JPH0513451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure detector, and particularly to a pressure detector that operates well in a high temperature atmosphere.

[Prior Art] The above-mentioned pressure detector has a cylindrical housing that protrudes into the measurement atmosphere, and forms a pressure chamber into which measurement pressure is introduced into the housing. Many devices are constructed of a diaphragm that deforms in response to changes in measured pressure, and the diaphragm is equipped with a strain gauge that generates an output signal in accordance with the strain of the diaphragm.

The strain gauges mentioned above are broadly classified into metal strain gauges and semiconductor strain gauges, and the latter has the advantage of being much more sensitive than the former, and conventionally, those using Si semiconductor are typical.

[Problems to be Solved by the Invention] By the way, the withstand temperature of strain gauges using Si semiconductors is limited to 150°C, and the semiconductor characteristics disappear at temperatures higher than this. This is due to the small band gap of Si, approximately 1.1 eV.

In order to improve the withstand temperature, the so-called SOI structure, in which a Si semiconductor diffusion gauge is formed on an insulator, or the so-called SOS structure, in which the above-mentioned diffusion gauge is formed on sapphire, are used. The temperature is about 250℃.

On the other hand, in recent years, there has been a strong demand to directly detect the explosion stroke of each cylinder, especially in electronic fuel injection control (EFI) of vehicle engines, and there has been a demand for pressure detectors that can directly detect the pressure inside the cylinders. However, with the above conventional semiconductor strain gauge, it is impossible to detect the pressure inside the cylinder, which is at a high temperature of 500 to 600° C. or more.

In view of these problems, it is an object of the present invention to provide a pressure detector that can be used satisfactorily even in a high temperature atmosphere of 500° C. or higher.

[Means for Solving the Problems] The configuration of the present invention will be explained with reference to FIG. It is formed and composed.

[Action, Effect] The introduced measurement pressure causes the diaphragm 31 to
1 is deformed, strain occurs in the diamond semiconductor film 48, and its resistance value changes greatly depending on the amount of strain. This makes it possible to know the magnitude of the measured pressure.

Since the diamond semiconductor film 48 has a large band gap of about 5.5 eV, it maintains its semiconductor properties and operates well even at high temperatures of 500° C. or higher. According to the pressure detector of the present invention using a strain gauge made of such a semiconductor film, engine cylinder pressure can be directly detected.

[Example] In FIG. 4, the cylindrical hanging 1 of the pressure detector has a mounting screw portion 11 on the outer periphery of the lower end portion 11 with a small diameter.
a is formed, and the outer periphery of the intermediate portion 12 is a hexagonal surface for screwing. A connector 2 is fixed to the upper opening of the housing 1 by caulking. Housing 1
A sensing body 3 is provided within the lower end portion 11 of the sensor. The sensing body 1 is a stainless steel cylinder with one end closed and forms a pressure chamber P. The large diameter flange 31 at the closed end is brought into contact with the stepped surface of the inner periphery of the housing 1, and its opening is connected to the lower end of the housing 1. It is located.

The center of the flange portion 31 of the sensing body 3 is made thin and serves as a diaphragm 311. A semiconductor strain gauge 4 whose structure will be described later is provided on the upper surface of the diaphragm 311. Flange part 3
A ceramic substrate 5 is provided in a recess on the outer periphery of the substrate 5. A conductive paste is printed and fired on the upper surface of the substrate 5 to form a signal extraction electrode (not shown), and a metal post 51 is connected to the extraction electrode. has been erected. Then, the semiconductor strain gauge 4 and the extraction electrode of the substrate 5 are connected with a gold wire 52,
The metal post 51 is connected to the pin 21 of the connector 2 by a lead wire 53.

As shown in FIG. 2, the strain gauge 4 is composed of four strain gauges 4A, 4B, 4C, and 4D, and each of the strain gauges 4A to 4D has the same structure. The strain gauges 4A and 4B have electrodes 41 and 42, respectively, and are connected to each other by a common electrode 43. In addition, the strain gauges 4C and 4D each have an electrode 4
4 and 45, and are connected to each other by a common electrode 46. Each of the electrodes 41 to 46 has wires 52A, 52B, 52C, 52D,
52E and 52F are connected, and eventually the strain gauge 4
A to 4D constitute a bridge circuit as shown in FIG.

