JP2838361B2 - Pressure sensor integrated pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor integrated with a pressure receiving tube.

[0002]

2. Description of the Related Art In recent years, a diffusion type pressure sensor utilizing a change in strain resistance of a semiconductor Si single crystal has been widely used. This sensor has advantages such as high sensitivity, temperature dependency can be corrected by a monolithically manufactured IC, and relatively small cost because a large number of small sensors can be manufactured by an IC process. However, when the sensor having this structure is used as a high-pressure sensor of about 500 kg / cm ² or more, there is a problem that separation occurs at a connection portion between Si as a sensor portion and a support for introducing fluid pressure to the sensor. Occurs.

[0003] The current high pressure sensor has a "displacement type" for reading the displacement of a pressure receiving device which balances with a measured pressure.
It can be broadly classified into a "strain type" in which a change in physical properties due to strain induced in a sensor material by pressure is read as an electric signal.

More specifically, the displacement type is a device of a type for reading the displacement of a Bourdon tube, a bellows, a diaphragm, etc., and is suitable for high pressure measurement. Does not meet the requirement.

On the other hand, the mainstream of the strain formula is a method of measuring the deformation of the diaphragm using a strain sensor. This type of apparatus has the advantages that the size can be reduced and the measurement circuit is simple because the strain resistance is measured.

However, as described above, the 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 because of its high sensitivity. is there. On the other hand, a device in which a metal strain gauge (sensor) is adhered to a diaphragm (pressure receiving portion) does not have such a problem, so that it is suitable for a high-pressure sensor and has the advantage of low temperature dependency. Have. However, in this type of device, the output is small, and the state of adhesion between the sensor and the diaphragm has a great effect on the device characteristics. Therefore, it is difficult to produce a device having excellent characteristics reproducibility.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pressure sensor which is small in size and excellent in reproducibility of element characteristics.

[0008]

The present inventor has conducted intensive studies in view of the above-mentioned state of the art, and as a result, has found that chromium oxide and crystalline chromium are mixed on the surface of the diaphragm of the pressure receiving tube. It has been found that a pressure sensor having a small size and excellent in reproducibility of element characteristics can be obtained when a strain sensor element composed of is formed.

That is, the present invention provides the following pressure sensor; In a pressure sensor integrated with a pressure receiving tube having a pressure receiving tube and a pressure receiving tube diaphragm, a strain sensor element made of chromium oxide mixed with chromium oxide and crystalline chromium is formed on the surface of the diaphragm via a silicon oxide thin film. Pressure sensor integrated pressure sensor.

The sensor element of the pressure sensor has a relatively small temperature coefficient of resistance (TCR), such as metal,
A thin film material having a large gauge factor and a large electric resistance as described above is most desirable.

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, Vol. N
o.3, p30-36 (1985)). Although this sensor has a large gauge factor (change in resistance due to strain) and a high specific resistance, amorphous Si has a drawback that the temperature coefficient of resistance is large. In addition, its production requires highly controlled silane utilization equipment and expensive plasma CVD or photo-CVD equipment, and requires strict attention to the operation using toxic silane gas.

On the other hand, the chromium oxide thin film used in the present invention satisfies all of the above-mentioned conditions required for the sensor element portion, and its manufacture is safe and relatively easy.

[0013] The pressure sensor integrated with a pressure receiving tube according to the present invention comprises:
FIG. 1 has a structure schematically shown as a cross-sectional view. FIG.
In the pressure sensor shown in FIG.
A chromium oxide thin film 7 is formed on the surface of the substrate through a silicon oxide thin film 5. The structure of this pressure sensor is similar to that of a known pressure sensor having an amorphous Si (or microcrystalline Si) thin film except that the sensor element is formed of a chromium oxide thin film in which chromium oxide and crystalline chromium are mixed. There is no difference.

The formation of the chromium oxide thin film as the sensor element is not particularly limited, but is usually performed as follows.

That is, after a silicon oxide thin film is formed on the surface of a diaphragm of a pressure receiving tube integrated pressure sensor by a CVD method, a chromium oxide thin film is formed by a sputtering method using metal Cr (preferably 99.99% or more) as a target. Form a film. Prior to sputtering, it is preferable to perform pre-sputtering with Ar gas to clean the target surface, and then introduce oxygen at the same partial pressure as when forming the chromium oxide thin film to perform pre-sputtering. During film formation, the diaphragm may be heated to, for example, about 350 ° C. The oxygen partial pressure during film formation is usually about 3 × 10 ^{−3 to} 6 × 10 ⁻⁴ torr.

