JPH0599883A - Small-sized glass electrode - Google Patents

Abstract

PURPOSE:To improve measurement sensitivity with respect to a small-sized glass electrode formed by means of micromachining technology. CONSTITUTION:A small-sized glass electrode comprises a glass substrate 1 formed with a reference electrode 3 made of silver/silver chloride and a pad 5 made of gold and connected in a circuit with the reference electrode 3 buried and a silicon substrate 2 which is selectively etched by means of micromachining technology equipped with an injection groove 6 for electrolytic solution made of potassium chloride buffer solution, a holding hole 7 for the electrolytic solution and a hydrogen ion permeable film 8 at a corresponding portion of the reference electrode 3. The glass substrate 1 and the silicon substrate 2 are subjected to anodic joint to form the small glass electrode, while the electrolytic solution is injected from the injection groove 6 into the electrolytic solution holding hole 7. The hydrogen ion permeable film 8 is made of a glass film having a thin glass film which is sensitively responsive to a change in hydrogen ion concentration and is thermally adhered to a rear face of the electrolytic solution holding hole 7 provided on the silicon substrate 2.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to small glass electrodes. The glass electrode is a sensor for quantifying the hydrogen ion (H ⁺ ) concentration in an aqueous solution, and is used not only in the chemical industry but also in the fermentation industry and the medical field.

Further, the glass electrode is used in combination with an enzyme to form an enzyme electrode and is used for measuring the concentration of sugar, alcohol and the like. For example, glucose is catalyzed by an enzyme called glucose oxidase and reacts with dissolved oxygen to oxidize to gluconolactone. The change in H ⁺ concentration produced during this reaction should be measured, and the glucose concentration should be measured from this change. You can

Further, the urea concentration can be measured by the same principle. The small glass electrode of the present invention can be used in various fields like the conventional glass electrode, but since it is small, it is possible to measure the H ⁺ concentration at a minute portion,
Moreover, since it is inexpensive, it can be used for disposable applications.

[0004]

2. Description of the Related Art A conventional glass electrode has a thin film thickness of about 100 μm and a glass thin film having an electric resistance of several hundred MΩ as a sensitive part, which is formed in a spherical shape at the tip of a glass cylinder.
It is equipped with a reference electrode made of silver / silver chloride (Ag-AgCl) inside and filled with potassium chloride (KCl) solution of a certain concentration.

[0005] When dipping the glass electrode with the sensitive part in a liquid including H ^+, because the glass electrode potential is generated in proportion to the concentration of the H ^+, thereby measuring the H ⁺ concentration You can

However, the commercially available glass electrode is made of glass with a size of a fountain pen, and the price is as high as tens of thousands of yen. On the other hand, an ion-sensitive field effect transistor (abbreviated as ISFET) has been developed as a small H ⁺ concentration sensor, which can be miniaturized because it is formed by using a semiconductor photoetching technique (photolithography).

However, the insulation of the substrate is important for a device such as ISFET that is used by being immersed in an aqueous solution. for that reason,
After dicing a large number of elements formed on a silicon (Si) substrate into a chip, silicon nitride is placed around the chip.
(Si ₃ N ₄ ) film is formed for insulation, or SOS (Silico
n on Sapphire) substrate or on a glass substrate
Methods such as forming in the form of TFT (Thin Film Transistor) are taken.

However, because of this, an increase in price is unavoidable, and it is difficult to manufacture at a price of tens to hundreds of yen. As a method for solving this problem, the inventor has proposed a small-sized glass electrode by using micromachine technology.
(Japanese Patent Application 02-400550, Japanese Patent Application 03-164750) The content is Ag / AgC
A glass substrate with a reference electrode made of 1 embedded in it and a Si substrate with a KCl buffer holding hole formed by selective etching of the (100) surface using micromachining technology were bonded together. A hydrogen ion permeable film is provided in the hole portion.

FIG. 1 is a plan view showing the structure of such a glass electrode. FIG. 1A shows a glass substrate 1, FIG. 1B shows a Si substrate 2, and FIG. The state where the Si substrate 2 is turned upside down and joined is shown.

