JP2005069685A - Pressure sensor integrated with pressure receiving pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor integrated with a pressure receiving pipe which shows a stable output without requiring temperature compensation even in an especially high temperature condition. <P>SOLUTION: This pressure sensor integrated with the pressure receiving pipe equipped with the pressure receiving pipe, and a pressure receiving pipe diaphragm is constituted so that a strain sensor element comprising a compound thin film having a composition formula (1) Cr<SB>1-(A+B)</SB>Si<SB>A</SB>C<SB>B</SB>(1) (In the formula, A is 0.01-0.9, B is 0.01-0.9, and A+B≤0.9) is formed on the diaphragm surface through a silicon oxide thin film and/or silicon nitride thin film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pressure receiving pipe integrated pressure sensor.
[0002]
[Prior art]
In recent years, a diffusion type pressure sensor using a strain resistance change of a semiconductor Si single crystal has been widely used. This sensor has advantages such as high sensitivity, temperature dependence can be corrected by a monolithically manufactured IC, and a large amount of small sensors can be manufactured by an IC process, so that it is relatively inexpensive. However, when the sensor of this structure is used as a high pressure sensor of about 500 kg / cm ² or more, there is a problem that peeling occurs at a connection portion between Si as a sensor portion and a support base for introducing fluid pressure into the sensor. Occur.
[0003]
Current high-pressure pressure sensors are largely divided into a “displacement type” that reads the amount of displacement of the pressure receiving device that balances the measured pressure, and a “strain type” that reads changes in physical properties due to strain induced in the sensor material by pressure as electrical signals. Can be separated.
[0004]
More specifically, the displacement type is a device that reads the displacement of a Bourdon tube, bellows, diaphragm, etc., and is suitable for high pressure measurement, but the device itself becomes large, so there is a need to reduce the size of the sensor. Does not match.
[0005]
On the other hand, the strain type is mainly a method of measuring the deformation of the diaphragm using a strain sensor. This type of apparatus can be miniaturized and has the advantage that the measurement circuit is simple because it measures strain resistance. In relation to this technique, for example, Patent Document 1 discloses a semiconductor sensing element that can be used as a semiconductor strain sensing element, a high-temperature semiconductor pressure sensor, or the like. Specifically, in a semiconductor type sensing element in which a silicon carbide thin film made of an organic silicon raw material is formed on an insulating substrate and detects a change in electric resistance value of the silicon carbide thin film, the silicon carbide thin film is 5 mol% in the film. A semiconductor-type sensing element containing 30 mol% or less of oxygen atoms is disclosed. However, as described above, because of high sensitivity, a pressure sensor using semiconductor Si, which has been widely used in recent years, has a drawback that the joint between the sensor and the pressure receiving tube cannot sufficiently withstand high pressure.
[0006]
On the other hand, a device with a metal strain gauge (sensor) bonded to a diaphragm (pressure receiving part) does not have such problems, so it is suitable for high-pressure sensors and has the advantage of low temperature dependence. I have. Conventionally, this type of device has a low output, and the adhesion state between the sensor and the diaphragm has a great influence on the element characteristics, so that the element characteristics are not sufficiently reproducible. A compact pressure sensor integrated with a pressure-receiving pipe and improved in element characteristic reproducibility has been disclosed. Specifically, the cited reference 2 discloses a pressure receiving pipe integrated pressure sensor including a pressure receiving pipe and a pressure receiving pipe diaphragm, in which a strain sensor element made of a chromium oxide thin film is formed on the diaphragm surface via a silicon oxide thin film. An integrated pressure sensor is disclosed.
[0007]
However, a pressure sensor integrated with a pressure receiving tube in which a strain sensor element made of a chromium oxide thin film is formed has a temperature dependency at 150 ° C. or higher, particularly 250 ° C. or higher, and therefore needs to be temperature compensated. There is also a decrease in output. In recent years, the development of a pressure sensor that can measure pressure easily and stably even under high temperature conditions is desired due to the need for fuel pressure control of internal combustion engines such as automobile engines and pressure control of industrial machinery used at high temperatures. It is rare. In other words, it is expected to develop an improved pressure sensor integrated with a pressure-receiving tube that does not require temperature compensation even under high temperature conditions and can exhibit a stable output.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-195792 [0009]
[Patent Document 2]
Japanese Patent Application Laid-Open No. 7-335911
[Problems to be solved by the invention]
A main object of the present invention is to provide a pressure receiving pipe integrated pressure sensor that does not require temperature compensation even under a high temperature condition and can exhibit a stable output.
