JPH0363538A - Pressure sensor - Google Patents

Abstract

PURPOSE:To allow the operation of the sensor in high-temp. environment by forming a diaphragm which senser the pressure of fluid of a diamond semiconductor film. CONSTITUTION:The diaphragm 3 which closes the aperture of a fluid introducing part 2 to be introduced with the high-temp. fluid is formed of the diamond semiconductor film 4 to constitute this pressure sensor 1. The diamond semiconductor film 4 is a film contg. a p type dopant or n type dopant in diamond. IIIb metal elements of the periodic table and/or the compds. thereof are usable as the p type dopant. The IIIb metal elements of the periodic table are exemplified by boron, aluminum, gallium, indium, thallium, etc., and the compds. of the IIIb metal elements of the periodic table are exemplified by a halide, hydride, ydroxide, oxide, carbide or nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure sensor. More specifically, the present invention relates to a high temperature pressure sensor that operates with good responsiveness even in high temperature environments.

[Prior art and problems to be solved by the invention] A conventional fluid pressure sensor uses Si in a diaphragm that senses gas pressure.
A thin plate of Ge or Ge is used. Since this thin plate has poor heat resistance, the fluid pressure sensor cannot be used in an environment of 100° C. or higher.

On the other hand, relatively recently, a diaphragm pressure sensor for living organisms has been proposed (Japanese Patent Laid-Open No. 62-1457
(See Publication No. 80).

However, since the pressure sensing element of this pressure sensor is an n-type silicon single crystal substrate, it is not suitable for measuring the pressure of a pressure medium at a high temperature of 100°C or higher. A crystal substrate and a protective layer formed on its surface! Since it is formed with a diamond thin film, which is an I film, the structure is complicated.

An object of the present invention is to provide a pressure sensor having a diaphragm with a simple configuration, and also to provide a novel pressure sensor that operates even in a high-temperature environment, particularly in an operating environment of 400°C or higher. It is in.

[Means for Solving the Problems] The present invention for solving the problems described above is a high-temperature pressure sensor characterized in that a diaphragm that senses fluid pressure is formed of a diamond semiconductor film.

The following is made by coating a Si substrate with a diamond S film.
The present invention will be explained in more detail.

A preferred embodiment of the pressure sensor of the present invention is shown in FIG.

As shown in FIG. 1, a pressure sensor 1 according to the present invention includes a diaphragm 3 formed of a diamond semiconductor film 4 for closing an opening of a fluid introduction section 2 into which high-temperature fluid is introduced.

The surface of this diamond semiconductor film 4 on the side opposite to the fluid introducing portion is lined with a substrate 6 having an opening 5 .

The opening 5 of the substrate 6 corresponds to the opening of the fluid introduction section 2. Therefore, the diaphragm 3 that is sensitive to the pressure of the fluid is formed only from this diamond semiconductor film 4.

Although the diamond semiconductor film 4 is exposed in a rectangular shape in FIG. 1, it is not limited to this shape, and various shapes such as a circle, an ellipse, and others can be adopted.

A piezoresistor 7 is connected to the four corners of the exposed surface of the diamond semiconductor film 4, and the piezoresistor 7 is connected to a resistance detection circuit 8 via a conductive scrap 9.

Next, each member forming the pressure sensor for unreleased IJ+ and the manufacture of the pressure sensor will be described in detail.

-Substrate- There is no particular restriction on the material of this substrate, as long as it has insulating properties and heat resistance, and a diamond semiconductor film can be formed on its surface, and it can be selected as appropriate depending on the purpose. I can do it.

As the substrate, for example, metal oxides, nitrides and carbides such as silicon, manganese, vanadium, thallium, aluminum, titanium, tungsten, molybdenum, germanium and chromium, AlzOz-Fe system, T
ic-Xi system, T ill knee Go system and 84C-F
Examples include e-based cermets and various ceramics.

Note that these substrates may be subjected to surface treatment or coating treatment to further improve the adhesion with the diamond semiconductor film formed by vapor phase synthesis, or may be coated with an insulating material such as alumina or silicon. A neutral intermediate layer may be provided, and by appropriately performing such a treatment, it is possible to further improve the V: adhesion between the diamond semiconductor film and the substrate.

There are no particular restrictions on the shape of the substrate, but it is usually flat.

1. Diamond Semiconductor Film - A diamond semiconductor film is a film containing a p-type dopant or an n-type dopant in diamond.

