JP3350458B2 - Gas sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for measuring a gas using a thin film made of an oxide semiconductor to perform qualitative and quantitative measurements, and in particular, to quantitatively determine an amine-based gas using a thin film mainly composed of tungsten oxide. The present invention relates to a gas sensor that operates. Such an amine-based gas sensor can be used, for example, for a bad odor gas monitor, particularly for a biological decay odor monitor and a human odor monitor, and is also used for a deodorizer, an air conditioner, a ventilation fan, etc. equipped with such a bad odor gas monitor sensor. can do.

[0002]

2. Description of the Related Art A gas sensor using an oxide semiconductor measures a change in electrical characteristics of the oxide semiconductor caused by attachment of a measurement target component contained in air or a supplied sample gas to the oxide semiconductor. It is. As a gas sensor using an oxide semiconductor, for example, a gas sensor provided with titanium oxide in a gas sensor and quantifying trimethylamine (hereinafter abbreviated as TMA) has been studied (Sensors and Ac).
tuators B, 10 (1993) 229-234, ibid. 235-239, ibid. 1
3-14 (1993) 623-624). TMA is known as a representative component of the odor of fish and shellfish, and a gas sensor for detecting TMA is used for monitoring the freshness of fish.

[0003]

When the gas sensor is used as a fish freshness monitor, there is no problem even if the sensitivity is about several hundred ppm. However, when used as a bad smell gas monitor, it is about the same as human smell, that is, 20-
It is necessary to detect TMA at a regulation value level of 70 ppb and 5 to 20 ppb in other regions. Accordingly, an object of the present invention is to improve the sensitivity of a gas sensor using an oxide semiconductor to an amine-based gas.

[0004]

A gas sensor according to the present invention comprises:
A thin film made of an oxide semiconductor is provided between electrodes formed on an insulating substrate, and an amine-based gas is measured by a change in electrical characteristics of the thin film between the electrodes when a component to be measured in the gas is attached to the thin film A gas sensor in which indium oxide, tin oxide, or antimony oxide is mixed with tungsten oxide as a thin film thereof is used.

[0005] Instead of using tin oxide, which has conventionally been used as a main material of an oxide semiconductor, tungsten oxide, which is empirically determined to be highly sensitive to a compound containing nitrogen, was selected as the main material. By mixing indium oxide, tin oxide or antimony oxide into tungsten oxide, high sensitivity to amine-based gas could be achieved. The mixing ratio of indium oxide or the like to tungsten oxide is preferably 0.5 to 5 wt%. The reason is as follows. Usually, the amount required for the additive to cover only one layer of the main oxide is 5 wt% of the main oxide.
%, But in this case we have
Experiments have confirmed that 0.5 to 5 wt% is preferable.

According to the method of manufacturing a gas sensor of the present invention, a thin film made of an oxide semiconductor is provided between electrodes formed on an insulating substrate, and the thin film formed between the electrodes when a component to be measured in a gas adheres to the thin film. A method for manufacturing a gas sensor that measures an amine-based gas by changing electrical characteristics.After forming electrodes on an insulating substrate, a tungsten oxide is formed on a region including between the electrodes by a physical film formation method in a vacuum. In this method, a thin film of indium oxide, tin oxide or antimony oxide is formed on a tungsten oxide thin film by a physical film forming method, and then the formed thin film is crystallized by firing. .

[0007] Through the above steps, tungsten oxide can be crystallized on the insulating substrate, and indium oxide, tin oxide or antimony oxide can be present on the surface and grain boundaries of the tungsten oxide thin film and dispersed throughout the thin film. Between the step of forming a tungsten oxide thin film and the step of forming a thin film of indium oxide or the like, it is preferable to form the film continuously without breaking the vacuum used for the physical film formation method. The reason is that once the vacuum is broken, unnecessary oxidation is caused to cause deterioration of characteristics, and deterioration due to adhesion of impurities in the air is considered.

[0008]

FIG. 1 is a plan view showing one embodiment. thickness
Is a silicon oxide film on the surface of the silicon substrate
From one end on a 2 mm × 15 mm insulating substrate 1 on which
In a region of 3 mm, a pair of gold electrodes 3 has a line width of 5 μm and a line interval.
It is formed in a comb shape of 5 μm. The pair of gold electrodes 3
The gold terminals 5 formed on the insulating substrate 1 and the gold terminals 5
An ohmmeter (not shown) through each of the connected gold wires 7
It is connected to the. On the upper surface of the gold electrode 3, the entire gold electrode 3
So that tungsten trioxide (WO _Three) The main material
A thin film 9 is formed. The thin film 9 is an opposite electrode
Electrical characteristics of the thin film 9 existing between the electrodes 3 and 3 and between the electrodes 3 and 3
Is measured. The thin film 9 is made of, for example, indium trioxide.
(In_TwoO_Three) Is mixed at a compounding ratio of about 1 wt%.

