KR100864536B1 - Method for forming a fine electrode using polydimethylsiloxane and Fine electrode formed by the same - Google Patents

Abstract

Disclosed are a method for forming a microelectrode using polydimethylsiloxane and a microelectrode formed thereby.

In the method for forming a microelectrode using polydimethylsiloxane according to the present invention, a polydimethylsiloxane substrate is formed by spin coating a blend of a polydimethylsiloxane prepolymer and a curing agent in a mass ratio of 20: 1 to 5: 1 on a silicon wafer. Performing a surface pretreatment of the polydimethylsiloxane substrate, sequentially depositing a titanium layer and a gold layer on top of the surface pretreated polydimetholylsiloxane substrate, and then patterning a microelectrode. Forming a photoresist on top, spin-coating a polydimethylsiloxane on top of the polydimethylsiloxane substrate, the photoresist is not formed, and after removing the photoresist formed on the patterned microelectrode, the patterned Packaging the microelectrode by performing gold electroplating on top of the gold layer. Include.

According to the present invention, by providing a method of packaging a polydimethylsiloxane microelectrode through the photolithography process and the plating of the electrode part, the cost is reduced due to a simple process, the failure rate is reduced, and the pretreatment and deposition conditions of the polydimethylsiloxane substrate are reduced. By optimizing, there is an effect of improving the adhesion of the metal micropattern.

Description

Method for forming a fine electrode using polydimethylsiloxane and Fine electrode formed by the same}

1 is a flowchart of a method for forming a microelectrode using polydimethylsiloxane according to the present invention.

Figure 2 shows the manufacturing process of the micropattern according to the present invention.

3 shows a manufacturing process of the microelectrode according to the present invention.

4 is a schematic diagram of gold electroplating applied to the present invention.

FIG. 5 is a voltage current density curve of gold electroplating according to FIG. 4.

6A is an image of an electrode portion before performing gold electroplating.

6B is an image of an electrode part after performing gold electroplating according to FIG. 4.

7A is an AFM image of the surface of a polydimethylsiloxane substrate before oxygen plasma treatment.

7B is an AFM image of the surface of a polydimethylsiloxane substrate after oxygen plasma treatment in accordance with the present invention.

Figure 8a is an image showing the flexibility of the patterned polydimethylsiloxane microelectrode according to the present invention.

8B is an enlarged view of FIG. 8A.

8C is an image of a patterned polydimethylsiloxane microelectrode according to the present invention.

Figure 9 shows a cutaway image of the skin of an ICR mouse implanted with a polydimethylsiloxane substrate of the present invention.

The present invention relates to a method of forming a microelectrode using polydimethylsiloxane (PDMS), and more particularly, to a method of forming a microelectrode using polydimethylsiloxane that is more flexible than other substrates and has excellent biocompatibility. .

Various microelectrodes for biosignal measurements have been produced and reported over the last decade, and most of these electrodes are fabricated using silicon-based Micro Electro Mechanical System (MEMS) technology.

However, silicon microelectrodes up to now have a variety of advantages such as ease of micromachining and biocompatibility using MEMS technology, and the flexibility of the fragile material, which is a property of coexisting materials, prevents flexibility. Insertion has a drawback that can damage the adjacent organs or tissues due to the movement of the body. In order to overcome these problems, insertable microelectrodes of various types and purposes have been manufactured using flexible substrates such as polyimide, paraline, SU-8, polydimethylsiloxane, and the like. Flexible electrodes are manufactured in various shapes due to the diversity of the biological environment according to the purpose of use, and applied to new substrates. Among them, polydimethylsiloxane is a polymer having a similar degree of flexibility to biological tissues, has a transparent material property, and is easily manufactured by softlithography, and thus is widely used as a material for microfluidic chips. It is used. In particular, since polydimethylsiloxane is excellent in biocompatibility, permeability to moisture and air, it has recently been applied to many microchips for cell culture. Therefore, if the electrode can be manufactured based on a material having excellent biocompatibility, there will be sufficient utility value as an electrode capable of measuring a biosignal or applying electrical stimulation while implanted in a living body for a long time. In particular, the implantable electrode for connecting with artificial eyes, artificial ears and brain cells must be directly connected to sensitive cells, so the biocompatibility of the implantable electrode is very important.