[0011]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventor has formed a strain sensor element comprising a specific compound thin film on the surface of the pressure-receiving tube diaphragm via a silicon oxide thin film and / or a silicon nitride thin film. The present inventors have found that the above object can be achieved and have completed the present invention.
[0012]
That is, the present invention relates to the following pressure sensor integrated pressure sensor.
1. In a pressure receiving pipe integrated pressure sensor having a pressure receiving pipe and a pressure receiving pipe diaphragm, the following composition formula (1) is applied to the diaphragm surface via a silicon oxide thin film and / or a silicon nitride thin film.
_{Cr 1- (A + B) Si} A C B (1)
[In formula, A is 0.01-0.9, B is 0.01-0.9: However, it is A + B <= 0.9]
A pressure sensor integrated with a pressure receiving tube, wherein a strain sensor element comprising a compound thin film represented by the formula (1) is formed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The pressure sensor integrated with a pressure receiving pipe of the present invention (hereinafter also referred to as “pressure sensor”) has the following composition formula (1) via a silicon oxide thin film and / or a silicon nitride thin film on the diaphragm surface.
_{Cr 1- (A + B) Si} A C B (1)
[In formula, A is 0.01-0.9, B is 0.01-0.9: However, it is A + B <= 0.9]
The strain sensor element which consists of a compound thin film shown by these is formed.
[0014]
In the composition formula (1), A may be 0.01 to 0.9, preferably about 0.1 to 0.7, and more preferably about 0.2 to 0.4. Although B should just be 0.01-0.9, about 0.1-0.7 are preferable and about 0.2-0.4 are more preferable.
[0015]
In the composition formula (1), the concentration of SiC with respect to Cr is preferably about 20 to 90 mol%, and more preferably about 40 to 80 mol%. More specifically, the concentration of Si with respect to Cr is preferably about 10 to 70 mol%, and more preferably about 20 to 40 mol%. The concentration of C relative to Cr is preferably about 10 to 70 mol%, and more preferably about 20 to 40 mol%.
[0016]
FIG. 1 shows a range represented by the composition formula (1), a preferable range, and a more preferable range as a ternary diagram regarding the concentrations of Cr, Si and C.
The strain sensor element comprising the compound thin film represented by the composition formula (1) is formed on the diaphragm surface via a silicon oxide thin film and / or a silicon nitride thin film (insulating layer). By using such a strain sensor element, a pressure sensor having a stable output can be obtained even under a high temperature condition of 350 to 400 ° C. That is, the pressure receiving pipe integrated pressure sensor of the present invention using such a strain sensor element exhibits a stable output without temperature compensation even under the above high temperature conditions.
[0017]
The strain sensor element may be formed directly on the silicon oxide thin film or the silicon nitride thin film as the insulating layer, or may be formed on the silicon oxide thin film after the silicon nitride thin film is formed thereon. In the latter case, the silicon nitride thin film serves as a protective layer (stress relaxation layer) for the silicon oxide thin film. Furthermore, the strain sensor element may be formed after the silicon oxide thin film is formed on the silicon nitride thin film. As the protective layer, in addition to the silicon nitride thin film, a thin film made of AlN, Al ₂ O ₃ , TiAlN, ZrAlN, ZrO ₂ , DLC, or the like can be used. Although the thickness of a protective layer is not specifically limited, Usually, about 0.5-1 micrometer, Preferably it is about 0.6-0.8 micrometer.
[0018]
On the strain sensor element, an Au / Ni layer (laminated film), a Pt / Ni layer (laminated film) or the like can be laminated as an electrode layer. A protective layer (sensor protective layer) may be further provided on the electrode layer. Examples of the sensor protective layer include a layer made of Si ₃ N ₄ , AlN, Al ₂ O ₃ , TiAlN, ZrAlN, ZrO ₂ , and DLC. Although the thickness of these sensor protective layers is not particularly limited, it is usually about 0.5 to 1 μm, preferably about 0.6 to 0.8 μm.
