JPH02140655A - Electrochemical detector and production thereof - Google Patents

Abstract

PURPOSE:To extremely diminish the inter-electrode spacing of two working electrodes to sub-micron order by determining the inter-electrode spacing by the thickness of insulating films. CONSTITUTION:A photoresist is applied on a silicon substrate 1 to 1mum thickness. The silicon substrate 2 is then put into an oven and is baked. Thereafter the substrate is subjected to contact exposing by using a chromium mask. This substrate 2 is developed in a resist developing soln. and is subjected to washing and drying, by which mask patterns are transferred onto the resist. Chromium and platinum are then successively deposited by sputtering thereon. The substrate 2 is immersed into methyl ethyl ketone and is subjected to an ultrasonic treatment by which the resist exclusive of the electrode forming parts is peeled and the lower working electrode 3 is formed. Silicon dioxide is thereafter deposited by sputtering to form the 1st insulating film 4. The resist is again peeled in the methyl ethyl ketone to form the upper working electrodes 5, 6. The surface of the substrate 2 is coated and the 2nd insulating film 6 is formed. The insulating films 8, 4 are etched to expose the electrode 3.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electrochemical detector that is formed on a substrate by integrating a working electrode, a reference electrode, and a counter electrode, and is used in flow cells or liquid phase chromatography. and its manufacturing method.

[Conventional technology]

For blood sugar level measurement, a device called a flow cell is used, which injects a sample into a carrier solvent flowing at a constant flow rate and measures the sample using a detector placed in a flow path. Furthermore, in liquid phase chromatography, a column for chromatography is inserted between a sample injection port and a detector, where the injected sample is separated and each component is detected.

Detection of this sample requires spectroscopic methods such as ultraviolet, visible, etc.
Refractive index measurement, conductivity measurement, electrochemical methods, etc. are known. In the electrochemical method, an electrode is placed in a flow path and a constant potential is applied to it. When a sample flowing on a carrier reaches the electrode, the redox current that occurs between the electrode and the electrode is generated. Detection is performed by monitoring. Electrochemical detection is thus simple, relatively sensitive, and does not respond to electrochemically inert substances or substances with redox potentials lower than the applied potential. It has the characteristic of being able to selectively detect specific substances. Furthermore, even electrochemically inactive substances such as glucose can be detected by modifying the electrode with an enzyme such as glucose oxidase.

[Problem to be solved by the invention]

However, with conventional electrodes, it is difficult to detect a mixture of substances having similar redox potentials or to detect extremely minute substances.

On the other hand, in a 70-cell, etc., the longer the length of the electrode in one direction of the flow, the longer the contact time with the detection substance.
There is a problem that the response becomes slow. Furthermore, if the distance between the reference electrode and the working electrode is long, an IR drop will occur corresponding to the liquid resistance between them, and the signal will become dull.

In order to suppress these problems, it is possible to miniaturize the electrodes, shorten the contact time, and shorten the distance between the working electrode and the reference electrode, but in this case, the electrode area is small, so the current value becomes small. This has the disadvantage that detection becomes difficult. Furthermore, since the current response depends on the electrode shape, different shapes will show different responses. Many of the microelectrodes are made of platinum in glass tubules.

Because it is manufactured by enclosing metal wires such as gold, carbon fiber, gold yk chloride, etc., it is impossible to obtain electrodes with exactly the same shape, and it is difficult to manufacture them in large quantities. Since there was a large variation between the electrodes produced, if quantitative data was required, it was necessary to test the electrodes in advance, which required a large amount of measurement time. For this reason, it has been extremely difficult to obtain quantitative data if the measurement electrode cannot be tested for reasons such as being contaminated or corroded.

In recent years, the application of phosphorography technology has been proposed as a method for manufacturing microelectrodes. In this method, a resist is applied to a substrate, an image mask with an electrode pattern is placed over it, exposed and developed, a thin metal film is formed by vapor deposition, etc., and then the resist is peeled off to form minute electrodes on the substrate. After creating a metal thin film on an insulating substrate, a resist is applied, an image mask with an electrode pattern is layered, exposed and developed, and the exposed parts of the metal film are removed using the remaining resist as a mask. Etching, electric,
Etching methods for obtaining polar patterns are known.

