JPH01223337A - Manufacture of small oxygen electrode - Google Patents

Abstract

PURPOSE:To obtain a gel with a fine volume having a flat surface thereof free from a volume change easily, by a method wherein a monomer solution is irradiated with light through a transparent member to convert in into gel and the top surface of the holes is covered with a gas permeable film. CONSTITUTION:Holes are made on a substrate 1 by anisotropic etching to form two electrodes 3A and 3B to the surface of the substrate 1 from the bottom of the holes through an insulation film 2. Then, the substrate 1 is covered with a photoresist excluding the holes and a part intended for an electric contact and then, immersed into a photopolymerizing monomer solution tending to form a gel 6 containing an electrolytic liquid to fill the holes along with the monomer solution. With the holes covered by a transparent member, light is irradiated to convert the monomer solution into gel and the top surface of the holes is covered with a gas permeable film 14 thereby facilitating the production of a gel with a fine volume having a flat surface thereof.

Description

[Detailed Description of the Invention] [Summary] Regarding the manufacturing method of a small oxygen electrode, the present invention aims to solve the problem of reduced reproducibility and reliability caused by evaporation of an electrolyte when manufacturing a small oxygen electrode that can be mass-produced. In order to solve this problem, a hole is made on the substrate by anisotropic etching, two electrodes are formed from the bottom of the hole to the surface of the substrate, and two electrodes are formed on the substrate through the hole and the electrical contact. The photoresist coated substrate is immersed in an electrolyte-containing gel-forming photopolymerizable monomer solution to fill only the holes with the seven-mer solution, and each hole is The monomer solution is irradiated with light while covered with a transparent member to gel the monomer solution, and the upper surface of the hole is covered with a gas permeable film.

(Industrial Application Field) The present invention relates to a method for manufacturing a small-sized oxygen electrode, and particularly to a method for manufacturing an oxygen electrode that is small, inexpensive, and can be mass-produced.

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

For example, from the perspective of water quality conservation, the amount of biochemical oxygen supply in water (Biological Oxygen Demand)
This small oxygen electrode can be used as a measuring device for dissolved oxygen concentration (abbreviated as BOD).

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 temperature measuring device.

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 (CJhO+z) reacts with dissolved oxygen using an enzyme called glucose oxidase (abbreviated as G00) as a catalyst to produce gluconolactone (C&H1).
1106), and the concentration of glucose can be measured from the amount of dissolved oxygen consumed by utilizing the fact that this reduces the amount of dissolved oxygen that diffuses into the oxygen electrode cell.

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 especially in the field of clinical medicine where it is attached to a catheter and inserted into the body. 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. Patent application filed (Japanese Patent Application 1986-7)
No. 1739). In this enzyme electrode, two electrodes are formed on a groove created by anisotropic etching on a silicon substrate with an insulating layer interposed therebetween, and an electrolyte-containing body is housed inside the groove, and finally, This is an oxygen electrode with a structure in which the upper surface of the groove is covered with a gas permeable membrane. This oxygen electrode is small, has little variation in characteristics, and is highly accurate.
Mass production is possible at low cost.

In the above-mentioned type of oxygen electrode, the electrolyte-containing body is
Usually it was a gel impregnated with an electrolyte, such as an agarose gel. However, with this electrolyte-containing body, according to the original method, it was necessary to repeatedly inject the agarose gel into minute grooves on the silicon substrate once with a micropipette.

The present inventors conducted research to further improve this point and make it more suitable for mass production. Using polyacrylamide gel, the present inventors used polyacrylamide gel to create a structure in which holes were placed in many microscopic holes drilled on a silicon substrate. found a way to inject the gel (
(Refer to Japanese Patent Application No. 61-148221), this method of manufacturing a small oxygen electrode involves forming a plurality of holes using photolithography and anisotropic etching, and then forming electrodes on a silicon substrate in various ways. , the substrate is coated with a negative resist except for the holes, and the substrate is coated with a photopolymerizable monomer containing an electrolyte;
Preferably, the carrier is immersed in an acrylamide solution, and each hole is filled with the solution and cured by irradiation with ultraviolet rays to form a porous carrier containing the electrolyte in the hole. 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, as 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 causes the layer to evaporate when the heat generated during gelation of acrylamide is added. is accelerated. Additionally, when the reaction was allowed to proceed in saturated steam to prevent evaporation, the aqueous solution itself absorbed water as it gelled, and it was found that the volume of the polyacrylamide gel could expand to more than double. . Such volume changes are very inconvenient in terms of reproducibility and reliability.

