JPS632054B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas sensor, and an object thereof is to provide a gas sensor that has improved conductivity and sensitivity to ethyl alcohol compared to conventional gas sensors formed using ultrafine oxide particles. It is in.

Previously, the present inventor proposed a sensitive film sensor that is composed of ultrafine oxide particles with an average particle size of about 10-odd Å to a hundred-odd angstroms, and whose resistance value changes sensitively to gas and water vapor ( (Special Application No. 100620, Showa 53). Although such sensitive membrane sensors have good sensitivity, some types of external agents require heating to operate the element. Therefore, in terms of power consumption, it is required to operate at as low a temperature as possible. Furthermore, when attempting to use it as a detection element in a gas alarm device or the like, there are practical problems such as difficulty in circuit configuration due to the high resistance value and susceptibility to noise from the power supply section and the outside.

Therefore, the present invention significantly improves the conductivity of the element,
At the same time, the present invention provides a gas sensor with a lower operating temperature for ethyl alcohol.

Hereinafter, one embodiment of the present invention will be described based on the drawings. In other words, the gas sensor of this embodiment is shown in Fig. 1A,
As shown in FIG. 2, a pair of electrodes 2 and 3 are formed on an insulating substrate 1 made of glass or ceramics, an ultrafine particle film 4 of a tin oxide semiconductor is formed thereon, and a palladium vapor-deposited film 5 is further formed thereon. It is formed by forming.

Next, a method for manufacturing the above gas sensor will be explained based on FIG. 2. That is, the insulating substrate 1 having the electrodes 2 and 3 is attached to the sample holder 12 in the vacuum evaporation apparatus 11 with the electrode surface facing downward. Further, in the evaporation boat 13 located below the insulating substrate 1, an evaporation material 14 made of tin or tin oxide is set. Further, a palladium evaporation material 16 is set in an evaporation boat 15 disposed close to the evaporation boat 13. After that,
A vacuum pump (not shown) connected to the exhaust port 17 is operated to evacuate the device 11 to bring the degree of vacuum inside the device 11 to the order of 10 ^-6 Torr, and then the oxygen gas inlet 18 is opened and the device 11 is evacuated. Oxygen gas is introduced into the chamber and the 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 tens of seconds to several minutes in an atmosphere of oxygen gas pressure of 0.5 Torr. A particulate film 4 is deposited. For example, if Sn is selected as the evaporation material 14 and a power of 120 to 160 W is applied to the boat 13, approximately 20μ of ultrafine particles with an average particle size of approximately 40A
A thick film of ultrafine tin oxide particles is formed. Next, the vacuum pump 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 ^-6 Torr. Next, the boat 15 is energized by the evaporation power source 20 to generate heat, and the palladium evaporation material 16 is evaporated for several seconds to several tens of seconds, thereby depositing the palladium evaporation film 5 on the ultrafine particle film 4. For example, when a power of 120 to 160 W is applied to the port 15 for 1 minute, a palladium deposited film 5 with a thickness of about 1000 Å is formed.

Figure 3 is a graph showing a relative comparison of sensitivity to ethyl alcohol. In the graph, A is a 20μ thick ultrafine particle film made only of tin oxide ultrafine particles prepared under an oxygen gas pressure of 0.5 Torr. Show, B
is about 1000 ml thick on top of the tin oxide ultrafine particle film of A above.
The figure shows a film formed by stacking palladium vapor-deposited films with a thickness of 1.5 Å. As is clear from the graph, in A,
While the temperature of the substrate 1 begins to exhibit sensitivity at around 120° C., in B, the temperature of the substrate 1 begins to exhibit sensitivity at around room temperature.

FIG. 4 is a graph comparing the electrical conductivity of B with that of A, and the electrical conductivity of B is about 67 times higher than that of A.

In the gas sensor of this example, the thickness of the palladium vapor deposited film 5 in the upper layer must be thick enough to allow the reducing gas to reach the ultrafine particle film 4 in the lower layer, but as shown in the specific example above, When the thickness of the palladium vapor-deposited film 5 is approximately several thousand angstroms or less, the sensitivity of the element is not impaired.

In the above embodiment, a resistance heating method was used as a method for evaporating the evaporation materials 14 and 16, but it goes without saying that other methods such as an induction heating method or an infrared heating method may also be used.

As described above, according to the gas sensor of the present invention, a tin oxide ultrafine particle film is formed on an insulating substrate on which an electrode is formed, and a palladium vapor-deposited film is laminated on the tin oxide ultrafine particle film. The electrical conductivity of the tin oxide ultrafine particle film can be improved, and the film can exhibit sensitivity to ethyl alcohol at a lower temperature than before.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Figure 1A is a plan view, Figure 1B is a view taken along the line X--X in Figure A, and Figure 2 is a schematic vertical cross-section for explaining the manufacturing method of the gas sensor. A top view, Figure 3 is a graph comparing the relative sensitivity to ethyl alcohol of membrane A composed only of ultrafine tin oxide particles and membrane B, in which a palladium vapor-deposited membrane is laminated on A, and Figure 4 is a graph of the sensitivity to ethyl alcohol of membrane A composed only of ultrafine tin oxide particles. It is a graph comparing the electrical conductivity of A with that of A. 1... Insulating substrate, 2, 3... Electrode, 4... Tin oxide ultrafine particle film, 5... Palladium vapor deposited film.

Claims (1)

[Claims] 1. A gas sensor characterized in that a tin oxide ultrafine particle film is formed on an insulating substrate on which an electrode is formed, and a palladium vapor-deposited film is laminated on the tin oxide ultrafine particle film.