JPS607353A - Gas sensitive element - Google Patents

Abstract

PURPOSE:To obtain a gas sensitive element which is excellent in response and durability by providing a specified catalytic layer on a gas sensitive body provided on a substrate. CONSTITUTION:A substrate 1 made of Al2O3 is equipped with a pair of electrodes 2 on its front and a heater 3 made of RuO2 on its back, and a gas sensitive body 4 is also provided on its surface by spattering method. On the body, a thin film of Al is formed by spattering, using the target of Al, and a porous anodic oxidized alumina layer 5 is formed by anodic oxidation. Over the layer, a catalytic metal layer 6 consisting of Pd-Pt is formed by spattering. A catalytic layer 7 composed of the alumina layer 5 and the catalytic metal layer 6 is stabilized by keeping the substrate at 440 deg.C for 30min by the heater. By this method, a gas sensitive element which is excellent in response and durability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a gas-sensitive element, particularly to a gas-sensitive element having a catalyst layer.

[Technical background of the invention and its problems] Various studies have been conducted on gas-sensitive elements using gas-sensitive materials, such as 5n02-based oxide semiconductors, whose resistance changes upon contact with various gases. There is. In such a gas-sensitive element, a catalyst is used for the purpose of increasing the detection sensitivity to gas, and one structure of a gas-sensitive element using this catalyst is one in which a catalyst layer is provided on a gas-sensitive member. Yes 0 Such a catalyst layer is generally made of P on a carrier such as M2O3.
A thick film containing a catalytic metal such as t is used. However, since the thick film is formed through a process of applying and sintering a paste-like raw material, there is a problem in that the reproducibility is very poor and the characteristics of the gas-sensitive element may vary. Furthermore, since the thickness of the thick film is on the order of 102 μm, there is a drawback that the response speed during gas detection is relatively slow. In addition, gas-sensitive elements are usually equipped with a heater.
Gas detection is performed while heating the gas sensing element, but such a thick film creates a temperature gradient within the catalyst layer, which tends to generate thermal stress, which may cause cracks in the catalyst layer. Ta. Furthermore, if the catalyst layer is thick, it is difficult to accurately set the temperature of the gas-sensitive element due to heat capacity, etc., and there is also the problem that the characteristics of the gas-sensitive element vary.

In order to overcome the drawbacks of using a thick catalyst layer as described above, research has been carried out on using a thin film of catalyst metal as the catalyst layer. Thin films are formed by sputtering, vapor deposition, etc. without going through a sintering process, and the film thickness can be reduced to a few nanometers with good reproducibility, so although the above-mentioned drawbacks can be overcome, new problems arise. A dot is produced.

In other words, the catalytic metal aggregates under high temperatures when the gas-sensitive element is used.
The problem is that it recrystallizes and reduces its catalytic ability. This is because the catalyst layer is a porous layer so that the gas comes into contact with the gas sensitive body.

This is because if such aggregation and recrystallization occurs, the porous state cannot be maintained.

[Object of the Invention] The present invention has been made in consideration of the above points, and an object of the present invention is to provide a gas-sensitive element having good responsiveness and excellent durability.

[Summary of the Invention] The present invention comprises a substrate, a gas sensitive member provided on the substrate and whose resistance value changes upon contact with a gas to be measured, a pair of electrodes provided on this gas sensitive member, and a gas sensitive member provided on the substrate. A gas-sensitive element having a catalyst layer provided on its surface, wherein the catalyst layer comprises a catalyst and a carrier made of a porous anodized alumina layer on which the catalyst is supported. It is element.

In the present invention, the substrate is AA'+Oa, 8iaN4
．． B.N.

A heat-resistant and insulating substrate such as a ceramic substrate such as 5R02 is used, and the electrodes are made of Au, Pt, etc., and formed by a screen printing method, sputtering method, vapor deposition method, etc.). These electrodes are provided facing each other on the gas sensitive member, and may be provided either between the gas sensitive member and the substrate or between the gas sensitive member and the catalyst layer.

In addition, the gas to be measured is a reducing gas such as CO or methane, and the commonly used 5nOz series, Z
An oxide semiconductor whose resistance value changes when it comes into contact with a gas to be measured, such as an nO-based or FezO3-based gas, is used.

These 5n02 series, Z110 series, and Fe2Q3 second Q semiconductors each have SnO2, ZnO, and FezOa as main components, and Nb'', Sb3+, Sb''+, and Af as necessary.
fl'', Cr3+, and other subcomponents are added.

This gas sensitive body is formed by a sputtering method, a vapor deposition method, a coating sintering method, a thermal decomposition method of an organic compound, or the like.

Next, the catalyst layer in the present invention will be described.

