KR940002511B1 - Gas sensor element of tin oxide film - Google Patents

Abstract

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Description

[Name of invention]

Tin oxide thin film gas sensor element

[Brief Description of Drawings]

1, 4 to 9 and 25 are X-ray diffraction diagrams of a tin oxide thin film semiconductor layer formed by an embodiment of the present invention.

10 to 13 and 24 are the same X-ray diffraction diagram according to the comparative example.

2 is a schematic cross-sectional view showing an example of a gas sensor element according to the present invention.

3, 14 to 19 and 26 are graphs showing the gas detection capability of the gas sensor element according to the embodiment of the present invention.

20 to 23 are graphs showing the gas detection capability of the gas sensor according to the comparative example.

Each number in FIG. 2 represents the following structural part.

* Explanation of symbols for main parts of the drawings

1 silicon wafer 3 SiO ₂ insulating layer

5: tin oxide thin film layer 7: platinum electrode

Detailed description of the invention

[Technical Field]

The present invention relates to a gas sensor device having a tin oxide thin film having semiconductor characteristics.

[Background]

The semiconductor gas sensor currently used is mainly manufactured by sintering. However, since the manufacturing method by sintering is complicated and contains various fluctuation factors which will influence the performance of a product, it cannot be said that it is satisfactory in the point of reliability, stability, durability, etc. of a product. Moreover, since the product by sintering cannot make a dimension below fixed, there exists a fault which is low in sensitivity. Therefore, development of thin-film semiconductor sensors has been promoted in place of sintered products, but there is no practical alternative to sintered products.

One reason why thin-film semiconductor sensors are difficult to use in practice is that thin-film semiconductor sensors are generally very good in hydrogen detection capability but hardly detect methane.

Therefore, for example, a method of oxidizing a substrate made of silicon to form an insulating film made of SiO ₂ and forming a SnO ₂ film doped with Pt thereon (Japanese Patent Laid-Open No. 54-24094), Although a method of doping P or B to a silicon substrate on which a SiO ₂ insulating film is formed (Japanese Patent Laid-Open No. 57-17849) and the like has been proposed, it is difficult to uniformly dopant atoms to be doped. No effect was obtained.

[Initiation of invention]

The inventors have conducted various experiments and studies in consideration of the phenomenon of the above technique, and as a result of deposition, at least one of metal powder and tin oxide is used under specific conditions by physical vapor deposition (PVD) or chemical vapor deposition (CVD). When the deposition layer is formed on the substrate, a thin film having a specific crystallographic orientation with respect to an interface to be in contact with the gas phase is formed. The obtained thin film is not only hydrogen but also hydrocarbons such as methane, ethane, propane, butane, oxygen, and the like. It has been found to exhibit excellent properties as a sensor of vapor phase components.

That is, this invention provides the gas sensor element shown next.

In the tin oxide thin film gas sensor element, the strongest diffraction ray intensity in the case of X-ray diffraction when the crystal orientation and crystallinity of the gas detection surface are CuK as the source is set to I ₁ , and the second, third, fourth and fifth When the second strongest diffraction line intensity is I ₂ , I ₃ , I ₄ and I ₅ ,

(a) The line strength of the (211) plane or (110) plane is the strongest, I ₂ / I ₁ ≤ 0.6, and the half width of I ₁ is 0.58 or more,

(b) I ₁ is the line strength of the (110) plane or (101) plane, and I ₁ is the line strength of the (101) plane or the (110) plane, where I ₂ / I ₁ ≥0.5, I ₃ / I ₂ <0.6, and the half width of I ₁ is greater than or equal to 0.54,

(c) I ₁ is the line strength of the (110) plane or (211) plane, and I ₂ is the line strength of the (101) plane or the (110) plane, where I ₂ / I ₁ ≥0.5, I ₃ / I ₂ <0.6, and the half width of I ₁ is greater than or equal to 0.58,

(d) I ₁ , I ₂ and I ₃ are the line strengths of any of the (110), (101) and (211) planes, respectively, where I ₃ / I ₁ ≥0.5, I ₄ / I ₅ <0.6 And if the half width of I ₁ is greater than or equal to 0.61,

(e) I ₁ , I ₂ , I ₃ and I ₄ are the line strengths of any of the (301) planes of the (110) plane, (101) plane and (211) plane, respectively, where I ₄ / I ₁ ≥0.5 , I ₅ / I ₄ <0.6, and the half width of I ₁ is not less than 0.73,

(f) I ₁ is the line strength of the (301) plane, and I ₂ / I ₁ ≤ 0.60, and the half width of I ₁ is 0.6 or more,

(g) I ₁ is the line strength of the (211) plane or (301) plane, and I ₂ is the line strength of the (301) plane or the (211) plane, where I ₂ / I ₁ ≥0.5, I ₃ / I Tin oxide thin film gas sensor element, characterized in that ₂ <0.6, and the half width of I ₁ is 0.3 or more.