As the p-type dopant, at least one of the elements belonging to group mb of the periodic table and/or a compound thereof can be used.

Examples of elements belonging to group mb of the periodic table include boron, aluminum, gallium, indium, thallium, and the like.

Compounds of elements in the mb group of the periodic table include norogenides,
Mention may be made of hydrides, hydroxides, oxides, carbides or nitrides.

Specific examples of the compounds include B, A, Ga, In, Tl, B2 Hb, Ba
H+o.

CH Go BCC10, (CI(3) 2 A-view CU, [
CCHz) A sentence BT2] 2, [(CI(3) 3 AJII 2, Gaz
H6゜(CH3) 3 Ga, (CH3)2
Ga BHa, (CH3)31! l, (C
Examples include H3)3Tl.

A preferred p-type dopant in the present invention is B2 H6
, B4 HIO, CH3BCJ12.

In addition, in this invention, mbg of 1 periodic table, a simple substance of an element, and its compound may be used individually by 1 type, and 2 or more types may be used together.

As the n-type dopant, at least one of the Vb group elements of the periodic table and/or a compound thereof can be used.

Examples of the Vb group elements include nitrogen, phosphorus, arsenic, antimony, and bismuth.

As the compound of the Vb group element, for example, N2, N
H3, PH3, A5H3, N2 H4, CH3AsBr
2, CH3ASH2, (CH3)3As,
(CH3) 3Bi, C standing CH25bC sentence, CH3S
bH2, (CF3):+Sb, etc. can be mentioned.

A diamond semiconductor film can be formed as follows.

That is, when a gas in which a carbon source gas and the dopant are excited is brought into contact with the substrate, a diamond semiconductor film is formed on the surface of the substrate.

As the carbon source gas, gases such as various hydrocarbons, halogen-containing compounds, oxygen-containing compounds, and nitrogen-containing compounds can be used.

Examples of the hydrocarbon compound include paraffin hydrocarbons, olefin hydrocarbons, acetylene hydrocarbons, diolefin hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons.

Examples of oxygen-containing compounds include ketones, alcohols, ethers, ketones, aldehydes, organic acids, dihydric alcohols, -carbon oxide, and carbon dioxide.

Examples of nitrogen-containing compounds include amines.

In addition, as the carbon source gas, although not a single substance, class 4 dangerous substances stipulated in the Fire Service Act, class 1 petroleum, class 2 petroleum,
Gases such as 3rd class petroleum and 4th class petroleum can also be used. It is also possible to use a mixture of the various carbon compounds mentioned above.

Among these carbon source gases, paraffinic hydrocarbons, olefinic hydrocarbons, which have high gas or vapor pressure at room temperature,
Gases of oxygen-containing compounds such as ketones, alcohols, -carbon oxide, and carbon dioxide gas are preferred.

Further, if desired, a carrier gas such as hydrogen gas or inert gas may be used together with the carbon source gas.

The content ratio of the dopant in the carbon source gas is
The ratio of the dopant element to the carbon source gas [(dopant element)/C] is usually 10-8 to 1O, preferably 10-1 to 10-1. This ratio is 1O-8
If it is less than that, a diamond semiconductor film having sufficient electrical conductivity may not be formed.

On the other hand, if it exceeds 10-1, a homogeneous and good diamond film may not be obtained.

The means for exciting the carbon source gas and dopant is not particularly limited as long as it is a method that can form crystalline diamond by a vapor phase method, such as plasma decomposition method using direct current or alternating current arc discharge, high frequency A method of plasma decomposition using induced discharge, a method of plasma decomposition using microwave discharge (including a magnetic field-CVD method).

A method in which decomposition is performed using light energy, an ion beam method in which plasma decomposition is performed in an ion chamber or an ion gun, and ions are extracted by an electric field, and a thermal decomposition method in which thermal decomposition is performed by heating with a hot filament (including the EACVD method).
, a direct current discharge method, a combustion flame method, a sputtering method, etc. can be employed.

According to the excitation means, the reaction usually proceeds under the following conditions, and a diamond semiconductor film is formed on the substrate.

That is, since the temperature of the surface of the substrate varies depending on the excitation means for the carbon source gas, it cannot be determined generally, but it is usually room temperature to 1,200°C, preferably room temperature to 1,100°C. .

