JP2556993B2 - Micropore electrode cell for electrochemical measurement and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrode cell for minute electrochemical measurement used in electrochemical analysis, flow cell, liquid phase chromatography and the like, and a method for producing the same.

[Conventional technology]

In general, electrochemical measurement electrode cells, so-called microelectrodes, are suitable for the analysis of microscopic regions such as in vivo or microvolume solution samples, so application to various sensors such as organic or inorganic materials has been attempted. There is. By the way, most of the fine electrodes are manufactured by enclosing platinum, gold, etc., metal wires, carbon fibers, metal chlorides, etc. in a glass thin tube. The response behavior of this fine electrode differs depending on the electrode shape, and the response speed increases as the electrode size decreases, so various electrode shapes and electrode miniaturization are performed for the purpose of measuring fast electrochemical reactions. Is being considered.

However, if the electrode radius is reduced to about 1 μm, the current that can be detected will drop below the nA order, and noise will increase and sensitivity will decrease during measurement, making it difficult to measure low-concentration samples. Was required.

It has also been proposed to increase the number of working electrodes in order to improve the sensitivity of the electrodes. This electrode has a structure in which a large number of carbon fibers are enclosed in an insulating resin, and the enclosed carbon fibers are etched in order to remove the effects of stirring and contamination of the solution. Is.

However, with this method, it is not possible to obtain electrodes having exactly the same electrode shape or shapes other than the disk electrode, and it takes time to manufacture and it is difficult to obtain a large amount, and there are drawbacks such as deterioration of the resin used for encapsulation. .

On the other hand, in recent years, application of the lithographic technique has been proposed as a method for producing a microelectrode. In this method, a resist is applied to a substrate, an image mask having an electrode pattern is overlaid, exposed and developed, and a metal thin film is formed by a vapor deposition method or the like, and then the resist is peeled off to form a minute electrode on the substrate. To obtain a lift-off method or after forming a metal thin film on an insulating substrate, apply a resist, overlay an image mask with an electrode pattern, expose and develop, and use the remaining resist as a mask to expose the exposed metal An etching method is known in which a film is etched to obtain an electrode pattern.

With this method, a large number of microelectrodes having an arbitrary shape and a fixed distance between electrodes can be produced on the substrate with good reproducibility. Therefore, if two working electrodes that are placed close to each other are produced, a ring disk electrode is obtained. It can be applied to electrode pairs that can perform similar measurements, electrochemical devices, and sensor base electrodes. By applying this method of manufacturing fine electrodes, it has been possible to use a micro electrochemical transistor (for example, J. Phys. Chem. 89.5133).
(1985)), electrochemical measurement of low-molecular or high-molecular complexes using a comb-shaped platinum electrode (Anal. Chem., 58,601 (198).
6)) and so on. Furthermore, a working electrode having a large number of fine circular patterns is prepared by coating a resist (polymethylmethacrylate: PMMA) on a conductive substrate and exposing a large number of fine circular holes in the resist by exposure and development (J .Electrochem.Soc. Vol.133, 752 (1986).).

[Problems to be Solved by the Invention]

However, if only such fine electrodes are densely arranged, it becomes the same as a normal size electrode, and the characteristics as a fine electrode are lost. Therefore, it is necessary to dispose the fine electrodes while keeping a certain distance, and there is a drawback that the whole becomes large in order to obtain a measurable current.

In view of the above points, the present invention has been made to solve the above problems, and an object of the present invention is to provide at least two electrodes in which the electrodes are arranged at the bottom, middle, or top of each of a large number of fine holes.
It is an object of the present invention to provide a microporous electrode cell that can perform electrochemical measurement with high sensitivity and responsiveness by using one working electrode, and a method for manufacturing the same.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an electrochemical measurement electrode cell having a working electrode for detecting a substance, wherein the working electrode is formed on an insulating substrate and is formed via an insulating film. Has a multi-layer structure composed of two or more electrodes, and a large number of holes are formed so that one end of the multi-layer structure reaches the electrode at the other end, and the material of the electrode is metal, semimetal or semiconductor. It is characterized by being.

