JPS5899741A - Gas sensing element and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a gas sensing element having a sufficiently high mechanical strength as well as high gas-sensitive characteristics, by providing a metal oxide layer obtained by means of thermal decomposition of an organometallic compound between a gas-sensitive body and an insulating substrate. CONSTITUTION:An insulative substrate 4 has a heating thick film heater 7 provided on one side thereof and Au electrodes 2, 3 provided on the other side by thick-film printing. Between these Au electrodes, a liquid obtained by diluting aluminum hexoate as an organometallic compound with propyl alcohol is applied and dried. Then, the surface of the organometallic compound film 10, between the electrodes 2, 3, is printed with a paste obtained by adding PdO to SnO2 powder having Sb2O3 added thereto and dispersing the same with an organic solvent, by a screen printer. This paste is dried and then baked to form a gas sensing element. As th above-mentioned organometallic compound, such a compound is employed as represented by the general formula: (Me)n(OR)m (wherein Me represents a metallic element, and R represents nitrogen, carbon, hydrogen or oxygen group).

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to improvements in a gas detector and a method for manufacturing the same.

(Prior Art and its Problems) Many examples of gas-sensitive elements using oxide semiconductors as gas-sensitive members have been proposed. In most cases, N-type oxide semiconductors are used, and the gas is detected by utilizing the fact that its resistance decreases upon contact with a reducing gas. P for semiconductors using Nio! Needless to say, when Ni oxide is used, its resistance value increases when it comes into contact with a reducing gas. In this case, in order to increase the sensitivity to gas, not only a semiconductor but also a catalyst is used, and a heater is provided to keep the element at a high temperature. For example, as shown in FIG. 1, an element is known in which a metal wire is embedded in a gas sensitive body (1) as a heater. In the case of this element, one of the pair of electrodes (2) and (3) also serves as a heater, making it difficult to equalize the temperature within the element and making assembly difficult. Furthermore, since the heating is not uniform, there is a risk that reliability over a long period of time may be lacking. On the other hand, as another example, as shown in the tIs-2 diagram, an insulator such as alumina is used as the substrate (4),
A heater (7) is provided on one side, and a pair of electrodes (2) are provided on the opposite side.
1, (3) and a structure in which a gas sensitive body (1) is provided.

In this case, as described above, the substrate (4) is generally made of a heat-resistant material such as alumina, magnesia, or mullite.

In the case of the conventional method, for example, the gas sensitive layer 1 in FIG.
is usually provided on a tangential substrate using a thick film printing method or the like. With such a configuration, the adhesion strength of the gas sensitive layer shown in FIG. 2 to the substrate was insufficient, and there was a risk of peeling off due to mechanical vibration or the like. Furthermore, even without mechanical vibration, the adhesive strength tended to decrease due to the impact caused by the interruption of the heater.

One way to improve this problem is to raise the baking temperature of the thick film, lengthen the baking time, or both, so that the thick film of the gas sensitive layer can bond to the substrate with sufficient strength. There is. However, this method also promotes sintering of the gas sensitive particles constituting the thickness, which greatly impairs the gas detection sensitivity, which is the original objective.

Another possible method is to mix a material that melts at a relatively low temperature, such as glass, into the thick film printing paste and bake it at a relatively low temperature. However, in this case as well, the molten glass covers the surface of the particles of the gas-sensitive material or penetrates between the particles, increasing the element resistance and significantly impairing the gas-sensitive characteristics.

(Object 7 of the Invention) In view of the above points, the present invention improves the drawback of the conventional example having low mechanical strength, and provides a gas sensing element having sufficient mechanical strength and high gas-sensitive characteristics, and a method for manufacturing the same. The purpose is to provide.

(Overview of the invention) The present invention comprises: an insulating substrate provided with a pair of electrodes; a gas sensitive body made of a metal oxide semiconductor provided between the electrodes on the insulating substrate; A gas detection element consisting of a thin film of metal oxide obtained by thermal decomposition of an organometallic compound and a pair of electrode element films on an insulating substrate, and a process of applying and drying the organometallic compound to form a thin film of metal oxide. A gas sensing element comprising a step of providing a gas sensitive body made of an oxide semiconductor, and a step of sintering the gas sensitive body and at the same time thermally decomposing the coated dried film of the organometallic compound to form a metal oxide thin film. This is a manufacturing method.