The pressure sensor according to the present invention is useful not only as a high pressure sensor but also as a low pressure sensor.

[0017]

According to the present invention, a pressure sensor integrated with a pressure receiving tube having a chromium oxide thin film having a small temperature coefficient of resistance, a large gauge factor, and a resistance similar to that of a semiconductor can be obtained.

This pressure sensor has a high output voltage and is excellent in linearity.

[0019]

EXAMPLES Experimental examples and examples are shown below to further clarify the features of the present invention.

In the following, the specific resistance was measured by a four-terminal method. The change in resistance due to pressure was measured at a measurement pressure of 5 kg / cm ² using a device of a type that applies pressure to the diaphragm by hydraulic pressure.

Experimental Example 1 A CV was placed on a SUS316 substrate (10 × 10 × 1 mm ³ ).
A SiO ₂ thin film (about 500 nm) is formed by the method D, and a Cr thin film or a CrO _x thin film (about 160 nm) is formed thereon by a DC sputtering method using 99.99% metallic Cr as a target.
nm). Prior to the deposition of chromium oxide, A
After pre-sputtering was performed for 15 minutes with r gas to clean the target surface, oxygen gas was further introduced at the same partial pressure as CrO _x film formation (however, oxygen was not introduced during Cr film formation) to form a film. Pre-sputter under the same conditions as for 10 minutes,
Next, a CrO _x film was formed.

Table 1 shows the conditions for forming the CrO _x film.

[0023]

[Table 1]

In a Cr thin film formed at an oxygen partial pressure of 0 Torr (oxygen-free state), the pressure change rate of resistance (ΔR / R) is small and the specific resistance is small, so that a pressure sensor having desired performance cannot be obtained. It has been found.

Therefore, a CrO _x thin film was formed under the introduction of oxygen gas. FIG. 2 shows the C fabricated without heating the substrate.
4 shows the oxygen gas partial pressure dependency of the resistance of the rO _x thin film. When the DC input power is 80 W, even if the oxygen partial pressure is changed, 5 × 1
The resistance does not change so much up to 0 ^-4 Torr, but the resistance becomes infinite at an oxygen partial pressure of 6 × 10 ^-4 Torr,
An insulator is formed. When the DC input power is 160 watts, the resistance tends to slightly increase as the oxygen partial pressure increases, but the specific resistance sharply increases at 8 × 10 ⁻⁴ Torr.

FIG. 3 shows a CrO _x thin film produced under the same film forming conditions as shown in FIG.
4 shows the oxygen partial pressure dependency of / R. The value indicated by the arrow on the left end is a value for a Cr thin film manufactured without introducing oxygen. It is clear from the results shown in FIG. 3 that the value of ΔR / R increases as the oxygen partial pressure increases. The TCR (temperature coefficient of resistance) when the value of ΔR / R was the maximum was 500 ppm.

When the substrate is heated, the oxidation is further promoted,
It is considered that the oxidation effect starts to appear from a low oxygen partial pressure, and the change in resistance and the change in strain resistance due to the oxygen partial pressure become moderate. Also, the higher the substrate temperature, the better the adhesion between the film and the substrate.

FIG. 4 shows the oxygen partial pressure dependence of the resistance of a CrO _x thin film produced in the same manner as above with the substrate temperature set at 350 ° C. For example, DC input power is 240 w
In the case of (1), the specific resistance starts to slightly increase at an oxygen partial pressure of 6 × 10 ⁻⁴ Torr, and an insulator is formed at 7 × 10 ⁻⁴ Torr,
The tendency of the resistance as a whole to depend on the oxygen partial pressure is almost the same as that when the film is formed without heating the substrate (see FIG. 2).

FIG. 5 shows the oxygen partial pressure dependence of ΔR / R of a CrO _x thin film produced under the same film forming conditions as those shown in connection with FIG. As in the case where the film was formed without heating the substrate, ΔR / R
Increased to 1.2 × 10 ^-3 at an oxygen partial pressure of 6 × 10 ^-4 Torr. This value is almost the same as the value of the pressure sensor using the Si single crystal. FIG. 6 shows the C thus produced.
4 shows the oxygen partial pressure dependence of the TCR for an rO _x thin film.
When the oxygen partial pressure is increased, it can be seen that the TCR decreases. At an oxygen partial pressure of 6 × 10 ^-4 Torr, TCR50
Extremely low values of ppm were obtained. 5 and 6
It is clear from the results shown in (1) that a CrO _x thin film having a large resistance change rate due to pressure and a small TCR was obtained.

