JP2623808B2 - Manufacturing method of small oxygen electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for manufacturing a small-sized oxygen electrode, which is intended to put into practical use a small-sized oxygen electrode that withstands high-temperature sterilization and has improved reliability in use. To make a hole,
After providing an oxide film on the substrate to form an insulating substrate, two electrodes are provided from the bottom of the hole to the surface of the substrate, and covered with a resist except for the hole portion and the electrode extraction portion. In a state where the resist-coated substrate is immersed in an aqueous solution of sodium alginate containing an electrolytic solution and only the hole is filled with the aqueous solution, the substrate is immersed in an aqueous solution of calcium chloride containing the electrolytic solution to form a porous film containing the electrolytic solution. After a porous carrier is formed in the hole, the resist-coated substrate is immersed in the electrolyte-containing sodium alginate in a small oxygen electrode in which the upper surface of the hole is covered with a gas-permeable membrane, and After filling, the substrate is immersed in an aqueous solution of a mixture of electrolyte-containing calcium chloride, metal alkoxide and hydrochloric acid to gel the aqueous sodium alginate solution and metal alkoxide. Ri constituting the manufacturing method of a small oxygen electrode.

[Industrial applications]

The present invention relates to a method for manufacturing a small oxygen electrode suitable for mass production and resistant to high-temperature sterilization.

Small oxygen electrodes are used for measuring dissolved oxygen concentration.

For example, the measurement of biochemical oxygen supply in water (Biological Oxigen Demand abbreviated as BOD) is performed from the viewpoint of water quality conservation, and an oxygen electrode is used to measure the dissolved oxygen concentration.

Also, in the fermentation industry, it is necessary to adjust the dissolved oxygen concentration in the fermenter to efficiently promote alcohol fermentation, an oxygen electrode is used as this measuring instrument, and an enzyme electrode is formed in combination with an enzyme. The measurement of the concentration of sugar, vitamins, etc. is performed.

In the field of clinical medicine, catheters (Kath
eter) and inserted into the body for use.

[Conventional technology]

An ordinary oxygen electrode is made of glass or a polymer compound, and has a cathode and an anode provided in an open-ended cell. The cell is filled with an electrolytic solution and the opening is covered with an oxygen-permeable membrane. Structure is taken.

However, as long as such a structure is adopted, the size cannot be reduced, and mass production is difficult.

Therefore, the present inventors performed anisotropic etching using a silicon (Si) substrate to form a large number of holes with high pattern precision, and then formed two electrodes using photolithography technology (photolithography). A new type of miniature oxygen electrode in which the electrolyte-containing body is accommodated in the hole and the upper surface of the hole is finally covered with a gas permeable membrane has been developed and filed.

(Japanese Patent Application No. 62-71739 (JP-A-63-238548), filed on March 27, 1987) This oxygen electrode is small in size, has little characteristic fluctuation, and is suitable for mass production.

And agarose gel (agar) was used as the electrolyte-containing body.

However, in the case of agarose gel, there is an inconvenience that it is necessary to repeatedly inject into the minute holes on the Si substrate one by one using a micropipette.

Therefore, the present inventors have found a method of using calcium alginate gel and simultaneously injecting the gel only into many small holes provided on the Si substrate, and have applied for the application.

(Japanese Patent Application No. 63-176978 (Japanese Unexamined Patent Application Publication No. 2-27254), filed on July 18, 1988) This manufacturing method uses a photolithography technique and an anisotropic etching technique to form a large number of holes, and then forms an electrode. On the Si substrate on which was formed, a negative resist was coated except for the holes.
The substrate is immersed in an aqueous solution of sodium alginate containing an electrolytic solution, and while each hole is filled with the aqueous solution, the substrate is immersed in an aqueous solution of calcium chloride containing an electrolytic solution. Is deposited in the holes.

FIG. 1 is a perspective view of the small oxygen electrode 1 thus manufactured, FIG. 2 is a sectional view of the small oxygen electrode taken along the line XX 'in FIG. 1, and FIG. FIG.

Now, the structure and the manufacturing process will be briefly described as follows.

In FIGS. 1 and 2, a silicon (Si) substrate 2 having a (100) surface is anisotropically etched by photolithography to form square holes, and then thermally oxidized. A thicker oxide film 3 made of silicon dioxide (SiO ₂ ) is provided for insulation, and the electrodes 4 and 4 ′ are formed so as to oppose the electrodes 4 and 4 ′ from inside the hole to the surface of the substrate 2.

Next, an electrolytic solution-containing gel 6 made of calcium alginate containing an electrolytic solution is put in the hole, and the hole is covered with a gas permeable membrane 7.

FIGS. 3A to 3D specifically show this manufacturing process.