Therefore, an object of the present invention is to solve the problem of deterioration in reproducibility and reliability caused by evaporation of the electrolyte when manufacturing an oxygen electrode that is small and can be mass-produced.

[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 the change in water content. 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 poured an acrylamide aqueous solution (containing an exacerbant, a polymerization accelerator, and an electrolyte) into the hole of the small oxygen electrode body, and then immediately poured the acrylamide solution into the upper part of the aqueous solution. We developed a method in which a transparent, thin material such as a plate (for example, a cover glass) or a membrane is placed to prevent moisture from flowing in or out, and the aqueous solution in this state is irradiated with light from a mercury lamp or fluorescent lamp to solidify the gel. According to the method of the present invention, it is possible to easily obtain a gel with a flat surface and almost no change in volume before and after the reaction.

The present invention is characterized in that a hole is formed on a substrate by anisotropic etching, and two holes are formed from the bottom of the hole to the surface of the substrate.
A main electrode is formed through an insulating film, the substrate is coated with a photoresist except for the hole portion and the portion for making electrical contact, and the photoresist-coated substrate is coated with an electrolyte-containing gel-forming photopolymerizer. The monomer solution is immersed in a transparent monomer solution to fill only the holes, and each hole is covered with a transparent member, and the monomer solution is gelled by irradiation with light. A method for manufacturing a small oxygen electrode characterized by being coated with a gas permeable membrane.

In carrying out the method of the present invention, a semiconductor substrate, particularly a silicon substrate, can be advantageously used as the base material of the electrode body.

The insulating film can be formed from a silicon oxide film or other materials. For example, when the substrate is a silicon substrate, the silicon oxide film can be advantageously formed by thermally oxidizing the substrate.

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 gold or platinum, 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 0.1 M potassium chloride aqueous solution, which does not easily attack the underlying silicon oxide film. In addition, as the anode side electrode, a metal electrode such as lead, silver, silver/silver chloride, etc., which is more likely to cause a chemical reaction than gold or platinum, is used, and as the cathode side electrode, a metal electrode such as gold or platinum is used, and as the electrolyte. For example, by using an alkaline aqueous solution such as a 1M potassium hydroxide aqueous solution, a galvanic type oxygen electrode can be manufactured. Formation of such an electrode can be advantageously performed by a film forming method such as vapor deposition or sputtering.

The photoresist coated on the substrate after the electric bridge is formed, except for the hole portions and the electrical contact portions, is preferably a negative type photoresist, such as OMR-83 manufactured by Tokyo Ohka Co., Ltd.
It is. This type of photoresist is useful when only the holes are filled with an electrolyte-containing gel-forming monomer solution because it has the property of repelling such a solution.

To form an electrolyte-containing gel, a substrate is immersed in a photopolymerizable monomer solution that has the property of forming such a gel, and with the solution filled in the hole, the substrate is slowly pulled up and the upper part of the hole is removed. This can be advantageously carried out by covering the monomer with a transparent member such as a plate or film and irradiating it with light such as ultraviolet rays to polymerize the monomer and turn it into a gel.

Suitable photopolymerizable monomers include acrylamide and the like.

Various electrolytes can be used as the electrolyte to be retained by the porous carrier. - Examples include sodium sulfate (NazSOn), potassium chloride (KCl), etc.

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.
Silicon substrate and silicon oxide film as an insulating film (
It is also an essential requirement that the adhesion with S10□) is good and that the electrolyte does not leak to the outside. Suitable gas permeable membrane materials include photoresists, preferably negative photoresists. Although Teflon (trade name) membrane is permeable to oxygen, it does not have adhesive strength and should be avoided.

[For production]

The small oxygen electrode according to the present invention mass-produces the small oxygen electrode using photolithography technology and thin film formation technology that are used in the formation of semiconductor integrated circuits. The process also needs to be done in a way that is suitable for mass production.

