Zinc tin oxide transparent electrothermal material and preparation method and application thereof

Abstract

This invention discloses a transparent zinc tin oxide (ZTO) electrothermal film comprising zinc oxide and tin oxide in a molar ratio of 6:4 to 8:2, with a film thickness of 50–200 nm. The film exhibits a transmittance ≥85% at 550 nm, a sheet resistance of 10–50 Ω / □, and resistivity changes of no more than 5% and 8% after 1000 h of energization at 100°C and 100 cycles at -40°C to 80°C, respectively. This invention also discloses a transparent electrothermal material containing this film, a method for preparing the material using roll-to-roll magnetron sputtering, and its application in transparent heating devices such as architectural glass, automotive windshields, electronic display panels, and medical equipment. This invention replaces expensive In with low-cost Zn / Sn, and through optimized target ratios, roll-to-roll sputtering in an oxygen-containing sputtering atmosphere, and an oxygen-containing atmosphere annealing process, achieves a balance between low cost, high electrothermal stability, high transmittance, and easy industrial mass production of the transparent electrothermal material.

Description

Technical Field

[0001] This invention belongs to the field of transparent functional materials technology, specifically relating to a zinc tin oxide (ZTO) based transparent electrothermal film, a transparent electrothermal material containing the film, its preparation method, and its application in transparent heating scenarios. Background Technology

[0002] Transparent electrothermal materials require high light transmittance in the visible light band, as well as good electrical conductivity and electrothermal conversion efficiency. They are widely used in fields such as building energy-saving glass, automotive windshield defrosting and defogging, constant temperature protection for electronic display panels, and heating of transparent components in medical equipment.

[0003] Currently, the mainstream transparent electrothermal materials and manufacturing processes in the industry suffer from the following core technological challenges: (1) ITO (Indium Tin Oxide) based material system: Indium is a rare and precious metal, and the raw material cost is high. The cost of the target material is about 3 to 5 times that of zinc tin oxide target material. ITO film has poor flexibility. When used on flexible substrates, microcracks are easily generated when the bending radius is less than 5 mm, which leads to sudden change in resistance or even open circuit, resulting in insufficient long-term electrical stability. In addition, ITO film has a large difference in thermal expansion coefficient with flexible polymer substrate (ITO is about 7.2 × 10⁻⁶). -6 / K, PET approximately 59×10 -6 Under high and low temperature cycling conditions, interfacial stress accumulates, resulting in a significant decrease in adhesion to the substrate, which easily leads to interfacial peeling and seriously affects the service life.

[0004] (2) Carbon-based material systems (carbon nanotubes / graphene, etc.): It is difficult to balance light transmittance and conductivity. In order to reduce the sheet resistance to below 50Ω / □, it is usually necessary to increase the film thickness or the density of the conductive network, which leads to the light transmittance dropping to below 80%. Under conditions where the temperature exceeds 85℃ or the material is powered for a long time (more than 500 hours), carbon-based materials will have an increased oxygen-containing functional group due to oxidation, and the resistivity drift rate can reach 15% to 30%. The electrothermal stability is poor, making it difficult to meet the high reliability requirements of high-end scenarios such as automotive windshield defrosting and industrial constant temperature control.

[0005] (3) Traditional preparation process: The magnetron sputtering method with single or dual target co-sputtering is mostly used. The equipment structure is complex and the parameter control is difficult. Moreover, it is mostly single-wafer intermittent production. The production cycle of a single wafer is about 3 to 5 minutes / wafer (including loading and unloading time). It cannot achieve continuous and large-scale manufacturing. The production efficiency is low, the energy consumption is high, and the product consistency is difficult to guarantee. The sheet resistance fluctuation within a batch can reach ±15%. In addition, the ZTO thin film prepared by conventional sputtering process has not undergone optimized post-treatment. There is a high residual stress inside the film. After long-term power supply and high and low temperature cycling, crystallinity changes and microstructure deterioration are prone to occur, resulting in serious resistance drift. The resistance change rate after 1000 hours of long-term power supply is usually more than 12%. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention is to provide a novel transparent electrothermal material and its preparation process that simultaneously meets the requirements of low cost, high electrothermal stability, high light transmittance and easy industrial mass production. This solves the three core contradictions in the field of existing transparent electrothermal materials: the contradiction between cost and performance (ITO system is costly), the contradiction between light transmittance and conductivity (carbon-based systems cannot achieve both), and the contradiction between high performance and easy mass production (traditional processes are inefficient and have poor consistency).

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a zinc tin oxide transparent electrothermal film comprising zinc oxide (ZnO) and tin oxide (SnO2), wherein the molar ratio of zinc oxide to tin oxide is 6:4 to 8:2; and the thickness of the zinc tin oxide transparent electrothermal film is 50 to 200 nm.

[0008] Furthermore, the zinc tin oxide transparent electrothermal film has a visible light transmittance of not less than 85% at a wavelength of 550 nm and a sheet resistance of 10 to 50 Ω / □.

[0009] Furthermore, the resistance change rate of the zinc tin oxide transparent electrothermal film after being energized at a constant temperature of 100°C for 1000 hours does not exceed 5%.

[0010] Furthermore, the resistance change rate of the zinc tin oxide transparent electrothermal film after 100 temperature cycles from -40°C to 80°C does not exceed 8%.