Next, the manufacturing method of this embodiment will be described.
A silicon oxide film is formed on the surface of a silicon substrate having a thickness of about 0.4 mm to form an insulating substrate. After forming the gold electrode 3 and the gold terminal 5 on the insulating substrate, the insulating substrate 1 was cut into a strip of 2 mm × 15 mm as shown in FIG. On the gold electrode 3 of the insulating substrate 1, WO _{3 is formed} to a thickness of, for example, 200 nm using an electron beam evaporation apparatus in a vacuum of 5 × 10 ⁻⁵ torr. Target material used is WO ₃ sintered body, the deposition rate from 0.1 to 0.
2 nm / sec.

Subsequently, In ₂ O ₃ as a second component oxide is formed to a thickness of, for example, 2 nm on the previously formed WO ₃ film without breaking the vacuum of the electron beam evaporation apparatus. The target material used was an In ₂ O ₃ sintered body, and the deposition rate was 0.2 nm / sec. Compounding ratio of In ₂ O ₃ with respect to WO ₃ in the thin film 9 is about 1.0 wt%. Next, baking was performed in air at 450 ° C. for 3 hours to crystallize the formed thin film.

A WO ₃ -based thin film to which In ₂ O ₃ , stannic oxide (SnO ₂ ), or antimony pentoxide (Sb ₂ O ₅ ) is added as a second component oxide is an amorphous thin film which is not fired after vapor deposition. However, it was crystallized by firing at 450 ° C. for 3 hours. It is considered that the thin film 9 is formed by dispersing In ₂ O ₃ throughout the WO ₃ film. To confirm this, X-ray diffraction measurement was performed.

[0012] Figure 2 is a WO ₃ film with the addition of SnO ₂ 4
It is an X-ray diffraction diagram after baking at 50 degreeC. (200), (201) in the figure
The peak is a diffraction peak attributed to triclinic WO ₃ ,
The (200) orientation was further enhanced as compared with the case of the non-added WO ₃ thin film to which the second component oxide was not added. Also, (20
0) No peak shift was observed, and no diffraction peak attributed to SnO ₂ was observed at all. From this, S
It is considered that nO ₂ does not form a solid solution in WO ₃ but exists on the surface and grain boundaries and is dispersed throughout the thin film. Almost the same diffraction pattern was obtained for the WO ₃ thin film to which In ₂ O ₃ or Sb ₂ O ₅ was added. The addition of the second component oxide strengthened the (200) orientation, and the second component oxide spread over the entire film. It turned out to be dispersed.

A heater was attached to this embodiment in a flow path of an apparatus through which air containing different concentrations of TMA could flow, and TMA sensitivity was measured. FIG.
Using this example, 5 ppm of T under a temperature condition of 350 ° C.
It is a figure showing the response curve when measuring MA. The vertical axis is output, and the horizontal axis is time (minutes). Resistance value in air is 3
× 10 ⁴ Ω, and the resistance value when TMA is supplied is 1
It was 25Ω. As a gas sensor using an oxide semiconductor, the response speed was fast, and the resistance value returned quickly when TMA was turned off. The resistance value returned to the initial value within 2 minutes. S in the figure is the sensitivity, and the resistance value in air (R
a) / (resistance value Rg in gas) The sensitivity here was 249.

In the same manner as in the above manufacturing method, the main material is W
SnO ₂ or S as the second component oxide of the thin film 9 of O ₃
Gas sensors containing b ₂ O ₅ at a blending ratio of about 1 wt% were prepared. FIG. 4 shows In ₂ O ₃ , SnO ₂ or Sb ₂ O ₅
FIG. 4 is a diagram showing resistance values at various operating temperatures in air of an embodiment provided with a WO ₃ thin film containing as a second component oxide. The vertical axis represents the resistance value (Ω), and the horizontal axis represents the temperature (° C.). These thin films have a thickness of several kΩ to several hundreds at each temperature.
It shows a resistance value of kΩ. Although illustration is omitted, Ra of the additive-free WO ₃ thin film is 400 to 600Ω and In ₂
By adding O ₃ , SnO ₂ or Sb ₂ O ₅ , Ra
Is increased.

