JPH0227254A - Small-sized oxygen electrode - Google Patents

Abstract

PURPOSE:To enable suppression of a drop in reproducibility and reliability attributed to evaporation of an electrolytic liquid by a method wherein a hole on the surface of a substrate is filled with a arginate gel containing the electrolytic liquid and the hole is covered with a gas permeable film to close. CONSTITUTION:A hole 5 is formed in an Si substrate 1 by an anisotropic etching and the entire surface thereof is covered with an SiO2 film 2 as insulation film. Gold electrodes 3A and 3B are applied in the hole 5 in a pair and parts thereof are extended to the outside of a groove separately. Then, a negative type photo resist is applied except for parts intended for the hole 5 and an electric contact. The substrate 1 is dipped into a sodium arginate aqueous solution (liquid A) and with the liquid A filling the hole 5, the substrate 1 is pulled up. Moreover, when it is immersed into a calcium chloride aqueous solution containing an electrolytic liquid, the liquid A is gelatinized instantaneously. Furthermore, the entire surface (except for an exposed part) of the top of the substrate 1 is covered with a gas permeable film 14. Thus, a gel 6 containing an electrolytic liquid of a fine volume with a flat surface is obtained with little change in volume before and after a reaction.

Description

[Detailed description of the invention] [Required] Regarding small oxygen electrodes, it is an object of the present invention to provide an acid rock electrode that is small and can be mass-produced at low cost and does not show deterioration in reproducibility and reliability due to evaporation of electrolyte. A substrate, a hole formed on the surface of the substrate by anisotropic etching, and a hole formed on the substrate with an insulating film interposed therebetween, the surface of the substrate being exposed from the bottom of the hole. , an electrolyte-containing alginate gel filled in the hole, and a gas permeable membrane covering and closing the hole.

[Industrial application field]

The present invention relates to a small-sized oxygen electrode, and particularly to an oxygen electrode that is small and can be mass-produced at low cost.

Small oxygen electrodes can be advantageously used for measuring dissolved oxygen concentrations in various fields.

For example, biochemical acid rock demand (BOD) in water is measured from the viewpoint of water quality conservation, and this small oxygen electrode can be used as a measuring device for dissolved oxygen concentration. Further, in the fermentation industry, in order to efficiently proceed with alcohol fermentation, it is necessary to adjust the dissolved oxygen concentration in the fermenter, and the small oxygen electrode of the present invention can be used as a measuring device for this purpose. Furthermore, the small oxygen electrode can be combined with an enzyme to form an enzyme electrode, which can be used to measure the concentration of sugars, vitamins, and the like. For example, glucose is oxidized to gluconolactone by reacting with dissolved oxygen using the enzyme glucose oxidase as a catalyst. Glucose concentration can be determined from consumption.

As described above, the small oxygen electrode of the present invention can be used in various fields such as environmental measurement, fermentation industry, and clinical medicine, but it is particularly suitable for use in the clinical medical field where it is attached to a °C catheter and inserted into the body. It is small, disposable, and inexpensive, making it very useful.

[Conventional technology]

Since conventional glass oxygen electrodes cannot be miniaturized or mass produced, the inventors developed a new type of small oxygen electrode using lithography technology and anisotropic etching technology. Applied for a patent (Patent application 1986-
No. 71739). This oxygen electrode is made by forming two electrodes through an insulating film over a hole formed on a silicon substrate by anisotropic etching, further accommodating an electrolyte-containing body inside the hole, and finally This is an oxygen electrode with a structure in which the upper surface of the hole is covered with a gas permeable membrane. This oxygen electrode is
It is small, has little variation in characteristics, and can be mass-produced in bulk, resulting in low cost.

In the above-mentioned type of oxygen electrode, the electrolyte-containing body is
Usually, the gel was impregnated with an electrolyte, such as an agarose gel. However, in the case of agarose gel, it was necessary to repeatedly inject it into many tiny holes on a silicon substrate one by one using a micropipette.

The present inventors conducted research to further improve this point and make it more suitable for mass production. Using polyacrylamide gel, -
We discovered a method that allows gel to be injected all at once (Patent application 1986-
No. 148221). The manufacturing method for this small oxygen electrode involves forming a plurality of holes using lithography technology and anisotropic etching technology, and forming a negative mold on a silicon substrate on which electrodes have been formed at the University of the Arts, except for the hole portions. coated with a resist, the substrate is immersed in a solution of a photopolymerizable monomer, preferably acrylamide, containing an electrolytic solution, and each hole is filled with the solution and cured by irradiation with ultraviolet rays,
It is characterized by forming a porous carrier containing an electrolyte in the holes. According to this manufacturing method, it is possible to form a porous carrier that selectively retains the electrolyte only in the minute holes that form the small oxygen electrode, thereby making mass production possible.