In addition, the manufacturing method of the present invention is such that a conductive thin film of a metal, a semimetal or a semiconductor and an insulating film are alternately laminated at least once each successively on a substrate whose surface or the whole is insulating,
Then, after forming a fine hole resist pattern thereon, a large number of fine holes are formed by an etching method until the bottommost conductive film surface appears.

[Action]

Therefore, in the present invention, in the conventional electrodes, it took time to reach a steady state because the target substance diffused perpendicularly to the electrode surface, and the current density was low. By making the diffusion hemispherical, the time to reach a steady state can be shortened and the current density can be increased. Furthermore, by setting two or more working electrodes so that the oxidation potential of one target substance on the adjacent electrodes and the reduction potential on the other side are repeated, oxidation and reduction are repeated between the adjacent electrodes. The current can be increased significantly.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings with reference to the embodiments.

FIG. 1 is a schematic view of a micropore electrode cell for electrochemical measurement according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an insulating substrate, which is, for example, a so-called silicon substrate with an oxide film in which a main surface of a silicon substrate 1a is covered with an oxide film 1b. 2 is a lower electrode as a working electrode formed of metal, semimetal or semiconductor on the surface of the oxide film 1b on the substrate 1, that is, an insulating surface, 3 is an insulating film formed on the lower electrode 2, and 4 is the insulating film. It is a surface electrode as another working electrode formed of the same metal, semimetal or semiconductor as the lower electrode 2 on the surface of the film 3. 5 is this surface electrode 4
A large number of fine holes (also called fine circular holes) formed in a circular shape from the upper surface to reach the film surface of the lowermost lower electrode 2 through the insulating film 3, and the surface electrode having the large number of fine holes 5 4 as an upper working electrode, and a lower electrode 2 facing each other at the bottom of the fine hole 5 and insulated from each other by the fine hole wall of the insulating film 3 as a lower working electrode, and these two working electrodes form a fine hole electrode cell. It is configured. In FIG. 1, reference numeral 7 denotes an opening for leading out an electrode, which is opened to connect an external lead to one end of the lower electrode 2.

Here, as the substrate 1 whose surface or the whole is insulative, besides a silicon substrate with an oxide film, a quartz plate, an aluminum oxide substrate, a glass substrate, a plastic substrate and the like can be cited. Gold, platinum, silver, chromium, titanium, stainless steel, etc. are used as the metal for the lower and surface electrodes 2, 4, and p and n type silicon, p and n type germanium, cadmium sulfide, and dioxide are also used as the semiconductors for the electrodes. Titanium, zinc oxide, gallium phosphide, gallium arsenide, indium phosphide, cadmium selenium, cadmium tellurium, molybdenum diarsenide, tungsten selenide, copper dioxide, tin oxide, indium oxide, indium tin oxide, and semimetals for electrodes. Examples of the conductive carbon include conductive carbon. Examples of the insulating film 3 include silicon oxide, silicon dioxide, silicon nitride, silicone resin, polyimide and its derivatives, epoxy resin, and thermosetting polymer.

Further, when manufacturing a micropore electrode cell as a microelectrode, a conductive thin film and an insulating film 3 are alternately laminated to form an electrode 2 or 4 on a substrate 1. A spatter, VCD, or coating method can be used. Then, a resist is applied on this substrate, an image mask having an electrode pattern is superposed thereon, or the pattern is directly exposed by using an electron beam or the like and developed to transfer the pattern to the resist on the substrate. Using the remaining resist pattern as a mask, the laminated film of each conductive film and insulating film is etched to form a plurality of fine working electrodes by forming fine holes. That is, a lower electrode 2, an insulating film 3 and a surface electrode 4 are sequentially laminated on an insulating substrate 1, a resist is applied thereon, and exposure and development are performed to form a fine hole resist pattern. Then, by etching the laminated film of the surface electrode 4 and the insulating film 3 based on this pattern, a large number of fine holes 5 in which the film surface of the lowermost lower electrode 2 is exposed can be formed.

As described above, according to the present embodiment, in the conventional electrode, the target substance was diffused perpendicularly to the electrode surface, so it took time to reach a steady state and the current density was low. By making the diffusion into a hemispherical shape by making the electrodes finer, it is possible to shorten the time until a steady state is reached and increase the current density. In addition, the working electrode is composed of two lower electrodes 2 and surface electrodes 4, and one of the adjacent electrodes is set to the oxidation potential of the target substance and the other is set to the reduction potential, so that the oxidation between the adjacent electrodes is performed. Since the reduction is repeated, the effective current can be greatly increased.