With this method, a large amount of microelectrodes with arbitrary shapes and a constant distance between the electrodes can be fabricated on the substrate with good reproducibility. Similarly, it can be applied to electrode pairs that can measure force, electrochemical elements, and pace electrodes for sensors. Applying this microelectrode fabrication method, microelectrochemical transistors (e.g., Journal of the Physical Chemistry Society of Japan (J,
Ph)'s, Chem, 89.5133 (1985)
)), <Electrochemical measurement of low molecules or polymer complexes using L-shaped platinum electrodes (Anal, Chem,, 5
8. 601 (1986)) etc. Furthermore, a resist is coated on a conductive substrate, exposed to light, developed, and a large number of fine circular holes are made in the resist to produce a large number of submicron-order working electrodes (Journal of the Electrochemical Society of Japan). , Electrochem, Soc.
.

Vol. 133, 752 (1986), )).

Lingraphy electrodes are suitable for quantitative measurements because there is little variation in electrode shape, size, electrode spacing, etc. However, when using light or lithographic technology, 0.5μ
It is difficult to separate patterns with a gag of about m, and it is difficult to produce minute electrode pairs with good reproducibility.

As a method for obtaining an electrochemical cell with a small electrode spacing, a method has been proposed in which a metal, an insulator, and a metal are sequentially laminated on a substrate, and then the end surfaces are exposed and used as electrodes. In this method, the electrode spacing can be extremely narrowed by using a dense insulating thin film, but since a large area cannot be obtained, the current value is low. Furthermore, since the end face of the thin film is used, there is a drawback that an electrode having any shape other than a band electrode cannot be obtained.

[! Means for Solving the Problem] As a result of intensive studies to improve the above-mentioned current situation, the inventor has found that
The working electrode, which used to be one, is now two, the target substance is oxidized at one electrode, the generated oxidant is reduced at the other, and after returning to the original target substance, it is oxidized again at the first electrode. We have discovered that sensitivity can be increased by performing so-called redox cycling. Furthermore, the sensitivity is improved by arranging these two working electrodes with a small gap between them, but the three-dimensional method is a method that can control the electrode spacing of submicron or less with good reproducibility and obtain electrodes with a large area. We discovered that the difference in level separates the stain poles,
This led to the present invention.

In addition, in a sample containing ascorbic acid, which is an interfering substance that is often present in biological samples, if ascorbic acid is oxidized with one electrode, the oxidized ascorbic acid undergoes further chemical changes and is no longer reduced; The detection signal/
It was found that the noise ratio was improved. Furthermore, if one of the interlocking square-shaped electrodes is used as a reference electrode, then -
They found that because the comb-shaped working electrode was very close to the reference electrode at any position, the uniformity of the set potential on the working electrode was improved and the signal was sharper.

To summarize the present invention, in a plurality of patterned thin film electrodes formed on an insulating base edge, each electrode is formed by a minute planar gap and/or a minute gap due to a three-dimensional step through an insulating layer. one or more working electrodes formed of a metal or a semiconductor or a metalloid, separated so that the entire surface or part of each electrode surface is exposed;
It is characterized in that the counter electrode and the reference electrode are integrally formed on the substrate. Furthermore, the present invention is characterized in that at least one of the working electrodes is used as a counter electrode or a reference electrode.

As shown in Fig. 1, an electrochemical detector can be manufactured using a single metal or a plurality of metals having a desired pattern shape on a substrate whose surface or the whole is insulating. After forming a conductive thin film of semimetal or semiconductor and covering the conductive thin film with an insulating film, a single conductive thin film having a desired pattern shape or a plurality of conductive thin films insulated from each other by a planar gap are coated on the insulating film. Then, using the upper conductive thin film as a mask, the insulating layer is etched until the underlying conductive thin film is exposed.One of the electrodes is used as the counter electrode, and the other is used as the redox electrode. It is characterized in that it is covered with a substance and used as a reference electrode and the rest as a working electrode.