[0011] In a second aspect, the present invention provides a transparent electrothermal material, comprising a substrate and a zinc tin oxide transparent electrothermal film disposed on the substrate, wherein the zinc tin oxide transparent electrothermal film comprises zinc oxide and tin oxide, wherein the molar ratio of zinc oxide to tin oxide is 6:4 to 8:2, and the thickness of the zinc tin oxide transparent electrothermal film is 50 to 200 nm.

[0012] Furthermore, the substrate is a transparent substrate.

[0013] Furthermore, an intermediate functional layer is provided between the substrate and the zinc tin oxide transparent electrothermal film.

[0014] Furthermore, the intermediate functional layer is a silicon oxide transition layer.

[0015] Furthermore, a protective layer is provided on the side of the zinc tin oxide transparent electrothermal film facing away from the substrate, and the material of the protective layer is selected from SiO2 or Al2O3.

[0016] Thirdly, the present invention provides a method for preparing the above-mentioned transparent electrothermal material, which employs a roll-to-roll magnetron sputtering process and includes the following steps: S1. Provide substrate; S2. The substrate is placed in the sputtering chamber of a roll-to-roll magnetron sputtering device, wherein a zinc tin oxide target is provided in the sputtering chamber, and the molar ratio of zinc oxide to tin oxide in the target is 6:4 to 8:2. Sputtering deposition is performed in an oxygen-containing sputtering atmosphere to deposit a zinc tin oxide thin film on the substrate. S3. Anneal the substrate with the zinc tin oxide film deposited on it in an oxygen-containing atmosphere.

[0017] Furthermore, the oxygen-containing sputtering atmosphere described in step S2 is a mixture of argon and oxygen.

[0018] Furthermore, step S1 also includes surface pretreatment of the substrate; the surface pretreatment includes ultrasonic cleaning and plasma surface treatment.

[0019] Furthermore, when the substrate is a flexible transparent polymer film, step S2 further includes depositing a silicon oxide transition layer before depositing the zinc tin oxide film.

[0020] Furthermore, after step S3, a protective layer of SiO2 or Al2O3 is deposited on the surface of the zinc tin oxide film using magnetron sputtering.

[0021] Fourthly, the present invention provides the application of the above-mentioned zinc tin oxide transparent electrothermal film or transparent electrothermal material in transparent heating devices. The transparent heating devices include, but are not limited to, architectural glass, automotive windshields, high-speed rail windshields, aircraft windshields, electronic display panels, transparent medical diagnostic and treatment equipment, smart home transparent panels, or outdoor transparent instruments and equipment.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. Overall costs have been significantly reduced. This invention uses abundant and inexpensive zinc and tin as raw materials to replace the expensive rare metal indium in traditional transparent electrothermal materials. Zinc and tin are both common metals with high abundance in the Earth's crust, and their raw material costs are far lower than those of indium. Simultaneously, the roll-to-roll magnetron sputtering process enables continuous large-scale production, significantly improving production efficiency compared to traditional single-wafer intermittent processes, and significantly reducing energy consumption and labor costs.

[0023] 2. Industry-leading electrothermal stability This invention fundamentally reduces the defect density and stabilizes the film structure by synergistically controlling a specific ZnO:SnO2 molar ratio window of 6:4 to 8:2, oxygen sputtering (O2 2 to 5 sccm), and air annealing (80 to 200°C). After 1000 hours of constant-temperature energization at 100°C, the resistance change rate does not exceed 5% (the optimal rate in the example is only 2.3%); after 100 cycles of high and low temperature cycling from -40°C to 80°C, the resistance change rate does not exceed 8% (the optimal rate in the example is only 4.8%). In comparison, traditional ITO materials exhibit resistance change rates of 12.3% and 15.7% under the same testing conditions, while carbon-based materials show resistance drift rates as high as 15% to 30%. The electrothermal stability of this invention is significantly superior to existing transparent electrothermal materials, extending the service life by 2 to 3 times.

[0024] 3. A perfect balance between light transmittance and conductivity. This invention achieves a transmittance of ZTO transparent electrothermal film of no less than 85% (up to 90%) at 550nm visible light by precisely controlling the target material ratio and film thickness, while keeping the sheet resistance within a practical range of 10 to 50Ω / □. This ensures both excellent transparency and efficient electrothermal conversion, solving the industry problem of carbon-based materials being unable to balance transmittance and conductivity.

[0025] 4. The process is simple and easy to mass-produce industrially. This invention employs a roll-to-roll magnetron sputtering process, requiring only three main steps: substrate pretreatment, sputtering deposition, and annealing. Parameters are easily controlled, and operation is simple. A single production line can achieve large-scale continuous production, significantly increasing capacity. Furthermore, this process is adaptable to various flexible substrates such as PET, PI, and PC, as well as rigid substrates like glass, with short changeover and debugging times, facilitating rapid industrialization.

[0026] 5. Wide applicability The transparent electrothermal material of this invention can be widely used in various transparent heating scenarios such as architectural glass, defrosting and defogging of automotive / high-speed rail / aircraft windshields, constant temperature protection of electronic display panels, heating of medical transparent components, and smart home panels. Moreover, under the same formulation system, different power density requirements from low power (building constant temperature) to medium and high power (automotive rapid defrosting) can be met simply by adjusting the film thickness, resulting in high application flexibility. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] Figure 1 This is a schematic diagram of the cross-sectional structure of the transparent electrothermal material prepared in Example 1 of the present invention.