In the above embodiments, the case where two surface electrodes and a lower electrode are used as the working electrodes has been described, but the present invention is not limited to this, and the electrodes are arranged at the bottom, middle, or upper part of each of a large number of fine holes. Two or more working electrodes can be arbitrarily combined and configured.

In addition, when manufacturing a micropore electrode cell, 2
In addition to integrating only one or more working electrodes, a reference electrode and a counter electrode can be integrally formed. That is, after a conductive thin film and an insulating film are alternately laminated one or more times on a substrate, this laminated film is etched in the same manner as in the above-described embodiment to form fine holes to form a large number of minute working electrodes. afterwards,
A resist is applied on the upper insulating film, and an image mask having an electrode pattern is laid on the resist, or an electron beam is used to directly expose and develop a pattern on a portion without fine holes to develop the pattern on the substrate. Transfer to resist. After that, a metal, semiconductor or semimetal thin film is formed by a sputtering method, vapor deposition, CVD, coating method, etc., and then a reference electrode and a counter electrode are prepared by a lift-off method of peeling the resist, and a working electrode, a reference electrode and a counter electrode. It is also possible to obtain a fine micropore electrode cell for electrochemical measurement in which is integrated.

In this case, in order to manufacture a reference electrode, a metal serving as a supporting material, an organic redox polymer, is plated on one of two electrodes other than the micropore working electrode in the electrode cell, and an electrolytic weight is applied. It is formed and manufactured by a legal method. Further, examples of the reference substance on the reference electrode include silver, silver chloride, polyvinyl ferrocene and the like.

According to the micropore electrode cell having the structure manufactured by such a method, the three electrodes of the working electrode, the reference electrode, and the counter electrode can be formed on the same substrate, which is suitable for measuring a small amount of sample or a minute area.

Next, specific examples for carrying out the method of the present invention will be described below with reference to FIG. 2, but it goes without saying that the present invention is not limited to these examples.

Example 1 A silicon wafer with an oxide film of 1 μm (manufactured by Osaka Titanium Co., Ltd.) was used as a substrate 1 (FIG. 2 (a)), and it was attached with a metal mask at a predetermined position in a sputtering device (Anerva: SPF-332H), and pressure was applied. Sputtering chromium is performed for 10 seconds at a power of 50 W in 1.3 Pa and argon, and then platinum is sputtered at a power of 70 W for 1 minute without breaking the vacuum to obtain a film thickness of 100.
A lower electrode 2 of a chromium-platinum film of nm was formed (Fig. 2 (b)). Next, the metal mask was removed and a silicon dioxide film 3 was deposited as an insulating film by a sputtering method (FIG. 2 (c)). At this time, power 50W, spatter for 10 minutes,
The film thickness of silicon dioxide was 300 nm. Another metal mask was attached again, and a chromium-platinum surface electrode 4 was deposited to a thickness of 100 nm (FIG. 2 (d)).

Then, Photoresist 6 (MP1400-27 manufactured by Shipley Co., Ltd.) was applied on the silicon substrate to a thickness of 1 μm. Place this resist-coated silicon wafer in the oven.
Baking was carried out under the conditions of ℃ and 30 minutes. Then, using a chrome mask, contact exposure was performed for 20 seconds with a mask aligner (manufactured by Canon Inc.). The exposed silicon wafer was developed in a resist developer (MF-319 manufactured by Shipley Co., Ltd.) at 20 ° C. for 60 seconds, washed with water and dried to transfer the mask pattern to the resist (FIG. 2 (e)).

After development, the substrate was placed in an argon milling device, and after etching platinum under the conditions of an argon gas flow rate of 12 SCCM, a pressure of 0.03 Pa, and a beam current of 90 mA, the substrate was placed in a reactive ion etching device and a C ₂ F ₆ gas flow rate of 25 SCCM. , Pressure 0.25Pa, 15
A large number of disk electrode patterns having fine holes 5 were formed by etching silicon dioxide for 10 minutes under the condition of 0 W (FIG. 2 (f)). At this time, the diameter of each disk electrode was 1 μm, and the number was 10,000. After that, the substrate was immersed in methyl ethyl ketone and subjected to ultrasonic treatment, and the resist other than the electrode forming portion was peeled off to obtain an electrode pattern. An outline of the micropore electrode cell for electrochemical measurement produced in this manner is shown in FIG.

