Cu / Al laminated metal grid flexible transparent electrode and preparation method thereof

Abstract

The invention relates to the technical field of flexible transparent electrodes, in particular to a Cu / Al laminated metal grid flexible transparent electrode and a preparation method thereof. The Cu / Al laminated metal grid flexible transparent electrode comprises a flexible substrate, a copper layer arranged on the flexible substrate and an aluminum layer arranged on the copper layer, and the aluminum layer located on the outer layer spontaneously forms an Al2O3 passivation layer with the thickness of 2-5 nm in air. The Al2O3 passivation layer can effectively prevent oxygen and moisture from permeating inwards, so that oxidation of the copper layer in a humid or high-temperature environment is fundamentally inhibited, long-term stability of the electrical property of the electrode is ensured, and meanwhile, due to the fact that the thickness of the copper layer is 150-250 nm, excellent conductivity is provided, and low square resistance is achieved; the latticed structure maintains high light transmittance of the electrode while ensuring a high conductive path. Finally, the structure has excellent oxidation resistance, high light transmittance, low sheet resistance and flexible stability under the support of a flexible transparent substrate with the thickness of 50-200 [mu] m, and meets the harsh requirements of a new generation of flexible optoelectronic devices on electrode performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible transparent electrodes, in particular to a Cu / Al laminated metal mesh flexible transparent electrode and a preparation method thereof. BACKGROUND

[0002] Flexible transparent electrodes (FTEs) are the key functional units in the new generation of flexible optoelectronic devices. In foldable displays, FTEs are used as conductive layers to drive pixels and transmit electrical signals, while maintaining optical transparency and electrical stability of the device under repeated bending conditions; in wearable sensors, FTEs not only serve as electrodes to achieve high-sensitivity signal acquisition, but also ensure the flexibility and comfort of the device under skin-adhesion and dynamic stretching conditions; in photovoltaic devices, FTEs are often used as transparent conductive electrodes to efficiently collect and transport photo-generated charges, while maintaining high transmittance to incident light, thus balancing energy conversion efficiency and optical performance.

[0003] In the prior art, although indium tin oxide (ITO) transparent conductive material has the advantages of high light transmittance and low sheet resistance, its brittleness and high preparation temperature make it difficult to meet the application requirements of flexible devices. To solve this problem, people have proposed various alternative solutions such as carbon-based materials, conductive polymers, and metal nanowires, but these materials generally have the limitation that they cannot simultaneously achieve good conductivity and light transmittance, and still cannot fully meet the performance requirements of flexible transparent electronic devices. In contrast, metal mesh transparent electrodes can achieve independent adjustment of conductivity and light transmittance through geometric structure design, and have broad application prospects.

[0004] In existing metal mesh materials, copper is widely used due to its excellent conductivity and low cost, but copper-based mesh is prone to oxidation in the atmosphere, which significantly degrades its electrical performance, thus limiting its application in flexible optoelectronic devices. Therefore, the existing technology still has the following problems: there is a lack of a flexible metal mesh transparent electrode material that simultaneously has low sheet resistance, high light transmittance, and excellent oxidation resistance, and there is an urgent need for a new material design scheme to overcome the above shortcomings. SUMMARY

[0005] The present application aims to provide a Cu / Al laminated metal mesh flexible transparent electrode and a preparation method thereof, which aims to solve the environmental stability problem of Cu-based flexible metal mesh transparent electrodes, avoid the rapid oxidation of copper in humid / high-temperature environments, and at the same time, achieve high light transmittance, low sheet resistance, and flexible stability.

[0006] To achieve the above object, the application provides a Cu / Al laminated metal mesh flexible transparent electrode, which comprises a flexible substrate, a copper layer arranged on the flexible substrate, and an aluminum layer arranged on the copper layer, the flexible substrate is preferably a transparent polymer film, the thickness of the flexible substrate is 50-200 μm, the thickness of the copper layer is 150-250 nm, the thickness of the aluminum layer is 10-50 nm, the outer surface of the aluminum layer is covered with an Al2O3 passivation layer, the Al2O3 passivation layer is formed by self-passivation of the aluminum layer in air and is used for blocking oxygen and moisture, and the thickness of the Al2O3 passivation layer is 2-5 nm. The copper layer, the aluminum layer and the Al2O3 passivation layer are arranged in a mesh structure.

