JP2501856B2 - Electrochemical sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrochemical sensor, and more specifically, to an electrolysis-type electric sensor for detecting or quantifying a specific gas component or the like by utilizing an electrolytic reaction. The present invention relates to a chemical sensor.

[Prior Art] A general basic structure of an electrolytic gas sensor is one in which three electrodes of a working electrode, a counter electrode and a reference electrode are provided in an electrolysis chamber, and a general working mechanism thereof is a working electrode. When a certain voltage is applied to, the gas component to be detected causes an oxidation or reduction reaction at the working electrode, and the ions generated at this time move in the electrolyte and cause a reduction or oxidation reaction at the counter electrode. Is. By measuring the current flowing between the working electrode and the counter electrode in association with this redox reaction, the target gas can be detected and quantified.

In addition, since the potential of the working electrode required to cause a reaction differs depending on the components of the detection gas, it is necessary to keep the potential of the working electrode constant according to the detection gas.
The voltage applied to the working electrode is controlled based on the reference electrode. However, there is also a sensor that is not provided with a reference electrode and has only a working electrode and a counter electrode.

By the way, since the conventional electrolytic gas sensor uses a liquid electrolyte such as H ₂ SO _{4 as} an electrolyte,
There are problems such as aging of electrolyte, liquid leakage, material corrosion, etc.
Since a tightly sealed structure is required, miniaturization is difficult, and sensitivity and output decrease over time, resulting in poor long-term stability, short life, and easy handling and management. There were drawbacks such as difficulties.

Therefore, instead of a liquid electrolyte, a gas sensor using a polymer solid electrolyte such as sulfonated perfluorocarbon has been developed. For example, U.S. Pat. No. 4,229,784, No. 4265714 or JP-A-53-115293. It is disclosed in Japanese Patent Publication No. This gas sensor has a sensing electrode (working electrode) and a reference electrode (reference electrode) on one surface of a fixed electrolyte membrane, and a counter electrode (counter electrode) on the opposite surface, which is more compact than a liquid electrolyte type sensor. And is excellent in terms of performance such as stability over time, and is easy to handle.

However, in this gas sensor, an electrode composed of a gas permeable film carrying a fine particle mixture of Pt, Au, etc. and polytetrafluoroethylene is adhered to a soft solid electrolyte membrane, which makes the production troublesome. In addition, there is a problem that it is difficult to make the sensor miniaturized and to make a sensor array.

In recent years, electronic circuit elements such as semiconductors have been miniaturized using microfabrication technology such as planar technology,
As a gas sensor used in combination with such an element, further miniaturization and higher performance are required.

Therefore, the applicant of the present invention has solved the above-mentioned problems of the conventional technology and developed a planar type gas sensor which can be manufactured by the micro processing technology similar to that of semiconductor elements and the like. FIG. 3 shows an example of the structure of such a planar type gas sensor. The working electrode 2, the counter electrode 3 and the reference electrode 4 are provided as electrodes on the upper surface of the insulating substrate 1, and each electrode has an electrochemical property. The reaction parts 20, 30 and 40 which operate and the terminal parts 21, 31 and 41 which are connected to the external circuit are provided, and the solid electrolyte layer 6 is provided so as to cover the reaction parts 20, 30 and 40 of each electrode and the spaces between them. ing.

The solid electrolyte layer 6 thinly covers the reaction parts 20 and the like so that the whole has a uniform thickness, and the upper surface of the solid electrolyte layer 6 is flat. Therefore, the detection gas or the like passes through the solid electrolyte layer 6 and diffuses on the reaction portion 20 of the working electrode to cause an electrochemical reaction.

The gas sensor has all electrodes on the same surface of the insulating substrate 1.
Since 2,3,4 are provided, the electrodes and the solid electrolyte layer are formed by using micro processing technology such as planar technology.
It has many excellent features such as extremely efficient processing, miniaturization and high performance of the sensor.