That is, a (100) plane is used as a substrate surface, and a Si substrate 2 having a thickness of 350 μm and a diameter of 2 inches is prepared by mixing a mixed solution of hydrogen peroxide (H ₂ O ₂ ) and ammonia (NH ₃ ) with concentrated nitric acid (HNO ₃ ). After that, the Si substrate 2 is wet-oxidized at about 1000 ° C. in the presence of water vapor, and a SiO 2 layer having a thickness of about 0.8 μm
_An oxide film 3 of ₂ is formed.

Next, a negative resist with a viscosity of about 60 cp (Ohka, Tokyo Oka)
After spin-coating MR-83) on the front and back of the Si substrate 2 to form a resist film, the resist film on the surface is projected and exposed.
Open the hole forming part.

Next, 50% hydrofluoric acid (HF): 50% ammonium fluoride (NH ₄ F) =
After immersing the Si substrate 2 in a 1: 6 aqueous solution to remove the exposed oxide film 3, the resist is subsequently removed using a sulfuric acid (H ₂ SO ₄ ): H ₂ O ₂ = 2: 1 solution. .

Next, potassium hydroxide (KO) with a liquid temperature of 80 ° C and a concentration of 35%
H) Anisotropic etching by immersion in aqueous solution
After etching to 00 μm, the Si substrate 2 is thoroughly washed with pure water.

Then, the SiO ₂ film used at the time of etching is
After removal using an aqueous solution of% HF: 50% NH ₄ F = 1: 6, wet oxidation is again performed to form an oxide film 3 made of SiO ₂ having a thickness of 0.8 μm.

Next, chrome (C) is deposited on the Si substrate 2 by a vacuum deposition method.
r) is formed to 400 Å and gold (Au) to 4,000 、, and then a resist pattern for forming an electrode is formed by using the same negative resist (OMR-83). ) 4g
And a solution prepared by dissolving 1 g of iodine (I ₂ ) in 40 ml of water. The Cr film was composed of 0.5 g of caustic soda and potassium ferricyanide [K ₃ Fe (CN) ₆ ].
Etching is performed using a solution dissolved in 4 ml to form electrodes 4, 4 '. (FIG. 3A) Next, a hole is formed on the Si substrate 2 and the Si excluding the electrode lead portion is removed.
After the resist film 5 is formed by covering the substrate 2 with a negative resist (OMR-83), the part not covered with the resist is immersed in a 1M NaOH solution to make it hydrophilic.

Next, sodium alginate was added to 0.1 mol of potassium chloride (K
B) Consisting of a solution A having a concentration of 0.2% dissolved in an aqueous solution of Cl) and an aqueous solution of 0.1 M KCl containing 0.15 mol of hydrochloric acid.
Prepare the solution.

Then, first, the Si substrate is immersed in the solution A, and when slowly pulled up, the resist film 5 has water repellency, so that the solution A remains only in the holes. You can do 6. Next, a small oxygen electrode is completed by coating the electrolyte-containing gel 6 with a gas permeable film 7 made of a resist or the like so as to cover the gel.

The above-mentioned method of manufacturing a small oxygen electrode is suitable for mass production and has enabled cost reduction. However, when used in the medical field, high-temperature sterilization is required. In the case of sterilization, there is a problem that the electrolyte-containing gel 6 breaks the gas permeable membrane 7 and oozes out, resulting in a failure.

[Problems to be solved by the invention]

As described above, the oxygen electrode proposed by the inventors is small in size and has a structure suitable for mass production, so that the cost can be reduced and various uses are expected.

However, when this oxygen electrode is used in clinical medicine, such as when it is attached to a catheter and inserted into the body, 120
It is necessary to perform high-temperature sterilization at 15 ° C. and 2 atm for about 15 minutes, and a structure that can withstand this high-temperature processing is required.

[Means for solving the problem]

The above problem is to form a hole in the Si substrate using anisotropic etching, provide an oxide film on this substrate to form an insulating substrate, and then oppose two electrodes from the bottom of the hole to the substrate surface. The resist-coated substrate is immersed in an aqueous solution of sodium alginate containing an electrolytic solution to fill the aqueous solution only in the holes. After forming a porous carrier containing an electrolytic solution in a hole by immersing it in a calcium chloride aqueous solution containing a liquid, the resist-coated substrate is applied to a small oxygen electrode having the upper surface of the hole covered with a gas-permeable membrane. After immersing in the electrolyte-containing sodium alginate to fill only the inside of the hole with the aqueous solution, the substrate is immersed in a mixed aqueous solution of calcium chloride, metal alkoxide and hydrochloric acid containing the electrolytic solution, and an aqueous sodium alginate solution and the like. Fine metal alkoxide can be solved by taking the manufacturing method of a small oxygen electrode to gel.

[Action]

The inventors of the present invention break down when sterilizing a small oxygen electrode at a high temperature due to the volume expansion of the electrolyte-containing gel, specifically because the calcium alginate gel is soft and easily expanded.

Therefore, we considered suppressing the volume change by confining the calcium alginate gel in a hard porous frame.