Examples of the substrate whose surface or the whole is insulating include a silicon substrate with an oxide film, a quartz plate, an aluminum oxide substrate, a glass substrate, and a plastic substrate. Gold is the metal for electrodes.

Examples include platinum, silver, chromium, titanium, and stainless steel. Semiconductors for electrodes include p- and n-type silicon, p- and n-type germanicum, cadmicum sulfide, titanium dioxide, zinc oxide, gasa 9-murine, galiwam arsenic, indicumulin, cadmiwam selenium, cadmiwam tellurium,
Molybdenum disulfide, tungsten selenide, steel dioxide,
Examples include indicum oxide and indium tin oxide. Examples of semimetals include conductive carbon. Examples of the insulating film include silicon oxide, silicon dioxide, silicon nitride, silicone resin, polyimide and derivatives thereof, epoxy resin, and thermoset polymers. The reference substance on the reference electrode is
Silver, iron chloride, polyvinylferrocene, etc. can be mentioned.

When creating microelectrodes, evaporation, sputtering,
A conductive thin film, an insulating film, or a conductive thin film of a metal, semiconductor, or semimetal is formed by CVD or a coating method. A resist is applied onto the substrate, and an image mask having an electrode pattern is overlaid thereon, or the pattern is directly exposed using an electron beam, etc., and the pattern is transferred to the resist on the substrate by development. Forming a conductive thin film or insulating film of metal, semiconductor, or semimetal on a substrate by etching the upper conductive film using a resist pattern as a mask to form an electrode, or by vapor deposition, sputtering, CVN, or coating method. After that, a resist is applied, an image mask having an electrode pattern is placed thereon, or the pattern is directly exposed using an electron beam, developed, and the pattern is transferred to the resist on the substrate. A conductive thin film of metal, semiconductor, or semimetal is formed by sputtering, CVD, or coating, and the lift-off method is used to remove the resist.
Fabricate one or more upper electrodes, leads, and pads. Next, an insulating film is formed on the substrate by vapor deposition, sputtering, CVD''!, or coating method, and then resist coating and N
Only the portion of the electrode used for measurement is exposed to light, development, and etching.

When etching is continued until the lower conductive layer is formed, the upper electrode pattern acts as a mask and etches the insulating layer, forming a lower electrode with a distance from the upper electrode approximately equal to the thickness of the insulating film. Can be configured. After producing the electrodes, one of the produced electrodes is plated with a metal and an organic redox polymer to serve as a supporting material, and formed by electrolytic polymerization to serve as a reference electrode.

[For production]

In the present invention, since the electrode spacing between the two working electrodes is determined by the thickness of the insulating film separating them, it can be extremely small, on the order of submicrons.

〔Example〕

Hereinafter, the present invention will be explained in detail by examples with reference to the drawings. It should be noted that the present invention is not limited only to the following examples.

FIGS. 1(a) to 1(g) are cross-sectional views illustrating an embodiment of the method for manufacturing an electrochemical detector according to the present invention,
FIG. 2 is a perspective view showing the structure of the electrochemical detector.

Example 1 First, as shown in FIG. 1 <a), a photoresist (Silapray G:
MP1400-27) was applied to a thickness of 1 μm. Next, this resist-coated silicon substrate 2 was placed in an oven and baked at a temperature of 80° C. for 30 minutes. After that, use a chrome mask to apply a mask aligner (manufactured by Canon:
PLF-521) was used for contact exposure for 20 seconds. The exposed silicon substrate 2 is coated with resist imaging liquid (manufactured by Shipley:
The mask pattern was transferred to the resist by developing the film in a 20° C. MP developer for 60 seconds, washing with water, and drying. Next, this resist patterned silicon substrate 2 was attached to a predetermined position in a sputtering device (5PF-332H manufactured by ANELVA), and chromium and platinum were successively deposited by sputtering. In this case, chromium was deposited for 15 seconds and platinum was deposited for 1 minute under a pressure cuff of 5 mTorr + power of 50 W to give a total film thickness of 1100 nm. Thereafter, this silicon substrate 2 was immersed in methyl ethyl ketone and subjected to ultrasonic treatment, and the resist other than the electrode forming portion was peeled off to form the lower working electrode 3 as shown in FIG. 1(b).