In the case of the gas sensor, the bonding property between a metal such as platinum, gold, or iridium, which is usually used as an electrode material, and the insulating substrate is not so good, and the electrode peels off from the insulating substrate, resulting in a decrease in sensitivity or output. There is. In particular, when a glass substrate or the like having a smooth surface is used for forming a fine electrode pattern, the above electrode peeling is likely to occur. Therefore, as shown in FIG. 4, between the electrode 2 (or 3, 4) made of a metal such as platinum and the insulating substrate 1, there is good bonding property to both the electrode 2 ... By providing the thin intermediate bonding layer 5 made of such metal as described above, the bonding force between the electrode and the insulating substrate is further increased.

[Problems to be Solved by the Invention]

However, in the case of the above-mentioned electrochemical sensor, the electrode 2
... is covered with the fixed 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 chromium having a relatively small resistance, a current also flows through the intermediate bonding layer 5 during the operation of the sensor, and as shown in FIG. The intermediate bonding layer 5 elutes into the solid electrolyte layer 6. This eluting material inhibits the reaction of the detection component in the working electrode 2 and the like, causing a decrease in the sensitivity of the sensor and a malfunction, and when the intermediate bonding layer 5 melts, the electrode may peel off.

Therefore, an object of the present invention is to prevent the elution of the intermediate bonding layer, prevent the sensitivity of the sensor from being lowered, and prevent the peeling of the electrode.

Although all of the above description has been made on the gas sensor, the structure of the gas sensor can be applied to an ion sensor by applying an ion in a liquid as a detection target that causes a reaction at a working electrode, and so on. The present invention is applicable to sensors in general, including gas sensors.

[Means for solving the problem]

In order to solve the above problems, the present invention provides a high resistance intermediate bonding layer between an insulating substrate and an electrode, and comprises an intermediate bonding layer material and an electrode metal material at the interface between the intermediate bonding layer and the electrode. The metal compound layer is formed.

[Action]

By forming the metal compound layer at the interface between the intermediate bonding layer and the electrode in this way, the intermediate bonding layer and the electrode are chemically bonded, and the bonding force between the two becomes very large. As a result, the electrode can be firmly bonded to the insulating substrate.

Further, since the intermediate bonding layer has a high resistance, no current flows through the intermediate bonding layer even when the sensor is operated, and the battery effect is not generated. Therefore, the elution of the intermediate bonding layer can be reliably prevented.

〔Example〕

Next, the present invention will be described in detail below with reference to the drawings illustrating an embodiment.

FIG. 1 shows a 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 4 are provided as electrodes on a rectangular insulating substrate 1 and the electrochemistry of each electrode 2 ... The reaction portion that operates is covered with the solid electrolyte layer 6. The arrangement and formation pattern of the electrodes 2 are carried out in the same structure as that of a normal gas sensor such as the above-mentioned conventional example, and thus detailed description thereof will be omitted.

An intermediate bonding layer 5 is provided between each electrode 2 ... And the insulating substrate 1. The intermediate bonding layer 5 may be provided only at the positions of the electrodes 2 ..., However, it is usually provided on the entire surface of the insulating substrate 1 as shown in the drawing. A metal compound layer 50 made of the material of the intermediate bonding layer 5 and the metal material of the electrodes 2 is formed at the interface between the intermediate bonding layer 5 and the electrodes 2.

FIG. 2 shows an example of a method of manufacturing the above gas sensor in the order of steps.

First, aluminosilicate glass is preferably used for the insulating substrate 1, but glass substrates such as borosilicate glass and quartz glass, ceramics substrates such as alumina, and the like can also be used, and further, conductive materials such as silicon and metal as appropriate. An ordinary insulating substrate material for a gas sensor or an electronic circuit element, such as one having an insulating film such as silicon oxide formed thereon, can be used.

On this insulating substrate 1, a high resistance intermediate bonding layer 5 made of polycrystalline silicon or the like is formed [step (a)]. Specifically, a thin film of polycrystalline silicon having a film thickness of about 500 Å is formed by, for example, a high frequency sputtering method targeting silicon. At this time, the substrate temperature is preferably about 300 ° C. The resistivity of the intermediate bonding layer 5 made of polycrystalline silicon thus obtained is about 10 ⁹ to 10 ¹⁰ Ωcm.