[0019]
A cross-sectional view showing one embodiment of the pressure sensor of the present invention is shown in FIG. In FIG. 2, a strain sensor element comprising an SiO ₂ layer 3 as an insulating layer, an Si ₃ N ₄ layer 4 as a stress relaxation layer, and a compound thin film represented by the composition formula (1) on the surface of the diaphragm 2 of the pressure receiving tube 1. 5, an Au / Ni laminated film 6 as an electrode layer, and an Si ₃ N ₄ layer 7 as a sensor protective layer are laminated in order.
[0020]
Hereinafter, a method for forming each layer in the pressure sensor of the present invention will be described as an example.
[0021]
The SiO ₂ layer which is an insulating layer can be formed by, for example, a sputtering method (RF method) using SiO ₂ as a target. Although the sputtering atmosphere is not particularly limited, for example, an Ar—O ₂ mixed gas is preferable. Although the pressure of mixed gas is not specifically limited, Usually, about 2-6 * 10 < ^-1 > Pa is preferable. The sputtering power output is about 350 to 1000 W, preferably about 800 to 900 W. The film thickness is not particularly limited, but is usually 1 to 3 μm, preferably about 1 to 2 μm. Although the substrate temperature at the time of film-forming is not specifically limited, Usually, about 350-400 degreeC is preferable.
[0022]
For example, if the stress relaxation layer is Si ₃ N _4, it can be formed by sputtering (RF method) in an Ar / N ₂ mixed gas using Si as a target. Although the pressure of mixed gas is not specifically limited, Usually, about 5-7 * 10 < ^-1 > Pa is preferable. The power output of sputtering is about 350 to 1000 W, preferably about 800 to 900 W. The film thickness is not particularly limited, but is usually 0.5 to 1 μm, preferably about 0.6 to 0.8 μm. Although the substrate temperature at the time of film-forming is not specifically limited, Usually, about 350-400 degreeC is preferable. The same conditions can be adopted when the stress relaxation layer made of the other material is formed using another target material, but may be individually adjusted as necessary.
[0023]
The strain sensor element portion can be produced by RF sputtering from a CrSiC target, for example. By changing the concentration of Si and C in the CrSiC target to be used, the concentration of Cr, Si and C contained in the strain sensor element can be adjusted to a desired value. The sputtering atmosphere is not particularly limited, but an Ar atmosphere is particularly preferable. Although the pressure of atmospheric gas is not specifically limited, Usually, about 2-5 * 10 < ^-1 > Pa is preferable. The power output of sputtering is preferably 350 to 600W. The film thickness is not particularly limited, but is usually about 0.1 to 0.5 μm, preferably about 0.2 to 0.4 μm. Although the substrate temperature at the time of film-forming is not specifically limited, Usually, about 350-400 degreeC is preferable.
[0024]
For example, if the electrode layer is an Au / Ni laminated film, it can be formed by first forming a Ni film by a sputtering method (RF method) and then forming Au by a sputtering method (DC method). As an atmosphere, Ar gas is preferable. Although the pressure of Ar gas is not specifically limited, Usually, about 2-6 * 10 < ^-1 > Pa is preferable. The power output of sputtering is about 350 to 1000 W, preferably about 800 to 900 W. The film thickness is not particularly limited, but the Ni film is usually 1 to 3 μm, preferably about 1 to 2 μm. The Au film is usually about 0.5 to 1 μm, preferably about 0.6 to 0.8 μm. Although the substrate temperature at the time of film-forming is not specifically limited, Usually, about 350-400 degreeC is preferable.
[0025]
In the step of forming each of the above layers, it is preferable to clean the target surface by performing pre-sputtering with Ar gas prior to sputtering.
[0026]
Contrast with the prior art As the strain sensor element part of the pressure sensor, the resistance temperature differential coefficient (TCR) is relatively small like metal, and the gauge factor (change due to resistance strain) is large like Si. A thin film material having a large electric resistance is most desirable. TCR is a temperature differential coefficient of electric resistance, and indicates a slope at a measured temperature.
TCR = (1 / R) dR / dT
[R is electrical resistance, T is temperature, unit is ppm / K].
[0027]
Conventionally, as a sensor element for a pressure sensor using a thin film material, a pressure sensor using an amorphous Si (or microcrystalline Si) thin film has been developed (for example, Toshio Honma: Sensor Technology, Vol. 5, No. 3). P30-36 (1985)). Although this sensor has a large gauge factor and a high specific resistance, it has the disadvantages that amorphous Si has a large resistance temperature differential coefficient. In addition, the production requires highly controlled silane utilization equipment and expensive clean room facilities, and since explosive silane gas and toxic doping gas are used, strict caution is required during operation. It is.