Experimental Example 2 From the results shown in Experimental Example 1, it was clarified that a highly sensitive pressure sensor element could be obtained by introducing oxygen to form a CrO _x thin film. To examine the structure, analysis by ESCA was performed. Almost the same results were obtained regardless of the substrate temperature.
FIG. 7 shows only the result at 50 ° C.

When the oxygen partial pressure is 0, a peak of only Cr appears. When the oxygen partial pressure was 1 × 10 ⁻³ Torr, only the amorphous CrO _x insulator was formed.

On the other hand, the oxygen partial pressure is 3 × 10 ^-4 to 8 × 1
In the range of 0 ^-4 Torr, crystalline Cr (crystal grain size of 50 to 10
0 Angstrom) and amorphous CrO
_x (about 1 ≦ x ≦ 2) was obtained as a chromium oxide thin film.

Example 1 CV was placed on a pressure receiving tube diaphragm of a pressure receiving tube made of SUS630.
A silicon oxide thin film (approximately 500 nm) is formed by the method D, a chromium oxide thin film (approximately 500 nm) is formed, and then a thin line pattern having a width of approximately 45 μm is etched by a photolithography method. A sensor element having a circuit was formed. The outline is
As shown in FIG. The conditions for forming the chromium oxide thin film are as follows:
Substrate temperature 350 ° C., oxygen partial pressure 4.5 × 10 ⁻⁴ Torr to 7.
It was 5 × 10 ⁻⁴ Torr.

Similar to a normal Si pressure sensor, the circuit was adjusted so that 4 mA could be output at a pressure of 0 and 20 mA at a full pressure.

The change in the sensor output with respect to the pressure was as shown in FIG. The working pressure range varies depending on the diameter of the pressure receiving tube and the thickness of the diaphragm. For example, when the diameter of the pressure receiving tube is 6 mm, the thickness is 0.5 mm for 5 kg / cm ² .
For 25 mm and 20 kg / cm ² , thickness 0.5 mm, 1
The thickness was 0.75 mm for 00 kg / cm ² .

As shown in FIG. 8, the pressure sensor according to the present invention shows a linear output with respect to the pressure. The maximum deviation from linearity was 0.1% or less.

In order to measure a higher pressure, the thickness of the diaphragm may be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an outline of a pressure receiving tube integrated pressure sensor according to the present invention.

FIG. 2 is a graph showing the oxygen gas partial pressure dependence of the resistance of a CrO _x thin film manufactured without heating a substrate.

FIG. 3 is a graph showing the oxygen partial pressure dependence of ΔR / R of a CrO _x thin film produced without heating a substrate.

FIG. 4 is a graph showing the oxygen partial pressure dependence of ΔR / R of a CrO _x thin film manufactured at a substrate temperature of 350 ° C.

FIG. 5 is a graph showing the oxygen partial pressure dependence of the resistance of a CrO _x thin film manufactured at a substrate temperature of 350 ° C.

FIG. 6 is a graph showing the oxygen partial pressure dependence of the TCR of a CrO _x thin film manufactured at a substrate temperature of 350 ° C.

FIG. 7 is a graph showing a structural analysis of a CrO _x thin film by ESCA.

FIG. 8 is a graph showing the relationship between the pressure and the output of the pressure sensor according to the present invention obtained in the first embodiment.

[Explanation of symbols]

1 ... receiving tube 3 ... diaphragm 5 ... SiO ₂ film 7 ... CrO _x film

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Takenaka 2-4 Chaya-cho, Kita-ku, Osaka-shi, Osaka Inside Nihon Linearx Co., Ltd. (56) References JP-A-5-13782 (JP, A) JP-A 2-152201 (JP, A) JP-A-2-76201 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 29/84 G01L 9/04 101 H01C 7/00

Claims (1)

(57) [Claims] 1. A pressure sensor integrated with a pressure receiving tube having a pressure receiving tube and a pressure receiving tube diaphragm, wherein a strain sensor element made of chromium oxide in which chromium oxide and crystalline chromium are mixed is formed on the surface of the diaphragm via a silicon oxide thin film. A pressure sensor integrated with a pressure receiving tube.