However, despite the biocompatibility of the polydimethylsiloxane, when forming the electrode based on the polydimethylsiloxane, in terms of materials such as the difference in lattice constant and thermal expansion coefficient between the polydimethylsiloxane, which is a silicon-based organic polymer, and the metal layer, Due to heterogeneity, the formation of the metal layer is difficult, and the adhesion between the metal layer and the polydimethylsiloxane is weak, so that the metal layers are easily separated from each other when the metal layers are patterned in a micro unit line width. The method of forming the metal pattern on the polydimethylsiloxane is silicon. There are methods of forming a metal micropattern on a substrate, transferring the formed metal micropattern to polydimethylsiloxane, and optimizing deposition conditions to form and pattern a metal layer directly on the polydimethylsiloxane. Able to form electrodes There is a problem that the degree of micromachining is not easy.

Accordingly, the technical problem to be achieved by the present invention is to provide a microelectrode packaging method using polydimethylsiloxane that is easy to be microfabricated, flexible and has excellent biocompatibility.

The present invention to achieve the above technical problem,

Spin coating a blend of a prepolymer of polydimethylsiloxane and a curing agent in a predetermined mass ratio onto a silicon wafer to form a polydimethylsiloxane substrate, surface pretreating the polydimethylsiloxane substrate, and the surface pretreated polydimetholtil Sequentially depositing a titanium layer and a gold layer on the siloxane substrate, and then patterning the microelectrode, forming a photoresist on the patterned microelectrode, and forming an upper portion of the polydimethylsiloxane substrate on which the photoresist is not formed. Spin coating polydimethylsiloxane on the substrate, and removing the photoresist formed on the patterned microelectrode, and then packaging the microelectrode by performing gold electroplating on the patterned gold layer. Provided is a method for forming a microelectrode using dimethylsiloxane.

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

However, embodiments of the present invention illustrated below may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the invention are provided to more fully illustrate the invention to those skilled in the art.

1 is a flowchart of a method for forming a microelectrode using polydimethylsiloxane according to the present invention.

Referring to FIG. 1, a polydimethylsiloxane substrate is formed by spin coating a blend of a prepolymer of polydimethylsiloxane and a curing agent at a predetermined mass ratio on a silicon wafer (step 110).

That is, after mixing the prepolymer of polydimethylsiloxane and a hardening | curing agent by predetermined mass ratio, and mixing well, a bubble can be removed by a vacuum desiccator.

On the other hand, when mixing the prepolymer and hardening | curing agent of polydimethylsiloxane by predetermined mass ratio, it is preferable that predetermined | prescribed mass ratio makes 20: 1-5: 1 of the prepolymer and hardening | curing agent of polydimethylsiloxane, respectively. If it is out of the content ratio, it is not preferable because it is a problem in forming a polydimethylsiloxane substrate.

Then, the blend of the prepolymer of polydimethylsiloxane and the curing agent removed from the vacuum desiccator and the curing agent are spin coated on a silicon wafer, and then cured using a vacuum oven to form a polydimethylsiloxane substrate.

Next, the surface of the polydimethylsiloxane substrate is pretreated (120).

As described above, due to heterogeneity in terms of material such as the difference in lattice constant and coefficient of thermal expansion between polydimethylsiloxane, which is a silicone rubber type, and the metal layer, formation of the metal layer is difficult and adhesion is weak. Since the metal layer is detached from the polydimethylsiloxane substrate, the polydimethylsiloxane substrate is surface pretreated to increase the adhesion between the polydimethylsiloxane and the metal layer.

The improvement of adhesion between the polydimethylsiloxane substrate and the metal layer can be realized by pretreating the surface of the polydimethylsiloxane substrate, which is a method of forming an interlayer on top of the polydimethylsiloxane substrate or of the roughness of the surface of the polydimethylsiloxane substrate. Ways to induce an increase.

More specifically, in order to increase the adhesion between the polydimethylsiloxane and the metal layer, an interlayer of 1 to 2 μm may be formed on the polydimethylsiloxane substrate.

When the thickness of the interlayer is less than 1 μm, it is not easy to form the interlayer in the manufacturing process, and when the thickness of the interlayer exceeds 2 μm, the adhesion between the polydimethylsiloxane substrate and the metal layer is weakened, which is not preferable. .

The interlayer may be at least one selected from the group consisting of cytop, polyethyleneglycol, 4-hydroxybutylacrylate, and a mixture thereof, which is one of fluoropolymers. have.

