A method for preparing a flexible micro-nano device based on carbon film

Abstract

The application provides a method for preparing a flexible micro-nano device based on a carbon film, and belongs to the field of micro-nano device manufacturing.The application provides a method for preparing a carbon film for preparing a flexible electrochemical sensor, and comprises the following steps: coating a slurry containing graphene oxide and a polymer on a first substrate, and then performing a carbonization reaction to form a graphite-like carbon film.The graphene oxide and the polymer are carbonized to form a continuous carbon film structure with high flexibility, excellent conductivity and good adhesion force.The carbonized film can be directly used for patterned microstructure processing on a wafer-level substrate, has good structure uniformity and repeatability, and is suitable for integrated manufacturing of a large batch of flexible microelectrode arrays.

Description

A method for fabricating flexible micro / nano devices based on carbon films Technical Field

[0001] This invention relates to the field of micro-nano device manufacturing, and more specifically to a method for fabricating flexible micro-nano devices based on carbon films. Background Technology

[0002] Existing flexible electrochemical sensors commonly employ traditional methods for constructing conductive layers, such as laser etching, screen printing, and manual coating. These processes have numerous limitations. For example, laser etching technology is limited by laser beam diameter and thermal diffusion effects, making it difficult to achieve micro- and nano-scale pattern resolution. Screen printing and manual coating methods suffer from uncontrollable thickness, poor pattern consistency, low resolution, and poor repeatability, and are incompatible with current mainstream micro- and nano-fabrication platforms. Furthermore, these methods largely rely on traditional conductive materials such as metal nanoparticles, carbon ink, or conductive polymers, which generally exhibit poor flexibility, adhesion, and electrochemical stability, making it difficult to meet the long-term stable operation requirements of wearable devices under deformation environments. Summary of the Invention

[0003] This invention provides a method for fabricating flexible micro / nano devices based on carbon films. The carbon films of this invention have good flexibility, adhesion, and electrochemical stability.

[0004] This invention provides a method for preparing a carbon film for use in flexible electrochemical sensors, comprising the following steps:

[0005] A slurry containing graphene oxide and polymer is coated onto a first substrate and then subjected to a carbonization reaction to form a graphite-like carbon film.

[0006] Preferably, the polymer comprises polyamic acid and / or polyacrylonitrile.

[0007] Preferably, the mass ratio of graphene oxide to polymer is 0.4 to 1:1.

[0008] Preferably, the solid content of the slurry is 0.8-1.5%.

[0009] Preferably, the thickness of the wet film obtained by coating is 800~2000nm.

[0010] Preferably, the carbonization reaction is carried out in an inert gas, the temperature of the carbonization reaction is 1000~1050℃, and the holding time is 1~2h;

[0011] The process of heating to the temperature of the carbonization reaction includes:

[0012] The temperature is increased uniformly from room temperature to 400℃ at a rate of 5℃ / min, then increased uniformly from 400℃ to 420℃ within 6 minutes, and then increased uniformly from 420℃ to 1000~1050℃ within 116 minutes.

[0013] The carbonization reaction is followed by cooling; the cooling process includes:

[0014] The temperature was uniformly reduced from 1000~1050℃ to 420℃ within 116 minutes, and then uniformly reduced from 420℃ to room temperature at a rate of 5℃ / min.

[0015] This invention also provides a method for fabricating flexible micro / nano devices, comprising the following steps:

[0016] A flexible substrate is deposited on the surface of the carbon film prepared by the preparation method described above. Then, an adhesive is used to bond the surface of the flexible substrate to the second substrate. After that, the carbon film is separated from the first substrate to obtain the device used to prepare the flexible electrochemical sensor.

[0017] The adhesive can be dissolved by polar organic solvents.

[0018] Preferably, when the adhesive is a photoresist, the bonding process further includes curing.

[0019] This invention also provides a method for preparing a flexible electrochemical sensor, comprising the following steps:

[0020] Photoresist is spin-coated onto the carbon film surface, followed by photolithography and etching to form electrode patterns; the electrode patterns include working electrode patterns, counter electrode patterns, and reference electrode patterns; the device is a flexible electrochemical sensor device prepared by the preparation method described in the above technical solution.

[0021] The adhesive between the flexible substrate and the second substrate in the device is dissolved in a polar organic solvent to separate the flexible substrate from the second substrate;

[0022] Connect the PADs in the working electrode pattern, counter electrode pattern, and reference electrode pattern to metal leads and encapsulate them by coating the connection points with UV adhesive.