The electrode cell for microelectrochemical measurement (hereinafter referred to as an electrochemical cell) is 0.1 mmol / l ferrocene, 0.1 mol / l supporting electrolyte (tetraethylammonium perchlorate)
Immersed in a solution of acetonitrile, and connect the lower and surface electrodes 2 and 4 to the dual potentiostat via lead wires respectively, fix the surface electrode 4 to -0.1V, and lower electrode 2 from 0V to 0.5V. The potential value was scanned at 100 mV / sec to measure the current value, and the result was compared with the case where only 10000 working electrodes of 1 μm were used.

As a result, a limiting current corresponding to the oxidation of ferrocene with a rise of 0.3 V (based on the silver reference electrode) was obtained. However, with the disk electrode having a diameter of 1 μm, the magnitude of the limiting current was only 0.46 μA, whereas with the electrode of this example, a value of 1.5 μA was obtained. On the other hand, comparing with the electrochemical cell having many working holes (diameter: 0.10 mm) of the same area as the many micropore disk electrodes of the electrochemical cell prepared in this example, the limiting current was observed in the former case. In the latter case, a peak associated with the oxidation-reduction reaction of ferrocene was observed, and the electrochemical cell of this example obtained a faster response than the electrode having the same area. In addition, the potential from 0V
When the current value is measured by stepping to 0.5V, the electrochemical cell of this example has a diameter of 0.10 mm as compared with the disk electrode.
It was found that the current value was 5.2 times as high as 0.4 seconds after the voltage application and the sensitivity was improved.

Example 2 In Example 1, spin-on glass was used instead of the sputtering method when forming the silicon dioxide film. Spin-on glass (OCD Type-7 manufactured by Tokyo Ohka Co., Ltd.) was spin-coated to a thickness of about 1 μm, and then baked at 450 ° C. for 1 hour. Then, an electrode was produced in the same manner as in Example 1.
The diameter of each micropore was 2 μm and the number was 2500.

Next, an electrochemical measurement was performed under the same conditions as in the above-mentioned example, and a comparison was made with a disk electrode having a diameter of 2 μm and a number of 2500. In both cases, the limiting current of the curve similar to that shown in Example 1 was obtained. The disk electrode having a diameter of 2 μm gives a limiting current of only 0.83 μA, whereas the electrode of this example shows a value of 2.4 μA. Further, even when the solution was stirred, the change in the potential-current curve was small. On the other hand, in comparison with an electrochemical cell having a large number of micropore disk electrodes of the electrochemical cell of the present Example prepared and a working electrode (diameter: 0.20 mm) of the same area, a limiting current was observed in the former case. In the latter case, a peak associated with the oxidation-reduction reaction of ferrocene was observed, and the electrochemical cell of this example provided a faster response than the electrode having the same area. Also,
When the electric current was measured by stepping the electric potential from 0 V to 0.5 V, the electrochemical cell of the present example had a 4.7-fold current value 0.4 seconds after the voltage was applied, as compared with the disk electrode having a diameter of 0.20 mm. It was found that the sensitivity was improved.

Example 3 A quartz substrate having a thickness of 0.32 mm was put together with a metal mask in a vacuum deposition apparatus (made by JEOL Ltd.), and chromium and gold were vacuum deposited. The film thickness was 200 nm. Next, CVD equipment (ANELVA PE
D-401) was used to form a silicon nitride film having a thickness of 1 μm on the substrate. Using another metal mask again, a chromium-gold surface electrode was formed. Then, an electron beam resist (φ-MAC, manufactured by Daikin Industries, Ltd.) was applied to a thickness of 1 μm. Put this resist coated quartz substrate in the open
Baking was performed at 0 ° C. for 60 minutes. After that, it was put in an electron beam exposure system (JEOL: JSM-840), and the electron beam acceleration voltage was 10K.
Exposure was performed under the conditions of V, exposure amount: 5 μC / cm ² .