If the temperature is lower than room temperature, the deposition rate of the diamond semiconductor film will be slow or the homogeneity of the precipitate will be lost. On the other hand, even if the temperature is higher than 1.200° C., no commensurate effect will be achieved, which will be disadvantageous in terms of energy efficiency, and the formed diamond semiconductor film may be etched.

The reaction pressure is usually 10-6 to 10' torr, preferably 10-5 torr to 800 torr.

If the reaction pressure is lower than 10-6 torr, the deposition rate of the diamond semiconductor film may be slow or the diamond semiconductor film may not be deposited.

On the other hand, even if it is made higher than 103 torr, the corresponding effect may not be achieved.

In addition, the total flow rate of raw material gas including carbon source gas is usually
1-1.0009GCM, preferably lO-500sc
It is cyr.

The reaction time cannot be determined unconditionally because it varies depending on the temperature of the surface of the substrate, the reaction pressure, the required thickness of the diamond semiconductor film, etc.

After the diamond semiconductor film is thus formed on the substrate, the substrate is etched by masking to expose the diamond semiconductor film on the substrate side as shown in FIG.

The etching process involves placing a mask on the surface of the substrate,
This can be carried out by a wet etching method using immersion in an acid solution or a dry etching method using a mixed gas of carbon tetrafluoride gas and hydrogen gas.

By the etching method, the unmasked surface of the substrate is etched to expose the surface of the diamond semiconductor film.

In this way, a diaphragm is obtained in which a diamond semiconductor film is formed on the surface of the substrate having an opening.

Assembly of a Device - In the pressure sensor of the present invention, the diaphragm is mounted on the pressure sensor body such that the diamond semiconductor film exposed through the opening in the substrate contacts the high temperature pressure fluid.

In the device shown in FIG. 1, the diaphragm is installed so as to close the opening of the fluid introduction section into which high-temperature pressure fluid is introduced.

[Example] Next, the present invention will be explained in more detail by giving examples and comparative examples.

(Example 1) A diaphragm was manufactured as follows.

A high-resistance Si (100) substrate was placed in the reaction chamber of a microwave plasma CVD apparatus.

Next, 53% of CO gas was introduced into the reaction chamber as a raw material gas.
CCm, hydrogen gas at 81 scc+s, B2 H
6 gases (cylinder gas diluted to 120 ppm with hydrogen were used) were introduced at 14 sccm, the pressure in the reaction chamber was set to 50 Torr, and the Si substrate temperature was set to 300 Torr.
The microwave power was set to 500 W using a microwave power supply with a zero frequency of 2.45 GHz at 0°C.

When plasma treatment was performed for 6 hours under these conditions, Si
A diamond semiconductor film with a thickness of 10 gm could be formed on the substrate.

As a result of measuring the specific resistance of this diamond semiconductor film, it was found that 1
It was 0Ω/0 mouth.

Next, the surface of the St substrate in the laminate thus obtained was covered with a mask having a rectangular opening, and then C
Etching with a mixed gas of Fs and H2 was performed to shape the resistance detection portion, and dicing was performed to manufacture a diaphragm.

A pressure sensor was manufactured using this diaphragm.

Using this pressure sensor, 400℃, 1 kg/cm2
When the pressure of the gas was measured, a high accuracy of FS of ±1.5% was obtained.

A thermal shock test was conducted in which temperature environments were alternately repeated at room temperature (25°C) and 400°C. Repeat the above i,ooo
Figure 2 shows the results when the test was repeated.

Both had an accuracy of ±1.0% FS, indicating that this pressure sensor exhibits good and stable functionality even at high temperatures.

(Comparative Example 1) A conventional pressure sensor using a Si substrate or a Ge substrate for a diaphragm could not function as a sensor in an environment of 400°C.

[Effects of the Invention] The pressure sensor of the present invention uses a laminate plate coated with a diamond semiconductor film as a diaphragm, or uses a diamond semiconductor film as a diaphragm, so that: 4
It can fully perform its functions even in an environment of 00°C or higher, and will make an important contribution to, for example, the automobile industry.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional perspective view showing an example of a pressure sensor;
The figure shows s#Ya of a pressure sensor in one embodiment of the present invention.
It is a diagram showing a test. 1... Pressure sensor 3... Diaphragm, 4... Diamond semiconductor film. Funeral map Figure 2: Thermal shock

Claims (1)

[Claims] (1) A pressure sensor characterized in that a diaphragm that senses fluid pressure is formed of a diamond semiconductor film.