JP2622589B2 - Microelectrode cell for electrochemical measurement and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microelectrode cell for electrochemical measurement in which a working electrode, a reference electrode, and a counter electrode are integrated and formed on the same substrate, and a method of manufacturing the same. It is.

[Prior Art] Conventionally, since a microelectrode is suitable for analysis of a small region such as a living body or a trace solution sample, application to a sensor or the like in combination with various organic or inorganic materials has been attempted. Most of the microelectrodes are manufactured by encapsulating a metal wire such as platinum or gold, a carbon fiber, a metal chloride, or the like in a thin glass tube. The response behavior of a microelectrode depends on the shape of the electrode, and the response speed increases as the size of the electrode decreases.Therefore, for the purpose of measuring high-speed electrochemical reactions, various electrode shapes and miniaturization of electrodes are required. Are being considered.

In recent years, application of a lithographic technique has been proposed as a method for manufacturing a microelectrode. In this method, a resist is applied to a substrate, an image mask having an electrode pattern is overlaid, exposed and developed, a metal thin film is formed by a vapor deposition method or the like, and then the resist is peeled off to form a fine electrode on the substrate. After preparing a metal thin film on an insulating substrate, a resist is applied, an image mask having an electrode pattern is overlaid, exposed, and developed, and the remaining resist is used as a mask to expose the exposed portion. An etching method of etching a metal film to obtain an electrode pattern is known. According to this method, a large number of microelectrodes having an arbitrary shape and a constant interelectrode distance can be formed on a substrate with high reproducibility, so that if two working electrodes are brought close to each other, a ring disk electrode can be formed. The present invention can be applied to an electrode pair capable of performing similar measurement, an electrochemical element, a base electrode of a sensor, and the like. By applying this microelectrode fabrication method, microelectrochemical transistors (eg, J. Phys. Chem. 89, 5133)
(1985)), electrochemical measurement of a low-molecular or high-molecular complex using a comb-shaped platinum electrode (Anal. Chem., 58, 601 (198)
6)) and so on. Furthermore, by applying a resist on a conductive substrate, exposing and developing, a large number of fine circular holes are formed in the resist, and a large number of submicron-order working electrodes have been fabricated (J. Electrochem. Soc., Vol. .133,752
(1986). ).

[Problems to be solved by the invention]

However, conventional microelectrode cells for electrochemical measurements are:
Since a lithographic technique using light is used in the manufacturing process, it is difficult to separate the patterns with a gap of 0.5 μm, and it is difficult to produce a fine electrode pair with good reproducibility. For this reason, in the above-mentioned method, it is impossible to obtain a completely identical electrode shape, it is troublesome to manufacture, it is difficult to obtain a large amount, and there is a large variation between the manufactured electrodes, so quantitative data is required. In such cases, it was necessary to test the electrodes beforehand, which required a great deal of measurement time. In addition, when it is not possible to carry out the test due to contamination or corrosion of the electrode by this measurement, it has been very difficult to obtain quantitative data.

As a method for solving this drawback, a method has been proposed in which a metal, an insulator, and a metal are sequentially laminated on a substrate, and the end face is exposed and used as an electrode. In this method, by using a dense insulating thin film, it is possible to narrow the gap between the electrodes. However, since a large area cannot be obtained, the current value is reduced. Furthermore, since the end face of the thin film is used, there is a disadvantage that an electrode having an arbitrary shape other than the band electrode cannot be obtained, and the solution has not been solved.

[Means for solving the problem]

In order to solve the above-mentioned drawbacks, the present invention comprises at least first and second thin-film electrodes separated by a three-dimensional space due to a step via an insulating film, and exposes the entire surface of each thin-film electrode or a part thereof. I have.

A step of forming a single or a plurality of first conductive thin films having a pattern shape on the insulating substrate and separated by a planar gap, and forming an insulating film on the insulating substrate including the first conductive thin film; A step of forming a film, a step of forming a single or a plurality of second conductive thin films separated by a planar gap having a pattern shape on the insulating film, and using the second conductive thin film as a mask, Etching the insulating film to expose the first conductive thin film.

(Operation)

 The three-dimensional gap separates each of the thin film electrodes with a minute gap.

