A thin-film memristor based on commercial fountain pen carbon ink and its fabrication method

Abstract

This invention discloses a thin-film memristor based on commercial pen carbon ink and its preparation method. The method uses halogen ions such as fluorine, chlorine, bromine, and iodine as modifiers for the pen carbon ink. Through solution blending, coating film formation, low-temperature annealing, and top electrode preparation, a vertical structure memristor of "conductive substrate / carbon thin film / top electrode" is obtained. Fluorine ions are a typical example of modification, with ammonium fluoride as the precursor, and the low-temperature annealing temperature is controlled between 80-150℃. This invention achieves controllable growth of conductive filaments by substituting, passivating, and regularizing the disordered oxygen-containing functional groups on the surface of the carbon ink with halide ions, significantly improving the on / off ratio, cycle stability, and device consistency of the memristor. The process uses a full solution method, requiring no vacuum equipment, is low-temperature and easy to operate, and is compatible with various printing and preparation processes. It can directly utilize commercial pen carbon ink to achieve low-cost, large-area mass production, and is suitable for various scenarios such as flexible non-volatile storage and artificial synapses.

Description

Technical Field

[0001] This invention belongs to the technical field of non-volatile memristors and neuromorphic computing devices, specifically relating to a thin-film memristor based on commercial pen carbon ink and its preparation method, and a memristor with commercial carbon ink as the functional layer modified by halide ion solution to improve resistive switching performance and stability and its preparation method. Background Technology

[0002] Memristors, as fundamental electronic devices with resistive memory characteristics, have significant application value in fields such as flexible storage, artificial synapses, and in-memory computing.

[0003] Conventional solution methods, such as the solution method for preparing carbon-based memristors using graphene oxide (GO) in a carbon material system, achieve flexible and bendable memristor functional layers through a process of "solution preparation → coating → high-temperature annealing." However, the random distribution of oxygen-containing functional groups on the GO surface leads to discrete switching thresholds and poor cycle stability (<100 cycles). It is evident that conventional preparation methods still suffer from bottlenecks such as complex raw material customization, high cost, high annealing temperatures, uncontrollable interfaces, and poor consistency. Summary of the Invention

[0004] This invention uses fountain pen carbon ink as a raw material, leveraging its advantages of stable dispersion, uniform carbon particle size, and low cost. This invention employs commercially available fountain pen carbon ink to fabricate memristors, offering significant advantages such as low cost, large-area printing capability, and simple process.

[0005] However, carbon particles are rich in oxygen-containing functional groups such as hydroxyl (-OH), carboxyl (-COOH), and epoxy groups on their surface. These groups are diverse, randomly distributed, and unevenly distributed, leading to the following problems: 1. The conductive network of the carbon thin film is non-uniform, and the particle contact barrier fluctuates greatly; 2. The formation / fracture behavior of conductive filaments under an electric field is random, resulting in low device on / off ratio and discrete threshold voltage; 3. Poor cycle stability, poor batch consistency, and susceptibility to environmental water and oxygen; 4. Large leakage current and narrow storage window, making it difficult to meet practical applications.

[0006] To address the above problems, this invention further proposes a method for treating halide ions. For example, F - Its strong electronegativity can efficiently replace polar functional groups such as -OH and -COOH on the carbon skeleton, transforming disordered oxygen-containing groups into structurally uniform CF bonds, fundamentally eliminating the performance dispersion caused by the random distribution of functional groups.

[0007] CF bonds possess extremely high bond energy, stabilizing the surface structure of carbon materials and inhibiting the oxidation, migration, and reconstruction of functional groups. This prevents the drift of resistive switching characteristics caused by interfacial structural changes during device cycling. Fluorination significantly reduces the polarity of the carbon surface, decreasing the adsorption of environmental factors such as water molecules and impurities, thus improving the device's operational stability in atmospheric environments and addressing the poor environmental adaptability of commercial carbon ink devices. Therefore, using commercial carbon ink directly as a raw material and employing simple, low-cost, and scalable halide ion modification to fundamentally stabilize functional groups, regulate conductive pathways, and improve memristor performance and consistency is crucial for the industrialization of flexible carbon-based memristors.