[0028]
On the other hand, the compound thin film represented by the composition formula (1) in the present invention has all of the above conditions required for the sensor element portion, and can be manufactured safely and relatively easily.
[0029]
The pressure sensor of the present invention is particularly useful as a high-temperature pressure sensor that exhibits a stable output without temperature compensation even under a high temperature condition of 350 to 400 ° C. Of course, it is useful not only as a high-temperature pressure sensor but also as a low-temperature pressure sensor.
[0030]
【The invention's effect】
According to the pressure sensor of the present invention, a stable output can be exhibited and temperature measurement can be easily performed without temperature compensation under a high temperature condition of room temperature to about 400 ° C., particularly 350 to 400 ° C. Moreover, since it is a pressure sensor integrated with a pressure receiving tube, it is small, has a high output voltage, and is excellent in linearity.
[0031]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the examples.
[0032]
Example 1
A SiO ₂ thin film (about 1.5 μm) was formed on a pressure-sensitive tube diaphragm made of SUS630 by sputtering, and then a strain sensor element (about 300 nm) made of a CrSiC thin film was formed. The SiC content in the strain sensor element is divided into 10 mol% (Cr _0.9 Si _0.05 C _0.05 ), 20 mol%, 30 mol%, 40 mol%, 50 mol%, and 60 mol%. Produced.
[0033]
With respect to the above six types of pressure sensors, the relationship between the SiC amount and the TCR with respect to the input power was examined. The result is shown in FIG. The input power is the wattage of RF power applied to the target.
[0034]
From the results of FIG. 3, it can be seen that as the SiC content increases, the TCR decreases and the temperature dependence decreases.
[0035]
FIG. 4 shows temperature drift measurement data when the pressure is 0 KPa (no pressurization) for the six types of pressure sensors. From the results of FIG. 4, it can be seen that as the SiC content increases, the temperature drift decreases and the temperature drift becomes the smallest in the range of 40 to 60 mol%.
[0036]
FIG. 5 shows temperature drift measurement data for the above six types of pressure sensors when the pressure is 500 KPa. From the result of FIG. 5, it can be seen that as the SiC content increases, the temperature drift decreases, and the temperature drift becomes the smallest in the range of 40 to 60 mol% as in FIG.
[0037]
FIG. 6 shows the relationship between pressure and sensor output for the pressure sensor of the present invention. From the results of FIG. 6, it can be seen that all the data are linearly related to the output, and a good sensor output is obtained.
[Brief description of the drawings]
FIG. 1 shows a range represented by the composition formula (1), a preferred range, and a more preferred range as a ternary diagram regarding the concentrations of Cr, Si and C in a compound thin film in the present invention.
FIG. 2 is a cross-sectional view showing an outline of a pressure receiving pipe integrated pressure sensor of the present invention.
FIG. 3 is a graph showing the relationship between SiC content relative to Cr and TCR.
FIG. 4 is a graph showing temperature drift measurement data with respect to SiC content when the pressure is 0 KPa (no pressurization).
FIG. 5 is a graph showing temperature drift measurement data with respect to SiC content when the pressure is 500 KPa.
FIG. 6 is a graph showing the relationship between pressure and sensor output.
[Explanation of symbols]
1 ... pressure pipe 2 ... diaphragm 3 ... SiO ₂ (insulating layer)
4 ... Si ₃ N ₄ (stress relaxation layer)
5 ... CrSiC thin film (strain sensor element)
6 ... Ni / Au laminated film (electrode layer)
7 ... Si ₃ N ₄ (sensor protective layer)

Claims (1)

In a pressure receiving pipe integrated pressure sensor having a pressure receiving pipe and a pressure receiving pipe diaphragm, the following composition formula (1) is applied to the diaphragm surface via a silicon oxide thin film and / or a silicon nitride thin film.
_{Cr 1- (A + B) Si} A C B (1)
[In formula, A is 0.01-0.9, B is 0.01-0.9: However, it is A + B <= 0.9]
A pressure sensor integrated with a pressure receiving tube, wherein a strain sensor element comprising a compound thin film represented by the formula (1) is formed.

Images