[0007] Preferably, the flexible substrate is one of polyethylene terephthalate film, polyimide film or polycarbonate film.

[0008] Preferably, the thickness of the copper layer is 200 nm, and the thickness of the aluminum layer is 30-50 nm.

[0009] Preferably, the mesh structure of the copper layer, the aluminum layer and the Al2O3 passivation layer is a hexagonal mesh, and the typical parameters of the hexagonal mesh are as follows: the side length is 100-200 μm, preferably 145 μm; and the line width is 5-20 μm, preferably 10 μm.

[0010] Preferably, the mesh structure of the copper layer, the aluminum layer and the Al2O3 passivation layer is a square mesh, a honeycomb mesh or a strip-shaped mesh.

[0011] The application further provides a preparation method of a Cu / Al laminated metal mesh flexible transparent electrode, which is used for preparing the Cu / Al laminated metal mesh flexible transparent electrode as described above and comprises the following steps. Pre-treatment: cleaning and plasma treatment of the flexible transparent substrate; Deposition treatment: sequentially depositing the copper layer and the aluminum layer on the substrate by using a magnetron sputtering process; Etching treatment: simultaneously patterning the copper layer and the aluminum layer into a preset mesh structure by using a photolithography and wet etching process to obtain a semi-finished electrode; Post-treatment: exposing the semi-finished electrode to air to form the Al2O3 passivation layer on the surface of the aluminum layer by self-passivation, thereby obtaining the Cu / Al laminated metal mesh flexible transparent electrode.

[0012] The specific content of the pre-treatment step is: sequentially performing ultrasonic cleaning of the flexible transparent substrate with acetone, isopropyl alcohol and deionized water, and then drying the flexible transparent substrate by blowing nitrogen, and then performing plasma treatment on the flexible transparent substrate to further remove surface contamination and improve the adhesion of the metal film to the substrate.

[0013] The specific content of the deposition treatment step is: The copper film is deposited on the flexible substrate by using a direct current magnetron sputtering method, thereby forming the copper layer. After the deposition of the copper layer is completed, the aluminum layer is continuously deposited by using magnetron sputtering without breaking the vacuum environment.

[0014] In the etching treatment step, the photoresist coating thickness is 1-2 μm, and the required pattern is obtained after soft baking, exposure and development. The wet etching solution can be selected from a sulfuric acid-hydrogen peroxide system or an ammonia-hydrogen peroxide system, and the etching rate is controlled to be 5-10 nm / s.

[0015] The Cu / Al laminated metal mesh flexible transparent electrode provided by the application comprises a flexible substrate, a copper layer arranged on the flexible substrate, and an aluminum layer arranged on the copper layer. The aluminum layer on the outer layer spontaneously forms an Al2O3 passivation layer with a thickness of 2-5 nm in the air. The Al2O3 passivation layer can effectively block the penetration of oxygen and moisture into the interior, thereby fundamentally inhibiting the oxidation of the copper layer in a humid or high-temperature environment and ensuring the long-term stability of the electrode electrical performance. At the same time, the copper layer has a thickness of 150-250 nm, which provides excellent electrical conductivity and realizes low sheet resistance. The grid structure ensures high electrical conductivity while maintaining high light transmittance of the electrode. Finally, under the support of the flexible transparent substrate with a thickness of 50-200 μm, the structure has excellent oxidation resistance, high light transmittance, low sheet resistance and flexibility stability, and meets the stringent requirements of the new generation of flexible optoelectronic devices on electrode performance. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort.

[0017] Figure 1 FIG. 1 is a structural schematic diagram of the Cu / Al laminated metal mesh flexible transparent electrode provided by the application.

[0018] Figure 2It is surface micro-morphology chart of Cu / Al laminated metal mesh flexible transparent electrode under scanning electron microscope provided by the application.

[0019] Figure 3 It is cross-section micro-morphology chart of Cu / Al laminated metal mesh flexible transparent electrode under scanning electron microscope provided by the application.

