
113
is increased. By utilizing a substantially non-ambiguous functional relationship that is satisfied between the change in capacity and the pressure of measuring fluid, it is aimed to measure the pressure.
Due to the above arrangement of the conventional pressure sensor, when using the strain gage formed on the silicon substrate, no satisfactory bonding strength can be secured between the cylindrical body and the silicon substrate on which the strain gage is formed, so that the pressure of the measuring fluid cannot be applied directly onto the silicon substrate to measure the pressure of the measuring fluid. Therefore, it was necessary that the pressure act onto a buffering agent in a different chamber by using the diaphragm that is deformed by the measuring fluid whereupon the pressure of the buffering agent is measured by using the strain gage on the silicon substrate.
When using the strain gage of silicon thin film formed on the metallic diaphragm, it was not easy to directly form the strain gage of silicon thin film on the metallic diaphragm for receiving pressure through mass production in a lump sum since devices for silicon substrates (for silicon processing) could not be concurrently used.
Moreover, in a pressure sensor of capacity detecting type, an insulating layer needs to be formed on the metallic diaphragm and an electrode for capacity detection need to be formed thereafter through photolithographic techniques or the like. In this manner, when using a metallic diaphragm, the metallic diaphragm needs to undergo film forming or photolithographic processes so that film forming devices or photolithographic devices that are suitably used for silicon substrates cannot be used. Further, using a silicon substrate resulted in a complicated structure of the pressure sensor so that a drawback was presented that no pressure sensor of low cost and high reliability could be manufactured.
SUMMARY OF THE INVENTION
It is an object of the present invention to realize a simple thermal pressure sensor for solving the conventional problems. A thermal pressure sensor is arranged to thermally detect a displacement value of a diaphragm which receives pressure, wherein variations in heat quantities that are deprived in accordance with displacements of the diaphragm are obtained from a heating element of a detecting elements or a portion heated by the heating element which is remote from the diaphragm by a specified distance.
It is an object of the present invention to obtain a pressure sensor of high reliability and of low cost wherein measuring elements can be formed onto a silicon substrate through mass production in a lump sum by using conventional manufacturing techniques and devices which are applied to silicon substrates, wherein no processing of the metallic diaphragm is required while utilizing a metallic diaphragm formed on a cylindrical body as a pressure receiving body, and wherein no additional chamber for holding buffering agents is required since no external force is directly executed on the

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