[Problem to be solved by the invention]

The method described in Japanese Patent Application No. 62-148221 mentioned above is an epoch-making manufacturing method in that very small oxygen electrodes can be produced in large quantities. However, a detailed study of this method revealed that there are problems that must be resolved before it can be put into practical use. In other words, when the dimensions of the holes that store the electrolyte become smaller, the surface area/volume ratio becomes extremely large, which not only makes it easier for the electrolyte to evaporate, but also when the heat generated during gelation of acrylamide is added, -
a. Evaporation is accelerated. Furthermore, it has been found that when the reaction is allowed to proceed in saturated steam to prevent evaporation, the aqueous solution itself absorbs water as it gels, and the volume of the polyacrylamide gel expands to more than double. Such volume changes are very disadvantageous in terms of reproducibility and reliability.

Therefore, an object of the present invention is to provide an oxygen electrode that is small, inexpensive, and mass-producible, and does not exhibit deterioration in reproducibility and reliability due to evaporation of the electrolyte.

[Means to solve the problem]

The present inventors conducted research with the understanding that the biggest cause of volume change during the production of polyacrylamide gel is a change in moisture, and as a result, we found that moisture evaporates (in dry air) or absorbs (in saturated water vapor). It has been found that if this is minimized, changes in gel thickness can be minimized and the exposed surface can be kept flat. In order to suppress such changes in water content, the present inventors have developed a method using alginate gel such as alginate lucium genove barium alginate instead of polyacrylamide gel. According to the method of the present invention, a gel can be obtained instantaneously, evaporation of water can be suppressed, and a gel with a flat surface that hardly changes in volume before and after the reaction can be easily obtained.

Specifically, the present invention includes a substrate, a hole formed on the surface of the substrate by anisotropic etching, and a hole formed on the substrate with an insulating film interposed therebetween. A small oxygen electrode characterized by having two electrodes reaching the surface, an electrolyte-containing alginate gel filled in the hole, and a gas permeable membrane covering and closing the hole. .

If the small-sized oxygen electrode of the present invention has noise or variations in characteristics that are thought to be caused by poor insulation in an aqueous solution, at least a hydrophobic insulating film on the back side of the electrode,
For example, it may additionally contain silicone rubber.

Preferably, the small oxygen electrode of the present invention is provided by forming a hole on a silicon substrate by anisotropic etching, forming two electrodes extending from the bottom of the hole to the surface of the substrate via an insulating film, and The top is covered with a photoresist except for the hole portions and the portions for electrical contact, and the photoresist-coated substrate is immersed in an electrolyte-containing alginic acid solution, and the aqueous solution is applied only to the hole portions. The substrate in this state is immersed in a calcium chloride aqueous solution containing an electrolytic solution to gel the IJium aqueous solution, and the upper surface of the hole is covered with a gas permeable membrane. .

In implementing the present invention, a metal substrate or a semiconductor substrate, particularly a silicon substrate, can be advantageously used as the base material or substrate of the electrode body.

The insulating film can be formed from a silicon oxide film or other materials. A silicon oxide film can be easily formed by thermally oxidizing a silicon substrate, for example.

The two electrodes can be varied depending on whether the electrodes being made are polar or galvanic. For example, when manufacturing a polar-mouth type oxygen electrode, both the picture electrode and the electrode are made of a gold electrode or a platinum electrode, and a voltage is applied between the two electrodes during measurement. In the case of a polar mouth type, it is preferable to use a neutral aqueous solution, such as a 0.1M potassium chloride aqueous solution, which does not easily attack the underlying silicon oxide film. In addition, lead is used as the anode side electrode.
An electrode made of a metal such as silver that causes less chemical reactions than gold or platinum is used, an electrode made of gold or platinum is used as the cathode electrode, and an alkaline aqueous solution such as a 1M potassium hydroxide aqueous solution is used as the electrolyte. For example, a galvanic type oxygen electrode can be manufactured. Formation of such an electrode can be advantageously performed by, for example, a film forming method such as vacuum evaporation or sputtering.

After forming the electrodes, preferably a photoresist is applied onto the substrate except for the hole portions of the substrate and the portions where electrical contact is to be made. This photoresist is preferably a negative type photoresist, such as OMR-83 manufactured by Tokyo Ohka. This type of photoresist is advantageous because it has the property of repelling an aqueous solution of sodium alginate containing an electrolyte when only the hole portions are filled with the aqueous solution.

Formation of an electrolyte-containing alginate gel can be achieved, for example, by immersing a substrate in an electrolyte-containing sodium alginate aqueous solution, slowly pulling up the substrate with the holes filled with the solution, and then immersing the substrate in this state into an electrolyte-containing solution. This can be advantageously carried out by immersion in an aqueous calcium chloride solution to form a gel. This technique may also be used to exchange sodium and calcium.

