JPS588743B2 - Gas/humidity sensor - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a gas/humidity sensor that detects gas and moisture, and activates a conventional sensor formed of a metal oxide ultrafine particle film to make it more sensitive to gas. An improved gas/humidity sensor is provided.

It has been discovered that the resistance value of a film composed of ultrafine metal oxide particles with an average particle size of about 100 to 1000 particles changes sensitively to gases and water vapor, and a sensor using this film has been developed. Proposed.

The present invention can further improve the sensitivity of conventional ultrafine particle sensitive membrane sensors.

An embodiment of the present invention will be described below with reference to the drawings.

Figure 1A shows a plan view of the sensor according to the present invention and x-x'
FIG.

As shown in FIG. 1, the sensor of the present invention first includes a pair of electrodes 2 and 3 on an insulating substrate 1 made of glass or ceramics.
An ultrafine particle film 4 of a metal oxide semiconductor such as tin, titanium, zinc, or nickel is further formed thereon.

A palladium ultrafine particle film or a hybrid film 5 of palladium ultrafine particles and the metal oxide ultrafine particles is further formed thereon.

The sensor of the present invention is generally manufactured as follows.

For example, an example of manufacturing an ultrafine particle film using tin oxide as the metal oxide will be described with reference to FIG.

An insulating substrate 1 having electrodes 2 and 3 as shown in FIG. 1 is attached to a sample holder 12 in a vacuum evaporation apparatus 11 so that the electrode surface faces downward in the drawing.

The evaporation boat 13 also includes Sn, evaporation material 14,
Set either SnO or SnO2.

Further, a palladium evaporation material 16 is set in the evaporation boat 15 disposed close to the evaporation boat 13.

After that, the vacuum pump (not shown in the drawing) connected to the exhaust port 17 is operated to perform exhaustion, and after the degree of vacuum in the device 11 is on the order of 10-6 Torr, the cock of the oxygen gas inlet 18 is opened. Oxygen gas is introduced into the apparatus 11, and its pressure is maintained at, for example, about 0.5 Torr.

Next, the boat 13 is energized by the evaporation power source 19 to generate heat, and the evaporation material 14 is evaporated for several seconds to several minutes in an atmosphere of 0.5 Torr gas.

For example, select Sn as the evaporation material 14 and
When a power of W is applied to the boat 13, the average particle size is about 40
A film 4 of ultrafine tin oxide particles having a thickness of approximately 20 μm and consisting of ultrafine human particles was formed on a substrate 1, as shown in FIG.

After the tin oxide ultrafine particle film is formed, the vacuum pump (not shown in the drawing) connected to the exhaust port 17 is operated again to evacuate the inside of the device 11 to a degree of vacuum on the order of 10-3 Torr. After that, the cock of the inert gas inlet 20 is opened to introduce an inert gas such as argon gas or helium gas into the apparatus 11, and the pressure is adjusted to 1. Keep it at about OTorr.

Next, the boat 15 is energized by the evaporation power source 21 to generate heat, and the evaporation material 16 is evaporated for several seconds to several minutes under an argon gas atmosphere.

For example, when a power of 120 to 160 W is applied to the boat 15 for 1 minute, an ultrafine palladium particle film 5 with an average particle size of several tens of micrometers and a thickness of 2 to 5 μm is formed on the tin oxide ultrafine particles 4 formed in the above process. formed on top of.

Here, the resistance heating method was used as an example to evaporate the evaporation material, but it goes without saying that other methods such as induction heating and infrared heating may also be used.

Ultrafine metal oxide particles are extremely sensitive to external agents such as gas and water vapor, but when ultrafine palladium particles are brought into close contact with ultrafine metal oxide particles as described above, the sensitivity becomes even higher.

Figure 3 shows a relative comparison of sensitivity to isobutane gas, where A is an ultrafine particle film with a thickness of 20 μm made only of ultrafine tin oxide particles produced under an oxygen gas pressure of 0.5 Torr. , B is a film in which a palladium ultrafine particle film having a thickness of 1 ln is further formed in close contact with the tin oxide ultrafine particle film of A under an argon gas pressure of 10 Torr.

At this time, the sensitivity of sensitive film B increased by about 1.9 times compared to sensitive film A.

Figure 4 shows that when changing the substrate temperature of the sensitivity of each sensitive film, isobutane gas is 500 ppm at each substrate temperature.
This shows the results of measuring the sensitivity of the rate of change in electrical resistance of the sensitive film against the substrate. It showed large values in all temperature ranges.

The temperature at which sensitivity appears is also lower for sensitive film B than for sensitive film A.

This is because when the sensitive film is exposed to reducing gas, the palladium in the palladium ultrafine particle film formed in close contact with the tin oxide ultrafine particle film reconverts to the reduced Sn02 in the tin oxide ultrafine particle film. This is because palladium oxidizes by providing oxygen and accelerates the reaction, and palladium itself repeats redox reactions and generates heat, thereby promoting the adsorption of reducing gases.

Therefore, the palladium ultrafine particle film formed on the tin oxide ultrafine particle film must have a thickness such that reducing gas can sufficiently reach the tin oxide ultrafine particle film, and an appropriate particle size. .

In the case of the present invention, the thickness of the palladium ultrafine particle film is approximately several μm, and the best results are obtained when the palladium ultrafine particle film has an average particle size of several dozen particles, which is about the same size as the tin oxide ultrafine particles. It was done.

As described above, according to the gas/humidity sensor of the present invention, by further superimposing a palladium ultrafine particle film on a film composed of metal oxide ultrafine particles, its sensitivity to external factors can be greatly improved. At the same time, the temperature during sensor operation can also be lowered.

[Brief explanation of the drawing]

FIG. 1 shows a sensor according to an embodiment of the present invention, in which A is a plan view and the opening is a sectional view taken along line xx' along line A. FIG. 2 is a diagram showing an example of an apparatus for manufacturing a tin oxide ultrafine particle film and a palladium ultrafine particle film, and FIGS. 3 and 4 are diagrams for explaining the effects of the sensor according to the present invention. . 1... Insulating substrate, 2, 3... Electrode, 4
... Ultrafine tin oxide particle film, 5... Ultrafine palladium particle film or a hybrid film of ultrafine palladium particles and ultrafine tin oxide particles.

Claims (1)

[Scope of Claims] 1. On a metal oxide ultrafine particle film with an average particle size of λ to 100 or more, formed on an insulating support base on which an electrode is installed, A gas/humidity sensor formed by closely adhering a film of ultrafine palladium particles of ~100 or more particles or a hybrid film of ultrafine palladium particles and ultrafine metal oxide particles each having an average particle diameter of ~100 or more particles. 2. The gas/humidity sensor according to claim 1, wherein the average particle diameter of the metal oxide ultrafine particle membrane and the average particle diameter of the palladium ultrafine particle membrane are approximately the same. 3. The gun according to claim 1, wherein the metal oxide ultrafine particle film is a tin oxide ultrafine particle film.
Humidity sensor.