[0023] A catalytic layer, an enzyme recognition layer, and a selective membrane are sequentially stacked on the working electrode pattern to form the working electrode. Silver / silver chloride ink is printed on the reference electrode pattern to form the reference electrode. Nafion / KCl is drop-coated onto the surface of the reference electrode to form a salt bridge, thus obtaining the flexible electrochemical sensor.

[0024] Preferably, the components in the catalytic layer include Prussian blue; the enzyme in the enzyme recognition layer includes glucose oxidase; and the selective membrane includes a Nafion membrane.

[0025] This invention utilizes graphene oxide and polymers to form a continuous carbon film structure with high flexibility, excellent conductivity, and good adhesion. This carbonized film can be directly patterned onto wafer-level substrates, exhibiting good structural uniformity and repeatability, making it suitable for the integrated manufacturing of large-scale microelectrode arrays. Compared to traditional printed carbon materials and glassy carbon materials formed by carbonization with photoresist SU8, this carbon film not only possesses higher surface conductivity and electrochemical activity but also offers advantages such as controllable film thickness and good pattern compatibility. It overcomes the technological bottlenecks in the fabrication of micro / nano-scale flexible electrodes using carbon materials, providing a novel material basis for constructing high-performance flexible electrochemical sensors.

[0026] This invention utilizes a flip-lift technique to completely transfer a pre-prepared carbonized conductive film on a first substrate to a flexible substrate, thereby constructing a flexible device structure (i.e., depositing a flexible substrate on the surface of the carbon film, then using an adhesive to bond the surface of the flexible substrate to a second substrate, and finally separating the carbon film from the surface of the first substrate). Compared to traditional methods that rely on highly corrosive solutions such as BOE (Buffered Oxide Etch) to etch the sacrificial layer, this flip-lift process eliminates the need for hazardous chemicals, simplifies the operation, and enhances safety. Furthermore, this method effectively maintains the structural integrity and conductivity of the carbonized film, improving the yield and uniformity of the film during the transfer process, making it particularly suitable for the mass production of large-area, highly consistent electrode arrays. This technology lays a solid foundation for the practical application of novel flexible electrochemical devices.

[0027] The manufacturing process of this flexible electrochemical sensor is safe, simple, convenient, and low-cost. It can achieve simultaneous detection of multiple biomarkers and is suitable for various health monitoring scenarios such as wearable and implantable devices. The photolithographic pattern has high resolution (<50μm) and structural precision superior to traditional printing methods. The conductive carbon film has low impedance (<500Ω), resulting in a low detection limit (LOD<0.1mM) and high sensitivity. In addition, the conductive carbon film of this invention has good flexibility, strong adhesion, and stable electrochemical response. It can be used for simultaneous monitoring of multiple biomarkers such as glucose and uric acid in sweat, and can be mass-produced, making it suitable for integration into flexible wearable devices. Attached Figure Description

[0028] Figure 1 is a Raman diagram of the conductive carbon film of Example 1;

[0029] Figure 2 is an XPS image of the conductive carbon film of Example 1;

[0030] Figure 3 shows the EIS diagrams of the conductive carbon films of Examples 1-2 and Comparative Example 1;

[0031] Figure 4 is a flowchart of the fabrication process of the flexible electrochemical sensor in the embodiment;

[0032] Figure 5 shows the sensor design layout of the flexible electrochemical sensor in the embodiment;

[0033] Figure 6 illustrates the glucose detection mechanism of the flexible electrochemical sensor in this embodiment;

[0034] Figure 7 shows the results of glucose concentration detection.

[0035] Figure 8 is a correlation curve plot of the peak current curves measured under the five conditions in Figure 7 and the corresponding concentration of added glucose.

[0036] Figure 9 shows the results of uric acid concentration detection.

[0037] Figure 10 shows the correlation curves between the peak values ​​of the current curves measured under the six conditions in Figure 9 and the corresponding concentrations of added uric acid. Detailed Implementation

[0038] This invention provides a method for preparing a carbon film for use in flexible electrochemical sensors, comprising the following steps:

[0039] A slurry containing graphene oxide and polymer is coated onto a first substrate and then subjected to a carbonization reaction to form a graphite-like carbon film.

[0040] In this invention, the mass fraction of graphene oxide in the slurry is preferably 0.5-1%, and in specific embodiments of this invention it can be 0.6%, 0.7%, 0.8% or 0.9%. The solvent in the slurry preferably includes DMF and DMAC.

[0041] In this invention, the solid content of the slurry is preferably 0.8-1.5%, and in specific embodiments of this invention it can be 0.9%, 1%, 1.1%, 1.2%, 1.3% or 1.4%.