However, the intermediate bonding layer 5 includes, in addition to the polycrystalline silicon,
Various high resistances, that is, insulating materials used for ordinary electronic circuit elements can be used, and specifically, the specific resistance of the intermediate bonding layer 5 is preferably 10 ⁹ Ωcm. As a method for forming the intermediate bonding layer 5, an appropriate method is used according to the material used, and the thickness thereof can be changed appropriately.

Next, an electrode layer 2'made of platinum is formed over the entire surface of the intermediate bonding layer 5 by the same high frequency sputtering method as described above to have a thickness of 5000 Å [step (b)]. At this time, the substrate temperature is preferably about 200 ° C. However, if the material of the electrode layer 2'is different, the substrate temperature is also changed.

Thus, when the platinum electrode layer 2'is formed on the intermediate bonding layer 5 made of polycrystalline silicon by the high frequency sputtering method, the platinum and the underlying silicon are heated by heating the silicon surface by high-energy particles or the like during sputtering. A low-temperature solid-state reaction occurs between and, at the interface between the electrode phase 2 ′ and the intermediate bonding layer 5,
A metal compound layer 50 of platinum and silicon is formed with a thickness of several 10Å.

When such a metal compound layer 50 is formed, the intermediate bonding layer 5 and the electrode layer 2 ′ are bonded to the compound through the metal compound layer 50, so that the bonding force becomes very large.
The thickness of the metal compound layer 50 can be 10 to 1000Å,
It is better to be as thin as possible so long as the above-mentioned joining strength can be enhanced.

As the material of the electrode layer 2 ′, besides platinum, a usual metal material for electrodes such as gold, silver, iridium, etc. can be used according to the application and structure of the sensor, and the thickness thereof is also set appropriately. As the method for forming the electrode layer 2 ′, in addition to the high frequency sputtering method, various ordinary thin film forming means such as an electron beam evaporation method can be adopted.

The metal compound layer 50 is formed simultaneously with the formation of the electrode layer 2'by the above-described platinum high frequency sputtering method,
A method of depositing platinum to be the electrode layer 2'on the intermediate bonding layer 5 and then heat-treating it at a temperature of about 300 ° C, or a method of sputtering a metal compound of platinum and silicon on the intermediate bonding layer 5 is used. A method of depositing and forming the metal compound 50 can also be adopted. The metal compound layer 50 can be formed not only by platinum and silicon but also by other materials and manufacturing methods.

Next, after applying a photoresist on the electrode layer 2 ', the photoresist is exposed and etched according to a normal photolithography process to form a photoresist layer 90 corresponding to the electrode pattern [process ( c)].

Using the patterned photoresist layer 90 as a mask, the electrodes 2, 3, 4 are formed by etching using an ion beam of argon [step (d)]. The processing conditions at this time are, for example, an acceleration voltage of 800 V, an ion gun current of 600 mA, a beam incident angle of 0 °, and an etching time of about 20 minutes. In this step, the lower metal compound layer 50 is also etched simultaneously with the electrode layer 2 '. However, the intermediate bonding layer 5 may be left as it is.

The etching method for forming the electrodes 2 ... In addition to the ion beam etching method described above, dry etching methods such as sputter etching and plasma etching, which are used for normal electrode formation, wet etching methods, or a combination of these methods are used. It can also be carried out.

Next, the photoresist layer 90 is removed [step (e)]. Then, a solid electrolyte layer 6 such as a sulfonated fluorocarbon is deposited on each of the electrodes 2 by a solution casting method or the like to be solidified [step (f)]. The thickness of the solid electrolyte layer 6 is about 1 to 10 μm.

The gas sensor manufactured through the above steps,
As shown in FIG. 1, an intermediate bonding layer 5 is provided on the entire surface of the insulating substrate 1, and a metal compound layer 50 is provided on the intermediate bonding layer 5.
Each electrode 2 is provided, and the solid electrolyte layer 6 covers these electrodes 2 and the like. The electrodes 2 may be coated with platinum black or may be subjected to activation treatment such as oxidation treatment.

As the solid electrolyte layer 6, for example, a gas permeable polymer solid electrolyte such as sulfonated perfluorocarbon (trade name: Nafion: manufactured by DuPont) is used. In addition, various solid electrolytes used for ordinary gas sensors and the like. Can be used, and for example, Sb ₂ O ₅ · 4H ₂ O · Zr (HPO ₄ ) ₂ · 4H ₂ O can also be used.