Here, the strain gauges 4A and 4B are connected to the diaphragm 3.
11 (FIG. 2), and its resistance value changes greatly depending on the amount of strain on the diaphragm 311. On the other hand, the remaining strain gauges 4C and 4D are not affected by the distortion of the diaphragm 311, so their resistance values do not change. Thus, the terminal T in FIG.
When power is supplied between terminals T3 and T2, an output signal corresponding to the amount of distortion of the diaphragm 311 is obtained between terminals T3 and T4.

The structure of the strain gauge 4B is shown in FIG. In the figure, 47 is a diamond single crystal plate, and on the entire surface of the single crystal plate 47 there is boron B as an impurity.
A P-type diamond semiconductor film 48 is formed. Each of the electrodes 4 is provided at both ends of the semiconductor film 48.
2 and 43 are formed, and these electrodes 42 and 43 are
It is constructed by laminating metal films of titanium 61, platinum 62, and gold 63 in order from the side in contact with the semiconductor film 48. Further, on the entire lower surface of the diamond single crystal plate 47, titanium 61 and platinum 6 are sequentially applied from the side in contact with this.
2. Each metal film of gold 63 is formed, and the gold film 6
3 is joined to the diaphragm 311 made of stainless steel using a brazing material 49. Other strain gauges 4
A, 4C, and 4D also have the same structure as above, and each has a diaphragm 311 and other flange parts 3.
It is joined on 1.

Each of the strain gauges 4A to 4D described above is manufactured as follows. That is, the diamond single crystal plate 47 is placed in a microwave CVD apparatus, and a mixed gas of methane (CH ₄ ), hydrogen, and a small amount (0.1 to 100 ppm) of diborane (B ₂ H ₆ ) is supplied thereto. The mixed gas is decomposed and excited by microwaves (2450MHz in this example) to become plasma, and the single crystal plate 4
7, a diamond semiconductor film 48 containing boron is deposited and grown. After that, the semiconductor film 48
The metal films 61 to 63 are sequentially formed on the upper surface and the lower surface of the single crystal plate 47 by vapor deposition or sputtering. Note that each of the wires 52A to 52F can be easily connected to the gold film 63 of each electrode 41 to 46 by wire bonding or the like.

The pressure sensor having the above structure is attached to the engine cylinder wall by the threaded portion 1a of the housing 1. Therefore, the cylinder pressure is applied to the diaphragm 311 through the cylinder of the sensing body 3,
Transform this. As the diaphragm 311 deforms, the resistance values of the strain gauges 4A and 4B change greatly, and a pressure signal is obtained between the terminals T3 and T4 (FIG. 3).

Such a pressure detector operates normally even in a high temperature atmosphere of approximately 500°C. This means that the band gap of Si, which is conventionally used in semiconductor strain gauges, is approximately 1.1 eV, whereas that of diamond is approximately 5.5 eV.
This is because it is extremely large and does not lose its semiconductor properties even at high temperatures.

By the way, the coefficient of thermal expansion of diamond is approximately 2.3×
10 ^-6 /°C (at 100°C), which is extremely small, and in an atmosphere with large temperature changes, bonding between the diamond single crystal plate 47 and the diamond semiconductor film 48 constituting the strain gauge and other metals becomes a problem.
Here, in the strain gauge, the metallization on the single crystal plate 47 and the semiconductor film 48 is made of titanium, which has a coefficient of thermal expansion that increases sequentially from these sides.
This is done with three layers of platinum and gold to maintain consistency in thermal expansion, thereby preventing the strain gauge from being destroyed due to rapid heating, such as when starting an engine. By the way, the coefficient of thermal expansion of titanium, platinum, and gold is 8.8 each.
×10 ^-6 /℃, 9.1× ^{10 -6} /℃, 14.2 ^{×10 -6} /℃
(at 100℃).

Furthermore, the diamond single crystal plate 47 has extremely high thermal conductivity and also extremely high electrical insulation. Therefore, the steam strain gauge corresponds to the SOI structure in Si semiconductors, and in this respect is also advantageous for high-temperature use.

The diamond semiconductor film 48 can also be formed by introducing boron into the upper surface of the diamond single crystal plate 47 by thermal diffusion or ion implantation, as shown in FIG.