[0020] Figure 4 It is step flow chart of preparation method of Cu / Al laminated metal mesh flexible transparent electrode provided by the application.

[0021] Figure 5 It is sample chart of Cu / Al thin film of Cu / Al laminated metal mesh flexible transparent electrode with different thickness of aluminum layer after double "85" aging experiment before photoetching etching provided by the application.

[0022] Figure 6 It is sheet resistance change chart of Cu / Al laminated metal mesh flexible transparent electrode with different thickness of aluminum layer after double "85" aging experiment of Cu / Al thin film before photoetching etching provided by the application.

[0023] 101-flexible substrate, 102-copper layer, 103-aluminum layer, 104-Al2O3 passivation layer. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below with reference to the accompanying drawings. The embodiments shown in the drawings are examples for explaining the present application and should not be construed as limiting the present application.

[0025] Referring to Figures 1 to 3 The present application provides a Cu / Al laminated metal mesh flexible transparent electrode, which comprises a flexible substrate 101, a copper layer 102 arranged on the flexible substrate 101, and an aluminum layer 103 arranged on the copper layer 102. The flexible substrate 101 is preferably a transparent polymer film, and the thickness of the flexible substrate 101 is 50-200 μm. The thickness of the copper layer 102 is 150-250 nm, and the thickness of the aluminum layer 103 is 10-50 nm. The outer surface of the aluminum layer 103 is covered with an Al2O3 passivation layer 104, which is formed by self-passivation of the aluminum layer 103 in air, and is used for blocking oxygen and moisture. The thickness of the Al2O3 passivation layer 104 is 2-5 nm. The copper layer 102, the aluminum layer 103, and the Al2O3 passivation layer 104 are arranged in a grid structure.

[0026] In the present embodiment, the aluminum layer 103 on the outer layer spontaneously forms a 2-5 nm thick Al2O3 passivation layer 104 in air, which effectively blocks the penetration of oxygen and moisture into the interior, thereby fundamentally inhibiting the oxidation of the copper layer 102 in a humid or high-temperature environment, ensuring the long-term stability of the electrode's electrical properties, while the 150-250 nm thick copper layer 102 provides excellent electrical conductivity, achieving low sheet resistance; the grid structure ensures high electrical conductivity while maintaining high light transmittance of the electrode. Ultimately, this structure, supported by the 50-200 μm thick flexible transparent substrate, has excellent oxidation resistance, high light transmittance, low sheet resistance, and flexibility, meeting the stringent requirements of the new generation of flexible optoelectronic devices for electrode performance.

[0027] Further, the flexible substrate 101 is preferably a polyethylene terephthalate film, a polyimide film, a polycarbonate film, or other heat-resistant transparent film. The substrate thickness is 50-200 μm to ensure the balance between flexibility and mechanical strength.

[0028] Further, the thickness of the copper layer 102 is preferably 200 nm, and the thickness of the aluminum layer 103 is preferably 30-50 nm.

[0029] In the present embodiment, the thickness of the copper layer 102 is preferably 200 nm to balance low sheet resistance and film continuity, as too thin a thickness will increase the resistivity, and too thick a thickness will reduce the light transmittance. When the thickness of the aluminum layer 103 is less than about 20 nm, surface morphology characterization (SEM or AFM) shows that the deposition of aluminum is in island-like distribution, and continuous coverage cannot be achieved. This is because during the initial film formation stage, aluminum atoms form isolated nucleation points on the Cu surface rather than layer growth, resulting in gaps between films and preventing the formation of a dense covering layer, thereby weakening the effective protection of the underlying Cu. As the thickness increases to 20-50 nm, the aluminum layer 103 gradually changes to a continuous and dense film structure, providing good oxidation resistance barrier. However, when the thickness exceeds 50 nm, optical transmission spectrum (UV-Vis) test results show that the light transmittance decreases significantly, as the reflection and absorption of visible light by the aluminum layer 103 is enhanced. Therefore, the thickness of the aluminum layer 103 is preferably 30-50 nm.