[0029] Figure 2This is a schematic diagram of the cross-sectional structure of the transparent electrothermal material with a silicon oxide transition layer prepared in Example 2 of the present invention.

[0030] Figure 3 This is a schematic diagram of the cross-sectional structure of the transparent electrothermal material with a protective layer prepared in Example 4 of the present invention.

[0031] Figure 4 This is a schematic cross-sectional view of the transparent electrothermal material with a silicon oxide transition layer and a protective layer prepared in Example 5 of the present invention.

[0032] Figure 5 This is a schematic diagram of the process flow of the roll-to-roll magnetron sputtering preparation method of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the core technical mechanism, material formulation, synergistic effects of components, distribution range of each component, preparation process, and applications of this invention will be systematically described below, and further detailed in conjunction with specific embodiments and comparative examples. It should be understood that the following embodiments are only for explaining this invention and are not intended to limit the scope of protection of this invention. Experimental methods not specifying specific conditions in the embodiments are generally carried out under conventional conditions or conditions recommended by the manufacturer.

[0034] Addressing the contradictions in the existing transparent electrothermal materials field regarding cost versus performance (high cost of ITO systems), light transmittance versus conductivity (carbon-based systems cannot achieve both), and high performance versus easy mass production (traditional processes are inefficient and inconsistent), this invention systematically innovates at both the material system and preparation process levels, resulting in the following core technological mechanisms: (I) Band-defect synergistic regulation mechanism of zinc tin oxide (ZTO) material system The fundamental principle behind achieving a balance between high transmittance and high conductivity in transparent conductive oxide (TCO) materials lies in their wide bandgap semiconductor characteristics—the bandgap is typically greater than 3.1 eV, ensuring that the material has no intrinsic absorption in the visible light region (photon energy 1.6–3.1 eV), thus maintaining high transmittance; simultaneously, a high concentration (10) of [unclear] is introduced through a non-stoichiometric method. 20 ~10 21 cm -3 Shallow donor defects (oxygen vacancies and interstitial metal atoms) on the order of magnitude provide ample charge carriers, enabling low resistivity.

[0035] However, while increasing the carrier density, excessively high oxygen vacancy concentration also introduces a large number of deep energy level defect states into the band gap. These deep energy levels undergo slow reconstruction and migration under the influence of long-term thermal and electric fields, resulting in continuous resistance drift, which constitutes the physical root cause of the poor long-term stability of existing transparent electrothermal materials.

[0036] This invention replaces the traditional In₂O₃-SnO₂ (ITO) system with a ZnO-SnO₂ binary system. Both ZnO and SnO₂ are wide bandgap semiconductors (ZnO approximately 3.37 eV, SnO₂ approximately 3.6 eV), and the resulting ZTO solid solution has a bandgap of 3.3–3.5 eV, far exceeding the photon energy of visible light, ensuring high transmittance. Regarding conductivity, Sn… 4+ Partially replaces Zn in the ZnO lattice 2+ Donor doping at specific locations provides additional electrons; simultaneously, the non-equilibrium process of sputtering deposition introduces a suitable amount of oxygen vacancies into the film, and both work together to provide sufficient carrier concentration. Compared to ITO, Zn in ZTO... 2+ and Sn 4+ Difference in ionic radius (Zn) 2+ Approximately 0.74 Å, Sn 4+ (approximately 0.69 Å) is less than In 3+ (approximately 0.80 Å) and Sn 4+ Due to the difference in crystal structure, the ZTO film exhibits less lattice distortion and higher lattice stability, resulting in lower defect relaxation and migration under long-term service conditions and superior electrical resistance stability. Actual measurements show that the resistivity change rate of the ZTO film of this invention can be controlled below 5% after 1000 hours of energization at 100°C, significantly better than the 12.3% of existing ITO materials.

[0037] (II) Thin film stabilization mechanism of oxygen sputtering-air annealing combined process Conventional transparent conductive oxide sputtering processes mostly use pure Ar atmosphere deposition, relying on the natural oxidation of the film in the air after deposition to adjust the oxygen content. This process has inherent defects: (1) a considerable proportion of the large number of oxygen vacancies formed during the deposition stage constitute irreversible deep-level defects, which cannot be completely repaired by subsequent oxidation; (2) the natural oxidation process is uncontrollable, and the oxygen concentration gradient in the depth direction of the film is uneven, causing the resistance to drift continuously during service.

[0038] This invention employs a combined process of "oxygen sputtering-air annealing": (1) During the sputtering stage, an appropriate amount of O2 is introduced simultaneously, so that the film approaches the stoichiometry during deposition, the oxide network is basically perfected during the film formation stage, and the initial defect state density is significantly lower than that of pure Ar deposited films; (2) After deposition, air atmosphere annealing (80-200℃) provides thermal activation energy, further relaxing the small amount of residual defects generated during sputtering, promoting the perfection and densification of grain boundaries, and using O2 in the air to repair residual oxygen vacancies on the surface and near the surface. This dual strategy of "deposition end control + post-annealing repair" reduces the defect density from the root and stabilizes the film structure, achieving excellent electrothermal stability.

[0039] (III) Coordinated optimization of proportioning window and process window The technical solution of this invention does not simply adopt the ZTO material system, but determines the synergistic matching relationship between a specific ratio window of ZnO:SnO2=6:4~8:2 and a specific process window of oxygen sputtering (O2 2~5sccm) and air annealing (80~200℃).