As the substrate of the gas sensor of the present invention, a silicon substrate, a ceramic substrate, a glass substrate, or the like is used. When using a silicon substrate, and its surface to form an insulating layer of SiO ₂ by a conventional method. A tin oxide layer is formed as a thin film semiconductor layer on a substrate. In order for the tin oxide layer to exhibit its characteristics as a semiconductor, some oxygen atoms disappeared from the complete oxide. That is, it is necessary to take the form which has a lattice defect. The presence of such lattice defects is confirmed by measuring the conductivity.

In the case of SiO ₂ having a lattice defect, the plane orientations of the crystals involved in gas detection are (110), (101), (211), and (301), which are slightly different in the relationship between the plane orientation and the selectivity of the gas to be detected. An example is schematically shown in Table 1.

TABLE 1

In the crystal of the tin oxide thin film semiconductor layer in the sensor of the present invention, the half width of the strongest diffraction line (I ₁ ) by the diffraction spectrum of X-rays using the CuK ray as a source is 80% or more of the experimental value, and the number of plane orientations Among the plurality of diffraction lines that appear, one of the conditions (a) to (g) must be satisfied. If the half width of I ₁ is less than the above-mentioned value, the crystal and the particle diameter become large, so the sensitivity is lowered and cannot be used as a sensor.

The gas sensor element of this invention is manufactured as follows, for example. First, an oxide insulating layer of SiO ₂ or the like is formed on the surface of silicon or the like of a substrate according to a conventional method, and then a tin oxide thin film semiconductor layer is formed by PVD or CVD. The conditions during the deposition operation can vary greatly depending on the material of the substrate, the type of metal tin and tin oxide as the deposition material source, the deposition method, and the like. 0 to 500 ° C, distance between the target and the substrate 1 to 500 mm, inert gas atmosphere gas pressure 1 × 10 ^-1 to 1 × 10 ^-4 torr, such as Ar, He, N ₂ , oxygen partial pressure in the atmosphere gas 0 ~ 1 × 10 ^-3 Torr, applied voltage 10 ~ 200V, high frequency output is about 100W ~ 10Hz. In particular, when using metal tin as the evaporation material source, the oxygen partial pressure in the atmosphere gas is set to 1 × 10 ⁻⁵ to 1 × 10 ⁻³ Torr. Moreover, it is preferable to make the ratio of the inert gas and oxygen in atmospheric gas into the latter 1-2 mol with respect to 10 mol of former electrons. When the ratio of oxygen is too small, oxygen in the thin film is insufficient to form SnO _2. On the other hand, when the ratio of oxygen is too large, lattice defects are reduced, so that the conductivity is too low to be used as a sensor.

When the temperature of the substrate exceeds 500 ° C, the crystal grain diameter becomes coarse and the gas detection ability is lowered. In addition, coarsening of the crystal grains causes a decrease in the half width so that it is easily checked. If the other conditions are out of the above-described range, the thin film cannot be formed, or crystals having a specific plane orientation cannot be produced and thus have no gas detection capability.

As the evaporation material source, metal tin and tin oxide are used. The gas sensor element of the present invention formed by vapor deposition can increase its stability and durability by annealing again, if necessary. The annealing treatment is performed by, for example, holding at 500 ° C. for about 4 hours in a dry air atmosphere.

When using the element of this invention as a gas sensor, what is necessary is just to form a platinum electrode, for example, on a thin film semiconductor layer by a conventional method, and to connect a predetermined lead wire.

According to the present invention, the following effects are achieved.

(1) A thin film semiconductor gas sensor is obtained without requiring a doping step. The gas sensor obtained has not only hydrogen but also the detection ability of hydrocarbons, such as methane, and oxygen. Moreover, the gas sensitivity is extremely high and a small amount of gas can also be detected.

(2) The manufacturing process is simple as compared with the case of sintering.

(3) As compared with the case of sintering, the element which has uniform performance is obtained.

(4) Since the obtained device is superior in mechanical strength to the device by the sintering method, the sensor characteristics do not easily change even during long-term use.

EXAMPLE

EXAMPLES Hereinafter, the present invention will be made clearer by way of examples.

Example 1

A silicon wafer (2 mm x 3 mm) as a substrate was heated at 1000 DEG C for 2 hours in an atmosphere containing oxygen and water vapor to form an SiO ₂ insulating layer on the surface, and then a parallel plate type high frequency magnetron sputtering device was provided. Using the SnO ₂ sintered compact as a target material, a vapor deposition operation was performed. The conditions at the time of vapor deposition are as following Table 2.