[0042] In this invention, the mass ratio of graphene oxide to polymer is preferably 0.4 to 1:1, and in specific embodiments of this invention it can be 0.5:1, 0.6:1, 0.7:1, 0.8:1 or 0.9:1; the polymer preferably includes polyamic acid and / or polyacrylonitrile.

[0043] In this invention, the first substrate preferably comprises a silicon substrate.

[0044] In this invention, the thickness of the wet film obtained after coating is preferably 800~2000nm, and in specific embodiments of this invention it can be 1000nm, 1200nm, 1500nm, 1600nm or 1800nm.

[0045] In this invention, the carbonization reaction is preferably carried out in an inert gas, and the temperature of the carbonization reaction is preferably 1000~1050℃, which in specific embodiments of this invention can be 1010℃, 1020℃, 1030℃ or 1040℃, and the time is preferably 1~2 hours. In this invention, the process of heating to the temperature of the carbonization reaction preferably includes:

[0046] The temperature is increased uniformly from room temperature to 400℃ at a rate of 5℃ / min, then increased uniformly from 400℃ to 420℃ within 6 minutes, and then increased uniformly from 420℃ to 1000~1050℃ within 116 minutes.

[0047] The carbonization reaction is followed by cooling; the cooling process includes:

[0048] The temperature was uniformly reduced from 1000~1050℃ to 420℃ within 116 minutes, and then uniformly reduced from 420℃ to room temperature at a rate of 5℃ / min.

[0049] The carbonization reaction results in carbonization and graphene oxide-based graphitization.

[0050] This invention also provides a method for fabricating a device for a flexible electrochemical sensor, comprising the following steps:

[0051] A flexible substrate is deposited on the surface of the carbon film prepared by the above-described technical solution. Then, an adhesive is used to bond the surface of the flexible substrate to the second substrate. After that, the carbon film is separated from the first substrate to obtain the device used to prepare the flexible electrochemical sensor.

[0052] In this invention, the flexible substrate preferably comprises Parylene C.

[0053] In this invention, the adhesive is preferably a photoresist; when the adhesive is a photoresist, the bonding process further includes curing.

[0054] The photoresist has greater adhesion than the carbon film adheres to the first substrate, allowing the carbon film to be flipped and peeled off the silicon wafer.

[0055] This invention also provides a method for preparing a flexible electrochemical sensor, comprising the following steps:

[0056] Photoresist is spin-coated onto the carbon film surface, followed by photolithography and etching to form electrode patterns; the electrode patterns include working electrode patterns, counter electrode patterns, and reference electrode patterns; the device is a flexible electrochemical sensor device prepared by the preparation method described in the above technical solution.

[0057] The adhesive between the flexible substrate and the second substrate in the device is dissolved in a polar organic solvent to separate the flexible substrate from the second substrate;

[0058] The working electrode pattern, counter electrode pattern, and reference electrode pattern are respectively connected to metal leads and encapsulated by applying UV adhesive at the connection points.

[0059] A catalytic layer, an enzyme recognition layer, and a selective membrane are sequentially stacked on the working electrode pattern to form the working electrode. Silver / silver chloride ink is printed on the reference electrode pattern to form the reference electrode. Nafion / KCl is drop-coated onto the surface of the reference electrode to form a salt bridge, thus obtaining the flexible electrochemical sensor.

[0060] In this invention, photoresist is spin-coated onto the surface of a carbon film, followed by photolithography and etching to form electrode patterns.

[0061] This invention does not impose any special limitations on the photolithography used; any method well-known to those skilled in the art can be employed. In this invention, the electrode pattern includes a working electrode pattern, a counter electrode pattern, and a reference electrode pattern.

[0062] After forming the electrode pattern, the present invention dissolves the adhesive between the flexible substrate and the second substrate in a polar organic solvent to separate the flexible substrate from the second substrate.

[0063] In this invention, the polar organic solvent preferably includes acetone, and the adhesive preferably includes AZ5214 photoresist.

[0064] After the flexible substrate is separated from the second substrate, the present invention connects the PADs in the working electrode pattern, counter electrode pattern and reference electrode pattern to metal leads and encapsulates them by coating the connection with UV glue.

[0065] The present invention does not impose any special limitations on the packaging; any solution known to those skilled in the art can be used.

[0066] After encapsulation, the present invention sequentially prepares a catalytic layer, an enzyme recognition layer and a selective membrane on the working electrode pattern to form a working electrode. Silver / silver chloride ink is printed on the reference electrode pattern to form a reference electrode. Nafion / KCl is drop-coated on the surface of the reference electrode to form a salt bridge, thus obtaining the flexible electrochemical sensor.

