JPS6029653A - Gas sensor - Google Patents

Abstract

PURPOSE:To improve safety, reliability and gas selectivity by manufacturing a film with a sputtering method and subjecting the films to a heat treatment. CONSTITUTION:Stannic oxide is made into ultrafine particles by making the gaseous pressure in the stage of sputtering higher than the gaseous pressure in the conventional sputtering technique (<=5X10<-2>Torr). The heat treatment has the effect of increasing packing density and at the same time of improving the gas selectivity of the gas sensor element by forming the structure contg. cracks 3 of <=10mum length on the surface. The ultrafine particle film after sputtering consists of a base plate 4, a low-density ultrafine particle layer 5 and a high- density ultrafine particle layer 6. The width of the cracks is controlled to <=1mum by forming such film structure, by which the gas selectivity is improved.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention shines in gas century! This invention relates to a metal oxide ultrafine particle gas sensor element with excellent gas selectivity.

[Background of the invention]

As city gas [C)'441 power sensor elements, S n O2 sintered type semiconductor elements currently occupy the majority of the market. However, there is a problem in that they malfunction when exposed to waste, mainly alcohol. Although elements that imitate catalysts have been developed, the current situation is that there are large variations between product lots, and that their characteristics deteriorate over time and are destroyed. Therefore, there is a need for a sensor element that has gas selectivity with respect to methane gas, is highly reliable, and does not deteriorate over time.

Gas selection 1'4g may be improved if the particle size of the metal oxide particles constituting the sensor element is made extremely fine.

As a method for manufacturing an ultrafine particle gas sensor, a method is known in which gold maple or its oxide is evaporated in a reduced pressure oxygen atmosphere (in-gas evaporation method) (Japanese Unexamined Patent Publication No. 55-27925, etc.).

However, the ultrafine particle sensor element produced by this in-gas evaporation method has the drawbacks of weak film strength and weak adhesion to the substrate, making it impractical.

[Purpose of the invention]

An object of the present invention is to provide a sensor element that brings out the effects of ultrafine particle formation as described above and does not have the drawbacks seen in the evaporation method in dregs.

[Summary of the invention]

In the in-gas evaporation method, a sensor element is fabricated by gradually depositing evaporated atoms on a substrate, but the drawbacks are that the adhesion force and the backing density of ultrafine particles are low. Therefore, an attempt is made to fabricate a film by the sputtering method and further add a hot part J'ffi to the film to obtain a structure with enhanced gas sensitivity.

[Embodiments of the invention]

Hereinafter, as an example of the present invention, device characteristics when stannic oxide is used as the gold oxide will be explained with reference to the drawings.

In the present invention, stannic oxide is made into ultrafine particles by increasing the gas pressure during sputtering to be higher than the gas pressure of conventional sputtering technology (less than +5×10 −2 torr). FIG. 1 shows the relationship between the gas output and the packing density 1 of ultrafine particle heat treatment m2, and the relationship where the packing density 2 was increased by heat treating the leeks at 550C for 12 hours. Figure 2 shows changes in the surface texture area due to heat treatment and
The figure also shows the improvement in gas selectivity due to heat treatment. 1st
As shown in Figures 2 and 2, the heat treatment according to the present invention has the effect of increasing the optical density and at the same time increasing the gas selectivity of the gas sensor element by creating a structure with cranks 3 of 10 μm or less in length on the surface. .

In addition, Fig. 4 is a cross-sectional view of the ultrafine particle film after sputtering, where 4 shows the substrate, 5 shows the low-density ultrafine particle layer, and 6 shows the high-density ultrafine particle layer. Fig. 5 shows the width of the surface crank and the gas selection. The crack width can be controlled to 1 μm or less by using the film structure according to the present invention as shown in Figure 4, which shows the relationship between
j can be done. As shown in FIG. 5, if the crank width is 1 μm or less, the smaller the crank width is, the higher the scum selectivity can be, which is effective in improving the characteristics of the gas sensor element.

〔Effect of the invention〕

According to the invention, it is possible to increase the gas selectivity of the gas sensor element by more than five times compared to the conventional one, and to obtain stability and reliability for a long period of one year or more, making it possible to produce a sensor element for a quality waste sensor. It's effective. -! In addition, it has excellent sludge selectivity for methane11, and at the same time shows almost no change over time and can be used as a methane gas sensor element.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the sputtering gas pressure and packing density of the ultrafine particle gas sensor before and after heat treatment, Figure 2 is a surface structure diagram of the ultrafine particle gas sensor after heat treatment, and Figure 3 is a diagram showing the ultrafine particles before and after heat treatment. Diagram showing the gas selectivity of the gas sensor, Figure 4 is a cross-sectional view of the sputtered film, and Figure 5 is a diagram showing the relationship between the width of the surface crack and the gas selectivity. 1... Light filling density before heat treatment 1 and 2...Filling density after heat treatment Fig. 1

Claims (1)

[Claims] 11 A gas sensor comprising a film of aggregation of ultrafine metal oxide particles having a grain size of 1 μn1 or less, closely attached to an insulating substrate provided with an electrode, and having a gas-sensitive part by measuring changes in electrical resistance. .