[0040] The ZnO:SnO2 ratio determines the intrinsic defect formation energy and chemical potential window of the thin film—the ZnO-rich region (6:4–8:2) has a lower oxygen vacancy formation energy and a wider thermodynamic stability range. Oxygen sputtering further suppresses the formation of uncontrollable deep-level defects based on this favorable intrinsic characteristic. Air atmosphere annealing repairs residual structural defects in the final stage. These three elements constitute a complete "ratio-atmosphere-temperature" synergistic control chain; any deviation in any link will lead to significant performance degradation. This systematic synergistic matching enables the present invention to effectively solve the technical problems existing in the prior art.

[0041] Based on the above-mentioned core technology mechanism, this invention provides specific implementation schemes in four aspects: zinc tin oxide (ZTO) based transparent electrothermal film, transparent electrothermal material containing the film, its preparation method, and its application in transparent heating scenarios.

[0042] (1) Zinc tin oxide transparent electrothermal film The main components of the zinc-tin oxide transparent electrothermal film provided in this invention include a composite oxide of zinc oxide (ZnO) and tin oxide (SnO2).

[0043] Zinc oxide and tin oxide are the main components of the ZTO transparent electrothermal film of this invention, and together they constitute the wide bandgap semiconductor framework of the film. The relative ratio of the two—the molar ratio of ZnO to SnO2—is 6:4 to 8:2.

[0044] Within this ratio range, ZnO is the main phase (60%–80% molar percentage), forming the wurtzite-type crystal structure framework and providing a wide bandgap, high transmittance, and the main electron transport channels; SnO2 is the dopant phase (20%–40% molar percentage), Sn 4+ Zn enters the ZnO lattice as a substitutional dopant 2+ Position, each Sn added 4+ This involves providing an additional free electron while introducing appropriate lattice stress, promoting the stable formation of oxygen vacancies during sputtering deposition. Together, these factors regulate the carrier concentration of the thin film to 10-1. 20 ~10 21 cm -3 The optimal range is determined so that the sheet resistance is controlled within a practical range of 10 to 50 Ω / □.

[0045] The zinc-tin oxide transparent electrothermal film provided by this invention has a thickness controlled between 50 and 200 nm. This thickness range, in conjunction with the aforementioned component ratio, determines the overall photoelectric performance of the film: 50 nm is the lower limit for a sheet resistance not exceeding 50 Ω / □; 200 nm is the upper limit for a visible light transmittance not less than 85%. Further, this thickness is preferably between 80 and 150 nm.

[0046] Furthermore, the ZTO target used for sputtering deposition in the zinc-tin oxide transparent electrothermal thin film provided by this invention has a density of not less than 95% (theoretical density percentage) and a purity of not less than 99.9% (mass content). A target density of ≥95% ensures stable glow discharge and uniform sputtering on the target surface during sputtering, reducing the splashing of micron-sized particles ("microparticles"); a purity of ≥99.9% avoids the introduction of deep-energy impurities such as Fe and Cu into the thin film, ensuring transmittance and stability.

[0047] The components in the zinc-tin oxide transparent electrothermal thin film material formulation of this invention are not simply superimposed, but work together through the following synergistic mechanism to achieve a balance of low cost, high light transmittance, high electrothermal stability, and easy mass production: First, the electronic synergy between ZnO and SnO2: Both ZnO and SnO2 are wide-bandgap n-type semiconductors. After they are combined to form a solid solution, the bandgap width is maintained above 3.3 eV, ensuring high light transmittance. 4+ For Zn 2+ Substitutional doping (Sn-Zn donor defects) is the main source of n-type conductivity in thin films. Simultaneously, a small number of oxygen vacancies participate in conduction as shallow donors. There is a mutually restrictive physical balance between the Sn doping amount and the oxygen vacancy concentration: increasing the SnO2 ratio increases the donor doping concentration, but excessive SnO2 (e.g., exceeding the 8:2 range) introduces a large amount of lattice distortion and locally SnO2-rich second phases into the ZnO lattice. These second phases and distortion regions become electron scattering centers and deep-level defect sources, not only reducing mobility but also acting as "source-well" sites for defect aggregation and diffusion during long-term service, leading to resistance drift. The 6:4 to 8:2 ratio given in this invention falls precisely within the optimal balance range between doping benefits and lattice stability.

[0048] Furthermore, the ternary synergy of formulation, thickness, and performance: the sheet resistance R of the thin film is related to the resistivity ρ and the film thickness d by the formula R = ρ / d. Within the formulation window of this invention, the resistivity ρ is stable at approximately (2~8) × 10⁻⁶. -4Within the Ω·cm range. When the film thickness is 50nm, the sheet resistance is approximately 50Ω / □, meeting conventional heating requirements while maintaining a transmittance of approximately 90%. When the film thickness is 200nm, the sheet resistance is approximately 10Ω / □, meeting the requirements for rapid high-power heating, while the transmittance remains at approximately 85%. The synergistic effect of thickness and formulation allows the material of this invention to meet various application scenarios, from low-power (constant temperature control of architectural glass) to medium-to-high-power (rapid defrosting of automotive windshields), simply by adjusting the deposition thickness within a unified formulation system.