FIG. 5 is a diagram showing the temperature dependence of the sensitivity of these examples to TMA having a concentration of 5 ppm. The vertical axis is sensitivity, and the horizontal axis is temperature (° C.). Although not shown, the sensitivity of the additive-free WO ₃ thin film is about 10 to 20, and it can be seen that the sensitivity increases by adding In ₂ O ₃ , SnO ₂ or Sb ₂ O ₅ . FIG. 6 is a diagram showing the concentration dependence of these examples on TMA. The vertical axis is sensitivity, and the horizontal axis is TMA concentration (ppm)
It is. It can be seen that these examples show high linearity over the concentration range of TMA from 0.01 to 5 ppm. The measurement was performed at a temperature of 400 ° C. in the example to which In ₂ O ₃ was added, and at 350 ° C. in the example to which SnO ₂ or Sb ₂ O ₅ was added.

FIG. 7 is a diagram showing a response curve when 10 ppb of TMA is measured at a temperature of 350 ° C. using an embodiment having a WO ₃ thin film containing SnO ₂ as a second component oxide. The vertical axis is output, and the horizontal axis is time (minutes).
The resistance value in air is 1.95 × 10 ⁵ Ω, and TMA
Was supplied, the resistance was 7.82 × 10 ⁴ Ω. As shown in the figure, a sensitivity of 2.5 is shown for TMA of 10 ppb.
It can be seen that the sensor can be a high-sensitivity sensor capable of detecting A.
Further, the 90% response time of the output is about 4 minutes, and the 90% recovery time is about 7 minutes, and it can be seen that the response time and the recovery time are considerably fast.

Although the present invention has been described above, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the invention described in the appended claims. Further, in these embodiments, the heater is attached later, but it is also possible to attach the heater on the back side or the front side of the substrate and integrate it with the sensor element. Furthermore, a composite sensor can be obtained by being mounted together with a gas sensor having sensitivity to gases other than TMA on the same substrate. For example, if it is mixed with a sulfur-based sensor, an amine-based and sulfur-based odor sensor can be obtained.

[0018]

According to the present invention, as a thin film of a gas sensor using an oxide semiconductor, WO ₃ is used as a main material, and In ₂ O ₃ , S
Since a material containing nO ₂ or Sb ₂ O ₅ as the second component oxide is used, the sensitivity to TMA can be improved.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an embodiment.

FIG. 2 is an X-ray diffraction diagram of a WO ₃ thin film to which SnO ₂ has been added after firing at 450 ° C.

FIG. 3 is a diagram showing a response curve when 5 ppm of TMA is measured under the temperature condition of 350 ° C. using the embodiment of FIG. 1;

FIG. 4 is a diagram illustrating resistance values at various operating temperatures in air of an embodiment including a WO ₃ thin film containing In ₂ O ₃ , SnO ₂ or Sb ₂ O ₅ as a second component oxide.

FIG. 5 is a diagram illustrating the temperature dependence of sensitivity to TMA having a concentration of 5 ppm in the same example.

FIG. 6 is a diagram showing the concentration dependency on TMA in the same example.

FIG. 7 shows an example in which a WO ₃ thin film including SnO ₂ as a second component oxide is used, and a temperature of 350 ° C. is used for 10 p.
It is a figure showing the response curve when measuring TMA of pb.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 3 Gold electrode 5 Gold terminal 7 Gold wire 9 Thin film

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-8-15195 (JP, A) JP-A-6-118043 (JP, A) JP-A-6-3330 (JP, A) JP-A-4- 29049 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/12

Claims (2)

(57) [Claims] A thin film made of an oxide semiconductor is provided between electrodes formed on an insulating substrate, and an amine is formed by a change in electrical characteristics of the thin film between the electrodes when a component to be measured in a gas adheres to the thin film. In the gas sensor for measuring a system gas, the thin film is an oxide composed of two components in which indium oxide, tin oxide or antimony oxide is mixed as a second component oxide with tungsten oxide as a main material. . 2. A thin film made of an oxide semiconductor is provided between electrodes formed on an insulating substrate, and an amine is formed by a change in electrical characteristics of the thin film between the electrodes when a component to be measured in a gas adheres to the thin film. In a method of manufacturing a gas sensor for measuring a system gas, after forming the electrode on an insulating substrate, a tungsten oxide thin film is formed on a region including between the electrodes by a physical film forming method in a vacuum, Forming a thin film of indium oxide, tin oxide or antimony oxide on the tungsten oxide thin film by a physical film forming method, and then firing and crystallizing the formed thin film. .