TABLE 2

The X-ray diffraction diagram of the thus obtained tin oxide thin film 140 'is shown in FIG. It is apparent that the intensity of diffraction lines corresponding to the alignment surface 211 is particularly large.

The platinum electrode (thickness about 1 micrometer) was formed in the vapor deposition thin film formation obtained above by sputtering, and the gas sensor element shown in FIG. 2 was obtained. In Fig. 2, reference numeral 1 denotes a silicon wafer, 3 denotes a SiO ₂ insulating layer, 5 denotes a tin oxide thin film layer, and 7 denotes a platinum electrode.

Subsequently, the gas sensor element is installed in a cell in an electric furnace, annealing is performed at 500 ° C. for 4 hours while flowing dry air, followed by (a) dry air, (b) dry air containing methane, or ( C) The dry resistance containing hydrogen was flowed, and the electrical resistance between electrodes at each temperature was measured. The results are as shown in FIG. As apparent from FIG. 3, it is clear that the gas sensor of the present invention not only has hydrogen detection capability, but also methane detection capability at 400 ° C or higher.

And in the graph which showed the result of FIG. 3 and the following each Example, each curve shows the result with respect to the next gas, respectively. Curve I…. Dry air, curve (II)... Dry air containing 0.35% methane, curve (III)... Dry air containing 0.1% hydrogen, curve (IV)... Dry air containing 0.35% hydrogen, curve (V)... Dry air containing 0.1% methane.

[Examples 2-8 and Comparative Examples 1-4]

A tin oxide thin film was formed on a substrate in the same manner as in Example 1 except that vapor deposition was carried out under the conditions shown in Table 3, and then a gas sensor device was obtained.

In Table 3, the intensity ratio with respect to the peak intensity and the highest peak intensity of each rotating surface corresponding to each orientation surface is shown together. The X-ray diffraction diagrams of the obtained tin oxide thin films are shown in FIGS. 4 to 13 and 25. Moreover, the characteristic of each obtained gas sensor is shown to FIG. 14 thru | or FIG. 23, and FIG.

TABLE 3a

As apparent from the results shown in FIG. 3, FIG. 14 to FIG. 23 and FIG. 26, the gas sensor element of the present invention is excellent in the detection capability of methane and hydrogen.

[Comparative Example 5]

According to the comparative example 1, the tin oxide thin film was formed on the board | substrate, and the gas sensor element was obtained. The X-ray diffraction diagram (with CuK rays as a source) of the obtained tin oxide thin film is as shown in FIG. 24, and has a single strong line intensity on the (200) plane.

Using the obtained gas sensor element, various gas detection tests were carried out in the same manner as in Example 1, but since the sensitivity to gas was not exhibited, it was found that it could not be used for practical use.

Claims (1)

In the tin oxide thin film gas sensor, the strongest diffraction line intensity in the case of X-ray diffraction when the crystal orientation and crystallinity of the gas detection surface are CuK as a source is set to I ₁ , and the second, third, fourth and fifth When the strong diffraction line intensity is set to I ₂ , I ₃ , I ₄ and I ₅ , (a) the line strength of the (211) plane or the (110) plane is the strongest, and I ₂ / I ₁ ≤ 0.6, and If the half width of I ₁ is 0.58 or more, (b) I ₁ is the line strength of the (110) plane or (101) plane, and I ₂ is the line strength of the (101) plane or (110) plane, and I ₂ / I ₁ ≥0.5, I ₃ / I ₂ <0.6, and the half width of I ₁ is not less than 0.54, (c) I ₁ is the line strength of (110) or (211) plane, and I ₂ is (101 (I) I ₂ / I ₁ ≥0.5, I ₃ / I ₂ <0.6, and the half width of I ₁ is not less than 0.58, or (d) I ₁ , I ₂ and I ₃ It is as any one of the line intensity of the surface, (101) plane and (211) plane, respectively _{(110), I 3 / I} 1 ≥0.5, I 4 / I 3 <0.6 High, and whether this full width at half maximum of the I ₁ at least 0.6, (e), I _1, I _2, I ₃ and I ₄ are each (110) plane, (101) plane, (211) plane and (301) any one of the surface As the line strength of I ₄ / I ₁ ≥0.5, I ₅ / I ₄ <0.6, and the half width of I ₁ is 0.73 or more, or (f) I ₁ is the line strength of the (301) plane, I ₂ / I ₁ ≤ 0.6, and the half width of I ₁ is not less than 0.60, (g) I ₁ is the line strength of (211) plane or (301) plane, and I ₂ is of (301) plane or (211) plane. A tin oxide thin film gas sensor element as a line strength, wherein I ₂ / I ₁ ≥0.5, I ₃ / I ₂ <0.6, and a half width of I ₁ is 0.3 or more.

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