[0067] In this invention, the method for preparing the working electrode preferably includes the following steps:

[0068] Prussian blue was electrochemically deposited onto the surface of the catalyst layer to form the catalyst layer.

[0069] After coating the surface of the catalytic layer with an enzyme-containing solution and drying it, an enzyme recognition layer is formed.

[0070] A selective membrane is coated on the surface of the enzyme recognition layer to form the working electrode.

[0071] In this invention, the scanning voltage for electrochemical deposition is -0.2~0.6V, the scanning speed is 50 mV / s, and the number of scans is 20.

[0072] In this invention, the concentration of the enzyme in the enzyme-containing solution is preferably 10 mg / mL.

[0073] In this invention, the components in the catalytic layer preferably include Prussian blue; the enzyme in the enzyme recognition layer includes glucose oxidase; and the selective membrane includes a Nafion membrane, which can prevent the enzyme recognition layer from detaching.

[0074] The flexible electrochemical sensor of the present invention can detect biomarkers in body fluids, wherein the body fluids preferably include one of sweat, blood, urine and interstitial fluid; and the biomarkers preferably include one or more of glucose, uric acid, lactic acid and dopamine.

[0075] The following detailed description of the method for fabricating flexible micro / nano devices based on carbon films provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0076] Example 1

[0077] 1) 0.04g GO and 7.8g DMF were ultrasonically mixed, and then a solution containing 0.06g polyamic acid (solid content of the solution was 1%, solvent was DMAC) was added and mixed. The mixture was then applied to a silicon substrate using slit coating to form a uniform wet film with a thickness of 1200nm. The resulting wet film was allowed to stand at room temperature for 15min and then dried in a vacuum drying oven at 45℃.

[0078] 2) The film obtained from drying in step 1) is heated from room temperature to 400°C at a uniform rate of 5°C / min, then heated from 400°C to 420°C at a uniform rate of 6 min, then heated from 420°C to 1000°C at a uniform rate of 116 min, and held at 1000°C for 2 h, then cooled from 1000°C to 420°C at a uniform rate of 116 min, and then cooled from 420°C to room temperature at a uniform rate of 5°C / min to form a conductive carbon film;

[0079] 3) A 1200nm thick Parylene C film was deposited as a flexible substrate;

[0080] 4) The silicon substrate coated with spin-coated AZ5214 photoresist is bonded to the Parylene C film and cured at high temperature;

[0081] 5) After curing, the carbon film is peeled off from the silicon substrate using a flip-and-strip technique, and photoresist is coated on the surface of the carbon film;

[0082] 6) Perform photolithography and development on the photoresist from step 5);

[0083] 7) Etch the carbon film according to the photolithography pattern in step 6) to form the working electrode pattern, the counter electrode pattern, and the reference electrode pattern;

[0084] 8) Dissolve the adhesive between the flexible substrate and the second substrate in acetone to separate the flexible substrate from the second substrate;

[0085] The working electrode pattern, counter electrode pattern, and reference electrode pattern are respectively connected to metal leads and encapsulated by applying UV adhesive at the connection points.

[0086] The silver wires are connected to the electrode PAD using silver paste, and then the surface is coated with UV adhesive for encapsulation.

[0087] PB was electrodeposited on the working electrode pattern (CV: -0.2~0.6V, 50mV / s, 20 scans) to form a PB layer;

[0088] 5 μL of 10 mg / mL GOx was dropped onto the surface of the PB layer, dried, and then covered with a 1% Nafion membrane.

[0089] The reference electrode pattern is printed with silver chloride ink, and then Nafion / KCl is drop-coated onto the reference electrode surface to form a salt bridge, thus obtaining a flexible electrochemical sensor.

[0090] Example 2

[0091] The only difference from Example 1 is that the mass ratio of GO to polyamic acid is 5:5 (the mass of GO is 50 mg).

[0092] Comparative Example 1

[0093] A 2 μm thick photoresist SU8 was spin-coated onto a silicon substrate. After photolithography and development, the substrate was hardened at 135°C for 2 hours and then carbonized. The carbonization conditions were the same as those in Example 1.

[0094] Figure 1 is a Raman diagram of the conductive carbon film of Example 1.

[0095] As shown in Figure 1, peak G (approximately 1600 cm) -1 : represents the C–C stretching vibration of graphene. Its intensity indicates that GO is reduced at high temperature and forms an ordered graphene layer, which improves the conductivity of the carbon film.

[0096] Figure 2 is an XPS image of the conductive carbon film of Example 1.