Alternatively, in order to increase the adhesion between the polydimethylsiloxane substrate and the metal layer, an increase in roughness of the polydimethylsiloxane substrate may be induced. This can lead to increased adhesion to the metal layer of the polydimethylsiloxane substrate by exposing the polydimethylsiloxane substrate to the oxygen plasma for a predetermined time.

Next, the polydimethylsiloxane substrate is surface pretreated, and then a titanium layer and a gold layer are sequentially deposited on the polydimethylsiloxane substrate (step 130).

After surface pretreatment of the polydimethylsiloxane substrate by forming an interlayer on top of the polydimethylsiloxane substrate to expose the adhesion between the polydimethylsiloxane substrate and the metal layer or by exposing the polydimethylsiloxane substrate to oxygen plasma for a predetermined time (120) Process), a titanium layer and a gold layer may be deposited on the surface of the pretreated polydimethylsiloxane substrate.

The titanium layer, which is a metal layer, may be deposited using an e-beam evaporation system. As such, the titanium layer may be deposited to form a patterning line that connects the flow of current in the electrode portion to be formed. On the other hand, it is preferable that the titanium layer, which is the metal layer, is deposited at 50 to 300 kPa, and the gold layer is deposited to 500 to 3000 kPa.

As such, after depositing a titanium layer on the surface of the polydimethylsiloxane, a gold layer may be deposited on the electrode to be formed.

Next, the microelectrode is patterned on the polydimethylsiloxane substrate on which the titanium layer and the gold layer are deposited (step 140).

In order to pattern the microelectrode on the polydimethylsiloxane substrate on which the titanium and gold layers are deposited, photoresist is first spin-coated. Then, ultraviolet rays are irradiated using a transparent film printed with an electrode shape, the photoresist is exposed, and then the photoresist of the photosensitive portion is developed. After developing the photoresist, the gold layer is etched by the gold etchant, and the titanium layer is etched by the titanium etchant. The photoresist is then removed.

More specifically, after depositing a titanium layer and a gold layer on the polydimethylsiloxane substrate, and spin-coated a photoresist for a photolithography process, it is dried using a hot plate.

When ultraviolet rays are irradiated using the transparent mask, the physical properties of the portions irradiated with the ultraviolet rays are changed. The mask is then stripped and placed in the developer at room temperature for a predetermined time to remove the photoresist where the physical properties have changed.

Then, the gold layer is sequentially etched into the gold etchant, the titanium layer is etched into the titanium etchant, and finally, a stripper is used to remove the remaining photoresist from the top layer, thereby completing the patterning process. .

More specifically, the titanium etchant may be composed of fluorine hydrogen (HF), hydrogen nitrate (HNO ₃ ) and distilled water (H ₂ O), when distilled water is based on 100% by volume, the fluorine hydrogen is 10 to 20 Volume%, hydrogen nitrate may be 20 to 40% by volume.

Subsequently, when the patterning is completed, an electrode part is formed by spin coating a photoresist on the patterned micropattern, and a photolithography process is performed (step 150).

That is, when the gold layer and the titanium layer are etched using the gold etchant and the titanium etchant, a patterned pattern of the titanium layer and the gold layer is left on the polydimethylsiloxane substrate, and one end of the patterned portion of the titanium layer and the gold layer is formed. The electrode portion is formed in the portion. In order to form this electrode portion, photolithography is performed after spin coating a photoresist on top of the patterned portion of the patterned polydimethylsiloxane substrate. Then, the pillar-shaped photoresist remains only on the electrode portion.

More specifically, the photoresist may be made of SU-8.

SU-8 is a negative photoresist used to make thick patterns with smooth walls. It is epoxy based, strong after treatment, rigid and chemically robust. The main strength of this SU-8 photoresist is that it remains in the device and can be used as a wave guide or even as a structure in MEMS devices.

SU-8 can also be used for large scale patterns in microfluidics because they can be made of very thick structures and adhered to each other. Since SU-8 is made of thick structures and can be bonded to each other, it can be used to fabricate devices with T-topping effects that create columnar shapes. SU-8 is mostly used for relatively large patterns of more than 50 micrometers, but some are used for fine patterns with high aspect ratios.

The property of SU-8 is suitable for making super-hydrophobic surfaces, which can enable columnar arrays with spacings of less than 50 micrometers. Superhydrophobic surfaces are non-hydrophilic surfaces with high surface roughness. These surfaces reduce the interaction between the water and the surface, allowing water droplets to roll on slightly sloped surfaces. This potentially useful effect is often observed on surfaces that are difficult to model. The SU-8 enables the user to have a well-defined surface of his choice, making it easy to control superhydrophobicity.

