JPH0227253A - Small-sized oxygen electrode - Google Patents

Abstract

PURPOSE:To enable a reduction in scattering of a response value by covering at least a back of a substrate with a hydrophobic insulation film to make it hard to be affected by a noise. CONSTITUTION:An Si substrate 1 has a hole 5 formed by an anisotropic etching and the entire surface thereof is covered with an SiO2 film 2 as insulation film. Moreover, the back of the substrate 1 is covered with a hydrophobic insulation film 7 hard to break. Gold electrodes 3A and 3B are applied on the hole 5 in a pair and parts thereof are extended to the outside of a groove. The hole 5 is filled with a porous material (gel) 6 containing an electrolyte. Moreover, the top of the hole 5 is covered with a gas permeating film 14 in such a manner as to cover the entire surface (expect for an exposed part) of the top of the substrate 1. This insulation film is made up of a negative type photoresist applied by a dip coating to cover both the side and back of the substrate 1. That is, a cell forming an oxygen electrode is electrically isolated completely from the outside world comprising an aqueous solution.

Description

[Detailed Description of the Invention] [Summary] Regarding a small oxygen electrode, it is an object of the present invention to provide an oxygen electrode that is small, low cost, and can be mass-produced without showing a decrease in reproducibility or reliability during measurement in an aqueous solution. A substrate, a hole made on the surface of the substrate by anisotropic etching, and an insulating film formed on the substrate, extending from the bottom of the hole to the surface of the substrate. In a small oxygen electrode having two electrodes, an electrolyte-containing porous material filled inside the holes, and a gas permeable membrane covering and closing the holes, the substrate further includes at least a back surface thereof. The structure is configured to include a hydrophobic insulating film.

[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, from the viewpoint of water quality conservation, biochemical oxygen demand in water i
ff (BOD) is being measured, and this small oxygen electrode can be used as a measuring device for the 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 catalyzed by the enzyme glucose oxidase,
It reacts with dissolved oxygen and oxidizes to gluconolactone, which reduces the amount of dissolved oxygen that diffuses into the oxygen electrode cell, which allows the glucose concentration to be measured from the amount of dissolved oxygen consumed.

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. In addition, it is 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 it was a gel 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). This method of manufacturing a small oxygen electrode involves forming a plurality of holes using lithography technology and anisotropic etching technology, and forming a negative electrode on a silicon substrate on which each electrode is formed. Covering the mold resist, immersing the substrate in a solution of a photopolymerizable monomer, preferably acrylamide, containing an electrolyte, and irradiating the substrate with ultraviolet rays while filling each hole with the solution to cure it,
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 we investigated the characteristics of this small oxygen electrode, we found noise, which was as large as the absolute value of the current.
It has been found that in some cases it is not possible to use it as an oxygen electrode. In addition, in order to put it into practical use, it is necessary to obtain the same current value for the same oxygen concentration, but in reality, the current value is on the order of nA for small ones, and on the order of nA for large ones, depending on the device obtained. It was found that there is a variation in the response value of the difference. Such noise or extreme variations in characteristics 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 show a decrease in reproducibility or reliability during measurements in an aqueous solution.

[Means to solve the problem]

The present inventors have discovered that the cause of the noise and variation in characteristics described above is poor insulation in an aqueous solution. It was also found that not only the side surface where the silicon substrate is exposed when cutting into chips, but also the back surface on which the 5in2 film is formed by thermal oxidation have poor insulation in water, and that this is insufficient.

The poor insulating properties of SiO□ were thought to be due to its hydrophilic nature, which easily caused electrical short-circuits between the substrate and the external aqueous solution. In order to solve this problem of poor insulation, the present inventors have discovered that a hydrophobic insulating film can be formed on at least the back surface of the chip of a small oxygen electrode. It was also found that the dispersion of response values was significantly improved.

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 having two electrodes reaching the surface, an electrolyte-containing porous material filling the inside of the hole, and a gas permeable membrane covering and closing the hole, wherein the substrate further includes at least This small oxygen electrode is characterized by having a hydrophobic insulating film on its back surface.

The small oxygen electrode of the present invention is preferably made by making a hole on a silicon substrate by anisotropic etching, forming two electrodes from the bottom of the hole to the surface of the substrate via an insulating film, and forming a hole on the back side of the substrate. After covering with a hydrophobic insulating film, the inside of the hole is filled with an electrolyte-containing porous material, and a gas permeable film is formed by dip coating or the like.

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 side electrodes are made of gold or platinum electrodes, 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.
If you use an electrode made of a metal such as silver that is more likely to cause a chemical reaction than gold or platinum, use an electrode made of gold or platinum as the cathode side electrode, and use an alkaline aqueous solution such as 1M potassium hydroxide aqueous solution as the electrolyte. , 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 the aqueous solution that is the raw material when only the hole portions are filled with an electrolyte-containing porous material.

The formation of a porous chamber material containing an electrolyte is described, for example, in Japanese Patent Application No. 62-1.
As described in No. 48221, a substrate is immersed in an acrylamide aqueous solution containing an electrolyte, the substrate is slowly pulled up while immersed in such solution, and the substrate in this state is further irradiated with ultraviolet rays to gel it. A method of forming an electrolyte-containing alginate gel, e.g., a method of forming an electrolyte-containing alginate gel, e.g., by coating a photoresist-coated substrate with an electrolyte-containing alginate gel).
A method of immersing the substrate in a sodium alginate aqueous solution to fill only the hole portion with the aqueous solution, and immersing the substrate in this state in an electrolyte-containing calcium chloride aqueous solution to gel the sodium alginate aqueous solution to form a calcium alginate gel. In the sol-gel method used in the process of synthesizing glass, for example, a substrate coated with a photoresist is immersed in a mixed solution of metal alkoxide, water, and an electrolyte, and the holes are filled with the mixed solution. This can be advantageously carried out by a method in which the electrolytic solution is gelled by a sol-gel method and the electrolytic solution is retained by the gel.