〔Example〕

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

Example 1 FIG. 1 is a schematic view of a microelectrode cell for electrochemical measurement showing a first example according to the present invention. In the figure, 1 is a silicon wafer serving as a substrate, 2 is an oxide film formed on the silicon wafer 1, 3 is a reference electrode, 4 is a silicon dioxide film, 5 is a working electrode formed on the silicon dioxide film 4,
Reference numeral 6 is a counter electrode formed on the silicon dioxide film 4. Here, the working electrode 5 and the counter electrode 6 form a comb-shaped electrode.

2 (a) to 2 (g) are cross-sectional views showing a method for manufacturing the microelectrode cell in FIG. In the figure,
7 is a silicon dioxide layer and 8 is a resist. In FIG. 1, the silicon dioxide layer 7 is omitted for convenience of explanation.

Next, the manufacturing method will be described with reference to FIGS. First, a 1 μm silicon wafer with an oxide film (manufactured by Osaka Titanium Co., Ltd.) (FIG. 2 (a)) is attached to a predetermined position in a sputter device (manufactured by Anelva, SPF332H), and chromium and silver are selectively sputter deposited. A reference electrode 3 is formed (FIG. 2B). Next, a silicon dioxide film 4 is formed using the same sputter device (FIG. 3C). At this time, the conditions of the spatter device are as follows: argon gas atmosphere, pressure
At 10 ^-2 Torr, chromium: 50 W, 10 seconds, silver: 70 W, 1 minute, silicon dioxide film: 50 W, 5 minutes
Silver: 150 nm, silicon dioxide film: 100 nm. Next, an electron beam resist (φ-
MAC, manufactured by Daikin Industries, Ltd.) to a thickness of 1.0 μm.
Then, the silicon wafer coated with the resist is placed in an oven and baked at 180 ° C. for 60 minutes. After that, it was put into an electron beam exposure apparatus (JEOL: JSM-840), and the pitch was adjusted under the conditions of an electron beam acceleration voltage of 10 kV and an exposure amount of 5 μC / cm ^2.
A 3.5 μm, 0.5 μm gap, 1.0 mm long, interdigitated comb electrode pattern is exposed. Next, after developing with a predetermined developing solution, the chromium and platinum films are spread with a sputter device (Anelva: S
PF332H) is formed to a thickness of about 200 nm, and the resist is removed with a solvent to form a comb-shaped electrode pattern that meshes with the working electrode 5 and the counter electrode 6. Thereafter, a photoresist (AZ1400-27, manufactured by Shipley Co., Ltd.) is applied on the substrate to a thickness of 1 μm, and alignment is performed, and the leads, pad portions, and counter electrode pattern of the interdigital electrode are exposed in close contact. Then, after development, spattering of chromium and platinum is performed again, and the resist is stripped in methyl ethyl ketone to form a comb-shaped electrode having leads and pads and a counter electrode pattern (FIG. 4D). Next, the substrate is put again in a sputter device (Anelva SPF332H), and the entire surface of the substrate is 100 nm.
The silicon dioxide layer 7 is formed as shown in FIG. Next, a photoresist 8 (AZP, manufactured by Shipley Co., Ltd.) is placed on the substrate.
1400-27) is applied to a thickness of 1 µm, and only the interdigitated comb-shaped electrode portion (1 mm x 0.25 mm), the counter electrode, and the pad portion are exposed and developed using a chrome mask, and the portion is exposed. Figure (f). Next, this substrate was placed in a reactive ion etching apparatus (DEM-451, manufactured by Anelva), and C ₂ F ₆
The resist pattern is masked under the conditions of gas, flow rate: 25 SCCM, pressure: 0.25 Pa, 150 W, and the silicon dioxide film 4 and the silicon dioxide layer 7 are etched for 5 minutes to expose the reference electrode 3 formed below. Thereby, the reference electrode 3,
A very small interdigitated microelectrode cell for electrochemical measurement is obtained between the working electrode 5 and the counter electrode 6 (FIG. 9 (g)).