[0049] Furthermore, the introduction of a silicon oxide transition layer synergistically enhances film adhesion at the interface: In flexible substrate applications, a chemically bonded gradient interface of "substrate-transition layer-ZTO film" is formed by introducing a silicon oxide transition layer. Silicon oxide forms Si-OC covalent bonds with the polar groups on the surface of the organic substrate, and Si-O-Zn covalent bonds with the ZTO film. This continuity of chemical bonding eliminates the weaknesses of physically adsorbed interfaces, transforming interfacial bonding from physical adsorption to chemical bonding. This significantly improves adhesion from level 3 (without the transition layer) to level 1, effectively solving the film peeling problem of flexible devices during bending and thermal cycling.

[0050] Furthermore, the introduction of a protective layer and a functional layer synergistically enhances durability: By introducing a SiO2 or Al2O3 protective layer and a ZTO functional layer, a hierarchical structure with functional separation is formed. The inner ZTO layer undertakes the electrothermal conversion function, while the outer protective layer undertakes the function of resisting environmental corrosion. The protective layer isolates the ZTO film from direct contact with external O2, H2O, and other corrosive substances, inhibiting surface oxidation and adsorption reactions during service and extending the maintenance time of electrothermal stability. At the same time, since the protective layer and the ZTO film are both oxide systems, they have good interface compatibility and do not introduce obvious optical reflection interfaces.

[0051] The following is a detailed description of the formulation of the zinc tin oxide transparent electrothermal film provided by this invention.

[0052] Zinc oxide (ZnO) serves as the main phase component of the ZTO thin film of this invention, constituting the crystal structure framework of the film. In the thin film of this invention, the molar proportion of ZnO is 60%–80% (i.e., ZnO:SnO2 = 6:4 to 8:2). When the molar proportion of ZnO is 60%–80% (i.e., ZnO:SnO2 = 6:4 to 8:2), the thin film is within its "optimal performance window," exhibiting a transmittance ≥85%, a sheet resistance of 10–50 Ω / □, and excellent long-term stability.

[0053] If the molar ratio of ZnO is less than 60% (i.e., ZnO:SnO2 < 6:4, SnO2 is more than 40%): Excess SnO2 leads to increased lattice distortion and the formation of SnO2-enriched second phases. These second phases have a different refractive index than the main ZnO phase and become light scattering centers, causing the transmittance to drop below 80%. At the same time, the second phase interface is prone to aggregation under thermal field, resulting in increased resistance drift.

[0054] If the molar ratio of ZnO is higher than 80% (i.e., ZnO:SnO2 > 8:2): Sn 4+ Insufficient donor doping concentration and limited oxygen vacancy compensation lead to a significant decrease in carrier density and a sharp increase in sheet resistance to over 100 Ω / □, which fails to meet the conductivity requirements for electrothermal conversion.

[0055] Tin oxide (SnO2) is primarily used as a donor dopant in this invention. 4+ Replacement of Zn in ZnO lattice 2+ Sites are formed to create Sn-Zn·· double-charged donor defects, providing additional free electrons to the thin film and significantly reducing resistivity. In the thin film of this invention, the molar proportion of SnO2 is 20%–40% (i.e., ZnO:SnO2 = 6:4 to 8:2). The appropriate donor doping concentration, combined with the oxygen vacancy concentration, effectively regulates the carrier concentration to 102. 20 ~10 21 cm -3 The optimal range has moderate resistance and long-term stability.

[0056] If the molar percentage of SnO2 is less than 20%, the donor doping concentration is insufficient and the sheet resistance is too high.

[0057] If the molar percentage of SnO2 is higher than 40%, excessive doping will lead to lattice distortion, and both transmittance and stability will decrease.

[0058] The thickness of the formed zinc-tin oxide transparent electrothermal film is directly related to its sheet resistance and transmittance. Given a constant resistivity ρ, increasing the film thickness d decreases the sheet resistance R=ρ / d (improving conductivity), but increases the optical path length and decreases the transmittance. In the film of this invention, the film thickness is controlled between 50 and 200 nm, allowing for a sheet resistance in the range of 10–50 Ω / □ and a transmittance ≥85% to be simultaneously satisfied, placing it within the synergistic range of photoelectric performance.

[0059] If the film thickness is less than 50nm: the sheet resistance is too high (the film is too thin) and the heating power requirement cannot be met.

[0060] If the film thickness is greater than 200nm: the transmittance is less than 85% (the film is too thick), which cannot meet the requirements of transparent applications.

[0061] Based on this, as a further optimization, the film thickness is preferably 80-150 nm: both transmittance and sheet resistance are in the optimal range (transmittance ≥86%, sheet resistance 15-35Ω / □).

[0062] An optional silicon oxide transition layer (SiO2) is disposed between the flexible substrate and the ZTO film, serving as a "chemical bridging layer" to significantly improve the adhesion of the ZTO film to the flexible substrate and prevent the film from peeling off during repeated bending and thermal cycling.

[0063] As further explained, the silicon oxide transition layer (SiO2) is preferably formed by reactive magnetron sputtering deposition, and the thickness of the formed layer is controlled at 10-15 nm. At this time, the transition layer can be continuous, the chemical bonding is sufficient, and the adhesion reaches level 1.

[0064] If the thickness of the silicon oxide transition layer is less than 10 nm, the transition layer is not continuous enough, and the adhesion enhancement effect is insufficient.

