JPS61106772A - Pressure sensitive element - Google Patents

Abstract

PURPOSE:To obtain a pressure sensitive element which can be used even at the time of a high temperature and also is excellent in both stability and sensitivity by forming an Si3N4 thin film on a conductive substrate which contacts tightly the end face of a cylindrical body leg part, and forming a Ge pressure sensitive film and a corrosion- resistant fetching electrode on the upper face of its central part. CONSTITUTION:On the back of a conductive substrate 1 consisting of Ti a cylindrical body leg part 3 whose end face 4 has been brought into tight contact is provided as one boy or so as to be separable. Also, an Si3N4 thin film 2 is formed to about 1mum on said substrate 1 by a plasma chemical vapor-depositing method. Subsequently, on the surface side of a part contacting a space in the cylindrical leg part 3 in the center part on said Si3N4 thin film 2 and a part of a position corresponding to between said center part and the leg part end face 4, Ge pressure-sensitive films 6, 7 of about 1mum thick, and fetching electrodes 8, 8' and 9, 9' made of a corrosion resistance metal such as Ti, stainless steel, etc., or an alloy, which are connected to the films are provided. In this way, a pressure sensitive element which can measure electrically the deformation quantity of said pressure sensitive film 6, 7 parts caused by a pressure from the space 5, as the variation quantity of a resistance value is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure sensitive element. More specifically, the present invention relates to a pressure sensitive element that can provide high precision and high reliability even under harsh environmental conditions.

[Conventional technology]

In recent years, various plants in the chemical, steel, water and sewage industries, etc. require sophisticated control, and improving the accuracy and reliability of detection ends has become a major issue in instrumentation. These demands are also increasing in the field of pressure transducers, which are most commonly used in the various plants mentioned above. Currently, the pressure-sensitive elements of pressure transducers commonly used are Si diaphragm pressure sensors. However, since the thickness of the pressure-receiving part is approximately several tens of micrometers, this type is used exclusively for vacuum or low pressure applications, and is currently hardly used for high pressure applications.

The pressure-sensitive element of the conventionally used high-pressure pressure transducer is
This method measures pressure by bonding a strain gauge to a diaphragm, but because it uses adhesive, it cannot be used at high temperatures, is unstable, and the strain gauge uses a metal film. It has drawbacks such as poor sensitivity.

[Problem that the invention seeks to solve]

In view of these circumstances, the inventor of the present invention has conducted various studies in search of a pressure-sensitive element for use in high-pressure pressure transducers that can be used even at high temperatures and has excellent stability and sensitivity. It has been found that a structure having the following structure can solve all of the above problems.

[Means to solve all problems]

Therefore, the present invention relates to a pressure-sensitive element, in which a silicon nitride thin film is formed on a conductive substrate with which the end face of the cylindrical body leg is brought into close contact with the back side, and a silicon nitride thin film is formed at the center of the silicon nitride thin film. A germanium pressure-sensitive film connected to an extraction electrode made of a corrosion-resistant metal or alloy is formed on the portion and the portion corresponding to the end surface of the leg, and pressure is applied from the space inside the leg of the back side cylindrical body. The amount of deformation of the pressure-sensitive membrane portion can be electrically measured as the amount of change in resistance value.

1 and 2 of the drawings are a plan view and a sectional view taken along the line ■-■ of one embodiment of the pressure-sensitive element according to the present invention, and in this embodiment, the cylindrical body leg is attached to the substrate material on the back side of the substrate. It is integrally formed from the same material.

Conductive substrate 1 (4,5X 4.5X O,05MI
(The dimensions below X i are an example) are made of a metal plate having a thickness that can exhibit elastic deformation, and titanium thin plates are particularly superior to stainless steel plates in terms of light weight and high strength. On this conductive substrate, a silicon nitride thin film 2 (thickness 1 μm) t-1 is formed as an insulating thin film, preferably by plasma chemical vapor deposition. Other materials such as silicon oxide and polyimide resin are often used as the insulating thin film, but the former is sensitive to humidity, and the latter has problems with heat resistance. On the other hand, silicon nitride thin films produced by plasma chemical vapor deposition not only have excellent moisture resistance and heat resistance, but also have good corrosion resistance such as acid resistance and alkali resistance. Furthermore, with regard to insulation, which is an important factor, the volume resistivity of plasma-enhanced chemical vapor deposited silicon nitride is 1015Ω.
・It is α or more, and silicon oxide (10”~・1014Ω・
C1n) or polyimide resin (1014~101sΩ・c
superior to rn).