[0008] This invention develops a commercial pen carbon ink memristor and solves its shortcomings such as unstable performance and poor consistency. It provides a memristor based on halogen-modified commercial pen carbon ink and its preparation method. Using halogen ions such as fluorine, chlorine, bromine, and iodine as modifiers and commercial carbon ink as the matrix, this invention employs a one-step solution blending modification method to achieve surface functional group regularization, controllable conductive filaments, and interface passivation of the carbon material. This significantly improves the memristor's on / off ratio, cycle stability, and device consistency. The entire process is a solution-based method, compatible with large-area flexible electronics fabrication processes such as spin coating, inkjet printing, slot coating, and screen printing.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A thin-film memristor based on commercial pen carbon ink comprises, from bottom to top: a conductive substrate, a halogen-modified carbon thin-film functional layer, and a top electrode. The carbon thin-film functional layer is prepared by adding a halogen source to commercial carbon ink, followed by solution blending, film formation, standing, and low-temperature annealing. The halogen source includes a soluble salt or complex containing a halogen element, wherein the halogen element is fluorine, chlorine, bromine, or iodine. Using commercial pen carbon ink as the functional layer material, and modifying it with halogen ions, passivates oxygen-containing functional groups, regulates the surface structure, and stabilizes the conductive filaments, thereby improving device consistency and cycle life, as well as resistive switching performance and stability.

[0011] Preferably, the halogen source specifically includes ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, or metal halides.

[0012] This invention also provides a method for fabricating the aforementioned thin-film memristor, comprising the following steps:

[0013] S1. Modified ink formulation: Using commercial fountain pen carbon ink as the base, add halogen source according to the preset ratio, stir and mix to obtain a uniform and stable mixed ink;

[0014] S2. Stirring and dispersing: Stir the mixed ink at a speed of 200~600 r / min to ensure that the halogen ions fully contact and react with the surface of the carbon material to obtain halogen modified carbon ink;

[0015] S3. Film formation: The halogen-modified ink is coated onto the conductive substrate to form a uniform thin film;

[0016] S4. Settling: Let the coated film stand for more than 8 hours to allow the halogen ions to fully react with the carbon surface;

[0017] S5. Low-temperature annealing: Annealing at 80~150 ℃ to remove solvent, stabilize film structure, strengthen the bonding between halide ions and carbon skeleton, and obtain halogen-modified carbon film functional layer.

[0018] S6. A top electrode is fabricated on a halogen-modified carbon thin film functional layer to form a memristor with a vertical structure of "top electrode / carbon thin film / conductive substrate".

[0019] Preferably, in step S1, the preset ratio is specifically: adding 2-20 mg of halogen source per 1 mL of commercial carbon ink. Preferably, the halogen source is ammonium fluoride.

[0020] Preferably, in S2, the stirring speed is 200~400 r / min.

[0021] Preferably, in S1, the conductive substrate is ITO conductive glass, FTO glass, flexible PET-ITO, PI-ITO, or a metal foil substrate.

[0022] Preferably, in S4, the settling time is 12 hours or more.

[0023] Preferably, in S5, the annealing temperature of the low-temperature annealing is 100-130 ℃; and the annealing time is 20-60 min.

[0024] Preferably, in S5, the top electrode is made of gold, silver, platinum, aluminum, or a conductive polymer material, and is prepared on the halogen-modified carbon thin film functional layer by thermal evaporation, magnetron sputtering, or printing.