Various electrolytes, such as potassium chloride and sodium sulfate, can be used as the electrolyte to be retained by the porous material as a carrier.

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 oxygen electrode according to the present invention is mass-produced using lithography technology and thin film formation technology that are used in the formation of semiconductor integrated circuits, and in order to be able to withstand practical use, It must be possible to obtain low noise and good reproducibility. As a method for this purpose, the present invention improves insulation by coating a hydrophobic insulating film on the surface and side surfaces of the substrate opposite to where the oxygen electrode is formed.

By doing the above, the cell forming the oxygen electrode is completely electrically isolated from the outside world made of aqueous solution, and it is possible to reduce variations in response values and noise. However, in the present invention, the above operation In order to achieve this more advantageously, a hydrophobic resin is applied to the back surface of the oxygen electrode after the formation of the cathode and anode, and this film is then coated by dip coating when forming the gas permeable film (also hydrophobic). This also provides insulation on the side surfaces.

〔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 to make them Bolaro 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. Furthermore, the back surface of the substrate is covered with a hydrophobic insulating film 7 that is hard to tear. 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. Further, the holes in the silicon substrate 1 are filled with an electrolyte-containing porous material (hereinafter referred to as gel) 6. Furthermore, a gas permeable film 14 is coated on the upper part of the hole so as to cover the entire upper part of the substrate 1 (excluding the exposed part in FIG. 1), and this is also used as an insulating film on the side and back surfaces. covered.

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. Here, a case will be described in which calcium alginate gel is used as an electrolyte-containing gel.

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.

Formation of 2.5i02 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 (OMR-83 manufactured by Tokyo Ohka Co., Ltd., viscosity 60 cP).

4. Resist coating The same negative photoresist as used in the above step was also applied to the back side of the wafer and baked at 130°C for 30 minutes.

5.5iO7 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 silicon Silicon was anisotropically etched in a 35% potassium hydroxide aqueous solution at 80°C. Etching depth 300μn
]. After etching was completed, the wafer was washed with pure water.

After completing this anisotropic etching, the 5102 film used during etching was removed. This is 50 as in step 5.
% hydrogen fluoride? a: 50% ammonium fluoride = 1:6
It was carried out in an aqueous solution.

? , Formation of SiO□ film In order to grow a 5iO7 film on the surface of the silicon wafer 1, 1. Following a similar cleaning step, the wafers were wet thermally oxidized. A Sin□ film 2 with a thickness of 0.8 μm was formed.

8. Formation of Chromium and Gold Thin Films Following the ROM thin film (400 people, adhesion of gold and substrate), a gold thin film (4000 people) was formed by vacuum evaporation.

9. Formation of resist pattern for electrode formation Negative photoresist (manufactured by Tokyo Ohka Co., Ltd. DMR-83, viscosity 60 cP)
) was used to form a resist pattern for electrode formation (not shown) on the SiO□ of the 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.

■Total etching solution: 4g Kr and 40g of Igla
Dissolved in ml of water.

■Chrome etching solution: 0.5 g NaOH and 1
g LFe(CN)a dissolved in 4 ml of 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 Formation of a hydrophobic insulating film on the back side of the substrate A hydrophobic insulating film (KR-282 manufactured by Shin-Etsu Silicone) is formed on the back side of the substrate 1.
was coated in a similar manner and baked at 250°C. This insulating film is indicated by 7.

12. Applying resist (Figure 3 (B)) Apply negative photoresist (manufactured by Tokyo Ohka Co., Ltd.) 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.

13. Cutting out the substrate A large number of oxygen electrodes formed on the substrate were cut into chips.

14. The tip of the hydrophilized tip in the hole was immersed in a 1M aqueous sodium hydroxide solution. As a result, the areas not covered with resist became hydrophilic.

15. Filling with calcium alginate 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 chip 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 hole 5. Ta. Next, when this chip was immersed in Solution B, Solution A instantly gelled. An electrolyte-containing gel 6 was obtained.

16. 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 by dip coating. This resist is immediately exposed and developed without pre-baking, and then the small oxygen electrode body is left in pure water or saturated steam overnight to remove the thinner from the resist, completing the gas permeable film and sidewall insulating film. I let it happen. This resist film is also formed on the back surface, which has an advantageous effect in further improving the insulation properties.

〔Effect of the invention〕

According to the present invention, the portion of the cell forming the acid rice electrode is completely electrically isolated from the external aqueous solution, making it less susceptible to noise and reducing variations in response values. Therefore, the reproducibility and
A compact, low-cost, mass-producible oxygen electrode is provided that does not exhibit a decrease in reliability.

[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 IT-II, 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 genepe 7 is a hydrophobic insulating film, 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. In a small oxygen electrode comprising a solid electrode, an electrolyte-containing porous material filled inside the hole, and a gas permeable membrane covering and closing the hole, the substrate further includes, at least on the back side thereof, A small oxygen electrode characterized by having a hydrophobic insulating film.