Next, the upper portion of the polydimethylsiloxane substrate on which the photoresist is not formed, that is, the portion other than the electrode portion, is spin coated using the polydimethylsiloxane (step 160).

That is, polydimethylsiloxane is spin-coated on the upper part of the polydimethylsiloxane board | substrate corresponding to parts other than an electrode part. Then, the upper portion of the polydimethylsiloxane substrate corresponding to the portion other than the electrode portion is deposited with the polydimethylsiloxane layer.

Finally, the photoresist formed in the electrode unit is removed (step 170), and gold electroplating is performed on the removed electrode unit to form a fine electrode (step 180).

When the photoresist formed on the electrode part is removed, the portion where the photoresist is removed is surrounded by a polydimethylsiloxane layer, and a micropattern in which a titanium layer and a gold layer are sequentially deposited is disposed under the portion surrounded by the polydimethylsiloxane layer. Will be formed. When the electroplating is performed on this part, the electroplated part may come in contact with the gold layer to serve as an electrode part.

On the other hand, the electroplating may be gold electroplating, the gold plating formed may be potassium gold cyanide or commercial gold electroplating, the present invention is not limited to the components or materials of gold plating.

More specifically, the height of the gold plating layer formed by the gold electroplating may be the same as the height of the spin-coated polydimethylsiloxane. As described above, the gold plating layer formed by gold electroplating serves as an electrode part in contact with the gold layer formed on the polydimethylsiloxane substrate.

Figure 2 shows a manufacturing process of the fine pattern according to the present invention.

Referring to FIG. 2, first, a surface-treated polydimethylsiloxane substrate 201 is prepared. The titanium layer 202 is formed on the polydimethylsiloxane substrate to form a line connected to the electrode, and then a gold layer 203 is deposited on the titanium layer.

The titanium layer 202 and the gold layer 203 deposited on the polydimethylsiloxane substrate may be deposited using an electron beam deposition system, and deposition conditions are shown in Table 1 below.

Thereafter, a photoresist (PR) 204 for the photolithography process is formed (230S).

Next, ultraviolet rays are irradiated using the transparent mask 205 on which the wiring pattern is printed (240S).

Then, the UV light is no longer passed through the portion 205a printed on the transparent mask, and the physical properties of the portion 205b not printed on the transparent mask are changed.

Thereafter, the transparent mask 205 is removed, and the photoresist 204 in which the physical properties are changed is removed by putting it in a developer at room temperature for several seconds (250S).

After removing the photoresist 204 in which the physical property is changed, first, the gold layer deposited on the polydimethylsiloxane substrate is selectively etched using a gold etchant.

Next, the titanium layer having the changed physical properties is etched among the titanium layers deposited on the polydimethylsiloxane substrate using a titanium etchant (270S). On the other hand, the titanium etchant may be composed of fluorine hydrogen (HF), hydrogen nitrate (HNO ₃ ) and distilled water (H ₂ O), the fluorine hydrogen (HF), hydrogen nitrate (HNO ₃ ) and distilled water (H ₂ O) The volume% may be 10-20% by volume of fluorine hydrogen (HF) and 20-40% by volume of hydrogen nitrate (HNO ₃ ) based on 100% by volume of distilled water (H ₂ O). The titanium layer having the changed physical properties is etched among the titanium layers deposited on the polydimethylsiloxane substrate by using the titanium etchant having the above ratio.

Finally, after etching the titanium layer, the photoresist formed at the top is removed using a stripper (290S).

As such, the patterned polydimethylsiloxane substrate is subjected to a packaging process and an electroplating process to be described below, and then cut into a form of an electrode to complete the electrode.

3 illustrates a process of forming a microelectrode according to the present invention.

In the present invention, the surface of the polydimethylsiloxane substrate may be pretreated using a method of forming an interlayer on top of the polydimethylsiloxane substrate and increasing a surface roughness in order to improve adhesion of the electrode.

On the other hand, to form an interlayer, a spin on the surface of the polydimethylsiloxane (CYTOP), polyethylene glycol (PEG), 4-hydroxybutyl acrylate (4-HydroxyButylAcrylate: 4-HBA) The coating may form an interlayer between 1 and 2 μm.