After that, sputtering equipment (manufactured by ANELVA: 5PF-332)
H) and sputter deposited silicon dioxide to form the first insulating material g! as shown in FIG. 1(c). ! 4 was formed. In this case, this first thermally edged film 4
The film was formed by sputtering using a pressure cuff and a power of 50 W for 10 minutes in an atmosphere of 5 mTorr + argon to obtain a silicon dioxide film with a thickness of 200 nm. Next, anti-reflective coating (
After spin code processing of ARC-2 (manufactured by Brewer Science), resist was applied again, exposed using a mask, developed, sputtered with chromium and platinum again, and the resist was peeled off in methyl ethyl ketone. Figure 1(d)
Comb-shaped upper working electrodes 5 and 6 having leads and pads as shown in FIG. 2 and a counter electrode 7 shown in FIG. 2 were patterned/formed. After that, spin-on glass (Tokyo Ohka: 0C)
After forming a second insulating film 8 covering the silicon substrate 2 as shown in FIG. 1 (el) using a resist film (DType-7), a resist is applied again to form the second insulating film 8 as shown in FIG. 1 (f). The silicon substrate 2 was exposed using a mask to expose the electrode portion and the pad portion.Next, this silicon substrate 2 was placed in a reactive ion etching device (manufactured by ANELVA: DEM-451), and CtFs gas was etched at a flow rate of 25 SCCM. , pressure 0.25
The second insulating film 8 and the first insulating film 4 are etched for 15 minutes using the resist pattern RP as a mask under conditions of Pa and power of 150 W, and the lower working electrode 3 is etched as shown in FIG. 1(g). exposed. This resulted in a comb-shaped electrochemical detector with very small interdigitation between the upper working electrode 5 and the lower working electrode 3. Finally, a lead wire is connected to one of the comb-shaped upper working electrodes 5.6, for example, the upper working electrode 6, and plating is performed for 10 seconds at a current density of 1 mA in a silver plating solution heated to a temperature of 60°C to remove silver. It was deposited to form a reference electrode 6'.

FIG. 2 shows the structure of the electrochemical detector thus produced, and the same parts as in the structure of FIG. 1 are given the same reference numerals. In the figure, the upper working electrode 5
The length of the lower working electrode 3 in the comb tooth direction is 2 mm, and the width thereof is 2 μm.

This electrochemical detector is attached to a flow cell, and with respect to the reference electrode 6', one potential of the upper working electrode 5 is set to 0.7 V, and the potential of the lower working electrode 3 is set to -0, 1. 1 μmo L/t of 7 Erosene 100 μt at a flow rate of 0
．． When injected under 8 mt/rnin, the comb electrode 5.6' responded immediately and showed a peak current value of 55 nA at 30 m5ec, returning to the original value at 50 m5ec.

When a similar experiment was conducted using a circular electrode with the same area as the above electrode, the peak current value was 0.29n at 50m5ec.
A hl'), returned to normal at 500m8・C.

Example 2゜A lead wire was connected to the upper working chamber t#, 5 of the shuttle produced in Example 1, and immersed in a mixed aqueous solution of glucose oxidase at a concentration of 5 mg/mt and potassium chloride at a concentration of 0.1 mat/L. Then, the potential of the electrode is set to O, S with respect to the reference electrode 6'.
Electrolysis was carried out for 30 minutes at a setting of V, and glucose oxidase molecules were immobilized on the electrolyte. This electrochemical detector was installed in a 70-cell, and the potential of the lower working electrode 3 was set to 0.7.
■, and add phosphate buffer (0.1 mol/l, p
When 100 μt of 1 mmot/l glucose dissolved in H=6.8) was injected at a flow rate of 0.8 mt/min, the comb-shaped electrodes 5 and 6' immediately responded, and 3
Shows a peak current value of 2.4μA at 0m5eC, 50mB
I got back to normal with ec. When a similar experiment was conducted with a circular electrode of the same area modified with glucose oxidase, the peak current value was 12 nA in soomsec,
It returned to normal in 2 seconds.