[0030] Further, the grid structure of the copper layer 102, the aluminum layer 103, and the Al2O3 passivation layer 104 is preferably a hexagonal grid with typical parameters of 100-200 μm, preferably 145 μm, in length, and 5-20 μm, preferably 10 μm, in line width.

[0031] Further, the grid structure of the copper layer 102, the aluminum layer 103 and the Al2O3 passivation layer 104 can be a square grid, a honeycomb grid or a strip grid.

[0032] Further, the surface of the Al2O3 passivation layer 104 can also be provided with a transparent protective layer, such as SiO2, TiO2 or an organic polymer coating, to further improve weather resistance. Please refer to Figure 4 The application also provides a preparation method of the Cu / Al laminated metal grid flexible transparent electrode, for preparing the Cu / Al laminated metal grid flexible transparent electrode as described above, comprising the following steps: S1, pretreatment: cleaning and plasma treatment of the flexible transparent substrate; S2, deposition treatment: using a magnetron sputtering process to sequentially deposit the copper layer 102 and the aluminum layer 103 on the substrate; S3, etching treatment: simultaneously patterning the copper layer 102 and the aluminum layer 103 into a predetermined grid structure by photolithography and wet etching process, to obtain a semi-finished electrode; S4, post-treatment: exposing the semi-finished electrode to air to form the Al2O3 passivation layer 104 on the surface of the aluminum layer 103 by self-passivation, thereby obtaining the Cu / Al laminated metal grid flexible transparent electrode.

[0033] In this embodiment, first, the copper layer 102 and the aluminum layer 103 are sequentially deposited by magnetron sputtering to form a metal stack; then the double-layer metal is simultaneously patterned into a grid structure by photolithography and wet etching, and the pattern is accurately controlled to balance high light transmission and low sheet resistance; finally, the Al2O3 passivation layer 104 is naturally formed on the surface of the electrode by taking advantage of the rapid self-passivation characteristics of aluminum in air, thereby solving the core problem of the copper layer 102 being easily oxidized to cause performance degradation without increasing the complexity of the process steps. This process is simple and efficient, and is compatible with the mass production process of flexible electronics, providing a reliable technical path for preparing flexible transparent electrodes with high stability and high performance.

[0034] Further, the specific content of the pretreatment step is: sequentially ultrasonic cleaning the flexible transparent substrate with acetone, isopropanol and deionized water (10-15 min for each step), and then blowing dry with nitrogen, ensuring that the surface is free of organic residues, and then performing plasma treatment on the flexible transparent substrate to further remove surface contamination and improve the adhesion of the metal film to the substrate.

[0035] Further, the specific content of the deposition treatment step is: The copper layer 102 is deposited on the flexible substrate 101 by direct current magnetron sputtering, so as to form the copper layer 102 (the sputtering target is a copper target with a purity of ≥99.99%; the working gas is high-purity argon with a pressure of 0.35-0.55 Pa; the sputtering current is 0.25 A-0.5 A; and the substrate temperature is maintained at room temperature to avoid thermal deformation of the substrate). After the deposition of the copper layer 102 is completed, the aluminum layer 103 is continuously deposited by magnetron sputtering without destroying the vacuum environment (the sputtering target is an aluminum target with a purity of ≥99.99%; the working gas is argon with a pressure of 0.35-0.55 Pa; and the sputtering current is 0.2 A-0.6 A).

[0036] Further, in the etching process, the photoresist coating thickness is 1-2 μm, and the required pattern is obtained after soft baking, exposure and development; The wet etching solution can be selected from a sulfuric acid-hydrogen peroxide system or an ammonia-hydrogen peroxide system, and the etching rate is controlled to be 5-10 nm / s.

[0037] Further, the semi-finished electrode in the etching process is placed in air for 1-2 h, and the aluminum layer 103 is spontaneously oxidized to form a stable Al2O3 passivation layer 104 with a thickness of about 2-5 nm.

[0038] If necessary, low-temperature annealing (≤145℃, 12-24 h) can be further used to improve the film layer adhesion and surface density. Please refer to Figure 5 and Figure 6 The application also provides test comparative examples of the Cu / Al laminated metal mesh flexible transparent electrode with different thicknesses of the aluminum layer 103.