[0065] If the thickness of the silicon oxide transition layer is greater than 15nm, the internal stress of the transition layer increases, and the marginal benefit of improved adhesion decreases.

[0066] Similarly, a protective layer (SiO2 or Al2O3), which is also an optional component, is used to be set on the side of the ZTO film away from the substrate to enhance wear resistance, oxidation resistance and moisture resistance, and extend service life.

[0067] As further explanation, the protective layer is selected from either SiO2 or Al2O3, with SiO2 emphasizing light transmittance and scratch resistance, and Al2O3 emphasizing dense protection and high-temperature stability.

[0068] Furthermore, the thickness of the protective layer is controlled within 10–30 nm, thereby forming a continuous and dense protective layer with good protective effect and without affecting photoelectric performance.

[0069] If the thickness of the protective layer is less than 10nm, the resulting protective layer will not be continuous enough, and the protective effect will be poor.

[0070] If the thickness of the protective layer is greater than 30nm, it will cause increased internal stress and make it prone to cracking, and may affect the light transmittance due to light interference.

[0071] Regarding the aforementioned transparent electrothermal material, this invention further provides a corresponding preparation method.

[0072] This invention employs roll-to-roll magnetron sputtering to prepare transparent electrothermal materials. As a vacuum thin-film deposition technology capable of large-scale continuous production, this process utilizes high-energy argon ions (Ar) generated by glow discharge in a low-vacuum environment. +The target surface is bombarded to sputter out the target atoms / molecules, which are then deposited on a continuously moving substrate to form a thin film. At the same time, the roll-to-roll mode transports the flexible or sheet-like substrate in a continuous roll form in a vacuum, and it passes through multiple functional stations such as pretreatment, sputtering deposition, and post-treatment in sequence to achieve assembly line production.

[0073] The following details the process by which the present invention prepares transparent electrothermal materials using roll-to-roll magnetron sputtering.

[0074] See Figure 5 The process of preparing transparent electrothermal materials using roll-to-roll magnetron sputtering in this invention specifically includes the following steps: Step S1: Provide a substrate and perform surface pretreatment on the substrate.

[0075] The substrate serves as the thin film deposition carrier in this process. Flexible transparent polymer films (such as PET / PI / PC) or rigid transparent glass are selected based on the application requirements of the final product.

[0076] The surface pretreatment here consists of two sub-steps: ultrasonic cleaning and plasma surface treatment, which are functionally sequential. Sub-step S1-1: Ultrasonic cleaning In this step, the substrate is immersed in a mixed solution of deionized water and anhydrous ethanol and cleaned by ultrasonic cleaning. After cleaning, it is dried by air drying or air drying.

[0077] Sub-step S1-2: Plasma surface treatment This step involves placing the cleaned substrate into a plasma treatment chamber and performing plasma treatment in a pure argon atmosphere (purity ≥ 99.999%). After treatment, the substrate is immediately transferred into the sputtering chamber in a transfer section protected by low dew point dry air.

[0078] This step involves high-energy Ar in the plasma. + The bombardment of the substrate surface by ions and neutral Ar particles produces a dual effect: first, physical sputtering cleaning removes any molecular-level organic adsorption layers that may remain after ultrasonic cleaning; second, surface chemical activation, where high-energy particle bombardment breaks the C-C and CH bonds in the polymer chains on the substrate surface, generating dangling bonds and free radical sites. These sites react with trace amounts of residual O2 or H2O within the cavity, generating polar oxygen-containing functional groups (such as CO, C=O, -OH, etc.) in situ. These polar groups significantly increase the surface energy of the substrate, improving the wetting, spreading, and nucleation behavior of subsequent sputtered particles.

[0079] Step S2: Roll-to-roll magnetron sputtering deposition of zinc tin oxide thin films.

[0080] This step enables the deposition of ZTO thin films on a continuously moving substrate. Prior to sputtering deposition, the target is pre-sputtered and cleaned.

[0081] Sub-step S2-0: Pre-sputtering cleaning of the target material.

[0082] This step is optional; it involves evacuating the sputtering chamber to a vacuum level of ≤5×10⁻⁶. -4 After Pa, high-purity argon gas (purity ≥99.999%, flow rate 20-30 sccm) is introduced, and the ZTO target is pre-sputtered and cleaned with a power of 200-300W for 5-10 minutes. The material generated by pre-sputtering is collected by a baffle and does not deposit on the substrate.

[0083] During storage and loading, a natural oxide layer inevitably forms on the surface of the target material, adsorbing environmental pollutants. This pre-sputtering cleaning step utilizes Ar... + Ion bombardment of the target surface preferentially removes the surface oxide and contaminant layers by sputtering, exposing a fresh target surface with uniform composition. Vacuum degree ≤ 5 × 10⁻⁶ -4 The background of Pa ensures that the cleaning process is not contaminated by residual gases.

[0084] Sub-step S2-1: Sputter deposition of ZTO thin film.