[0025] The innovative aspect of this invention lies in its first-ever use of common commercial carbon ink as a raw material to achieve a high-performance memristor. By directly using commercially available fountain pen carbon ink, complex purification, synthesis, or dispersion processes are eliminated, significantly reducing material costs and the manufacturing threshold, highlighting the core innovation of readily available and rapidly mass-producible commercial ink. A broad-spectrum halide ion modification strategy, using fluorine as an example, allows for the extension of the mechanism. A unified modification mechanism for halide ions (F, Cl, Br, I) is proposed, utilizing the strong electronegativity of halogens to substitute, passivate, and regulate random oxygen-containing functional groups on the carbon surface, transforming a disordered interface into a uniform and stable one. This invention uses F... - This is a typical embodiment, which also covers chlorine, bromine, and iodine modification, providing broader protection and greater innovation.

[0026] This invention also addresses the fundamental problem of unstable performance in commercial carbon ink memristors. Halogen ions achieve a triple effect: (1) Functional group regularization: replacing -OH, -COOH, etc., to form high bond energy CX bonds, eliminating randomness in distribution, and reducing device fluctuations; (2) Controllable conductive filaments: introducing uniform defect sites, making the nucleation and growth of conductive filaments more orderly, with more stable placement / reset and a higher on / off ratio; (3) Improved interface and environmental stability: reducing surface polarity, reducing water and oxygen adsorption, suppressing leakage current, and improving cycle life and storage stability.

[0027] This invention utilizes a full solution method, low temperature, no vacuum, and is printable and compatible. It can be completed simply by stirring, coating, and low-temperature annealing, without the need for plasma, vapor deposition, or high-temperature sintering. It is suitable for flexible substrates, large-area, roll-to-roll, and mass production, demonstrating significant industrialization value.

[0028] The performance improvement of the product prepared by this invention is significant. The modified device exhibits the following characteristics: a more symmetrical and full IV hysteresis loop, an increase in on / off ratio of 1-2 orders of magnitude, a more concentrated threshold voltage, lower leakage current, stronger cycle stability, and significantly improved device consistency.

[0029] Compared with the prior art, the present invention has the following outstanding advantages:

[0030] 1. Extremely versatile raw materials: It can directly use commercial carbon ink, without the need for custom synthesis, resulting in low cost, easy procurement, and rapid industrialization.

[0031] 2. Broad-spectrum and efficient modification effect: Halogen ions (F, Cl, Br, I) can all significantly improve performance, with fluorine being the best representative. The modification mechanism is clear and the effect is reproducible.

[0032] 3. Breakthrough in stability and consistency: Through synergistic optimization of functional groups, conductive pathways, and interfaces, the industry pain points of "instability and inconsistency" in commercial carbon ink memristors are thoroughly improved.

[0033] 4. The process is extremely simple and scalable: it uses a full solution method, low-temperature annealing, and requires no vacuum equipment. It is compatible with spin coating, inkjet printing, slot coating, etc., and is suitable for large-area flexible electronics manufacturing.

[0034] 5. Wide range of applications: It can be used in flexible non-volatile storage, artificial synaptic devices, neuromorphic computing, wearable sensors, printed logic circuits, electronic skin, etc. Attached Figure Description

[0035] Figure 1 A schematic diagram of a memristor structure made from commercial fountain pen carbon ink;

[0036] Figure 2 Scanning electron microscope image of a carbon ink film;

[0037] Figure 3 Current-voltage sweep characteristic curve of carbon ink-based memristor;

[0038] Figure 4 IV characteristic curve of fluorinated carbon ink-based memristor. Detailed Implementation

[0039] A method for preparing a memristor based on halide-ion modification of commercial carbon ink includes the following steps:

[0040] Modified ink preparation: Using commercial carbon ink as the base, add halogen source, stir and mix according to the preset ratio to prepare uniform and stable halogen modified carbon ink;

[0041] Thoroughly disperse the mixture: Place the mixed ink in a magnetic stirrer and stir at a speed of 200~600 r / min to ensure that the halogen ions fully interact with the surface of the carbon material.