All of the semiconductor strain gauges 4A to 4D may be formed on a single-chip diamond single crystal plate 47. This is shown in FIGS. 6 and 7. In the figure,
The single-crystal plate 47 has a size that almost covers the center of the flange portion 31 of the sensing body 3, and a meandering linear diamond semiconductor film 48 is formed on the single-crystal plate 47 to form strain gauges 4A to 4A, respectively.
4D is configured. Each strain gauge 4A to 4D
are connected to each other via electrodes 41, 42, 43, and 44, forming a bridge circuit as described above. Each of the electrodes 41 to 44 has a three-layer structure including a titanium film 61, a platinum film 62, and a gold film 63, as in the above embodiment. The semiconductor film 48 is formed by microwave CVD while masking areas other than the film forming portion.

When the diaphragm 311 is deformed by the introduced pressure, the strain gauges 4A and 4B located directly above the diaphragm 311 are distorted, their resistance values change, and a pressure signal is obtained. Such a structure also provides the same effects as those of the above embodiments. In this structure, the degree of freedom in arranging the strain gauges 4A to 4D is restricted compared to the above embodiments, but the manufacturing process is simplified.

It should be noted that the diamond semiconductor film 48 in each of the above embodiments is made by adding phosphorus to diamond, for example.
It may also be doped with n-type semiconductor.

Metal films of titanium, platinum, and gold can be produced by mixing each metal powder with a solvent such as terpionelle to form a paste, printing a pattern on the paste, and then firing it in a hydrogen, nitrogen, or water vapor atmosphere. It can also be formed by a method such as thermal spraying.

In the three-layer metal film described above, the platinum film can be omitted when the pressure detector is used at a relatively low temperature (approximately 400° C.). Further, the electrode does not necessarily have to have a three-layer structure, and only a titanium film may be used, but the above-mentioned three-layer structure with a gold film as the outermost layer is preferable in order to easily connect wires.

As described above, since the pressure detector of the present invention is constructed using a diamond semiconductor strain gauge, it can be used satisfactorily in a high-temperature atmosphere, and is particularly suitable for detecting engine cylinder pressure.

[Brief explanation of the drawing]

1 to 4 show one embodiment of the present invention, FIG. 1 is a sectional view of a strain gauge, and FIG.
2 is an overall plan view of the strain gauge, FIG. 3 is a connection diagram of each strain gauge, FIG. 4 is an overall sectional view of the pressure detector, and FIG. 5 is another embodiment of the present invention. 6 and 7 show still other embodiments of the present invention, FIG. 6 is an overall plan view of the strain gauge, and FIG. 7 is a cross-sectional view of the strain gauge shown in FIG. FIG. DESCRIPTION OF SYMBOLS 1... Housing, 2... Connector, 3... Sensing body, 31... Flange part, 311...
...Diaphragm, 4, 4A, 4B, 4C, 4D...
...Strain gauge, 41, 42, 43, 44, 45, 4
6... Electrode, 47... Diamond single crystal plate, 4
8...Diamond semiconductor film, 49...Brazing material,
52, 52A, 52B, 52C, 52D, 52
E, 52F...Wire, 61...Titanium film, 62
...Platinum film, 63...Gold film, P...Pressure chamber.

Claims (1)

[Claims] 1. A cylindrical housing that protrudes into the measurement atmosphere, a pressure chamber into which measurement pressure is introduced is formed within the housing, and a part of the wall of the pressure chamber is adapted to change the measurement pressure. In a pressure sensor comprising a diaphragm that deforms according to the strain of the diaphragm and a strain gauge that emits an output signal according to the strain of the diaphragm, the strain gauge is formed by forming a diamond semiconductor film on a diamond single crystal plate. A pressure detector characterized in that it is configured by: 2. The pressure sensor according to claim 1, wherein the diamond semiconductor film is formed by depositing a mixed gas plasma of methane, hydrogen, and diborane (B ₂ H ₆ ) on the diamond single crystal plate. 3. The pressure sensor according to claim 1, wherein the diamond semiconductor film is formed by introducing boron into the diamond single crystal plate by thermal diffusion or ion implantation. 4. The pressure sensor according to claim 1, wherein the diamond single crystal plate is joined to the metal diaphragm through titanium, platinum, and gold metal films sequentially laminated from the single crystal plate side. . 5. The pressure sensor according to claim 1, wherein metal films of titanium, platinum, and gold are sequentially stacked on the diamond semiconductor film from the semiconductor film side to form electrodes.