In the illustrated embodiment, the solid electrolyte layer 6 includes the electrodes 2 ...
However, the solid electrolyte layer 6 may be provided only between the reaction parts that are involved in the electrochemical action of the electrodes 2 ...

The electrodes 2 ... Are formed by using various ordinary planar techniques such as the above-mentioned photolithography method and a method of directly depositing the electrodes 2 ... In accordance with an electrode pattern like a mask vapor deposition method. There is also a method of forming.

In the manufacturing process described above, only the electrode 2 and the metal compound layer 50 are simultaneously etched, and the step of etching the intermediate bonding layer 5 is omitted. In the case of an intermediate bonding layer made of a metal having a low resistance as in the past, the intermediate bonding layer should be etched and separated for each electrode 2 in order to prevent a short circuit between the electrodes 2, 3 and 4. However, in the present invention, since the resistance of the intermediate bonding layer 5 is high, the intermediate bonding layer 5 may remain on the entire insulating substrate 1.

However, if it is necessary to further enhance the insulation between the electrodes 2, the intermediate bonding layer 5 may be separated by etching for each electrode 2. In this way, if the intermediate bonding layer 5 is separated for each electrode 2, and the insulation between the electrodes 2 is increased, even if the detection current is extremely small depending on the structure and application of the gas sensor. Performance such as sensor reliability, stability, and S / N ratio can be secured.

Further, in each of the above-described embodiments, the solid electrolyte layer 6
If a gas selective permeable filter is provided on the solid electrolyte layer 6 or the working electrode 2, the target detection gas can be selectively selected.
It can be sent to the side to further improve the detection accuracy. Further, by providing a water reservoir layer on the solid electrolyte layer 6, the sensitivity can be improved.

Other than that, the present invention can be implemented by combining various structures or shapes adopted in a normal gas sensor unless the gist of the present invention is changed.

Furthermore, although each of the above-described embodiments has been described with respect to the gas sensor, it can also be applied to various electrochemical sensors such as an ion sensor and a biosensor that have the same configuration and react with an ion component in a liquid. When used in a liquid, the solid electrolyte does not have to be gas permeable, and the structure is appropriately changed depending on the application.

〔The invention's effect〕

As described above, the present invention uses the metal compound layer to
It is possible to firmly bond the electrode metal and the intermediate bonding layer. Since the intermediate bonding layer and the insulating layer originally have a sufficient bonding force, as a result, the electrode metal is firmly bonded to the insulating layer. Therefore, the reliability of the sensor can be improved, stable performance can be exerted for a long period of time, and the life can be greatly extended.

In particular, even if a smooth insulating substrate is used to form a high-density fine electrode pattern, it has a high bonding force, does not cause electrode peeling as in the past, and can maintain excellent performance as a sensor. .

Moreover, due to the high resistance of the intermediate bonding layer, there is no fear of elution due to the battery effect during the operation of the sensor even when it is in contact with the solid electrolyte layer. Therefore, the problem that the elution material hinders the detection reaction and causes the deterioration of the sensor performance does not occur, and the reliability and stability of the sensor can be improved, and at the same time, the problem that the intermediate bonding layer elutes and causes electrode peeling occurs. It won't happen.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a gas sensor according to the present invention,
FIG. 2 is a process sectional view sequentially showing the manufacturing process, FIG. 3 is a perspective view of a conventional example, and FIG. 4 is a sectional view of an essential part of an electrode portion. 1 ... Insulating substrate, 2,3,4 ... Electrode, 5 ... Intermediate bonding layer, 5
0 ... Metal compound layer, 6 ... Solid electrolyte layer

Claims (1)

(57) [Claims] 1. 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 so as to cover at least the reaction portions of the electrodes, and a high electrode is provided between the insulating substrate and the electrodes. An electrochemical sensor, wherein an intermediate bonding layer for resistance is provided, and a metal compound layer made of a material for the intermediate bonding layer and a metal material for the electrode is formed at the interface between the intermediate bonding layer and the electrode. .