This microelectrode cell for electrochemical measurement is immersed in an aqueous solution of 0.1 mmol / iron ferricyanide at 40 ° C., and each pad is connected to a potentiostat via a lead wire. ) From -0.3V to 0.5V
When the potential was scanned at 10 mV / sec and cyclic voltammogram measurement was performed using the other comb-shaped electrode (counter electrode 6) as the counter electrode, a reversible peak accompanying the redox of iron ferricyanide was obtained. Electrochemical measurement was possible even in the resistance solution.

Also, 0.9 g of polyethylene oxide (manufactured by Aldrich, weight average molecular weight: 600,00), 0.2 g of lithium trifluoromethanesulfonate, and 1 mg of ferrocene are dissolved in 100 ml of a mixed solvent of acetonitrile and methanol 9: 1, and the solution is placed in this microelectrode cell. Then, the solvent was dried and a polymer film was obtained.

In addition, the pad of each electrode is connected to a potentiostat, and the potential of one of the electrodes is 100mV / sec from -0.3 to 0.7V.
Scanning, a peak associated with the oxidation-reduction reaction of ferrocene was observed. The difference between the oxidation peak and the reduction peak is 80mV
The value was close to the theoretical value of the reversible redox reaction (63 mV), and quantitative electrochemical measurements could be performed even in solid electrolytes.

Example 2 FIG. 3 is a schematic view of a microelectrode cell for electrochemical measurements showing a second example according to the present invention. In the figure, 11 is a quartz substrate, 12 is a silicon dioxide film, 13 is a working electrode, 14 is a reference electrode, 15 is a counter electrode, and 16 is a working electrode. Here, the working electrodes 13 and 16 form comb electrodes.

Next, a manufacturing method of the second embodiment will be described. First, a quartz substrate with a thickness of 0.3 mm was placed on a spatter device (Anelva: SPF3
32H), and the working electrode 16 is formed by selectively depositing chromium and platinum on the sputter. Next, a silicon dioxide film 12 is formed using the same sputter device. At this time, the conditions of the spatter device were an argon gas atmosphere,
At a pressure of 10 ^-2 Torr, chromium: 50 W, 10 seconds, platinum: 70 W, 1
Sputter for 50 minutes, silicon dioxide film: 3 minutes, chromium and platinum: 100 nm, silicon dioxide film: 100 nm. Next, a photoresist (AZ1400-27 manufactured by Shipley Co.) is applied on the silicon dioxide film 12 to a thickness of 1 μm.
Put the resist coated quartz substrate in an oven at 80 ° C, 30
Bake for minutes. Then, using a photomask,
20 electrode patterns using a mask aligner (Canon)
Contact exposure is performed for 2 seconds. The pattern was a comb-shaped electrode having a size of 2 mm × 0.25 mm, a reference electrode, a counter electrode, and their leads and pads, each having a pitch of 5 μm and a gap of 2 μm.
The exposed quartz substrate 11 is developed in a resist developing solution (AZ Developer, AZ Developer) at 20 ° C. for 120 seconds, washed with water and dried to transfer the mask pattern to the resist. After the development, the substrate was put into a spatter again, and chromium: 50 W, 5 seconds, platinum: 70 W, spattered for 2 minutes, and 200 n
After forming the film of m, the resist is stripped in methyl ethyl ketone to form electrode patterns of the working electrode 13, the reference electrode 14, and the counter electrode 15. Next, the substrate is put again in the sputter device, and a silicon dioxide film is formed to a thickness of 150 nm. Thereafter, a photoresist (AZ1400-27 manufactured by Shipley Co., Ltd.) is applied to this substrate to a thickness of 1 μm, and only a comb-shaped electrode portion (2 mm × 0.25 mm), a reference electrode, a counter electrode, and a pad portion are applied using a chrome mask. Exposure and development. Next, the substrate was placed in a reactive ion etching apparatus (DEM-451, manufactured by Anelva), and C ₂ F ₆ gas, flow rate: 25 SCCM, pressure: 0.25 Pa, 150 W, and the resist pattern was used as a mask for 2 minutes. Then, the lower electrode is exposed by etching the silicon dioxide 12. The tip of the reference electrode is immersed in a plating solution at 60 ° C. as a reference substance for 10 seconds to paint silver.