Although various electrolytes can be used as the electrolyte to be retained by the porous carrier, potassium chloride is preferred, for example. Sodium sulfate is not preferred because it causes precipitation.

Gas permeable membranes are hydrophobic and do not allow aqueous solutions to pass through them, but they are initially liquid and can be dip coated or spin coated, and can be used as electrode materials, substrates such as silicon substrates, and insulating films. It is also essential that the electrolyte has good adhesion to the silicon oxide film, etc., and that the electrolyte does not leak outside. Suitable gas permeable membrane materials include photoresists, preferably negative-tone photoresists, and the like. Although Teflon (trade name) membrane is oxygen permeable, it does not have adhesive strength.
Use must be avoided.

[For production]

The small-sized oxygen electrode according to the present invention uses lithography technology and book-forming technology used to form semiconductor integrated circuits to produce nine small-sized oxygen electrodes. The filling method must also be suitable for mass production. As a method of this invention, the present invention forms a porous material containing an electrolyte in holes all at once.
The substrate is immersed in an aqueous solution of sodium alginate containing an electrolytic solution to fill the holes, and the substrate is immersed in an aqueous solution of calcium chloride containing an electrolytic solution to form a gel.

By doing the above, it is possible to fill a large number of holes with the electrolyte at once. However, in the present invention, in order to perform the above operation more advantageously, a hydrophobic photoresist is used as the resist used for lithography. , preferably using a negative photoresist.

That is, the negative photoresist is rubber-based and hydrophobic, and has the property that even when immersed in an aqueous solution, the portion covered with the resist repels water.

Utilizing this, in the present invention, parts other than the holes are coated with a negative resist and then immersion treatment is performed.

In addition, in the present invention, for example, calcium alginate gel is used, but since the gelation reaction between sodium alginate and calcium chloride occurs instantaneously in an aqueous calcium chloride solution, it is easy to suppress changes in water content in the gel. A gel with a flat surface and almost no change in volume before and after the reaction can be easily obtained.

〔Example〕

Next, a preferred example of a method for manufacturing a small oxygen electrode according to the present invention will be explained with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a preferred example of a small-sized oxygen electrode according to the present invention. The illustrated oxygen electrode has a rectangular parallelepiped shape, the sensitive part is covered with a gas permeable membrane 14, and the electrodes 3A and 3B are connected to an attached device.
A part of it is exposed. In this example, the electrodes 3A and 3B were made of gold electrodes as well as the picture electrodes in order to have a polar mouth type.

The structure of the small oxygen electrode shown in FIG. 1 can be understood in detail from FIG. 2, which is a sectional view taken along the line II--II. A silicon substrate 1 has holes formed by anisotropic etching, and a silicon oxide film 2 is deposited as an insulating film on the entire surface thereof. Two gold electrodes 3A and 3B are deposited in pairs in the holes of the silicon substrate 1. As shown in FIG. 1, a portion of each of the gold electrodes 3A and 3B extends to the outside of the groove. Furthermore, the holes in the silicon substrate 1 are filled with an electrolyte-containing gel 6. Furthermore, the board 1 is placed at the top of the hole.
A gas permeable membrane 14 is coated to cover the entire upper surface (excluding the exposed portion in FIG. 1).

The small oxygen electrode shown in FIGS. 1 and 2 is, for example,
It can be advantageously manufactured by the manufacturing process shown in sequence in FIG. Note that the main body after forming the electrodes shown in FIG. 3(A) can be manufactured through the following steps.

In the following explanation, 1.
Although the case where only one oxygen electrode is formed on a wafer is described, it should be understood that in reality, multiple small oxygen electrodes are formed simultaneously.

1. Wafer Cleaning A 2-inch (100)-sided silicon wafer with a thickness of 350 μm was prepared and cleaned with a mixed solution of hydrogen peroxide and ammonia and concentrated nitric acid.

2.3 Formation of I02 film A silicon wafer was subjected to wet thermal oxidation to form a SiO□ film with a thickness of 0.8 μm on the entire surface.

3. Formation of etching pattern An etching resist pattern was formed on the wafer using a negative photoresist (TOKYO OHKABUKU OMR-83, viscosity 60 cP).

4. The same negative photoresist used in the above step was applied to the back side of the resist-coated wafer and baked at 130t for 3°.

5. Sin, film etching 50% hydrofluoric acid: 50% ammonium fluoride = 1:
The wafer was immersed in an aqueous solution of No. 6, and the exposed portion 8102 not covered with photoresist was removed by etching. Subsequently, the resist was removed using a sulfuric acid/hydrogen peroxide solution (2:1).

