JPH01216259A - Electrochemical sensor - Google Patents

Abstract

PURPOSE:To preclude a decrease in the sensitivity of the sensor and to prevent an electrode from being peeled off by providing an intermediate joint layer between an insulating substrate and the electrode, and covering the external surface of the intermediate joint layer completely with the electrode. CONSTITUTION:Intermediate joint layers 50 made of metal such as chromium are provided between electrodes 2 and the insulating substrate 1. The intermediate joint layers 50, however, have top surfaces and flanks covered completely with the electrodes 2 except the bottom surfaces joined with the insulating substrate 1. Consequently, the intermediate joint layers 50 never contact a solid electrolyte layer 6 and even when the sensor is put in operation, no battery effect is caused, so the intermediate joint layers 50 are securely prevented from being dissolved out.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electrochemical sensor, and more specifically, an electrolytic sensor that detects or quantifies a specific gas component using an electrolytic reaction. This relates to chemical sensors.

[Conventional technology]

The general basic structure of an electrolytic gas sensor is that three electrodes, a working electrode, a counter electrode, and a reference electrode, are provided in an electrolyte, and its working mechanism is that a constant voltage is applied to the working electrode. When applied, the gas component to be detected undergoes an oxidation or reduction reaction at the working electrode, and the ions generated at this time move within the electrolyte and undergo a reduction or oxidation reaction at the counter electrode. By measuring the current flowing between the working electrode and the counter electrode accompanying this redox reaction, it is possible to detect and quantify the target gas.

The potential of the working electrode required to cause the reaction is
Since the potential of the working electrode varies depending on the components of the detected gas, it is necessary to keep the potential of the working electrode constant depending on the detected gas. Therefore, the voltage applied to the working electrode is controlled with reference to the reference electrode.

However, there is also a sensor that does not include a reference electrode and consists only of a working electrode and a counter electrode.

By the way, conventional electrolytic gas sensors use the electrolyte as
For example, since a liquid electrolyte such as H*So is used, there are problems such as electrolyte change over time, liquid leakage, and material corrosion, and it is difficult to miniaturize because it must have a tightly sealed structure. Furthermore, since the sensitivity and output decrease over time, there are drawbacks such as poor long-term stability, short lifespan, and difficulty in handling and management.

Therefore, instead of liquid electrolytes, gas sensors using solid polymer electrolytes such as sulfonated perfluorocarbons have been developed; for example, U.S. Pat.
It is disclosed in Japanese Patent No. 115293 and the like.

This gas sensor has a sensing electrode (working electrode) and a reference electrode (reference electrode) on one side of the solid electrolyte membrane, and a reverse electrode (counter electrode) on the other side, making it more compact than the liquid electrolyte type. It has excellent performance such as stability over time, and is easy to handle.

However, in this gas sensor, an electrode made of a gas-permeable membrane supporting a fine particle mixture of Pt, Au, etc. and polytetrafluoroethylene is bonded to a soft solid electrolyte membrane, which makes manufacturing difficult. In addition, there was a problem in that it was difficult to miniaturize and form a sensor array.

In recent years, electronic circuit elements such as semiconductors have been miniaturized using micro-processing technology such as planar technology, and gas sensors used in combination with such elements have also been developed using ultra-miniaturized layers and high Performance is required.

Therefore, the applicant has developed a planar gas sensor that solves the problems of the prior art described above and can be manufactured using the same microprocessing technology as semiconductor devices. Figure 3 shows
An example of the structure of such a Brehner-type gas sensor is shown, in which a working electrode 2. Opposite 3
and a reference electrode 4, each of which consists of a reaction section 20, 30, 40 that performs an electrochemical action and a terminal section 21, 31.41 that is connected to an external circuit.
0.30.40 and covering therebetween, solid electrolyte M6
is provided. Therefore, the detection gas and the like pass through the solid electrolyte layer 6 and diffuse onto the reaction part 20 of the working electrode, causing an electrochemical reaction.

The above gas sensor has all electrodes 2 on the same surface of an insulating substrate l.
．． 3.4, the electrodes and solid electrolyte layers can be formed extremely efficiently using micro-processing technology such as Brenna technology, making it possible to miniaturize the sensor and improve its performance. It has excellent characteristics.