Then, the titanium layer and the gold layer are sequentially deposited on each polydimethylsiloxane substrate using an electron beam deposition system, and then a microelectrode may be patterned using a photolithography process.

Referring to FIG. 3, first, a polydimethylsiloxane substrate 201 patterned with a titanium layer 202 and a gold layer 203 is prepared (S300).

Next, the titanium layer 202 and the gold layer 203 are sequentially stacked to form the photoresist 207 on the patterned portion, and then photolithography is performed to leave only the electrode portion of the pillar-shaped photoresist 207. Developing is performed (310S).

Next, the polydimethylsiloxane 208 is injected into the upper portion of the polydimethylsiloxane substrate except for the columnar photoresist formed on the electrode portion, and the polydimethylsiloxane 208 layer is formed to have the same thickness as the height of the electrode portion on which the photoresist is formed. Is formed using spin coating and then cured for a predetermined time (320S).

Thereafter, the photoresist remaining on the electrode portion is removed using a PG remover (330S).

After the patterning is completed, the polydimethylsiloxane microelectrode is completed by performing a gold plating process on the packaging and the electrode part (340S). Patterning may be carried out by the process according to FIG. 2 described above, and finally, a gold plating layer 209 is formed on the electrode portion by gold electroplating.

Gold electroplating can be carried out using potassium gold cyanide (PGC) and commercial gold plating solution (YL gold acid gold).

4 is a schematic diagram of gold electroplating applied to the present invention.

Referring to FIG. 4, the gold electroplating applied to the present invention is a polydimethylsiloxane substrate in which photoresist remaining on an electrode part is removed using a PG remover, and a portion of a gold electroplating solution ( After immersing in Gold Electroplating Solution), a platinum plate and a polydimethylsiloxane substrate may be connected to each other to form a gold plating layer on a portion where SU-8 is removed from the polydimethylsiloxane substrate. As described above, gold electroplating is performed to complete the microelectrode on the polydimethylsiloxane substrate.

On the other hand, the height of the gold plating layer is formed to be the same as the height of the polydimethylsiloxane formed by the spin coating and then cured for a predetermined time (S320S).

In the case of performing gold plating, the thickness of the plating layer may be formed in a desired thickness by adjusting the type of plating solution, the strength of the current, and the like. And, if the current density is high under the same conditions, many plating liquids are transferred, so that a plating layer having a thickness set in a faster time can be formed.

Example

Polydimethylsiloxane  Preparation of microelectrode using

Step 1: Pretreatment of Polydimethylsiloxane Substrate

First, the polydimethylsiloxane prepolymer and the curing agent were mixed at a mass ratio of 10 to 1 and mixed well, and then the mixed blend was bubbled in a vacuum desiccator. Then, poured onto a silicon wafer and spin-coated at 150 rpm for 30 seconds, and cured at 120 ° C. for 2 hours using a vacuum oven to form a polydimethylsiloxane substrate having a thickness of about 100 μm.

When the polydimethylsiloxane substrate is directly used as a flexible substrate, the adhesion between the polydimethylsiloxane and the metal layer should be increased. In the present invention, two methods were used. One is to use interlayers and the other is to increase the roughness of the polydimethylsiloxane surface. As the interlayer, CYTOP, Poly Ethylene Glycol (PEG), 4-HydroxyButylAcrylate (4-HBA), and the like were used. The roughness of the siloxane surface was exposed to oxygen plasma for 15 seconds using a reactive ion etching chamber (RIE chamber) (RIE 2000, SNT) to induce an increase in surface roughness. The adhesive force of the metal is difficult to measure by the conventional method due to the characteristics of the flexible electrode, and the present invention was evaluated by a tape test because it secures the adhesive force of a metal electrode of a predetermined level or more.

The increase in surface roughness was observed by AFM (Atomic Force Microscopy, DI 3100VIA), and the formation of gold electroplating on the electrode was observed by SEM (Scanning Electron Microscopy, S-4300, Hitachi). The metal layer was formed using an E-beam evaporation system, and the deposition conditions were optimized in the range of Table 1 to improve adhesion.

Step 2: Form the Fine Pattern

In the present invention, the surface of the polydimethylsiloxane substrate is pretreated using a method of forming an interlayer on top of the polydimethylsiloxane substrate and a method of increasing the surface roughness in order to improve the adhesion of the electrode, and then to each polydimethylsiloxane substrate. The titanium layer and the gold layer were sequentially deposited using an electron beam deposition system, and then the microelectrode was patterned using a photolithography process.