[0042] Film formation: The modified ink is coated onto a conductive substrate to form a uniform thin film;

[0043] Placement: The coated film is left to stand overnight to allow the halogen ions to react repeatedly with the carbon surface;

[0044] Low-temperature annealing: Annealing at 80~150 ℃ removes solvent, stabilizes film structure, and strengthens the bonding between halide ions and carbon skeleton;

[0045] The top electrode is fabricated to form a memristor with a vertical structure of "top electrode / carbon thin film / conductive substrate".

[0046] Preferably, the halide ion modification is performed using fluoride ions (F... - A typical example is a product that uses ammonium fluoride as a precursor; the doping ratio is 2-20 mg of ammonium fluoride per mL of commercial carbon ink; the total amount prepared can be scaled up as needed.

[0047] Preferably, the stirring speed is 200-400 r / min, with 300 r / min being optimal; the stirring time should not be too long (too long a stirring time can easily lead to sedimentation).

[0048] Ideally, the coated carbon ink film should not dry immediately. It should be left to stand for a period of time to allow the carbon surface to fully reconstruct, preferably 12 hours.

[0049] Preferably, the annealing temperature is 100-130 ℃, with an optimal temperature of 120 ℃; the annealing time is 20-60 min, with an optimal time of 30 min.

[0050] Preferably, the conductive substrate is ITO conductive glass, FTO glass, flexible PET-ITO, PI-ITO, metal foil substrate, etc.

[0051] Preferably, the top electrode is made of gold, silver, platinum, aluminum, conductive polymer, etc., and can be prepared by thermal evaporation, magnetron sputtering, printing, etc.

[0052] The present invention provides a memristor based on commercial carbon ink modified with halogen ions, comprising a conductive substrate, a halogen-modified carbon thin film functional layer, and a top electrode; the carbon thin film functional layer is prepared by adding a halogen source to commercial carbon ink through solution blending, film formation, placement, and low-temperature annealing; the halogen source includes soluble salts or complexes containing fluorine, chlorine, bromine, and iodine, preferably ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, metal halides, etc.

[0053] like Figure 1 The bottom conductive substrate provides mechanical support for the entire device and serves as the bottom electrode, forming a complete electrical circuit with the top electrode. It is commonly made of materials such as ITO conductive glass, silicon wafers, or metal foil. The middle layer is a carbon thin film prepared by printing, spin coating, and other processes using commercial carbon ink. Its surface is designed with a regularly arrayed circular microporous structure, which is the functional unit of the device. The top electrode is mostly made of inert metals such as gold, silver, and platinum or conductive polymers. It works with the bottom electrode to apply voltage and collect electrical signals. An external voltmeter is used to monitor the voltage and current changes across the device in real time to characterize the electrical response characteristics of the carbon thin film layer.

[0054] like Figure 2 The functional layer film is composed of carbon nanoparticles, which form a mesoporous film.

[0055] like Figure 3 The voltage scan, within a range of ±2.5 V, is used to perform a round-trip voltage scan (from 0 → positive voltage → 0 → negative voltage → 0, completing one full cycle) to obtain the IV response. The horizontal axis represents the applied bias voltage (Voltage, V), and the vertical axis represents the device's response current (Current, A). The two blue curves form a closed "hysteresis loop," which is the most essential characteristic of a memristor, demonstrating that the device has a memory characteristic of resistance changing with voltage history, consistent with the basic definition of a memristor.

[0056] The hysteresis loop corresponds to the switching between the high-resistivity (HRS) and low-resistivity (LRS) states of a memristor, which is the "set-reset" process. During the positive voltage scan (0→+2.5 V), as the voltage increases from 0, the device is initially in a high-resistivity state (the current rises slowly with the voltage). When the voltage reaches the set threshold (Set), the conductive filaments in the carbon ink (formed by carbon particles, defects, or ion migration) gradually connect, the device resistance decreases sharply, and the current rises rapidly, completing the switch from HRS to LRS. During the voltage retrace (+2.5 V→0), the device maintains a low-resistivity state, and the current decreases along the high-conductivity path, forming the upper part of the hysteresis loop. Negative voltage scan segment (0→-2.5 V): After the reverse voltage is applied, the device remains in a low-resistance state; when the voltage reaches the reset threshold, the conductive filament melts / breaks under the action of Joule heating or electric field, the device resistance rises sharply, the current drops sharply, and the reset from LRS to HRS is completed; during voltage retracement (-2.5 V→0), the device maintains a high-resistance state, the current rises along the low-conductivity path, forming the lower half of the hysteresis loop.