After development, the substrate was placed in an Algomi ring apparatus, gold was etched under the conditions of an argon gas flow rate of 12 SCCM, a pressure of 0.03 Pa, and a beam current of 90 mA, and then placed in a reactive ion etching apparatus. A 10: 1 mixed gas is used as an etchant, gas pressure 2.6Pa, flow rate 50SCCM, power 100.
An electrode was obtained by etching silicon nitride under the condition of W for 10 minutes. The diameter of the produced disk electrode was 0.5 μm and the number was 40,000.

Next, an electrochemical measurement was performed under the same conditions as in the above-mentioned example, and a comparison was made with a disk electrode having a diameter of 0.5 μm and a number of 40,000. In both cases, the limiting current of the curve similar to that shown in Example 1 was obtained. With the disk electrode having a diameter of 0.5 μm, the magnitude of the limiting current was only 0.92 μA, whereas with the electrode of this example, the value was 3.5 μA. On the other hand, in comparison with an electrochemical cell having a large number of micropore disk electrodes and a working electrode (diameter: 0.10 mm) of the same area in the produced electrochemical cell of this example, a limiting current was observed in the former case. ,
In the latter case, a peak associated with the oxidation-reduction reaction of ferrocene was observed, and it was found that the electrochemical cell of this example had a faster response speed than the electrodes having the same area.

Further, when the current value is measured by stepping the potential from 0 V to 0.5 V, the electrochemical cell of the present example has a 5.5-fold current value 0.4 seconds after voltage application, as compared with the disk electrode having a diameter of 0.10 mm. It was found that the sensitivity was improved.

Example 4 A silicon wafer with an oxide film of 1 μm (manufactured by Osaka Titanium Co.) was used as a substrate, and a sputtering device (manufactured by Anerva: SPF-) was used.
332H) with a metal mask at a predetermined position, pressure 1.3Pa, argon, power 50W, chrome spatter 1
Do it for 0 seconds and continue without breaking the vacuum with a power of 70W 1
The platinum was sputtered for a minute to form a lower electrode of a 100 nm thick chromium-platinum film. Next, the metal mask was removed and a silicon dioxide film was deposited by the sputtering method. At this time, perform power 50W, sputter for 10 minutes, and remove silicon dioxide.
The film thickness was 300 nm. Attach another metal mask again,
A chromium-platinum surface electrode was deposited to a thickness of 100 nm, and then the metal mask was removed to deposit a silicon dioxide film by a 300 nm sputtering method. After that, a photoresist (MP1400-27 manufactured by Shipley Co., Ltd.) was applied on the silicon substrate to a thickness of 1 μm. The resist-coated silicon wafer was put into an open and baked at 80 ° C. for 30 minutes. Then, using a chrome mask, contact exposure was carried out for 20 seconds with a mask aligner (manufactured by Canon Inc.). The exposed silicon wafer is
In a resist developer (made by Shipley, MF-319), 20 ℃, 6
It was developed for 0 seconds, washed with water and dried to transfer the mask pattern to the resist. After development, the substrate was placed in a reactive ion etching apparatus (DEM-451 manufactured by Anelva), and etching of silicon dioxide was performed for 10 minutes under the conditions of a C ₂ F ₆ gas flow rate of 25 SCCM, a pressure of 0.25 Pa, and a power of 150 W. Then, put it in an argon milling machine, and then the flow rate of argon gas is 12SCCM,
After etching platinum under the conditions of pressure 0.03Pa and beam current 90mA, put it in the reactive ion etching equipment again,
A large number of disk electrode patterns with fine holes were formed by etching with C ₂ F ₆ gas. At this time, the diameter of each disk electrode was 1 μm, and the number was 10,000. Thereafter, the substrate was immersed in methyl ethyl ketone and subjected to ultrasonic treatment, and the resist except for the portion where the electrode was formed was removed to obtain an electrode pattern.