The catalyst layer includes a catalyst and a carrier made of a porous anodized alumina layer on which the catalyst metal is supported. This catalyst is used to improve gas-sensitive characteristics such as gas responsiveness and gas selectivity, and the phase substance prevents deterioration of gas-sensitive characteristics due to agglomeration of catalyst metal when using a gas-sensitive element. It is used to

As a catalyst, excluding μh (PL group elements, i.e. Pt, P
d, Rh, Ir, at least one of Os or CuO,
It can also be achieved by using a metal oxide catalyst such as NiO.

When the Ptfi element is used, the life is long, the stability is excellent, and the response speed is also improved. Furthermore, when CnO or the like is used, it is possible to improve the sensitivity to iso-C4H10 or the like.

The anodized alumina layer is vapor-deposited, forming a phase body.

The aluminum layer is formed by forming a sialuminum layer by sputtering or the like and then subjecting it to a normal anodic oxidation treatment.

The polar oxidation is A6. When a voltage is applied using Ta or the like as an anode in a certain electrolyte, the atomic acid 5i (H
2O-+H2+0)b5positive41iTe#,Ta)-reaction L,AA'203°Ta205 is formed, and an oxide film with good adhesion can be obtained.

Among these aluminum, as oxidation progresses, heat is generated due to the film resistance of A-1203, and this M2O3 is partially melted, forming holes C pits. At this time, if phosphoric acid, shiulic acid, sulfuric acid, etc. are used,
It is well known that the M2O3 layer is a porous layer,
For example, it is used for coloring technology by adsorbing dyes, etc. The anodized alumina layer formed in this way has a pore diameter of 3 to 5 Qnm and a pore density of 108 to 101 o/cI/
It is well known that a porous membrane having a uniform 4-pore distribution of 18 degrees can be obtained.

(F, KellJer eta7. J, Bde
ctrochem, Soc, 100411 (1953
)reference).

This anodized alumina layer is very strong because the pores are formed after forming a uniform film. Furthermore, since the gas-sensitive material is a bond between oxides, the adhesion strength is high, and the material has excellent strength as a gas-sensitive element.

Furthermore, the reproducibility of the porous state such as pore density and pore diameter is very good, and the characteristics of the gas-sensitive element can be manufactured with very good reproducibility. In addition, since a very uniform porous state is achieved, the sensitivity to gas, the response speed, and other curvature are greatly improved when the contact state between the gas sensitive body and the measurement atmosphere gas is good. Furthermore, since a thin film formed by a vapor deposition method, a sputtering method, etc. is used, the thickness of the catalyst layer can be made considerably thinner than that of a thick film catalyst, so characteristics such as response speed to the gas to be measured are improved.

When using a thick film formed by applying and sintering a catalyst layer material in the form of a base, a film thickness of only about 102 μm can be obtained, but in the present invention, for example, a film thickness of 1000 nm can be obtained.
A catalyst layer of the following degree can be obtained.

Furthermore, when a thick film formed through a sintering process is used, thermal distortion during sintering remains, resulting in poor durability. In addition, there is a limit to the sintering temperature in order not to deteriorate the characteristics of the gas sensitive material, and sufficient strength cannot be obtained, resulting in poor durability.

As described above, the present invention using the anodic oxidation method is much superior to the case where a thick film catalyst is used.

The catalyst in the catalyst layer may be mixed into the carrier, or a layer made of the catalyst may be formed on the carrier layer, so that the catalyst layer has a two-layer structure.

When mixed into a carrier, an aluminum layer mixed with a catalyst may be formed in advance and then anodized. For example, a thin film in which the catalyst metal is mixed with aluminum can be formed by sputtering using a mixture of the catalyst metal and aluminum, or a target having a desired area ratio adjusted. Also, two-dimensional sputtering method,
This thin film can also be formed by an original vapor deposition method or the like.

If the content of this catalytic metal is too small, the catalytic ability of the catalyst layer will not be fully exhibited, and if it is too large, the catalyst layer will not be able to maintain its insulation properties. Gas detection is performed by measuring changes in the resistance value of the gas sensitive body, but if the absolute R property of the catalyst layer provided on the gas sensitive body is not maintained, not only the resistance value of the gas sensitive body itself but also Since the resistance value between the gas sensitive body and the catalyst layer is measured, the accuracy of gas detection decreases. Furthermore, if the resistance value of the catalyst layer becomes smaller than the resistance value of the gas sensitive body, it becomes difficult to measure the resistance value of the gas sensitive body, and it becomes virtually impossible to detect a busy gas. Therefore, the weight ratio of the catalyst in the catalyst layer is preferably about 1% to 80% by weight relative to M2O3.

The thickness of this catalyst layer is preferably in the range of about 5 nm to 11,000 nm, because if it is too thin, the catalytic ability will not be fully exhibited, and if it is too thick, the responsiveness to the gas to be measured will be poor.