[0057] like Figure 4 After fluorination, the resistive switching behavior of the device is more controllable and more stable. In the positive voltage scan segment (0→+2.5 V), the setting process of the device switching from a high resistance state to a low resistance state is steeper, and the current difference between the high and low resistance states is significantly increased. In the negative voltage scan segment (0→-2.5 V), the resistive switching threshold of the reset process is clearer, the window area and symmetry of the hysteresis loop are greatly improved, and the transition near 0 V is smoother, with no obvious leakage or breakdown phenomena.

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A thin-film memristor based on commercial fountain pen carbon ink, characterized in that, From bottom to top, it includes: a conductive substrate, a halogen-modified carbon thin film functional layer, and a top electrode; the carbon thin film functional layer is prepared by adding a halogen source to commercial fountain pen carbon ink, followed by solution blending, film formation, standing, and low-temperature annealing at 80~150℃; the halogen source includes soluble salts or complexes containing halogen elements, and the halogen elements are fluorine, chlorine, bromine, or iodine.

2. The thin-film memristor as described in claim 1, characterized in that, The halogen source specifically includes ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, or metal halides.

3. The method for fabricating a thin-film memristor as described in claim 1, characterized in that, Includes the following steps: S1. Modified ink formulation: Using commercial fountain pen carbon ink as the base, add halogen source according to the preset ratio, stir and mix to obtain a uniform and stable mixed ink; S2. Stirring and dispersing: Stir the mixed ink at a speed of 200~600 r / min to ensure that the halogen ions fully contact and react with the surface of the carbon material to obtain halogen modified carbon ink; S3. Film formation: The halogen-modified ink is coated onto the conductive substrate to form a uniform thin film; S4. Settling: Let the coated film stand for more than 8 hours to allow the halogen ions to fully react with the carbon surface; S5. Low-temperature annealing: Annealing at 80~150 ℃ to remove solvent, stabilize film structure, strengthen the bonding between halide ions and carbon skeleton, and obtain halogen-modified carbon film functional layer. S6. A top electrode is fabricated on a halogen-modified carbon thin film functional layer to form a memristor with a vertical structure of "top electrode / carbon thin film / conductive substrate".

4. The method for fabricating a thin-film memristor as described in claim 3, characterized in that, In S1, the preset ratio is specifically: 2~20 mg of halogen source is added per 1 mL of commercial fountain pen carbon ink.

5. The method for fabricating a thin-film memristor as described in claim 4, characterized in that, The halogen source is ammonium fluoride.

6. The method for fabricating a thin-film memristor as described in claim 4, characterized in that, In S2, the stirring speed is 200~400 r / min.

7. The method for fabricating a thin-film memristor as described in claim 4, characterized in that, In S1, the conductive substrate is ITO conductive glass, FTO glass, flexible PET-ITO, PI-ITO, or a metal foil substrate.

8. The method for fabricating a thin-film memristor as described in claim 4, characterized in that, In S4, the settling time is more than 12 hours.

9. The method for fabricating a thin-film memristor as described in claim 4, characterized in that, In S5, the annealing temperature for the low-temperature annealing is 100–130 °C; the annealing time is 20–60 min.

10. The method for fabricating a thin-film memristor as described in claim 4, characterized in that, In S5, the top electrode is made of gold, silver, platinum, aluminum or a conductive polymer material, and is prepared on the halogen-modified carbon thin film functional layer by thermal evaporation, magnetron sputtering or printing.

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