On this silicon nitride thin film, there is a thick film made of the same material as the substrate material on the central part and the part corresponding to the position between it and the leg end surface 4 of the cylindrical body 3, in other words, on the back side of the conductive substrate. A germanium pressure-sensitive film (thickness: 1 μm) 5 and 7 is entirely formed on the front side of the portion in contact with the cylindrical space (diameter: 3 mm) 5 formed by chemical etching of the plate material. This germanium pressure-sensitive film has a gauge factor (G) of 30, which is more than an order of magnitude larger than that of a metal film, and a temperature coefficient of resistance (TOR) as small as 200 ppm/°C. Therefore, the value of TCR/G is also 7.
It is better than that of metal film by about 10%.

These germanium pressure-sensitive membranes have an extraction electrode (1 ltm thick) made of a corrosion-resistant metal or alloy such as titanium, stainless steel, or Hastelloy C, which has good corrosion resistance and improves reliability. 8' and 9°9' are connected, respectively.

[Effect]

As shown in Figures 3 and 4, measurement using such a pressure-sensitive element is carried out by measuring the total resistance value of the rhombus-shaped portion of the germanium pressure-sensitive film by applying pressure from the space inside the leg of the cylindrical body on the back side of the conductive substrate. This is done by electrically measuring the amount of change.

The bottom part of the cylindrical body leg has a base 11 having a cylindrical space 10.
The germanium pressure-sensitive film is fixed 12 on the top by adhesive, welding, etc., and when pressure is applied from this space side, each germanium pressure-sensitive film is deformed to the tension side or compression side, and the resistance of each pressure-sensitive film at this time is '1fr:
R, and R2, and as shown in FIG. 4, when the entire circuit is assembled with a standard resistor R6, the output is expressed by the following equation.

In other words, compressive strain (R2) results in an increase in resistance, and tensile strain (R1) results in a decrease in resistance, and a single directly proportional straight line is formed there, so the change in output is greatly amplified. If we determine the relationship between this output and pressure in advance,
Pressure conversion is possible from this output value.

Note that in this illustrated embodiment, the cylindrical body legs are integrally formed on the back side of the substrate, but in cases where the cylindrical body legs are not used at high temperatures, the cylindrical body legs can be formed so as to be separable on the back side of the substrate. let me,
It can also be used by bonding the end face of the cylindrical body leg to the back surface of the substrate.

〔Effect of the invention〕

The pressure-sensitive element of the present invention uses a plasma chemical vapor deposited silicon nitride thin film as an insulating film, so it has excellent voltage resistance, moisture resistance, and stability, and also uses a germanium thin film as a pressure-sensitive film. As a result of using a thin titanium plate for the pressure receiving plate and forming a pressure sensitive film directly through an insulating film, (1) No creep, (2) Can be used at high temperatures, (3) Excellent stability, (
4) Can be used for high pressure measurement).

[Brief explanation of drawings]

1 and 2 are a plan view and a sectional view taken along line H--H of one embodiment of a pressure-sensitive element according to the present invention. FIG. 3 is a schematic diagram showing a measurement situation using this pressure sensitive element. Further, FIG. 4 is a circuit diagram for measuring the amount of deformation of the pressure-sensitive membrane portion as the amount of change in the total resistance value. (Explanation of symbols) 1... Conductive substrate 2... Silicon nitride thin film 3... Cylindrical body leg 4... Leg end surface 5. ... Leg internal space 6.7 ... Germanium pressure sensitive membrane 8.9 ...
・・Takeout electrode

Claims (1)

[Claims] 1. A silicon nitride thin film is formed on a conductive substrate that brings the end face of the cylindrical body leg into close contact with the back side, and a central portion on the silicon nitride thin film and the connection between it and the end face of the leg are formed. A germanium pressure-sensitive film connected to an extraction electrode made of a corrosion-resistant metal or alloy is formed at a position corresponding to the gap, and the amount of deformation of the pressure-sensitive film part due to pressure applied from the inner space of the leg of the back side cylindrical body is controlled. A pressure-sensitive element that can be electrically measured as the amount of change in resistance. 2. The pressure-sensitive element according to claim 1, wherein the cylindrical body leg is integrally formed on the back side of the substrate. 3. The pressure-sensitive element according to claim 1, wherein the cylindrical body leg portion is separably formed on the back side of the substrate. 4. Claim 1 in which the conductive substrate is a titanium thin plate
Pressure-sensitive element described in section. 5. The pressure sensitive element according to claim 1, wherein the silicon nitride thin film is formed by plasma chemical vapor deposition.