If a two-layer structure is desired, an aluminum layer may be formed in advance to form an anodized alumina layer, and then a catalytic metal layer such as Pt may be formed by sputtering, vapor deposition, or the like.

Since the pores formed by anodic oxidation have a maximum diameter of about 5 nm, the thickness of the catalytic metal layer is preferably about 5 nm or less so as not to block the pores. In addition, if the polar oxidized alumina layer is too thin, the catalytic metal layer will wrap around the walls of the pores, making it impossible to maintain insulation between the catalytic layer and the gas sensitive material. It becomes difficult to read the change in resistance value. Moreover, if it is too fast, the gas response will be poor, so a film thickness of about 5 nm to 11,000 nm is preferable.

[Effects of the Invention] As explained above, by using a catalyst layer using an anodized alumina layer as a carrier as in the present invention, the response to the gas to be measured is improved, and the catalyst layer is also strong. Therefore, durability is also improved.

[Embodiments of the invention] Examples of the present invention will be described below.

FIG. 1 is a diagram showing an embodiment of the present invention, and is a sectional view of a sensitive gas element.

The surface of an M2O3 substrate (1) measuring 7cm x 4cm x 0.3cm is mirror-polished, and a pair of comb-shaped electrodes made of Au are provided as electrodes (2) using a screen printing method. A heater (3) made of RuO2 is provided on the back surface of the M2O3 substrate (1) by screen printing. Electrode (2) and heater (
3) are provided with leads (2γ and (3γ), respectively. If the electrode is made into a thin film by vapor deposition, etc., the lead connection part can be made into a thick film to increase the adhesive strength with the substrate at the lead connection part.Next Next, a gas sensitive material (4) with a film thickness of 25 nm is formed between the electrodes (2) by a sputtering method using a target in which 5n02 is doped with Sb5+. It is preferable to perform this in a mixed atmosphere, and after forming a thin film, raise the temperature to 500°C in the air to stabilize the oxide semiconductor. After this, using a target made of M, a gas sensitive material (4
), a thin M thin film (thickness IQ nm) of 0.01 m, for example, is formed by sputtering in an Ar atmosphere of Hg or more. This υ thin film is anodized, for example, in a 0.2 m01/l Scheler's acid solution at a room temperature of 3 V to form a porous anodic oxidized alumina layer (5).

Next, using a 2Pd-PL alloy as a target, for example, 0.
01 mmHfZOA "1 nm thick Pd-P is deposited on the anodized alumina layer (5) by sputtering in an atmosphere.
A catalyst metal layer (6) consisting of t is formed. Thereafter, it is heated by a heater, for example, developed and maintained at about 440° C., and a catalyst layer consisting of an anodized alumina layer (5) and a catalyst metal layer (6) is preferably used to stabilize the force.

The characteristics of the gas-sensitive element formed as described above are shown in FIGS. 2 and 3.

Figure 2 is a diagram showing the gas response characteristics in an atmosphere of 3000 pl)m of H2 gas.The temperature of the 0-sensitive gas element is 2
00°C, H2 gas was introduced from l=Q to t22 (min), and at the time of 3 minutes after introduction (1=5
(min) ), and the change in resistance value of the gas sensitive body was observed. The resistance value (R) was expressed as a relative value, with the resistance value in the atmosphere being 1000 (curve a). Comparative Example 1 is also shown in which only the same catalyst metal as in the above example was sputtered to a film thickness of 11 m without using a phase material (curve b
).

As is clear from FIG. 2, it can be seen that in the present invention, both the start-up at the time of gas introduction and the return at the time of exhaust are performed more quickly, and the response properties are superior.

Also, the sensitivity is, for example, Rair at t = 3 (min).
(Resistance value in the atmosphere)/Rgas (Resistance value in gas) is compared, the example of the present invention is 200% higher than the comparative example-1.
It turns out that it is more than twice as large.

Thus, it can be seen that the present invention has excellent sensitivity and response characteristics.

Further, FIG. 3 shows the change in resistance value over time with respect to the saturation value of the resistance value of the gas sensitive member in an atmosphere of 200 ppm H2 gas. Comparative Example-2: P by coating and sintering
t -P d l5-11203 (P j/j doubt 20
3 = 1/100 (weight ratio), Pt/Pd==1/
A catalyst layer having a composition of 2 (atomic ratio) and a thickness of several hundred μm is easily provided on the surface of a 5n02-based gas sensitive body.
Similar measurements were made. In both Example and Comparative Example-2, the element temperature was about 100'O.

In the case of the embodiment of the present invention (curve a), the resistance value saturates at one degree of decentralization and becomes a stable value, whereas in the case of comparative example-2 (curve b
), it can be seen that the resistance value does not saturate even after 3 minutes and gradually approaches the saturation value. Therefore, the gas-sensitive element of the present invention has better gas responsiveness.