Cytop, Polyethylene Glycol (PEG), 4-HydroxyButylAcrylate (4-HBA) on the surface of the polydimethylsiloxane to form an interlayer in this embodiment. Were spin-coated at 5000 rpm for 50 seconds to form an interlayer of about 1.5 μm.

In addition, the increase in surface roughness exposed the polydimethylsiloxane substrate to oxygen plasma in a reactive ion etching chamber (RIE chamber) for 15 seconds to induce the roughness of the surface of the polydimethylsiloxane substrate.

At this time, the amount of oxygen introduced was 20 sccm, the degree of vacuum was 100mtorr, the power was 100W. The titanium layer and the gold layer were sequentially deposited on the upper surface of the surface-treated polydimethylsiloxane substrate.

Thereafter, photoresist (PhotoResist: PR) AZ5214 (Clariant) for a photolithography process was spin-coated at 5000 rpm for 1 minute, and then dried at 110 ° C. for 1 minute using a hot plate to form a thickness of about 1 μm.

Subsequently, using a transparent mask on which a wiring pattern was printed, an ultraviolet ray having a wavelength of λ of 365 nm and a radiation intensity of 300 mW / cm 2 was irradiated for 8 seconds, the transparent mask was removed, and then the developer (AZ 300MIF) was removed at room temperature. , Clariant) was removed for several seconds to remove the photoresist of the changed properties.

After removing the photoresist of the portion where the physical properties were changed, first, the gold layer deposited on the polydimethylsiloxane substrate was selectively etched using a gold etchant.

Next, the titanium layer having the changed physical properties was etched among the titanium layers deposited on the polydimethylsiloxane substrate using a titanium etchant.

In this embodiment, the titanium deposited on the polydimethylsiloxane substrate using a titanium etching solution in which the volume% of hydrogen fluoride (HF), hydrogen nitrate (HNO ₃ ), and distilled water (H ₂ O) is 1: 2: 7. After etching the titanium layer having the changed physical properties among the layers, the photoresist AZ5214 formed on the top was removed using a stripper (AZ 300MIF, Clariant).

As such, the patterned polydimethylsiloxane substrate is subjected to a packaging process and an electroplating process to be described below, and then cut into a form of an electrode to complete the electrode.

Step 3: Formation of Microelectrode

First, a polydimethylsiloxane substrate 201 patterned with a titanium layer and a gold layer was prepared. Then, after the patterning is completed, SU-8, a type of photoresist, is formed by stacking a titanium layer and a gold layer in sequence and forming a thickness of 40 μm at 3000 rpm for 50 seconds on the patterned portion, and then performing photolithography. Developing was performed, leaving 10,000 columns of SU-8.

Next, polydimethylsiloxane was injected into the upper portion of the polydimethylsiloxane substrate except for the SU-8 in the shape of a column, and spin-coated at 3000 rpm for 55 seconds to have a height similar to that of the SU-8 remaining in the electrode. The polydimethylsiloxane layer was formed to a thickness of about 40 μm and then cured for 2 hours on a hot plate at 80 ° C.

Thereafter, SU-8 remaining in the electrode part was removed using a PG remover.

Step 4: completion of the fine electrode through the plating process

After the patterning was completed, the polydimethylsiloxane microelectrode was completed by performing a gold plating process on the packaging and the electrode part. Patterning may be performed by the process according to FIG. 3 described above, and finally, a gold plating layer was formed on the electrode part by gold electroplating. This was completed by forming a gold plating on the electrode portion from which SU-8 was removed by gold electroplating. Gold electroplating was carried out using potassium gold cyanide (PGC) and commercial gold plating solution (YL gold acid gold) at a temperature of 40 ℃.

5 is a current density curve according to the voltage during the gold electroplating. Specifically, FIG. 5 shows a current density distribution of a gold plating solution according to voltage in gold electroplating.

Referring to FIG. 5, it can be seen that the current density distribution has a small value that is maintained almost constant up to a voltage of 0.8V. If the voltage applied to the gold plating solution is 0.8 V or more, the current density distribution increases to correspond to the applied voltage. In this embodiment, the applied voltage is adjusted to have a current density of 0.020 mA / mm 2 at a voltage of about 1.2 V. Kept constant.