The electrode of this example was immersed in an acetonitrile solution in which 0.1 mmol / l ferrocene and 0.1 mol / l supporting electrolyte (tetraethylammonium perchlorate) were dissolved, and the lower and surface electrodes were respectively connected to the dual potentiostat via lead wires. Connected, the surface electrode was fixed at -0.1V, the lower electrode was subjected to potential scanning from 0V to 0.5V at 100 mV / sec to measure the current value, and only 10000 working electrodes of 1 μm disk electrode were used. Compared to the case. In both cases, a limiting current corresponding to the oxidation of ferrocene with a rise of 0.3 V (based on the silver reference electrode) was obtained. With the disk electrode having a diameter of 1 μm, the magnitude of the limiting current was only 0.46 μA, whereas with the electrode of this example, the value was 1.3 μA. on the other hand,
Compared with the electrochemical cell having a large number of micropore disk electrodes of the electrochemical cell of the present Example prepared and the working electrode (diameter: 0.10 mm) of the same area, the limiting current was observed in the former, whereas the latter A peak associated with the oxidation-reduction reaction of ferrocene was observed in, and the electrochemical cell of this example obtained a faster response than an electrode having the same area. Also, when measuring the current value by stepping the potential from 0V to 0.5V,
It was found that the electrochemical cell of this example obtained a current value 4.9 times as high as that of the disk electrode having a diameter of 0.10 mm as compared with the disk electrode having a diameter of 0.40 seconds after voltage application for 0.4 seconds.

Example 5 Using the electrode cell prepared in Example 1, the concentration was 3 μmol /
l epinephrine and 50 μmol / l ascorbic acid, 0.1 mol
Immerse in an aqueous solution of / l supporting electrolyte (sodium phosphate), the surface electrode is -0.3V, the lower electrode is 0V to 0.7V
The potential value was scanned at 100 mV / sec to measure the current value, which was compared with the case where only 10,000 working electrodes having a diameter of 1 μm were used.

On the 1 μm disk electrode, the response of epinephrine was hidden due to the oxidation current of ascorbic acid.
In the lower electrode of the electrode cell of this example, a response in which the transient response of ascorbic acid was superimposed on the limiting current of epinephrine was superposed, and only the limiting current of the reduction of epinephrine was observed on the surface electrode side, which was quantified without being disturbed by ascorbic acid. Was possible.

〔The invention's effect〕

As described above, in the electrochemical measurement micropore electrode cell of the present invention, the working electrode constituting the cell is formed on the insulating substrate, and they are formed on each other via the insulating film. It has a multi-layered structure composed of three or more electrodes, and a large number of holes are formed so as to reach the electrode at the other end from one end of the multi-layered structure, and the material is a metal, a semimetal or a semiconductor. Therefore, compared to conventional microelectrodes, it has many advantages such as high sensitivity and large response speed and current value even when compared with working electrodes having the same electrode area, and measurement with a simple device. It is also extremely effective for high-sensitivity analysis of low-concentration samples.

Further, according to the method of the present invention, in order to produce a micropore electrode cell for electrochemical measurement comprising a working electrode having a pattern having a large number of micropores by using the lithographic technique, a working electrode of any size and shape can be prepared. It is inexpensive and can be obtained in large quantities.

[Brief description of drawings]

FIG. 1 is a schematic view of a micropore electrode cell for electrochemical measurement according to an embodiment of the present invention, and FIGS. 2 (a) to 2 (f) are sectional views showing steps in the manufacturing process of this embodiment. 1 ... Substrate, 1a ... Silicon substrate, 1b ... Oxide film, 2 ...
... Lower electrode, 3 ... Insulating film (silicon dioxide film), 4 ...
… Surface electrodes, 5 …… micropores, 6 …… resist.

Claims (2)

(57) [Claims] 1. An electrochemical measurement electrode cell having a working electrode for detecting a substance, wherein the working electrode is formed on an insulating substrate, and is composed of two or more electrodes formed through an insulating film. It has a multi-layer structure configured, and a large number of holes are formed so as to reach the electrode at one end from the other end of the multi-layer structure, and the material of the electrode is metal, semimetal or semiconductor. Micropore electrode cell for electrochemical measurement. 2. A conductive thin film of a metal, a semimetal or a semiconductor and an insulating film are alternately laminated at least once one by one on a substrate whose surface or the whole is insulative, and then a fine hole resist pattern is formed thereon. After the formation, a method for producing a micropore electrode cell for electrochemical measurement, comprising a step of forming a large number of micropores by an etching method until the bottommost conductive film surface appears.