In other words, the present invention is characterized in that a metal oxide layer obtained by thermal decomposition of an organometallic compound is provided between the gas sensitive body and the insulating substrate in the conventional gas sensing element shown in FIG. It is believed that there is sufficient adhesion strength between the insulating substrate and the gas-sensitive member, and that excellent gas-sensitive characteristics can be obtained.

More specifically, the organometallic compound used in the present application is generally represented by ic (Me)n(OR)m. Note that Me represents a metal element, and 几 represents a group consisting of nitrogen, carbon, hydrogen, or oxygen, respectively. In the present application, metal alcohol compounds, metal alkoxides, naphthenic acid, etc. can be used as organometallic compounds.

Further, organometallic compounds are usually liquids with high viscosity, but they can also be solids. These are well soluble in alcohols such as propyl alcohol, organic solvents such as tetralin, terpineol, etc., and can be diluted freely. If necessary, add a diluent to adjust the organometallic compound to an appropriate viscosity. Next, after screen-printing, for example, an organic metal compound on the insulating substrate, a gas-sensitive single layer made of a paste-like metal oxide semiconductor is provided.When this is fired,
The thin film of the organometallic compound decomposes into extremely fine oxide particles, which form a structure in which the gas sensitive body and the insulating substrate are mechanically bonded.

As mentioned above, such a reaction occurs at a relatively low temperature, and in the case of many organic metals, sintering at a temperature of 500 to 600°C is sufficient. Moreover, the particles are bonded by a chemical reaction and not simply a mechanical bond, so they are extremely strong.

Furthermore, since the sintering temperature is relatively low, grain growth of the metal oxide semiconductor does not occur, and the gas sensitivity properties are extremely high.

Moreover, the decomposition reaction of the organometallic compound mentioned above produces a large amount of CO.
Since 0 is generated, pores from which gas can escape are automatically secured in the gas sensitive body.

Furthermore, in the present invention, when an organometallic compound containing the same metal element as the main component of the gas sensitive material is used, when the organometallic compound is decomposed in the firing process of the element, the metal element in the organometallic compound is The obtained gold JI has good "wetting" with the main component particles of the gas sensitive material, improving adhesive strength, and even after firing, the obtained gold JI
Since the I acid compound thin film and the gas sensitive body have oxides containing the same metal element, their thermal 111 tensile coefficients are similar, resulting in excellent peeling resistance.

In addition, by making the insulating substrate the same as the main component of the gas sensitive body (however, the resistance value of the insulating substrate is high due to electronic control), the thermal expansion coefficients of the gas sensitive body and the insulating substrate are similar, and firing It can prevent peeling due to time and subsequent heat shock.

Furthermore, if the resistance value of the metal acid compound thin film obtained by thermal decomposition of an organometallic compound is made higher than the resistance value of the gas sensitive material, it means that a multi-resistance material is connected in parallel with the gas sensitive material. Gas sensitivity can be increased.

Next, a specific manufacturing example of the gas sensing element according to the present invention will be shown.

First, an insulating substrate is cut according to the size of the element, and two pairs of detection electrodes are provided on one surface of the insulating substrate. Further, a heater layer for heating the element is provided on the other surface. Next, on the detection electrode side of this insulating substrate, an organometallic compound diluted by organic abrasion or the like is applied as necessary to at least the portion where the gas sensitive body and the insulating substrate are in contact. Thereafter, this is dried at room temperature, and further dried in a dryer at, for example, 100°C for 1 hour 11! jt Dry. The organometallic film produced in this manner has now been completely dried and its volatile components have been sufficiently volatilized. A paste in which a gas sensitive material is dispersed in an organic #1 medium is printed on this organometallic compound film. After thoroughly drying the printed gas sensitive material paste at room temperature, it is placed in a dryer at 100°C, for example.
After drying for several hours and firing in an electric furnace or the like, each lead wire is attached to obtain a gas-sensitive element. In this case, the firing temperature is 300℃
A gas sensing element sufficiently firmly bonded to one insulating substrate can be obtained at a temperature of ~800°C.