This microelectrode cell for electrochemical measurement is immersed in an acetonitrile solution in which 0.1 mmol / of ferrocene and 0.1 mol / of a supporting electrolyte (tetraethylammonium perchlorate) are dissolved, and each pad is connected to a bipotentiostat via a lead wire. When the lower electrode is fixed at -0.3 V and the electric potential is scanned from -0.3 V to 0.5 V at 100 mV / sec and the upper comb electrode is fixed at -0.3 V, the former is the oxidation reaction of ferrocene and the latter is the reduction. A limiting current based on the reaction was observed. Comparing the absolute value of the magnitude of both current values, the trapping rate
98% were obtained. Also, the potential of one comb-shaped electrode -0.3V
When the potential of the other comb electrode was applied to a potential of 0.7 V, the steady state was reached 90 msec after the application of the voltage, and the response was quick. Further, after placing the microelectrode cell for electrochemical measurement in a vacuum and introducing 10 mTorr of water vapor, when a voltage of 1 V was applied between the upper and lower comb-shaped electrodes, a current of 5 μA was obtained, and a current of 5 μA was obtained. It has been found that electrochemical reactions of molecules can be measured.

Example 3 As a third example, a method for manufacturing a microelectrode cell for electrochemical measurements will be described. Chrome on a 0.3mm thick quartz substrate
It is the same as the second embodiment until the platinum and silicon dioxide films are sputter deposited. Next, a photoresist (AZ-1400-27 manufactured by Shipley Co.) is applied on the silicon dioxide film to a thickness of 1 μm. The resist-coated quartz substrate is placed in an oven and baked at 80 ° C. for 30 minutes. Thereafter, contact exposure is performed for 20 seconds by a mask aligner (manufactured by Canon Inc.) using a chrome mask. The pattern is 2 μm wide
A 1 μm × 1 mm grid electrode, a reference electrode, a counter electrode and their leads and pads were formed over the entire gap of 2 μm. The exposed quartz substrate is developed in a resist developer (AZ Developer, Shipley) at 20 ° C. for 120 seconds, washed with water and dried to transfer the mask pattern to the resist. After the development, the substrate was put again in a spatter device, and chromium: 50 W, 5 seconds, platinum: 70 W, spattered for 2 minutes, and 200 nm
After the formation of the film, the resist is stripped in methyl ethyl ketone to form an electrode pattern. Next, this substrate is put again in the sputter device, and a silicon dioxide film is formed to a thickness of 150 nm. Thereafter, a photoresist (AZ1400-27 manufactured by Shipley Co., Ltd.) is applied on this substrate to a thickness of 1 μm, and only the grid electrode portion, the reference electrode, the counter electrode, and the pad portion are exposed and developed using a chromium mask. Next, the substrate was subjected to a reactive ion etching apparatus (DEM-4, manufactured by Anelva).
51) Inside, C ₂ F ₆ gas, flow rate: 25SCCM, pressure: 0.25Pa,
Under the condition of 150W, using the resist pattern as a mask for 2 minutes,
Etching of silicon dioxide is performed to expose the lower electrode. The tip of the reference electrode is immersed in a plating solution at 60 ° C. as a reference substance for 10 seconds to paint silver.

This microelectrode cell for electrochemical measurement is immersed in an acetonitrile solution in which 0.1 mmol / of ferrocene and 0.1 mol / of a supporting electrolyte (tetraethylammonium perchlorate) are dissolved, and each pad is connected to a bipotentiostat via a lead wire. When the lower electrode is fixed at -0.3 V and the electric potential is scanned from -0.3 V to 0.5 V at 100 mV / sec and the upper comb electrode is fixed at -0.3 V, the former is the oxidation reaction of ferrocene and the latter is the reduction. A limiting current based on the reaction was observed. Comparing the absolute values of the magnitudes of the two current values, a trapping rate of 99% or more was obtained, and it was found that most of the oxidized ferrocene molecules at the lower electrode were trapped at the upper electrode.

Also, 0.9 g of polyethylene oxide (manufactured by Aldrich, weight average molecular weight: 600,000) was dissolved in a mixed solution of 0.02 g of trifluoromethanesulfonic acid, 0.02 g of ferrocene, and 9 mg of acetonitrile: methanol, and the solution was placed on the microelectrode cell. After drying, the solvent was dried to obtain a polymer film. Then connect the electrodes to the bipotentiostat,
The potential of the lower working electrode was scanned from -0.3 V to 0.5 V at 10 mV / sec, the upper electrode was fixed at -0.3 V, and the current value was measured. As a result, a high capture rate of 97.5% was obtained.