In addition, in the case of the above gas sensor, the bonding properties between the metals commonly used as electrode materials, such as platinum, gold, and iridium, and the insulating substrate are not very good, so there is a problem that the electrodes may separate from the insulating substrate, resulting in a decrease in sensitivity and output. There is. In particular, when a glass substrate with a smooth surface is used to form a fine electrode pattern, the electrode peeling as described above is likely to occur. Therefore, as shown in FIG. 4, between the electrode 2 (or 3.4) made of metal such as platinum and the insulating substrate 1,
...By providing a thin intermediate bonding layer 5 made of a metal such as chromium or titanium with good bonding properties on both the electrode and the insulating substrate, the bonding strength between the electrode and the insulating substrate can be further increased. It is being done.

[Problem to be solved by the invention]

However, in the case of the electrochemical sensor described above, the electrode 2.
... are covered with the solid electrolyte layer 6, the intermediate bonding layer 5 also comes into contact with the solid electrolyte layer 6.

Then, since the conventional intermediate bonding layer 5 is made of a metal material such as ROHM with a relatively low resistance, current also flows through the intermediate bonding layer 5 during the operation of the sensor, and the battery effect causes the fourth
As shown in the figure, the intermediate bonding layer 5 is eluted into the solid electrolyte layer 6, and this eluted material inhibits the reaction of the detection component at the working electrode 2 etc., causing a decrease in sensor sensitivity and malfunction. If the intermediate bonding layer 5 melts, the electrodes may peel off.

Therefore, an object of the present invention is to prevent elution of the intermediate bonding layer to prevent a decrease in sensitivity of the sensor and to prevent peeling of the electrode.

Although all of the above explanations have been made regarding gas sensors, the structure of the above gas sensor can be used as an ion sensor if the detection target that causes a reaction at the working electrode is ions in a liquid, and can be used as an electrochemical sensor for various uses. This invention is applicable to sensors in general, including gas sensors.

[Means to solve the problem]

In order to solve the above problems, the present invention provides an intermediate bonding layer between the insulating substrate and the electrode, and completely covers the outer surface of the intermediate bonding layer with the electrode.

[For production]

In this way, by covering the intermediate bonding layer with the electrode, the intermediate bonding layer does not come into contact with the solid electrolyte layer,
Even when the sensor is activated, no battery effect occurs, so elution of the intermediate bonding layer can be reliably prevented.

〔Example〕

Next, the present invention will be described in detail below with reference to drawings showing embodiments.

FIG. 1 shows the cross-sectional structure of a gas sensor according to the present invention, in which a working electrode 2. A counter electrode 3 and a reference electrode (not shown in the drawings) are provided, and a reaction section that performs various electrochemical actions is covered with a solid electrolyte layer 6. Note that the arrangement and formation patterns of the various types 2... are implemented in a structure similar to that of a normal gas sensor, such as the structure example shown in FIG. 3 described above, and detailed explanations will be omitted.

An intermediate bonding layer 50 made of metal such as chromium is provided between each electrode 2 and the insulating substrate 1.

However, the entire outer surface of the top and side surfaces of the intermediate bonding layer 50, except for the bottom surface bonded to the insulating substrate 1, is completely covered with the electrodes 2, so that there is no exposed part. .

Among the gas sensors having the above structure, the insulating substrate 1 is
Aluminosilicate glass is preferably used, but glass substrates such as borosilicate glass and quartz glass, ceramic substrates such as alumina, etc. can also be used, and silicon oxide etc. An ordinary insulating substrate material for gas sensors or electronic circuit elements, such as one on which an insulating film is formed, can be used.

The intermediate bonding layer 50 bonded onto this insulating substrate l is
A metal such as chromium or titanium that has good bonding properties to both the insulating substrate l and the electrode 2... is used in the same manner as the normal electrode forming method, and the same pattern as that of the electrode 2... The pattern is formed on the insulating substrate 1 to a thickness of about 10 to 1000 layers. Specifically, for example, after forming an intermediate junction 1i50 on the entire surface of an insulating substrate l by sputtering or vapor deposition, a predetermined mask pattern is formed using a photoresist or the like, and then wet or dry etching is performed. What is necessary is to remove unnecessary portions of the intermediate bonding layer 50 by.

Next, as the electrode 2..., a normal electrode material such as platinum or gold is used, and is formed by means such as wet plating so as to selectively and completely cover the outer surface of the intermediate bonding layer 50. Ru. However, as long as the outer surface of the intermediate bonding layer 50 can be selectively and completely covered, the electrodes 2 can also be formed by applying a suitable planar technique or the like other than the wet plating method. The thickness of the electrodes 2 is appropriately set depending on the structure and purpose of the sensor. Each electrode 2 may be coated with platinum black or subjected to activation treatment such as oxidation treatment.