On the other hand, Figure 6a is an image of the electrode portion before the gold electroplating, Figure 6b is an image of the electrode portion after the gold electroplating according to FIG. 6A and 6B, FIG. 6A illustrates a polydimethylsiloxane substrate from which SU-8 remaining in an electrode portion is removed using a PG remover, and FIG. 6B illustrates SU-8 of FIG. 6A. The gold plating layer formed on the removed polydimethylsiloxane substrate is shown. In this example, a gold electroplating of about 40 mu m equal to the height of the polydimethylsiloxane substrate was performed after 8 hours.

Evaluation example  One : Polydimethylsiloxane  Substrate Metal layer  Improved adhesion

As a result of verifying the effect using the interlayer to improve the adhesion between the polydimethylsiloxane and the metal layer, the respective interlayers used between the polydimethylsiloxane and the metal layer are the metal layer in the case of polyethylene glycol and 4-hydroxy butyl acrylate. The adhesion to and improved, and in the case of Cytop, it was confirmed that the adhesion to the polydimethylsiloxane substrate was improved.

AFM images of the polydimethylsiloxane substrate according to the oxygen plasma treatment process for increasing the roughness of the surface of the polydimethylsiloxane substrate are shown in FIGS. 7A and 7B.

7A and 7B, FIG. 7A is an AFM image of the surface of a polydimethylsiloxane substrate before oxygen plasma treatment.

7B is an AFM image of the surface of a polydimethylsiloxane substrate after oxygen plasma treatment in accordance with the present invention.

Referring to FIG. 7A, the surface of the polydimethylsiloxane substrate before the oxygen plasma treatment has a flat surface structure, and thus it is impossible to expect the adhesion to the metal layer to be improved. Referring to FIG. 7B, it is confirmed that the surface roughness after the oxygen plasma treatment increases. As a result of evaluating the adhesive force by a tape test, it was found that the adhesive force of the side which increased the surface roughness was excellent.

This is caused by an increase in the mechanical strength between the polydimethylsiloxane substrate and the metal layer due to the increased surface roughness of the polydimethylsiloxane substrate as in electroless plating. In the fabrication of metal thin films using vacuum deposition, physical properties such as adhesion and preferential orientation are significantly affected by deposition conditions.

In this embodiment, after the surface treatment of the polydimethylsiloxane substrate with oxygen plasma for 15 seconds within the range of the deposition conditions of Table 1, the titanium layer is deposited to 100 Å at a deposition rate of 0.5 Å / s to improve adhesion, gold on it The highest deposition rate was obtained at 1000 Å at 1 Å / s.

Evaluation example  2: formation of metal micropatterns

FIG. 8A shows the patterned polydimethylsiloxane microelectrode, FIG. 8B is an enlarged view of FIG. 8A, and FIG. 8C shows the patterned flexible polydimethylsiloxane microelectrode.

8A and 8B, it can be seen that a microelectrode having a line width of 20 μm can be realized on a polydimethylsiloxane substrate having a length of 6 mm.

에서

이 4∼5 ㎜이고,

가 20㎛,

가 1100Å인 경우 상기 수치 값을 대입하고 전극의 형상을 고려하면 측정값과 일치하는 결과값을 얻을 수 있다.On the other hand, the specific resistance of the microelectrode deposited on the silicon wafer under the optimum deposition conditions of Table 1 described above was 4.14 × 10 ⁸ Ωm, and the electrical resistance of the electrode measured by the tester was slightly different depending on the length of each electrode. Resistance, but showed 70 ~ 110Ω, which is the formula of electric resistance

in

Is 4-5 mm,

20 μm,

When the value is 1100 입 By substituting the numerical value and considering the shape of the electrode can obtain a result value that matches the measured value.

Evaluation example  3: durability and biocompatibility evaluation

Polydimethylsiloxane is known to cause expansion phenomena due to the good permeability of oxygen and solution. Such expansion phenomenon may lead to peeling of the metal fine pattern due to expansion when the polydimethylsiloxane substrate manufactured as an electrode is implanted in the body in the future. Therefore, in order to evaluate the durability of the patterned microelectrode, changes were observed after 6 months storage at room temperature in Hanks'Balanced Salt Solution (HBSS). The polydimethylsiloxane was cut to maintain the shape of the patterned electrode. The thickness of the polydimethylsiloxane substrate used was 100 μm, and the thickness of the metal layer was 100 μs of titanium and 1000 μs of gold.