[0039] Example 1: Preparation of the Cu / Al laminated metal mesh flexible transparent electrode with a standard thickness: A PET substrate with a size of 5 cm×5 cm is ultrasonically cleaned with acetone, isopropanol and deionized water for 10 min each, and then dried in a vacuum oven at 80℃ for 30 min.

[0040] A copper layer 102 with a thickness of 200 nm is deposited in a direct current magnetron sputtering system (Ar pressure 0.4 Pa, current 0.4 A), and then a 30 nm aluminum layer 103 is deposited under the condition that the vacuum is not destroyed (Ar pressure 0.4 Pa, current 0.45 A).

[0041] A hexagonal mesh pattern is prepared by photolithography, the mesh side length is 145 μm, the line width is 10 μm, and the etching solution is an H2SO4 / H2O2 mixture.

[0042] The sample is naturally exposed in air for 2 h, and a dense Al2O3 passivation layer 104 is formed on the surface of the aluminum layer 103.

[0043] Test result: the light transmittance is 81.5% at 550nm wavelength, and the sheet resistance is 4.6Ω / □.

[0044] Example 2: Preparation of the Cu / Al stacked metal mesh flexible transparent electrode with a thin aluminum layer 103 (10nm): The substrate and copper layer 102 are prepared as in Example 1.

[0045] A 10nm aluminum layer 103 is deposited.

[0046] The patterned mesh parameters are: side length 145μm, line width 10μm.

[0047] Test result: after 24h aging at 85℃, 85%RH, the sheet resistance rises to 9.6Ω / □, indicating insufficient protection.

[0048] Example 3: Preparation of the Cu / Al stacked metal mesh flexible transparent electrode with a thick aluminum layer 103 (50nm): The substrate treatment is the same as in Example 1.

[0049] After depositing a 200nm copper layer 102, a 50nm aluminum layer 103 is deposited, with other parameters remaining the same.

[0050] The patterned mesh is a hexagonal mesh with a side length of 145μm and a line width of 10μm.

[0051] After the sample is exposed to air for 2h, an Al2O3 passivation layer 104 of about 3-5nm is formed on the surface of the aluminum layer 103.

[0052] Test result: after 60h aging at 85℃, 85%RH, the sheet resistance remains essentially unchanged. In comparison, the copper electrode without aluminum coverage has a sheet resistance that rises to 10 times the initial value within 36h, completely failing.

[0053] The technical effects of the present technical solution are summarized as follows: (1) Significant oxidation resistance: traditional bare copper electrodes are extremely susceptible to oxidation in air or humid heat environments, leading to rapid increases in sheet resistance. For example, in the present invention, the copper electrode without aluminum coverage completely failed after 36h aging at 85℃, 85%RH. The Cu / Al double-layer electrode of the present invention has significantly enhanced oxidation resistance as the thickness of the aluminum layer 103 increases. The sample with a 50nm aluminum coverage showed excellent stability, with almost no change in sheet resistance after 60h aging under the same conditions.

[0054] (2) Excellent photoelectric performance: The light transmittance of the electrode of the application reaches 81.5% at a wavelength of 550 nm, and the sheet resistance is only 4.58 Ω / □, which is significantly better than that of an ITO electrode (light transmittance of 81.6% and sheet resistance of up to 43 Ω / □). This shows that the application has far superior electrical performance while maintaining high light transmittance.

[0055] (3) Good flexibility stability: Through the bending experiment, the electrode of the application maintains stable conductivity in flat and curved states. Even under the condition of repeated bending with a small radius, the sheet resistance remains basically unchanged, proving that it meets the needs of flexible displays and wearable devices.

[0056] (4) Application value: Based on the Cu / Al double-layer mesh electrode prepared by the application, a touch sensor is successfully constructed. Experiments show that when the sensor is touched by a single point, the capacitance value increases from 10 pF to 22 pF, showing obvious signal response. At the same time, under different distances (9 cm, 5 cm, 3 cm), the palm gradually approaches the sensor, and the sensitive change of the capacitance can be detected, indicating that the electrode has important application potential in interactive electronic devices.