[0097] As shown in Figure 2, in X-ray photoelectron spectroscopy (XPS), two common peaks, C 1s and O 1s, provide key information about the surface chemical composition and functional groups of the material. C 1s peak analysis reveals the graphene / carbonized structure in the material.

[0098] Figure 3 shows the EIS diagrams of the conductive carbon films of Examples 1-2 and Comparative Example 1.

[0099] As shown in Figure 3, under the same conditions, GP5:5 has the lowest charge transfer resistance and the strongest charge transfer capability.

[0100] Figure 4 is a flowchart of the fabrication process of the flexible electrochemical sensor in the embodiment. In Figure 4, a~h correspond to steps 1)~8) in the embodiment.

[0101] Figure 5 shows the sensor design layout of the flexible electrochemical sensor in the embodiment.

[0102] Figure 6 illustrates the mechanism of glucose detection by the flexible electrochemical sensor in this embodiment: H2O2 is first generated by enzyme catalysis, and then H2O2 is reduced by Prussian blue catalysis to achieve indirect detection.

[0103] Figure 7 shows the results of glucose concentration detection.

[0104] Test procedure: Glucose solution was added dropwise to PBS, and the glucose concentration response in the solution was tested.

[0105] Figure 8 is a correlation curve plot of the peak current curves measured under the five conditions in Figure 7 and the corresponding concentration of added glucose.

[0106] The limit of glucose detection (S / N=3) is 61.2 μM.

[0107] Figure 9 shows the results of uric acid concentration detection; Figure 10 shows the correlation curves between the peak values ​​of the current curves measured under the six conditions in Figure 9 and the corresponding concentrations of added uric acid.

[0108] Test procedure: Uric acid solution was added dropwise to PBS, and the concentration response of uric acid in the solution was tested.

[0109] The detection limit for uric acid (S / N=3) was 0.043 μM.

[0110] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating a flexible electrochemical sensor, characterized in that, Includes the following steps: A slurry containing graphene oxide and a polymer is coated onto a first substrate and then subjected to a carbonization reaction to form a graphite-like carbon film, thus obtaining a carbon film. The mass fraction of graphene oxide in the slurry is 0.5-1%, and the polymer includes polyamic acid. The thickness of the wet film obtained by coating is 800-2000 nm. A flexible substrate is deposited on the surface of the carbon film, and then the surface of the flexible substrate is bonded to a second substrate using an adhesive. The carbon film is then separated from the first substrate to obtain a device for fabricating a flexible electrochemical sensor. The adhesive is a photoresist; the adhesive can be dissolved by polar organic solvents; Photoresist is spin-coated onto the carbon film surface, followed by photolithography and etching to form electrode patterns; the electrode patterns include working electrode patterns, counter electrode patterns, and reference electrode patterns. The adhesive between the flexible substrate and the second substrate in the device is dissolved in a polar organic solvent to separate the flexible substrate from the second substrate; the PADs in the working electrode pattern, counter electrode pattern, and reference electrode pattern are connected to metal leads and encapsulated by coating the connection points with UV adhesive; a catalytic layer, an enzyme recognition layer, and a selective film are sequentially prepared on the working electrode pattern to form the working electrode; silver / silver chloride ink is printed on the reference electrode pattern to form the reference electrode; and Nafion / KCl is drop-coated on the surface of the reference electrode to form a salt bridge, thus obtaining the flexible electrochemical sensor.

2. The preparation method according to claim 1, characterized in that, The mass ratio of graphene oxide to polymer is 0.4 to 1:

1.

3. The preparation method according to claim 1, characterized in that, The solid content of the slurry is 0.8-1.5%.

4. The preparation method according to claim 1, characterized in that, The carbonization reaction is carried out in an inert gas at a temperature of 1000-1050℃ for 1-2 hours. The process of heating to the carbonization reaction temperature includes: uniformly heating from room temperature to 400℃ at a rate of 5℃ / min, then uniformly heating from 400℃ to 420℃ over 6 minutes, and then uniformly heating from 420℃ to 1000-1050℃ over 116 minutes. The carbonization reaction is followed by cooling. The cooling process includes: uniformly cooling from 1000-1050℃ to 420℃ over 116 minutes, and then uniformly cooling from 420℃ to room temperature at a rate of 5℃ / min.

5. The preparation method according to claim 1, characterized in that, The bonding process also includes curing.

6. The preparation method according to claim 1, characterized in that, The catalyst layer contains Prussian blue; the enzyme in the enzyme recognition layer contains glucose oxidase; and the selective membrane contains a Nafion membrane.

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