[0085] This step involves placing the pretreated substrate (or substrate with a pre-deposited transition layer, see below) into the sputtering chamber of a roll-to-roll magnetron sputtering system. The sputtering chamber contains a zinc-tin oxide target with a zinc oxide to tin oxide molar ratio of 6:4 to 8:2, a density ≥95%, and a purity ≥99.9%. A mixed sputtering atmosphere of high-purity argon (≥99.999%) and high-purity oxygen (≥99.99%) is introduced into the sputtering chamber, with an argon flow rate of 30–50 sccm and an oxygen flow rate of 2–5 sccm. The vacuum level of the sputtering chamber is maintained at 1 × 10⁻⁶ by adjusting the throttle valve opening. -3 ~5×10 -3 Pa. Turn on the DC pulse or RF sputtering power supply at a power density of 2.5–4.5 W / cm². 2 Sputter deposition is performed. The sputtering distance (i.e., the distance from the target surface to the substrate) is set to 8–12 cm. The substrate is driven by an unwinding and rewinding mechanism, passing through the sputtering area at a constant speed. The substrate temperature is controlled at 25–80°C by a back-side cooling / heating roller.

[0086] Under the above conditions, a ZTO transparent electrothermal film with a thickness of 50–200 nm was deposited on the substrate.

[0087] Sub-step S2-2: Deposition of silicon oxide transition layer.

[0088] This step is optional and applicable to flexible substrates. When the substrate is a flexible transparent polymer film, this step is performed before step S2-1. A silicon target (purity ≥99.999%) is installed at the upstream position of the sputtering chamber. Pure argon gas (purity ≥99.999%, flow rate 25–35 sccm) is introduced into the chamber. A small amount of O2 (e.g., flow rate 0.5–2 sccm) can be introduced as needed to compensate for the oxygen saturation of the silicon oxide. The power density is 2.0–3.0 W / cm³. 2 Reactive sputtering is performed at a substrate moving speed of 1.0–1.5 m / min to deposit a silicon oxide transition layer with a nominal thickness of 10–15 nm on the substrate surface.

[0089] This step forms the silicon oxide transition layer using a lower power density than ZTO sputtering to protect the flexible substrate from excessive bombardment by high-energy particles. After deposition, the substrate immediately enters the ZTO sputtering deposition process at the next station on the same production line. The two stations are transported in a vacuum or low dew point (≤-40℃) inert gas protective environment to ensure that the surface of the transition layer is not contaminated and to ensure a good chemical bonding interface with the subsequent ZTO layer.

[0090] Here, a transition layer is first formed in step S2-2, followed by the formation of a ZTO thin film in step S2-1, thus forming a continuous deposition sequence. The active Si-O bonds on the surface of the transition layer react with the subsequently arriving Zn, Sn, and O particles to form Si-O-Zn and Si-O-Sn chemical bonds, firmly anchoring the ZTO thin film to the substrate surface. This solves the technical problem of poor adhesion of flexible substrates from the perspective of interfacial chemistry.

[0091] Step S3: Annealing.

[0092] The substrate with ZTO film deposited in step S2 is fed online into the annealing furnace section.

[0093] Specifically, the annealing atmosphere is air (natural convection), the annealing temperature is 80-200℃, the annealing time is 20-90 minutes (the effective residence time of the substrate in the constant temperature section of the furnace), and after annealing, the substrate is naturally cooled or controlled cooled to below 40℃ in the cooling section.

[0094] Step S4: Deposition of protective layer.

[0095] As an optional follow-up step, after annealing and cooling, the substrate is sent back into the sputtering chamber (or a protective layer deposition station is configured on a continuous production line) to deposit a SiO2 or Al2O3 protective layer on the ZTO thin film surface using magnetron sputtering.

[0096] Specifically, in this step, the sputtering power is 180–200 W, the argon flow rate is 25–30 sccm, the substrate moving speed is 1.5–2 m / min, and the deposition thickness is 10–30 nm. After the protective layer is deposited, supplementary annealing (at a temperature of 120–140 °C for 20–30 min in air atmosphere) can be performed as needed to eliminate internal stress in the protective layer.

[0097] In this step, the protective layer deposition uses radio frequency or intermediate frequency magnetron sputtering to reduce plasma damage to the underlying ZTO film. After the protective layer deposition is completed, supplementary annealing (120-140°C, 20-30 min, air atmosphere) can be performed as needed to eliminate internal stress in the protective layer.

[0098] The preparation process based on the above scheme realizes the following progressive steps: substrate preparation (S1: cleaning + activation) → interface engineering (S2-2 optional: transition layer) → functional layer deposition (S2-1: ZTO thin film) → structural stabilization (S3: annealing) → surface protection (optional: protective layer). Each step is connected to the previous one. The previous step creates a suitable surface state and structural basis for the next step, and the next step adds functions on the basis of the previous step, forming a complete progressive preparation scheme of "surface preparation → interface bonding → function creation → structural improvement → durable protection".

[0099] The ZTO transparent electrothermal film and transparent electrothermal material obtained based on the aforementioned material formulation and preparation process have comprehensive advantages, including low cost, high light transmittance (≥85%), suitable sheet resistance (10~50Ω / □), excellent long-term electrothermal stability (resistance change rate ≤5% after 1000h of energization at 100℃, resistance change rate ≤8% after 100 cycles of high and low temperatures), good adhesion (≤1 grade), and continuous mass production capability. They are widely used in the following transparent heating scenarios: (1) Construction field: By depositing the ZTO transparent electrothermal film of the present invention onto the surface of building curtain walls or window glass and connecting it to a low-voltage (such as 24V or 48V DC) power supply system, the glass can achieve self-heating function, which can be used for energy-saving heating of buildings in cold regions, anti-condensation and anti-icing of glass curtain walls, etc. Compared with existing screen-printed metal heating wires, the film of the present invention is transparent and has no visual obstruction, heats evenly, and can cover the entire glass surface, with a uniform heat field distribution.