Here, a reference electrode 3 made of Ag / AgCl, a lead wire 4 made of Au, and a pad 5 made of Au are embedded and formed on the glass substrate 1, respectively. On the other hand, Si
The substrate surface of the substrate 2 is (100), and by anisotropically etching the substrate surface, the electrolyte injection groove 6 and the electrolyte holding hole 7 are formed.
An H ⁺ permeable film 8 that functions as a sensitive film is formed on a part of this.

Further, in FIG. 1C, the broken line shows the internal glass electrode forming region, and the pad 5 and the H ⁺ permeable film 8 appear on the Si substrate 2 side. In addition, FIG. 2 shows FIG. 1C.
2 is a cross-sectional view taken along the line XX ′ of FIG. 1, in which a Si substrate 2 having an H ⁺ permeable film at the bottom of the holding hole 7 and a glass substrate 1 having a reference electrode 3 are bonded together by an anodic bonding method. It shows the state.

Here, the H ⁺ permeable film 8 is a Si substrate, for example, 10
Wet oxidize at 50 ℃ for 200 minutes to remove SiO ₂ film by about 1μ.
It is used by forming it to a thickness of m and further forming a glass film having high sensitivity to H ⁺ by sputtering or the like.

Since the glass electrode thus formed is small and a large number of glass electrodes can be manufactured at a time by using the micromachine technology for the Si wafer, the cost can be reduced.

However, since the H ⁺ permeable membrane 8 thus formed has a thickness of about 1 μm and is extremely thin, it is easily damaged, and it has been a problem that careful handling is required.

Therefore, as a method of improving the strength of the H ⁺ permeable film 8, the glass substrate was thinned by etching, and the glass substrate was brought into contact with the back surface of the Si substrate 2 in which the holding hole 7 for the electrolytic solution was also provided and heat-bonded.

Specifically, Pyrex glass is made of HF and HNO ₃
After etching to a thickness of about 20 μm using a mixed solution of and to make a thin film, anisotropically etch the Si substrate and bring it into contact with the back surface of the Si substrate having the holding hole 7 penetrating it, and heat it to 800 ° C. Glued together.

By taking such a method, the mechanical strength could be improved.

[0018]

The glass electrode proposed by the inventor has been downsized, and the cost can be reduced to a disposable level.

However, the sensitivity to H ⁺ concentration was not sufficient and it was necessary to improve the sensitivity.

[0020]

SUMMARY OF THE INVENTION In the small glass electrode having the structure proposed by the inventor, the hydrogen ion permeable film has a glass thin film which is sensitive to changes in hydrogen ion concentration. This can be solved by configuring a small glass electrode, which is characterized by being made of a glass film and thermally bonded to the back surface of the electrolytic solution holding hole provided in the silicon substrate.

[0021]

The potential generated on the glass electrode is expressed by the following Nernst equation. E = const −0.059 pH (1) However, this formula is a theoretical formula, and it is not easy to construct it so as to show a potential that matches this formula.

The inventor previously found that the H ⁺ permeable membrane has a thickness of 20 to 50 μm.
It was formed by using Pyrex glass of m, but when using this material, the coefficient representing the inclination in the Nernst equation −0.
059 (-59 mV) is only about -0.03 (-30 mV).

Therefore, it is necessary to improve this glass material. Here, lithium is used as the glass for the glass electrode.
Although (Li) glass and sodium-calcium (Na-Ca) glass are known, such a material has high heat resistance and strength as an H ⁺ permeable film for a small glass electrode proposed by the inventor. Not used from the point. That is, heat treatment at about 800 ° C. is required for adhesion to the Si substrate, which is not suitable in terms of heat resistance. After heat-bonding, considerable distortion remains in the glass, but this distortion cannot be endured. Etc.

Therefore, according to the present invention, a glass film such as Pyrex glass, which has insufficient properties as an H ⁺ permeable film, is formed by using a glass having excellent properties such as Li glass by a sputtering method or a vacuum deposition method. Is used to obtain a glass electrode that substantially satisfies the Nernst theoretical formula.