As a result of observing the change of the polydimethylsiloxane substrate disposed on the HBSS for 6 months, no rupture or peeling of the metal fine pattern was observed, and the thickness change of the polydimethylsiloxane substrate was hardly observed within 3 µm. In addition, it can be seen that almost no change in the electrical resistance as shown in Table 2 above.

The microelectrode of polydimethylsiloxane used for the evaluation had the shape as shown in FIG. 8A, and the line width was 100 μm. In Table 2, numbers 1 to 5 are numbers arbitrarily assigned in order from the longest electrode. There was no significant difference between the initial electrical resistance and the electrical resistance measured by the tester after storage for 6 months in HBSS.

To evaluate the biocompatibility of polydimethylsiloxane microelectrode, a piece of 2 mm × 2 mm polydimethylsiloxane substrate, which had undergone the same process as microelectrode fabrication, was implanted in the subcutaneous ICR mouse and 42 days later, the skin where the sample was implanted was incised. The biopsy was performed.

9 is a cutaway photograph of an ICR mouse implanted with a piece of polydimethylsiloxane for histology. The biocompatibility of the polydimethylsiloxane electrode is excellent because no abnormality was found in the tissues around the implanted polydimethylsiloxane.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical details of the appended claims.

As described above, according to the present invention, by providing a method for packaging a polydimethylsiloxane microelectrode through a photolithography process and plating of an electrode portion, it is possible to reduce costs and reduce failure rate due to a simpler process, and polydimethylsiloxane By optimizing the pretreatment and deposition conditions of the substrate using the there is an effect that can improve the adhesion of the metal micropattern.

Claims (13)

Spin-coating a blend of a prepolymer of polydimethylsiloxane and a curing agent in a mass ratio of 20: 1 to 5: 1 on a silicon wafer to form a polydimethylsiloxane substrate; Surface pretreating the polydimethylsiloxane substrate; Sequentially depositing a titanium layer and a gold layer on top of the surface pretreated polydimetholylsiloxane substrate and patterning a microelectrode; Forming a photoresist on the patterned microelectrode, and spin-coating the polydimethylsiloxane on the polydimethylsiloxane substrate on which the photoresist is not formed; And  And removing the photoresist formed on the patterned microelectrode, and packaging the microelectrode by performing gold electroplating on the patterned gold layer. The method of claim 1, The surface pretreatment is Exposing the polydimethylsiloxane substrate to an oxygen plasma to pretreat the surface of the polydimethylsiloxane substrate. The method of claim 1, The surface pretreatment is The method of forming a microelectrode using polydimethylsiloxane, characterized in that it comprises the step of forming an interlayer on top of the polydimethylsiloxane substrate. The method of claim 3, wherein The interlayer is a microelectrode forming method using a polydimethylsiloxane, characterized in that formed by spin coating. The method of claim 3, wherein The interlayer is a micro-electrode forming method using a polydimethylsiloxane, characterized in that it comprises any one compound selected from the group consisting of cytope, polyethylene glycol, and 4-hydroxy butyl acrylate. The method of claim 3, wherein The interlayer is formed with a thickness of 1 ~ 2㎛ microelectrode formation method using a polydimethylsiloxane. The method of claim 1, Patterning the microelectrode, Spin-coating a photoresist on the deposited gold layer and curing a portion to be patterned using a transparent mask on which a wiring pattern is printed; Removing the transparent mask and selectively removing the photoresist; And And etching the deposited titanium and gold layers to pattern the microelectrode on the polydimethylsiloxane substrate. The method of claim 7, wherein The titanium layer is etched by wet etching, The etchant used for the wet etching includes H ₂ O, HF and HNO ₃ , HF is 10-20% by volume and HNO ₃ is 20-40% by volume based on 100% by volume of H ₂ O. Microelectrode formation method using a polydimethylsiloxane, characterized in that. The method of claim 7, wherein The titanium layer and the gold layer, the method of forming a microelectrode using a polydimethylsiloxane, characterized in that deposited by the electron beam deposition system. The method of claim 7, wherein The titanium layer is deposited to 50 ~ 300Å, the gold layer is deposited to 500 ~ 3000Å microelectrode formation method using a polydimethylsiloxane, characterized in that deposited. delete The method of claim 1, The height of the gold plating layer formed by the gold electroplating method of forming a fine electrode using a polydimethylsiloxane, characterized in that the same as the height of the spin-coated polydimethylsiloxane. A microelectrode using polydimethylsiloxane prepared by the method according to any one of claims 1 to 10.

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