[0057] The above only discloses one preferred embodiment of the application, and of course cannot limit the scope of the rights of the application. Those skilled in the art can understand that all or part of the processes of the above-mentioned embodiments can be implemented, and equivalent changes made in accordance with the claims of the application still fall within the scope of the application.

Claims

1. A Cu / Al stacked metal mesh flexible transparent electrode, characterized in that, it comprises a flexible substrate, a copper layer disposed on the flexible substrate, and an aluminum layer disposed on the copper layer, the flexible substrate is preferably a transparent polymer film, the thickness of the flexible substrate is 50-200 μm, the thickness of the copper layer is 150-250 nm, the thickness of the aluminum layer is 10-50 nm, the outer surface of the aluminum layer is covered with an Al 2 O 3 passivation layer, the Al 2 O 3 passivation layer is formed by self-passivation of the aluminum layer in air, and is used to block oxygen and moisture, the thickness of the Al 2 O 3 passivation layer is 2-5 nm; the copper layer, the aluminum layer and the Al 2 O 3 passivation layer are all arranged in a mesh structure. 2.The Cu / Al stacked metal mesh flexible transparent electrode according to claim 1, characterized in that, the flexible substrate is preferably one of a polyethylene terephthalate film, a polyimide film or a polycarbonate film. 3.The Cu / Al stacked metal mesh flexible transparent electrode according to claim 1, characterized in that, the thickness of the copper layer is preferably 200 nm, and the thickness of the aluminum layer is preferably 30-50 nm. 4.The Cu / Al stacked metal mesh flexible transparent electrode according to claim 1, characterized in that, the mesh structure of the copper layer, the aluminum layer and the Al 2 O 3 passivation layer is preferably a hexagonal mesh, and the typical parameters of the hexagonal mesh are: side length 100-200 μm, preferably 145 μm; line width 5-20 μm, preferably 10 μm. 5.The Cu / Al stacked metal mesh flexible transparent electrode according to claim 1, characterized in that, the mesh structure of the copper layer, the aluminum layer and the Al 2 O 3 passivation layer can be a square mesh, a honeycomb mesh or a strip mesh.

6. A method for producing a Cu / Al stacked metal mesh flexible transparent electrode, for producing the Cu / Al stacked metal mesh flexible transparent electrode according to claim 1, characterized by, comprising the following steps: pretreatment: cleaning and plasma treatment of the flexible transparent substrate; deposition treatment: using a magnetron sputtering process to sequentially deposit the copper layer and the aluminum layer on the substrate; etching treatment: patterning the copper layer and the aluminum layer into a predetermined mesh structure by photolithography and wet etching process to obtain a semi-finished electrode; post-treatment: exposing the semi-finished electrode to air to form the Al 2 O 3 passivation layer on the surface of the aluminum layer by self-passivation, thereby obtaining the Cu / Al stacked metal mesh flexible transparent electrode. 7.The preparation method of the Cu / Al stacked metal mesh flexible transparent electrode according to claim 6, characterized in that, the specific content of the pretreatment step is: sequentially ultrasonic cleaning the flexible transparent substrate with acetone, isopropyl alcohol and deionized water, and then blowing dry with nitrogen, ensuring that the surface is free of organic matter residues, and then performing plasma treatment on the flexible transparent substrate to further remove surface contamination and improve the adhesion of the metal film to the substrate. 8.The preparation method of the Cu / Al stacked metal mesh flexible transparent electrode according to claim 7, characterized in that, the specific content of the deposition treatment step is: depositing a copper film on the flexible substrate by direct current magnetron sputtering to form the copper layer; After the copper layer is deposited, the aluminum layer is deposited by magnetron sputtering without breaking the vacuum environment.

9. The method of claim 8, wherein the Cu / Al stack metal mesh flexible transparent electrode is prepared by the following steps: coating a photoresist on a glass substrate, soft baking, exposing, developing, etching, and removing the photoresist. In the etching process, the photoresist has a thickness of 1-2 μm, and the desired pattern is obtained by soft baking, exposing, and developing. The wet etching solution can be a sulfuric acid-hydrogen peroxide system or an ammonia-hydrogen peroxide system, and the etching rate is controlled to be 5-10 nm / s.

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