[0025]

EXAMPLE FIG. 3 is a cross-sectional view for explaining a manufacturing process of a glass electrode proposed by the inventor, and the present invention will be described by using this. Fabrication of glass substrate: Pyrex glass substrate (Iwaki 7740) with a diameter of 2 inches is spin-coated with a negative photoresist, heated and dried at 150 ° C for 30 minutes, and then photo-etching technology (photolithography ) Was used to expose a large number of reference electrodes, lead-out conductors, and pads forming regions by opening windows, and the same resist was similarly coated and coated on the back surface and dried.

Next, the glass substrate 1 was treated with 50% hydrofluoric acid (HF):
It was immersed in a mixed solution of concentrated nitric acid (HNO ₃ ): ammonium fluoride (NH ₄ ) F = 1: 1: 8 for 80 minutes and etched to a thickness of 3 μm. Next, the resist is treated with sulfuric acid (H ₂ SO ₄ ): hydrogen peroxide (H ₂ O ₂ ).
Peeling was performed using a mixed solution of 2: 1. (Above FIG. 3A) Next, the glass substrate 1 is thoroughly washed with a mixed solution of H ₂ O ₂ and ammonia (NH ₄ OH) and pure water, and then dried, and then the glass substrate 1 is placed on the glass substrate 1. An Au thin film was formed by the vacuum evaporation method.

Since the adhesion between Au and glass is very poor, a thin chromium (Cr) film was previously vapor-deposited on the substrate to improve the adhesion. Here, the film thickness of Cr is 400Å and Au is 4000Å.

A positive type resist film (OFPR-5000, made by Tokyo Ohka) is spin-coated on this glass substrate 1 and a photoetching technique is used to form the reference electrode 3, lead wire 4 and pad 5 forming region shown in FIG. 1A. Then, the resist film was covered with a resist, and the Au film and the Cr film were selectively etched to form a reference electrode pattern composed of the reference electrode 3, the lead wire 4 and the pad 5.

The etching solution for Au and Cr is as follows. Au etchant: 4 g KI and 1 g I ₂ dissolved in 40 ml water, Cr etchant: 0.5 g NaOH and 1 g K ₃ Fe (CN) ₆ 4
It is dissolved in ml of water.

Next, silver (Ag) was vapor-deposited on the portion where the reference electrode 3 was formed, and a positive resist was applied, heated and dried, exposed and developed in the same manner as above, and the resist was coated only on the portion where the reference electrode was formed. .. Then, Ag was etched, and then the resist was dissolved and removed to form a silver film on the reference electrode forming portion.

The composition of the Ag etching solution is 29% NH ₄ O.
H: 31% H ₂ O ₂ : pure water = 1: 1: 20. Next, the entire substrate was thoroughly washed with pure water and then immersed in a 0.1 M FeCl ₃ solution for 10 minutes to form a thin AgCl layer on the Ag surface.

Then, the entire substrate was thoroughly washed with pure water, whereby the reference electrode 3, the lead wire 4 and the pad 5 were completed. (Fig. 3B above) Formation of Si substrate: Prepare a Si substrate 2 having a thickness of 350 μm and a (100) surface as the substrate surface and a diameter of 2 inches, and use this for H ₂ O ₂ and NH ₄ OH.
It was thoroughly washed with the mixed solution of 1 and pure water and then dried.

Next, the Si substrate 2 was wet-oxidized at 1050 ° C. for 200 minutes to form a SiO ₂ film 10 having a film thickness of 1 μm on the entire surface. Next, a negative type resist (OMR-83, made by Tokyo Ohka Co., Ltd.) having a viscosity of 60 cP was applied to the Si substrate surface, followed by exposure / development and rinsing to form a resist pattern on the substrate.

The Si substrate 2 is 50% HF: 40% NH ₄ F =
The exposed part of SiO ₂ was removed by being immersed in a 1: 6 mixed solution. (FIG. 3C above) Next, the resist film was stripped in a mixed solution of H ₂ SO ₄ : H ₂ O ₂ = 2: 1.