Example 3 The electrochemical detector prepared in Example 1 was attached to a liquid phase chromatography system, and the potential of the upper working electrode 5 was set to 0.7 V with respect to the reference electrode 6', and the potential of the lower working electrode 3 was set to -0. 1■
100 μL of a mixed solution of ascorbic acid with a concentration of 100 μmol/L and dopamine with a concentration of 100 μmol/L was injected at a flow rate of 0.8 mL/min. As a result, oxidation current of ascorbic acid was observed only on the upper working electrode 5 side 3 minutes after injection, and the current decreased significantly on the lower working electrode 3 side. Furthermore, 8 minutes after the injection, the oxidation current of dopamine (85 nA
).

On the lower working electrode 3 side, a reduction current of oxidized dobami/ was observed. When the same thing was done without connecting the lower working electrode 3 and setting the potential of the upper working electrode 5 to 0.7■, the oxidation current of dopamine was the same as when the lower working electrode 3 was connected. It was 1/20th (4.2 nA).

Example 4: A quartz substrate with a film thickness of 0.3 mm was sputtered! (manufactured by ANELVA: 5PF332H) was mounted at a predetermined position, and chromium and platinum were sequentially sputtered to form a film.

Sputtering was performed in an argon atmosphere at a pressure of 10" Torr for 10 seconds for chromium = 50 W and 1 minute for platinum at 0 W to obtain a film thickness of chromium and platinum i of 1100 nm. Thereafter, a photo film was deposited on the chromium and platinum-coated quartz substrate. Resist (manufactured by Silapray: MP14o.

27) was applied to a thickness of 1 μm. This resist-coated quartz substrate was placed in an open chamber at a temperature of 80C.

It was baked for 30 minutes. Thereafter, contact exposure was performed for 20 seconds using a chrome mask and a mask aligner (manufactured by Canon). The exposed quartz substrate is treated with a resist developer (
Shipley Co. g: MP Developer) at a temperature of 20°C and 60°C.
Develop for seconds and wash with water.

Dry and transfer the mask pattern to the resist.

Next, the substrate was sputtered using an electron cyclotron resonance sputtering device (
Anelva (ECR sputter)), argon gas pressure 10 Torr, RF power 200W.

Platinum was etched at a drawing voltage of 300 µm.

After removing the resist with methyl ethyl ketone, the substrate was put into the sputtering equipment again and the argon pressure was set at 10” Torr.
* Sputtering was performed with silicon dioxide for 10 minutes, chromium for 10 seconds, and platinum for 1 minute at a power of 100 W to form a platinum/chromium film of 1100 nm of silicon dioxide with a thickness of 200 nm. After that, electron beam resist (manufactured by Daikin Industries, Ltd.: φ-
MAC) was applied to a thickness of 1 μm. This resist-coated quartz substrate was placed in an oven and baked at 180° C. for 60 minutes. After that, it was placed in an electron beam exposure device (manufactured by JEOL Ltd.: JSM-840), and the acceleration voltage of the electron beam was 10k.
V.

Interlocking interdigitated electrode patterns with a pitch of 3.5 μm, a gap of 0.5 μm and a length of 1.0 mm were exposed at an exposure dose of 5 μC/m”. After development with a specified developer, a chromium and platinum film was formed. Platinum was etched using an ECR sputtering device (manufactured by ANELVA), and the resist was removed with a solvent to form interlocking interdigitated electrode patterns.