In addition to the 8nO system as described in detail in the Examples below, the gas sensitizers include zflQ +Q, 5 mo 1 '
76 It is preferable to use Ar101 type. In this case, zinc hexaate as an organometallic compound is 10~
It is preferable to use 40 Wt diluted with 60 to 90 wt% propyl alcohol.

In the present invention, the metal oxide thin film obtained by thermal decomposition of an organometallic compound has a temperature of 3000 K to 20000 K.
It is preferable to form X.

The structure of the gas detection element according to the present invention manufactured in this way is shown in cross section as the third factor. In the figure, 1 is a gas sensitive body, 2 and 3 are detection electrodes, 4 is an insulating substrate, 5.6 is a detection lead wire, 7 is a heater, 8°9 is a heater lead wire, 1
0 is a metal oxide thin film produced by decomposition of an organometallic compound.

(Examples of the Invention) The specific manufacturing method of the device of the present invention will be shown in Examples below, and the mechanical strength and characteristics of the device according to each Example are shown in Table 1 together with Reference Examples.

Example 1 A thick film heater (7) is provided on one side of an alumina substrate (4) serving as an insulating substrate, and Au electrodes (2) and (3) are provided on the other side by thick film printing. A solution prepared by diluting aluminum pexaate as an organometallic compound with propyl alcohol is applied between the electrodes and dried at room temperature for 1 hour.・After drying for about 1 hour in a dryer set at 100°C, take it out and cool it sufficiently to room temperature. Next, 2 wt1 of sb, o was added to the surface of the organometallic compound film using an ordinary screen printer, and 8 nO of PdO was added to the powder. A paste prepared by adding 0.5 wt to the paste and dispersing it in an organic solvent was printed so as to extend between the electrodes (2 bars 3).

This paste was dried at room temperature for 1 hour, further dried at 100°C for 1 hour, and then fired at 600°C to 800°C in an electric furnace. Attach each lead wire (5) +6) to this element, turn on the power, and after the element is sufficiently stabilized, put it into the measurement tank.
-C4H1°, Ht, and Co were injected as much as possible to 2000 PPm each to suppress the resistance change.

In addition, the adhesive strength is determined by preparing adhesive tapes with different adhesion strengths and attaching them to the surface of the resulting gas-sensitive material.When one end of the tape is folded 180 degrees and peeled off in parallel, the gas-sensitive material adheres to the adhesive tape and peels off. The decision was made as to whether or not to do so.

The results are shown in Examples 1-1 to 1-3 in Table 1.

Further, elements obtained in the same manner as in Example 1 except that the organometallic compound was not used are shown as Reference Examples 1-1 to 1-3.

Example 2 The organometallic compound was manufactured using the same substrate method as in Example 1, and the gas sensitive material was the same. The organometallic compound used was tin hexaate to which aluminum hexaate was added so that the atomic ratio of M was 3 mo 4 F %. And so. The measurement method is Example 1
The result is 1st! Examples 2-1 to 2-3.

Example 3 As an insulating substrate, 1,0. Using SnO containing 3 moj of
Further, between the detection electrodes, organometallic compounds such as aluminum hexaate, tin hexaneate, zirconium hexaate, and tin naphthenate diluted with propylene 4U alcohol were used, and the other conditions were the same as in Example 1. Example 3 - Obtaining the gas detection element according to the invention and presenting its measurement results
They are shown in Table 1 as 1 to 3-5.

Margin below The results shown in Table 1 will be explained below.

The composition of the gas sensitive body is the same in all reference examples and examples, and the gas sensitivity is expressed as R(1/Rgas), where the element resistance in air is Rgas, and the resistance in each gas is Rgas.
It was shown as follows. Adhesive strength β was determined from the presence or absence of peeling when adhesive tapes of various adhesive strengths were applied to the gas sensitive member and one end of the tape was folded back and peeled off parallel to the adhesive surface.