Furthermore, Fig. 4 shows the change in sensitivity over time.

The gas-sensitive element has an element temperature of 100'O when detecting gas,
The resistance value Rgas was measured after 3 minutes in the air atmosphere, and Ra1
r/Rgas was calculated as gas sensitivity. This measurement is 2
Heat cleaning was performed at 400° C. for 1 minute after measuring Rgas.

For comparison, the same measurements were carried out in the aforementioned Comparative Example-1 and Comparative Example-2.

As is clear from FIG. 4, the embodiment of the present invention (curve a)
Compared to the comparative example-
1 (curve b) and Comparative Example-2 (curve C), it can be seen that the sensitivity decreases after about several hundred hours.

Thus, it can be seen that the gas-sensitive element of the present invention has extremely excellent durability.

Next, H2 gas (3000 p
Table 1 shows the sensitivity to pm). Gas sensitive body is 2
5n02 (Nb doped) with a thickness of 5 nm was used, the anodized alumina layer was 1Q nm thick, and the catalyst metal layer was 1 nm thick.

As a comparative example, a catalyst metal layer was directly formed without using an anodized alumina layer.

Table 1 As is clear from Table 1, the Examples of the present invention have higher sensitivity than the Comparative Examples.

Next, an example in which a catalyst was mixed into the compound will be shown. The structure is the same as that shown in FIG. 1 except that the catalyst layer is one layer.

The gas sensitive body is made of niobium pentoxide 0.8 w to control the resistance value.
Using a tin oxide target containing t%, a film thickness of 3 Q nm was formed by sputtering.

Using a target prepared with an area ratio of M and Pt of 97:3 on this gas sensitive body, ]QmTOrr Ar 10
A 50 nm thick M-
A Pt mixed film was formed. Then, it was partially acidified in a 0.2 mOl/l shiulic acid solution at an applied voltage of 10 V to perform anodic oxidation. The Pt layer in this catalyst layer was about 10 wt%. The resistance value of the gas-sensitive element thus formed was ±20%.
Sensitivity to H2 gas (Ra1r/Rgas)
It was also possible to manufacture the film with a variation of ±1010 degrees and extremely high reproducibility. In addition, in continuous tests at 200"0, the resistance change rate was within ±10% after one year, indicating excellent durability.Furthermore, at 400"0 (2 minutes):
Almost no deterioration of the element was observed even in a heat cycle test at 100°C (2 minutes).
The sensitivity to H2 gas 10,001)I)m at 0°C was as high as approximately 10,000m, and the response characteristics were very sensitive, taking less than a second to reach the saturation value of 90ch.

Figure 5 shows the thickness and sensitivity of the catalyst layer (H2ioooppm).
shows the relationship between It can be seen that a film thickness of about 5 nm to 11000 nm is suitable.

Furthermore, Figure 6 shows the amount of catalyst metal (pt) (wt) and sensitivity (
H210 showed 1000pp and an air resistance value Ra1r (device temperature 200°C). It can be seen that the sensitivity is excellent in the range of 1 wt% to 80 t%, especially in the range of 20 wt% or less. Moreover, if it exceeds 80 wt%, the resistance value of the catalyst layer decreases, and the resistance of the element decreases, which is thought to be one of the reasons for the decrease in sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a gas-sensitive element showing an embodiment of the present invention, FIGS. 2 and 3 are response characteristic diagrams, FIG. 4 is a time-lapse characteristic diagram, and FIG. 5 is a film thickness-sensitivity characteristic diagram. Figure 6 is a Pt amount-sensitivity and resistance characteristic diagram. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Electrode, 4... Gas sensitive body, 5... Carrier layer, 6... Catalyst metal layer, 7... Catalyst layer. Agent Patent attorney Kensuke Chika (and 1 other person) Figure 1 IQrJD Figure 2 1t (rn;n) Filler 4 Figure 1 Special fM (/lr,)

Claims (4)

[Claims] (1) A substrate, a gas sensitive element provided on the substrate and whose resistance value changes upon contact with the gas to be measured, a flame pair of electrodes provided on the gas sensitive element, and a pair of electrodes provided on the surface of the gas sensitive element. 1. A gas-sensitive element having a catalyst layer comprising a catalyst layer and a carrier comprising a porous anodized alumina layer on which the catalyst is supported. (2) The catalyst layer includes a carrier layer formed on the gas sensitive member and a layer made of a catalyst formed on the carrier layer.
The gas-sensitive element according to claim 1, which has a layered structure. (3) The gas-sensitive element according to claim 1, wherein the catalyst layer is comprised of a carrier layer mixed with a catalyst. (4) The gas-sensitive element according to claim 1, wherein the catalyst is made of at least one of Pt, Pd, Rh, Ir, and Os.