Specifically, a mixed gel of calcium alginate gel and sol-gel glass is used.

That is, when a calcium alginate gel is produced by reacting an aqueous solution of sodium alginate containing an electrolytic solution with an aqueous solution of calcium chloride (CaCl ₂ ), a sol-gel glass is simultaneously produced to form a mixed gel of both.

Here, the sol-gel glass is made of tetraethoxysilane [Si (OC ₂ H ₅ ) ₄ ], tetramethoxysilane [Si (OC
A metal alkoxide such as H ₃ ) ₄ ] can be obtained by performing hydrolysis and dehydration condensation using hydrochloric acid (HCl) as a catalyst.

That is, when tetraethoxysilane is used as a metal alkoxide, HCl (catalyst) Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH (1) (hydrolysis reaction) Si (OH ₄ ) → SiO ₂ + 2H ₂ O (2) A gel glass is formed by (dehydration condensation reaction).

Thus, the present invention provides a hard porous carrier containing an electrolyte.
By forming it in a number of holes provided in the Si substrate, volume expansion is suppressed even in high-temperature processing.

Next, various electrolytes can be considered, but use of KCl is preferable because of its high mobility, whereas sodium sulfate (Na ₂ SO ₄ ) is not preferable because it causes precipitation with Ca.

In addition, the gas permeable membrane covering the surface of the small oxygen electrode is hydrophobic and does not allow aqueous solution to pass through, but it can be dip-coated or spin-coated and can be used on Si substrates, electrodes, SiO ₂ films, etc. It is necessary to use a material having good adhesion, and for this purpose, a negative resist, silicone resin, or the like is preferably applied to a thickness of about 10 μm.

The reason for making the resist negative is that it is rubber-based and often has water repellency.

[Example] The production of the small electrode according to the present invention is the same as the conventional method except for the method of filling the calcium alginate gel.

Therefore, in the manufacturing process of FIG. 3 described above, the embodiment of the method of filling the calcium alginate gel shown in FIG. 3C is as follows.

 First, the following two types of solutions were prepared.

Solution A: A solution obtained by dissolving sodium alginate in a 0.1 M KCl solution to a concentration of 0.2%.

Solution B: 0.15 KCl and 5% CaCl in 0.15 M HCl aqueous solution
A solution obtained by adding tetraethoxysilane at a ratio of 3: 1 to the solution obtained by adding ₂ .

First, when the Si substrate after the process up to FIG. 3 (B) is immersed in the solution A and gently lifted, the solution A is repelled from the resist film because the negative resist film 5 has water repellency. It remains only in the hole.

When the Si substrate 2 was immersed in the solution B, the solution A instantaneously gelled, and an electrolyte-containing gel having a flat surface with almost no change in volume before and after the reaction was obtained.

Next, a negative resist is applied thereon to a thickness of about 2 μm using a spin coating method in the same manner as in the prior art, and then exposed and developed immediately without pre-baking. Leave the oxygen electrode in pure water or saturated steam for 24
At the same time as the gel glass was sufficiently reacted, the thinner in the resist was removed to complete the gas permeable film.

〔The invention's effect〕

By implementing the present invention, it is possible to easily fill a porous carrier containing an electrolytic solution and hardly causing a volume change into a hole of a Si substrate, thereby producing a small-sized oxygen electrode that can be sterilized at high temperature and is low in cost. be able to.

[Brief description of the drawings]

1 is a perspective view of the small oxygen electrode, FIG. 2 is a cross-sectional view of the small oxygen electrode taken along the line XX 'in FIG. 1, and FIG. 3 is a manufacturing process of the small oxygen electrode. In the figure, 1 is a small oxygen electrode, 2 is a Si substrate, 3 is an oxide film, 4 and 4 'are electrodes, 5 is a resist film, 6 is an electrolyte-containing gel, and 7 is a gas permeable film.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Fumio Takei 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (1)

(57) [Claims] A silicon substrate is subjected to anisotropic etching to form a hole, an oxide film is provided on the substrate to form an insulating substrate, and two electrodes are formed from the bottom of the hole to the substrate surface. Provided,
The substrate was coated with a resist except for the hole portion and the electrode take-out portion, and the resist-coated substrate was immersed in an aqueous solution of sodium alginate containing an electrolytic solution to fill only the holes with the aqueous solution. After forming a porous carrier containing an electrolytic solution in a hole by immersing it in a calcium chloride aqueous solution containing a liquid, and then covering the upper surface of the hole with a gas-permeable membrane, After immersing in the electrolyte-containing sodium alginate and filling only the inside of the hole with the aqueous solution, the substrate is immersed in a mixed aqueous solution of calcium chloride, metal alkoxide and hydrochloric acid containing the electrolyte, and the sodium alginate aqueous solution and the metal are dissolved. A method for producing a small oxygen electrode, which comprises gelling an alkoxide.