As a method for this purpose, the present invention forms a porous polymer containing an electrolyte in the holes all at once. Specifically, the silicon substrate is placed in a mixed solution of a photopolymerizable wood-loving monomer 7 and an electrolyte aqueous solution. A porous polymer is created by dipping the polymer into holes and irradiating it with light such as ultraviolet rays through a transparent member, and acrylamide is suitable as the wood-philic monomer. Here, the electrolyte is preserved in the pores of the porous polymer.

With the above method, a large number of holes can be filled with the electrolytic solution at once, but the problem in this case is that the porous polymer is also formed on the silicon substrate surface other than the holes.

In order to prevent this, in the present invention, a water-based photoresist, preferably a negative type photoresist, is used as the resist used in the photolithography technique. In other words, negative photoresist is rubber-based and has hydrophobic properties, so even if it is immersed in an aqueous solution, the area covered with the resist will repel water.
There is a tendency to become Utilizing this, the present invention covers portions other than the holes with a negative resist and performs immersion treatment.

Further, in the present invention, light irradiation is performed through a transparent member. Since the photopolymerizable monomer solution inside the hole is covered with this transparent material, it is possible to suppress the inflow and outflow of water and the evaporation of the electrolyte, and the surface is flat with almost no change in volume before and after the reaction. gel 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 described 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 oxygen electrode shown in FIG. Portions of electrodes 3A and 3B are exposed for connection to an attached device. In this example, the electrodes 3A and 3B were made of gold electrodes as well as the picture electrodes in order to have a Bolaro type.

The structure of the small oxygen electrode shown in FIG. 1 can be understood in more detail from FIG. 2, which is a cross-sectional view taken along line nn. The silicon substrate 1 has holes formed by anisotropic etching. It also has a silicon oxide film (S) on its entire surface.
In, film) 2 is deposited as an insulating film. Two gold electrodes 3A and 3B are deposited in pairs in the holes of the silicon substrate l. As shown in FIG. 1, a portion of each of the gold electrodes 3A and 3B extends to the outside of the groove. Further, the holes in the silicon substrate 1 are filled with an electrolyte-containing gel 6. Further, the upper part of the hole is covered with a gas permeable film 14 so as to cover the entire upper part of the substrate l (excluding the exposed part in FIG. 1).

The miniature oxygen electrodes shown in FIGS. 1 and 2 can be advantageously manufactured, for example, 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, in order to make it easier to understand, we will describe the case where only one oxygen electrode is formed on one wafer (silicon substrate), but in reality, many small oxygen electrodes are formed at the same time. I would like you to understand that

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

2. Formation of a Sin film A silicon wafer is wet thermally oxidized to form a film with a thickness of 0 on the entire surface.
．． 8-Sin film was formed.

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

4. The same photoresist used in the above step was also applied to the back side of the resist-coated wafer and beta-treated at 130°C for 30 minutes.

5. Etching of Si0g film The wafer was immersed in an aqueous solution of 50% 0% fluorine fi: 50% ammonium fluoride, and the exposed portion of the 5in2 film not covered with photoresist was removed by etching. Subsequently, the resist was removed using a sulfuric acid/hydrogen peroxide (2:1) solution.

(i, Anisotropic etching of Si Anisotropic etching of silicon was performed in a 35% potassium hydroxide aqueous solution at 80°C.Etching depth 300I!
m. After etching was completed, the wafer was washed with distilled water.

After completing this anisotropic etching, the SiOg film used during etching was removed. This removal work is carried out in step 5 above.
．． This was carried out using a mixed solution of hydrofluoric acid/ammonium fluoride in the same manner as in .

? , Formation of SiO□ film In order to grow a 5ift film on the anisotropically etched portion of the silicon wafer, the wafer was subjected to wet thermal oxidation. Film thickness 8
000 5iot membranes were formed.

8. Formation of resist pattern for electrode formation A resist pattern for electrode formation was formed on the 5iOz film of the wafer using a negative photoresist (Tokyo Ohka OMR-83).