According to the results in Table #11, as shown in Reference Examples 1-1 to 1-3, the adhesive strength is extremely weak when using only the gas sensitive material. In addition, in Examples 2-1 to 2-3 and 3-1 to 3-3, in which silica sol or alumina sol was used as a curing agent in this gas sensitive body, a slight improvement in adhesion strength can be seen. In many cases, cracks occur within the surface, and when the firing temperature is raised to improve the bond strength, the sensitivity to each gas decreases rapidly. On the other hand, in the examples of the present invention, no cracking occurs at all, and when the firing temperature is increased, the adhesion strength is improved, and the gas sensitivity is maintained at a sufficient level. 'Furthermore, it is desirable that the organometallic compound used has an electrical resistance greater than the element resistance after firing, but no practical problem occurred even when used alone.

Further, Reference Examples 4-1 to 4-3 and Examples 3-1 to 3-5 are cases where the main component of the substrate is the same as the main component of the gas sensitive material, and cases where an organometallic compound is used and cases where an organometallic compound is not used. This is a comparison. As a result, the method of the present invention showed sufficient strength even when fired at 600° C. by using a substrate having the same main components as the gas sensitive member, but the conventional method did not have much effect. Note that the gas sensitivity in Example 3 is for the case of firing at 700°C.

Furthermore, this device was subjected to a single drop test and the results are shown in Table 2. The test method was to attach the device to a cylindrical iron object weighing 200F, and to measure the height from 1m to approximately 3cm40".
O dropped onto a cedar board placed on concrete Table 2 below (margin) [×: mostly peeled Δ: partially peeled ○no change] From this result, the method of the present invention shows that even though the method of the present invention is fired at a low temperature, No peeling occurred in all cases.

Although each of the above examples has been described using a gas sensitive material mainly composed of 8nOi, similar effects can be obtained using IHtOs.
t pe, o, , ZHOt 'rio,, '
It was also obtained when other materials such as 101 were used as the main component.

(Effects of the Invention) As is clear from the above results, the gas sensing element according to the present invention has excellent mechanical strength against peeling, dropping, etc. and excellent gas-sensitive characteristics, and can be said to be extremely effective in practice. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of the structure of a conventional gas detection element. Figure #12 is a sectional view showing another example of the structure of a conventional gas detection element. FIG. 3 is a sectional view showing an example of the structure of the gas detection element according to the present invention. 1... Gas sensitive body, 2, 3... Electrode material... Insulating substrate io... Thin film of metal oxide obtained by thermal decomposition of an organometallic compound - Agent: Kensuke Norichika, patent attorney (et al.) 1 person) 1st
Figure 2 Figure 3

Claims (1)

[Scope of Claims] l) an insulating substrate provided with a pair of electrodes, a gas sensitive body made of a metal oxide semiconductor provided between the electrodes on the insulating substrate, and between the gas sensitive body and the insulating substrate; 1. A gas sensing element comprising: a thin film of a metal oxide obtained by thermal decomposition of an organometallic compound; 9.2) A step of providing a pair of electrodes on an insulating substrate, a step of manipulating a coated dry film of an organometallic compound to provide a gas sensitive body made of a metal oxide semiconductor, and simultaneously sintering the gas sensitive body A method for manufacturing a gas sensing element, comprising the step of thermally decomposing the applied dry film of the organometallic compound to form a gold-oxide thin film. 3) '111'F A gas sensing element or a method for manufacturing the same, in which the organometallic compound in claim 1 or 2 contains the same metal element as the main component of the gas sensing element. 4) Claim 181 or 2 of the claim 4, the gas sensing element or its gas sensing element characterized in that the resistance value of the metal oxide thin film obtained by thermal decomposition of an organometallic compound is higher than the resistance value of the gas sensitive member. Production method. 5) A gas sensing element according to claim 1 or 2, wherein the insulating substrate is the same as the main component of the gas sensitive body and is a sintered body having a higher resistance than the gas sensitive body. or its manufacturing method.