JPS6030894B2 - Manufacturing method of gas/humidity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a gas/humidity sensor using a metal oxide ultrafine particle film, which has higher sensitivity to gas than a conventional sensor formed using a metal oxide ultrafine particle film. The present invention provides a method for manufacturing an improved gas and humidity sensor that also has high conductivity.

It has been discovered that the resistance value of a film composed of ultrafine oxide particles with an average particle size of about 10-10A to 100-100A changes sensitively to gas and water vapor. A sensor has been proposed.

The present invention relates to a heat treatment method for further improving the sensitivity and conductivity of such an ultrafine particle sensitive film sensor.

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

FIG. 1 is a plan view of a gas humidity sensor according to the present invention.

As shown in the figure, this sensor first forms a pair of electrodes 2 and 3 on an insulating substrate 1 made of glass or ceramics, and then a metal oxide semiconductor such as tin, titanium, zinc, or nickel is formed on top of the electrodes 2 and 3. It is produced by forming an ultrafine particle film 4 and then heating it in oxygen or an atmosphere containing oxygen. As an example of the method of the present invention, an example of fabricating an ultrafine particle film sensor using tin oxide as the metal oxide will be described with reference to FIG.

The vertical 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. Furthermore, tin or its oxide is set in the vapor deposition boat 13 as the evaporation material 14 . After that, the vacuum pump (not shown in the drawing) connected to the exhaust port 15 is operated to perform exhaustion, and after the degree of vacuum inside the device 11 is on the order of 1 volt, the cock of the gas introduction row 6 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 17 to generate heat, and the evaporation material 14 is evaporated for a few seconds to several minutes in an atmosphere of 0.5 tons of oxygen gas. For example, when tin is selected as the evaporation material 14 and a power of 120 to 160 W is applied to the boat 13, a film 4 of ultrafine particles of tin oxide with a thickness of about 20 French m and consisting of ultrafine particles with an average grain size of about 40 A is formed. As shown in FIG. 1, it was formed on a substrate 1. After the tin oxide ultrafine particle film is formed, the cock of the air inlet 18 is opened to introduce air into the device 11 and bring the pressure to atmospheric pressure. Thereafter, in order to heat the insulating substrate 1 attached to the sample holder 12, the heater 19 set on the sample holder 12 is energized from the heater power source 2, and the ultrafine particle film 4 of tin oxide is heated at, for example, 500q0 So 10
Heat for about a minute. The resistance value R of the ultrafine particle film 4 measured between the pair of electrodes 2 and 3 changes as shown in FIG.
When heated for 7 minutes or more, it reaches a steady value. Although the above explanation has been made using the resistance heating method as an example to evaporate the evaporation material, it goes without saying that other methods such as induction heating and infrared heating may also be used.

Although the formed tin oxide ultrafine particle film 4 was heat-treated in the evaporator 11, the same effect can be obtained even if it is heated in the atmosphere after being taken out from the evaporator 11. Differences in size and shape have no bearing on the effects of the present invention. Ultrafine metal oxide particles are extremely sensitive to external agents such as gas and water vapor, but as mentioned above, ultrafine metal oxide particles are heated at high temperatures in oxygen or an atmosphere containing oxygen. The key point of the present invention, which is that the sensitivity is thereby improved and the conductivity is also improved, will be specifically explained below.

Using tin oxide as the metal oxide, oxygen gas pressure 0.5T
In contrast to the gas humidity sensor according to the present invention in which a tin oxide ultrafine particle film with a thickness of 20#m was heat-treated in air at 500°C for 10 minutes, a tin oxide film without any heat treatment A comparative test was conducted using an ultrafine particle membrane as a comparative example.

In the test, sensitivity to ethyl alcohol (blood concentration of 10) was measured for these samples by maintaining the temperature of each sample at 250° C. at an ambient temperature of 25° C. and humidity of 60%.