Next, the substrate was put into the sputtering apparatus again, and a silicon dioxide film was formed to a thickness of 150 nm. Thereafter, a 7-otoresist (manufactured by Shipley Co., Ltd.: AZ1400-27) was applied on the substrate.
) to a thickness of 1 μm and use a chrome mask to form the comb-shaped electrode part and the reference electrode.

Only the counter electrode and pad portions were exposed and developed. Next, the substrate was etched using a reactive ion etching device (manufactured by ANELVA: DEM).
-451) Put C, F, and gas at a flow rate of 258 CCM
Using the resist pattern as a mask, silicon dioxide was etched for 2 minutes under conditions of a pressure of 0.25 Pa and a power of 150 W to expose the upper and lower electrodes. Further, the reference electrode portion was plated with silver as a reference material in the same manner as in Example 1.

This electrochemical detector was installed in the cell 70~, and the potential of one of the upper working electrodes was set to 0.7V and the potential of the lower working electrode was set to 1V and 1V, respectively, with respect to the reference electrode.
llL of 7 Erosene 100 μt at a flow rate of 0.4 mt/mi
When injected under n, the comb electrode responded immediately with a peak current value of 160 nA at 24 m5ec;
'I returned to normal at 13m5@c.

Examples 5-8 In Example 1, the distance between the upper working electrode and the lower working electrode was 10100n by changing the sputtering time of silicon dioxide (Example 5).

Table 1 shows the peak current values at the upper working electrode at 300 nm (Example 6), 500 nm (Example 7), and 11000 nm (Example 8).

Table 1 [Effects of the Invention] As explained above, the electrochemical detector of the present invention has two
Since the electrode spacing between the two working electrodes is determined by the thickness of the insulating film that separates them, it can be made extremely small, on the order of submicrons, and oxidation (or reduction) occurs at one electrode.
The other electrode can reduce (or oxidize) the oxidized substance by nearly 100%. Redox cycling, which detects the substance that has returned to its original state, has improved sensitivity by more than 100 times compared to previous detectors. In addition, for samples that have been difficult to measure due to ascorbic acid being an interfering substance, one electrode can oxidize the ascorbic acid to make it electrochemically inactive, and then the target substance can be detected with the other electrode. By doing this, it was possible to detect it without being interfered with by ascorbic acid. Furthermore, since it is manufactured using phosphorography technology, measurement cells with working electrodes, reference electrodes, and counter electrodes of any size, shape, and distance between electrodes can be obtained in large quantities at low cost, and measurements can be easily performed using external equipment. Because it has many advantages, it has extremely excellent effects, such as being extremely useful as an electrochemical detector for flow cells and liquid phase chromatography.

[Brief explanation of the drawing]

Figures 1(a) to ω) are cross-sectional views illustrating the process of manufacturing an electrochemical detector according to the present invention, and Figure 2 is a perspective view showing an embodiment of the electrochemical detector according to the present invention. be. 1... Silicon oxide Jl, 2-... e silicon substrate, 3... Lower working electrode, 4... First insulating film, 5, 6... Upper working electrode, 6 '...Reference electrode, T...Counter electrode, 8...Second insulating film. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] (1) A plurality of patterned conductive thin film electrodes are formed on an insulating substrate, and each conductive thin film electrode is separated by a minute planar gap and/or a minute gap formed by a three-dimensional step through the insulating film. an electrochemical detector, wherein at least a portion of the surface of each conductive thin film electrode is exposed. (2) After forming a single conductive thin film having a desired pattern shape or a plurality of conductive thin films insulated from each other with a planar gap on an insulating substrate, and covering the conductive thin film with an insulating film, the insulating film A single conductive thin film or a plurality of conductive thin films insulated from each other with a planar gap are formed on top again having a desired pattern shape, and then, using the upper conductive thin film as a mask, the insulating film is etched until the lower conductive thin film appears. An electrochemical detector characterized in that one of the electrodes is used as a counter electrode, the other is coated with a redox substance and used as a reference electrode, and the remaining electrodes are used as a working electrode. Production method.