6. Anisotropic etching of Si Anisotropic etching of silicon was performed in a 35% potassium hydroxide aqueous solution at 80°C. Etching depth 300μ
After completing m0 etching, the wafer was washed with pure water.

After completing this anisotropic etching, the 5iO7 film used during etching was removed. This is 50 as in step 5.
% hydrofluoric acid; 50% ammonium fluoride = 1:6 aqueous solution.

7. Formation of 3in2 film In order to grow a 5in2 film on the surface of the silicon wafer 1, 1. Following a similar cleaning step, the wafers were wet thermally oxidized. A SlO□ film 2 with a film thickness of 0.8 μm was formed.

8. Formation of a gold thin film and a gold thin film Following the formation of a thin film (400 people, for adhesion between the gold and the substrate), a thin gold film (4000 people) was formed by vacuum evaporation.

9. Negative photoresist for electrode formation (Tokyo Ohkabukuro OMR-83, viscosity 60 cP)
) was used to form a resist pattern for electrode formation (not shown) on 8102 of wafer 1.

10. Gold and chromium etching The substrate on which the resist pattern was formed was immersed in the following gold and chromium etching solutions (1) and (3) in this order, and the exposed gold and chromium portions were removed by etching. Furthermore, after washing with pure water, sulfuric acid/hydrogen peroxide solution (2:
1) The resist was removed using a solution.

■Gold etching solution: 4gKI and Igl□ 40
Dissolved in ml of water.

■Etching solution: Q, 5 g NaOH and 1 g K3Fe(CN)s dissolved in 4 ml water.

FIG. 3(A) shows the state in which the gold electrode is formed.

In the figure, 3A and 3B are electrodes, and 5 is a hole.

11. Applying resist (Figure 3 (B)) Apply negative photoresist (Tokyo Ohka Bag) to the surface of the main body other than the hole 5 and the pad area for electrical contact.
Coated with OMR-83, viscosity 60 cP) 4.

This was done by applying a photoresist to the surface of the wafer, exposing and developing after pre-beta.

12. The hydrophilized wafer in the hole was immersed in a 1M hydroxide solution. As a result, the areas not covered with resist became hydrophilic.

13. Filling with alginate calcium gel (Figure 3 (C)
) The following two types of solutions were prepared for forming electrolyte-containing gels.

Solution A: Sodium nyalginate dissolved in 0.1M potassium chloride aqueous solution. Sodium alginate concentration 0,
2%.

Solution B: Calcium chloride dissolved in a 0.1M potassium chloride aqueous solution. Calcium chloride concentration 5%.

When the wafer shown in Fig. 3 (B) was immersed in liquid A and slowly pulled up, the negative photoresist film 4 was hydrophobic, so the liquid A was repelled from the resist film and remained only in the CC holes. . Next, when this wafer was immersed in Solution B, Solution A instantly gelled. An electrolyte-containing gel 6 was obtained.

14. Covering the gas permeable membrane (Fig. 3 (D)) The gas permeable membrane 14 is coated on the electrolyte-containing gel 6 so as to cover the gel.
coated. In this example, the same negative photoresist as used in step 3 was used as the gas permeable film. That is, a negative photoresist (manufactured by Tokyo Ohka Co., Ltd. OMR-
83 (trade name), viscosity 60 cP) was applied to a thickness of about 2 μm by spin coating. This resist was immediately exposed and developed without prebaking, and then a small oxygen electrode was left in pure water or saturated steam overnight to remove the thinner from the resist, completing a gas permeable membrane.

〔Effect of the invention〕

According to the present invention, it is possible to easily obtain in a short time a gel with a flat surface and a microscopic structure that does not easily change in volume. Permeable membrane damage is reduced and yield is improved. In addition, since it becomes easier to control the distance between the gas permeable membrane and the cathode, which affects the characteristics of small oxygen electrodes, it is possible to easily control the distance between the gas permeable membrane and the cathode. Variations can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a preferred example of a small oxygen electrode according to the present invention, FIG. 2 is a cross-sectional view of the electrode in FIG. 1 along line II-I+, and FIGS. (D) is a sectional view sequentially showing the second half of the manufacturing process of the small oxygen electrode shown in FIGS. 1 and 2. In the figure, 1 is a substrate, 2 is an insulating film, 3A and 3B are electrodes,
4 is a photoresist film, 5 is a hole, 6 is an electrolyte-containing genope, and 14 is a gas permeable film.

Claims (1)

[Claims] 1. A substrate, a hole made by anisotropic etching on the surface of the substrate, and 2. A hole formed on the substrate via an insulating film, extending from the bottom of the hole to the surface of the substrate. 1. A small-sized oxygen electrode, comprising a solid electrode, an electrolyte-containing alginate gel filled inside the hole, and a gas permeable membrane covering and closing the hole.