Sensitivity is R. /RG (where R is the resistance value of the tin oxide ultrafine particle film measured in the air, and RG is the resistance value of the film at a concentration of 10% of ethyl alcohol). The table below shows the relative values when the comparative example is set as 1.0. As is clear from this table, it can be seen that according to the present invention, a gas temperature separator with extremely superior sensitivity and conductivity can be obtained compared to the conventional ones.

In addition, although this example showed the effect on ethyl alcohol, if the operating temperature of the sensor is set to 350°C, the same effect will be obtained on reducing gases such as isobutane gas, and depending on the operating temperature, various gases and humidity It was effective against Thus, by the method of the present invention,
The reason why the characteristics of the sensor are greatly improved is because the heat treatment is performed in an atmosphere containing oxygen, so the tin oxide ultrafine particles are sufficiently oxidized and the abundance ratio of Sn02 in the ultrafine particle film becomes extremely large. It is speculated that this may be one of the causes.

This can be seen from the fact that the color of the tin oxide ultrafine particle film changes from yellow-white to white upon heat treatment, and from the results of X-ray diffraction measurements. However, it goes without saying that the heat treatment temperature must not be higher than the temperature at which the ultrafine particle film exhibits a cohesion phenomenon. It is preferable to carry out the heat treatment until the metal oxide ultrafine particles are sufficiently oxidized, and in the case of the examples of the present invention, the best results were obtained by heat treatment at a temperature of 350 oo to 550 oo for 10 minutes. It goes without saying that the heat treatment temperature and time will vary depending on the manufacturing conditions of the ultrafine metal oxide particles, mainly oxygen gas pressure, but at least the heat treatment temperature must be higher than the operating temperature, or the heat treatment temperature and time must be higher than the operating temperature. As shown in FIG. 3, it is desirable to set the conditions so that the resistance value R becomes a steady value.

The samples used for the measurements of the gas humidity sensor according to the present invention shown in the table above were prepared by producing ultrafine tin oxide particles in oxygen gas at 0.5 Torr, then heating them in air at 500°C for 10 minutes. Gas sensitivity and conductivity were then measured at an operating temperature of 250°C.

On the other hand, the sample used for the measurement of the comparative example shown in the table was 0.5T.
After making it in the same way in oxygen gas of ON, it was heated to 2500℃ without heat treatment for 10 minutes at 50000℃.
After heat treatment was performed at 0 and the resistance value R of the oxide ultrafine particle film reached a steady value, gas sensitivity and conductivity were measured at an operating temperature of 250 degrees. That is, the example in the table shows that both gas sensitivity and electrical conductivity are improved by increasing the heat treatment temperature higher than the operating temperature. As described above, according to the manufacturing method of the present invention, by heat-treating a film composed of ultrafine metal oxide particles, the conductivity and sensitivity to external factors can be greatly improved, making it extremely practical. Highly valuable gas
A humidity sensor can be realized.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a sensor according to the method of the present invention. FIG. 2 is a diagram showing an example of an apparatus for producing an oxide ultrafine particle film. FIG. 3 shows an example of the change over time in the resistance value of a metal oxide ultrafine particle film when the film is heated from room temperature to 500°C. 1...Insulating substrate, 2
, 3... Electrode, 4... Ultrafine particle film. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] After forming a metal oxide ultrafine particle film with an average particle size of 10-odd Å to 100-odd angstroms on an insulating support substrate on which a pair of electrodes are installed, oxygen or an atmosphere containing oxygen is formed. Inside, 3
A method for manufacturing a gas/temperature sensor, characterized in that heat treatment is performed at a temperature of 50° C. or higher at which the metal oxide ultrafine particle film does not sinter. 2. Claim 1, characterized in that the heat treatment temperature of the metal oxide ultrafine particle film is higher than the operating temperature of the sensor.
Method for manufacturing the gas/humidity sensor described in Section 1. 3. The method for manufacturing a gas/humidity sensor according to claim 1 or 2, wherein the heat treatment is performed until the resistance value of the metal oxide ultrafine particle film reaches a steady state. 4. The method for manufacturing a gas/humidity sensor according to claims 1, 2, and 3, wherein the metal oxide ultrafine particle film is a tin oxide ultrafine particle film.