Next, the Si substrate 2 was dipped in 35% KOH at 80 ° C. to anisotropically etch silicon to form a holding hole 7 for storing the electrolytic solution in the reference electrode portion. Next, if the SiO ₂ used as a mask is left on the surface of the Si substrate, a higher temperature is required for anodic bonding, so that the Si substrate 2 is 50
% HF: 40% NH ₄ F = 1: 6 Immerse in a mixed solution to completely remove SiO ₂ . Adhesion of thin glass plate to Si substrate: Pyrex glass (
Iwashiro 7740 glass) was etched in a mixed solution of 50% HF: concentrated HNO ₃ = 2: 1 to a thickness of 150 μm, and then thoroughly washed.

This glass film 13 is placed on the back surface (the upper bottom side surface of the holding hole 7 having a trapezoidal cross section) of the Si substrate 2 which is penetrated by anisotropic etching of the Si substrate, and heated to 750 ° C. to be bonded. Let (If the glass film is thick, the concentration of 50%
The glass-fused substrate is immersed in HF, and the glass is etched to the required thickness. For example, the thickness may be reduced to about 20 μm. Then, the glass thin film 14 was set on the glass film 13 by sputtering Na-Ca glass to a thickness of 500 nm on the glass film 13, and the H ⁺ permeable film 8 was formed. (Adhesion of FIG. 3D) Adhesion of Glass Substrate and Si Substrate The glass substrate 1 and the Si substrate 2 thus formed are immersed in pure water, sufficiently ultrasonically cleaned and dried, and then the two are bonded to each other. The glass substrate and the silicon substrate were anodically bonded by applying the substrate 2 on the positive electrode side and the glass substrate 1 on the negative electrode side at a temperature of 250 ° C. and applying 1200 V between the substrates. (Fig. 3E above) Cutting out the substrate and injecting the electrolyte solution: After cutting out a large number of glass electrode elements thus formed on the substrate into chips with a dicing saw, 0.1 mol chloride in a phosphate buffer solution was used. A large number of devices were completely immersed in a beaker containing an electrolyte solution containing potassium (KCl), and the entire device including the beaker was placed in a sealed container and degassed with a vacuum pump.

Next, after no air bubbles come out from the electrolyte injection hole 6 (groove), air is introduced into the sealed container. By this operation, the electrolytic solution 11 entered the space inside the electrode, and then the injection hole of the electrolytic solution was sealed with an adhesive to obtain a small glass electrode. (Fig. 3F)

[0038]

EFFECTS OF THE INVENTION The glass film of the glass electrode formed by using the present invention has improved pH sensitivity and can exhibit the characteristics which substantially match the Nernst theoretical formula.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of a glass electrode proposed by the inventor.

FIG. 2 is a cross-sectional view taken along line XX ′ in FIG.

FIG. 3 is a cross-sectional view showing a manufacturing process of a glass electrode to which the present invention is applied.

[Explanation of symbols]

1 Glass Substrate 2 Si Substrate 3 Reference Electrode 4 Lead Wire 5 Pad 6 Injection Groove 7 Holding Hole 8 H ⁺ Transmission Film 10 SiO ₂ Film 11 Electrolyte Solution 13 Glass Film 14 Glass Thin Film

Claims (2)

[Claims] 1. A glass substrate in which a reference electrode made of silver / silver chloride and a pad made of gold which is circuit-connected to the reference electrode are embedded and formed, and a micromachine technique is used (100).
The surface is selectively etched, and an electrolytic solution injection groove made of a potassium chloride buffer solution, a holding hole for the electrolytic solution, and a silicon substrate provided with a hydrogen ion permeable film at a corresponding portion of the reference electrode are anodically bonded. In a small glass electrode configured by injecting an electrolytic solution into the electrolytic solution holding hole from the injection groove, the hydrogen ion permeable film is a glass film provided with a glass thin film that is sensitive to changes in hydrogen ion concentration. The small glass electrode is characterized by being heat-bonded to the back surface of the electrolytic solution holding hole provided in the silicon substrate. 2. The borosilicate glass film and the sodium formed on the borosilicate glass film by a vapor deposition method.
The small glass electrode according to claim 1, wherein the small glass electrode is calcium glass.