For the solid electrolyte layer 6, a gas-permeable polymer solid electrolyte such as sulfonated perfluorocarbon (trade name: Nafion, manufactured by DuPont) is used, but other types of solid electrolytes used in ordinary gas sensors etc. are used. can be used, for example, 5bzOi-4H! 01Zr (H
PO, ), ・48t O, etc. can also be used.

In the illustrated embodiment, the solid electrolyte layer 6 includes each electrode 2...
・Although it is provided to cover the entire area, each electrode 2...
The solid electrolyte M6 may cover only the area between the reaction parts involved in the electrochemical action.

Next, in the embodiment shown in FIG. 2, a second intermediate junction jEi 51 made of another material is provided to cover the outer surface of the first intermediate junction Jii 50 described above, and the second intermediate junction jEi 51 made of another material is provided. Electrodes 2... are formed covering the outer surface.

This second intermediate junction N51 is the first intermediate junction Jit5
A material is used that is less eluted into the solid electrolyte 6 than zero and has good bonding properties with the first intermediate bonding layer 50 and the electrodes 2 .

The second intermediate bonding layer 51 is formed in the same manner as the intermediate bonding layer 50 or the electrode 2 described above.

In this way, by providing the second intermediate bonding layer 51, even if there is a pinhole in the electrode 2..., the second intermediate bonding layer 51 is provided.
551, it is possible to more reliably prevent the first intermediate bonding layer 50 from being eluted.

That is, if it is difficult to select a material for the intermediate bonding layer 50 that has both bonding properties to both the insulating group Fil and the electrodes 2... and insolubility to the solid electrolyte 6, the first intermediate bonding layer Jii50 The material of the second intermediate bonding layer 51 is selected by considering only the bondability to the insulating substrate l.
can be selected by considering only the non-elution property to the solid electrolyte 6 and the bonding property to the electrodes 2 . . . , which widens the range of material selection.

Furthermore, in each of the above embodiments, if a gas selective permeability filter is provided on the solid electrolyte layer 6, the target detection gas can be selectively sent to the solid electrolyte layer 6 or the working electrode 2 side, and the detection gas can be selectively sent to the solid electrolyte layer 6 or the working electrode 2 side. Accuracy can be partially increased. Furthermore, by providing a water reservoir layer on the solid electrolyte layer 6, sensitivity can be improved.

In addition, unless the gist of the present invention is changed, various structures or shapes employed in ordinary gas sensors can be combined and implemented.

Furthermore, although each of the above-mentioned embodiments has been described with respect to a gas sensor, the same structure can also be applied to various electrochemical sensors such as ion sensors and biosensors that react to ionic components in a liquid. Note that when used in a liquid, the solid electrolyte does not need to be gas permeable, and the structure may be changed as appropriate depending on the application.

〔Effect of the invention〕

As described above, in the present invention, the outer surface of the intermediate bonding layer, which is provided to improve the bondability between the electrode and the insulating substrate, is completely covered by the electrode, and the intermediate bonding layer does not come into contact with the solid electrolyte layer. Therefore, the intermediate bonding layer does not elute during the operation of the sensor, unlike in the conventional case.

Therefore, it is possible to eliminate all problems such as reduced sensitivity and shortened sensor life due to elution of the intermediate bonding layer, and peeling of electrodes, improving the reliability and stability of electrochemical sensors and significantly extending the service life. Extension is possible.

Especially 1. Even when a smooth insulating substrate is used to form a high-density, fine electrode pattern, it has high bonding strength, prevents electrode peeling like in the past, and maintains excellent performance as a sensor.

In addition, there is no need to select a material for the intermediate bonding layer with particular consideration to its insolubility in the solid electrolyte layer, and ordinary metal materials can be used, and the manufacturing method can be a general planar technology, making it easy to manufacture. It is easy and inexpensive.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of a gas sensor according to the present invention; Fig. 2 is a sectional view showing another embodiment; Fig. 3 is a schematic perspective view showing the structure of a general gas sensor; Fig. 4 is a schematic sectional view of a gas sensor according to the present invention; FIG. 7 is a sectional view of a main part showing an electrode portion of a conventional example. 1... Insulating substrate 2.3.4... Electrode 50...
Intermediate bonding N 51...Second intermediate bonding layer 6...
Solid electrolyte layer agent Patent attorney Takehiko Matsumoto Figure 4

Claims (1)

[Claims] 1. In an electrochemical sensor in which a plurality of electrodes are provided on the same surface of an insulating substrate and a solid electrolyte layer is provided covering at least between the reaction parts of each electrode, an intermediate bonding layer is provided between the insulating substrate and the electrodes. an electrochemical sensor characterized in that the outer surface of the intermediate bonding layer is covered with an electrode.