As described above, in the microelectrode cell for electrochemical measurement according to the present embodiment, each electrode is separated by the planar gap obtained by the lithographic technique and the three-dimensional gap due to the step through the silicon dioxide film. Each electrode can be separated with high reproducibility using a small gap. For this reason,
The characteristics of each microelectrode cell are stabilized, and the conventional inspection work becomes unnecessary, and the measurement time can be reduced.

In addition, since the gap between the thin film electrodes can be reduced, there is an effect that the speed of electrochemical measurement and the sensitivity can be increased.

In the above embodiments, a silicon substrate with an oxide film and a quartz substrate have been described as insulating substrates, but an aluminum oxide substrate, a glass substrate, a plastic substrate, or the like can be used. In addition, as a metal for the electrode, gold,
Chromium, titanium, stainless steel, and the like can be given. Semiconductors for electrodes include p and n type silicon, p and n type germanium, cadmium sulfide, titanium dioxide, zinc oxide, gallium phosphide, gallium arsenide, indium phosphide, cadmium selenium, cadmium telluride, molybdenum disulfide, selenide Examples thereof include tungsten, copper dioxide, tin oxide, indium oxide, and indium tin oxide. In addition, examples of the semimetal include conductive garbon. Examples of the insulating film include silicon oxide, silicon nitride, silicone resin, polyimide and derivatives thereof, epoxy resin, and thermosetting polymer. Examples of the reference substance on the reference electrode include silver chloride, polyvinyl ferrocene, and the like.

Further, in the above embodiment, a spatter was used for manufacturing the microelectrode cell, but a metal, semiconductor, or semimetal conductive thin film, insulating film, or conductive thin film may be formed by vapor deposition, CVD, or a coating method. .

〔The invention's effect〕

As described above, the present invention uses the first and second thin-film electrodes separated by the three-dimensional space due to the step between the insulating films, so that the thin-film electrodes can be separated with good reproducibility at a minute gap. can do. For this reason, the characteristics of each electrochemical measurement microelectrode cell are stabilized, and the conventional inspection work is unnecessary, and the measurement time can be shortened.

Further, since the gap between the thin film electrodes can be reduced, the speed and sensitivity of the electrochemical measurement can be increased.
In addition, the present invention has an effect that an electrochemical measurement of electricity can be performed in a high-resistance sample such as a solution, a solid, and a gas containing no electrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a microelectrode cell for electrochemical measurement showing a first embodiment according to the present invention, and FIG. 2 is a view of the microelectrode cell for electrochemical measurement in FIG. Sectional view showing a manufacturing method,
FIG. 3 is a schematic view of a microelectrode cell for electrochemical measurement showing a second embodiment according to the present invention. 1 ... silicon wafer, 2 ... oxide film, 3, 14 ... reference electrode, 4, 12 ... silicon dioxide film, 5, 13, 16 ... working electrode, 6, 15 ... counter electrode, 7 ... Silicon dioxide layer, 8 ...
... resist, 11 ... quartz substrate.

Claims (2)

(57) [Claims] 1. A microelectrode cell having a plurality of thin film electrodes formed on an insulating substrate, wherein: a first thin film electrode formed on a main surface of the insulating substrate; and at least one of the first thin film electrodes. An insulating film formed on an insulating substrate including the first thin film electrode so as to be exposed; and an insulating film formed on the insulating film by being insulated and separated from the first thin film electrode by the insulating film. A microelectrode cell for electrochemical measurement, comprising at least a second thin film electrode and exposing the entire surface or a part of the surface of each thin film electrode. 2. A step of forming a single or a plurality of first conductive thin films having a pattern shape and separated by a planar gap on an insulating substrate, and an insulating substrate including the first conductive thin film. A step of forming an insulating film thereon; a step of forming a single or a plurality of second conductive thin films separated by a planar gap having a pattern shape on the insulating film; Etching the insulating film using a mask to expose the first conductive thin film.