9. Gold electrodes 3A and 3B were formed by vapor depositing gold to a thickness of 2,500 yen using the resist pattern formed on the electrode formation site as a mask. In addition, prior to this gold vapor deposition, chromium was vapor deposited to a thickness of 300 mm in order to improve the adhesion of the gold electrode. A cross section is shown in FIG. 3(A).

After forming the electrode, remove unnecessary resist with sulfuric acid, fill the hole (5 in Figure 3 (A)) formed in the electrode body by anisotropic etching with electrolyte-containing gel, and allow gas permeation. coated with a sexual membrane. These steps will be explained with reference to FIG.

10. Applying resist (Figure 3 (B)) Apply negative photoresist (Tokyo Oka type O
MR-83, viscosity 60 cp) 4.

This was carried out by coating the entire front and back surfaces of the wafer with photoresist, and performing exposure and development after pre-beta.

11. Filling and exposure of electrolyte-containing photopolymerizable monomer solution (Figure 3 (C)) For forming electrolyte-containing gel, the following four types of solutions were prepared: Liquid A Niacrylamide) (Main agent) ) 30g and N.

0.8g of N'-methylenebisacrylamide (crosslinking agent) I M Dissolved in NazSOa aqueous solution.

B liquid: Riboflavin (vitamin Bz, curing accelerator) 4■
0. IM Dissolved in NatSO4 aqueous solution.

Solution C: 0.23g of N,N,N',N'-tetramethylethylenediamine (polymerization initiator) 0.1? I Na
Dissolved in tSOn aqueous solution.

Solution D: O, lM Na-rich SOi aqueous solution.

These solutions were Afi: B solution: C solution: D solution = 4:1:1
:1 to obtain an electrolyte-containing gel-forming upper solution. When the wafer shown in FIG. 3(B) was immersed in this monomer solution 7 and slowly pulled up, since the photoresist 114 is hydrophobic, the monomer solution 7 was repelled from the resist film and remained only in the holes 5. Ta. Next, a transparent cover glass 8 having a thickness of 0.1 mm was placed over the wafer surface, and the glass was irradiated with light from a mercury lamp (not shown) for 10 minutes. Polymerization of the seven polymers proceeded.

12. Completion of gelation (FIG. 3(D)) After confirming that polymerization was completed and gel 6 containing electrolyte was formed, the cover glass was removed.

13. Covering the gas-permeable membrane (Fig. 3 (E)) The gas-permeable membrane 14 is coated on the electrolyte-containing gel 6 so as to cover the gel.
coated. In this example, as a gas permeable membrane, the process lO
The same negative photoresist used in the Niresist application was used.

That is, a negative photoresist OMR-83 (trade name) was applied by spin coating to a thickness of about 2 mm. This resist was immediately exposed to light without baking, and then a small oxygen electrode was left in pure water or saturated steam overnight to draw out the thinner in the resist, completing a gas-permeable film.

〔Effect of the invention〕

According to the method of the present invention, it is possible to easily obtain a gel with a small volume and a flat surface with no change in volume, making it easier to form a gas permeable membrane on the surface. 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, when manufacturing many small oxygen electrodes on one wafer at the same time, the characteristics The above variation can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a preferred example of a small-sized oxygen electrode according to the present invention, FIG. 2 is a cross-sectional view along the line segment ■-■ of the electrode in FIG. 1,
FIGS. 3A to 3E are cross-sectional views sequentially showing the latter 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
5 is a photoresist film, 5 is a hole, 6 is an electrolyte-containing gel, and 14 is a gas permeable film. Perspective view of small oxygen electrode Fig. 1 Cross-sectional view of electrode sensitive part Fig. 2 14... Manufacturing process of gas permeable membrane small oxygen electrode Fig. 3

Claims (1)

[Claims] 1. Drill a hole on the substrate by anisotropic etching, form two electrodes from the bottom of the hole to the surface of the substrate via an insulating film, and connect the hole and electrical contacts on the substrate. The photoresist-coated substrate is immersed in a gel-forming photopolymerizable monomer solution containing an electrolytic solution to fill only the hole portions with the monomer solution, and each hole is A method for manufacturing a small oxygen electrode, comprising: gelling the monomer solution by irradiating it with light while covered with a transparent member; and covering the upper surface of the hole with a gas-permeable film.