[0100] (2) Transportation field: The ZTO transparent electrothermal film of the present invention is integrated into the windshield or side window glass of automobiles, high-speed trains and airplanes (for example, sandwiched in the PVB interlayer or deposited on the inner surface of the glass). Driven by the vehicle's 12-48V power supply system, the windshield can be quickly defrosted and defogged, replacing the traditional screen-printed tungsten wire or silver paste heating wire, eliminating the problem of driver's vision obstruction and improving safety.

[0101] (3) Electronics field: The ZTO transparent electrothermal film of the present invention is integrated onto the cover glass or polarizer surface of a liquid crystal display panel (LCD), OLED panel or transparent touch screen to provide constant temperature heating function in low temperature environment, ensuring that the liquid crystal material can still respond normally below 0°C, and preventing the display screen from failing in cold outdoor applications.

[0102] (4) Medical field: The material of the present invention can be used for constant temperature heating of medical transparent diagnostic and treatment equipment and sterile transparent protective components, such as anti-fogging of operating room observation windows and transparent doors of constant temperature incubators.

[0103] (5) Other fields: including smart home transparent panels (such as smart mirror anti-fog), outdoor transparent instruments and equipment anti-fog and anti-freeze, etc.

[0104] In the above applications, power density can be flexibly matched by adjusting the ZTO film thickness and driving voltage according to specific heating power requirements. For example, in constant temperature scenarios for architectural glass (power density requirement approximately 200–500 W / m²),... 2 A solution with a film thickness of 80–120 nm and a sheet resistance of approximately 20–40 Ω / □ can be selected; in the scenario of rapid defrosting of automotive windshields (power density requirement of approximately 500–1000 W / m), a solution with a film thickness of 80–120 nm and a sheet resistance of approximately 20–40 Ω / □ can be selected; 2 A film thickness of 150–200 nm and a sheet resistance of approximately 10–20 Ω / □ can be selected.

[0105] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the following examples are only for providing best practice models of the present invention and should not be construed as limiting the scope of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to conventional operating methods and conditions, or according to the conditions recommended by the manufacturer.

[0106] <Ingredients> The sources of the raw materials used in the following examples and comparative examples are as follows: ZTO target material (ZnO:SnO2=7:3, density 96%, purity 99.95%, cylindrical target with diameter 150mm × length 1800mm): self-made; ZTO sputtering target (ZnO:SnO2=6:4, density 95%, purity 99.9%, same specifications): self-made; ZTO sputtering target (ZnO:SnO2=8:2, density 97%, purity 99.98%, same specifications): self-made; ZTO target material (ZnO:SnO2=5:5, density 95%, purity 99.9%, same specifications): self-made (for comparative example); ZTO target material (ZnO:SnO2=9:1, density 95%, purity 99.9%, same specifications): self-made (for comparative example). ITO sputtering target (In2O3:SnO2=9:1, density 98%, purity 99.99%): commercially available (for comparative analysis). PET film (100μm thickness, 91% transmittance @550nm, haze <1%): commercially available; PI film (80μm thickness, 89% transmittance @550nm): Commercially available; PC film (125μm thickness, 90% transmittance @550nm): Commercially available; Ordinary soda-lime glass (1mm thick, polished surface, surface roughness 0.03μm): commercially available; Anhydrous ethanol (analytical grade, purity ≥99.7%): commercially available; Deionized water: homemade (resistivity ≥18MΩ·cm, filtered through a 0.22μm microfiltration membrane); High-purity argon (purity ≥ 99.999%): commercially available; High-purity oxygen (purity ≥ 99.99%): Commercially available.

[0107] <Testing Methods> The transparent electrothermal materials prepared in the following embodiments and comparative examples were subjected to performance tests according to the following methods: (1) Visible light transmittance: The transmittance was measured at a wavelength of 550 nm using an ultraviolet-visible spectrophotometer (integrating sphere accessory). The blank substrate was used as a reference. After subtracting the substrate absorption, 9 points were evenly selected in a 100 mm × 100 mm area for each sample, and the average value was taken. Measurement environment: temperature 23 ± 2 ℃, relative humidity 50 ± 5%.

[0108] (2) Sheet resistance: A four-probe tester was used for measurement. The probe spacing was 1 mm. Nine points were evenly selected in a 3×3 grid within an area of ​​100 mm × 100 mm for each sample. The average value and standard deviation were calculated to evaluate the uniformity. The measurement environment was the same as in (1).

[0109] (3) Adhesion: The adhesion was tested according to GB / T 9286-1998 "Cross-cut Test for Paints and Varnishes". Using a cross-cut tester (1 mm blade spacing, for film thickness ≤ 60 μm), 11 cuts were made perpendicularly to each other in a 100 mm × 100 mm sample area to form 100 1 mm × 1 mm squares, with the cutting depth reaching the substrate surface. After applying the specified tape (peel strength 6.5 N / 25 mm), the tape was peeled off at a uniform speed at a 60° angle. The extent of square detachment was checked under a 5x magnifying glass and rated according to a 0-5 standard, with 0 being the best (the cut edges are completely smooth and no squares have detached).

[0110] (4) Long-term resistance change rate (1000 hours): The sample was cut into strips of 50mm × 100mm. Electrodes were coated with silver paste at both ends along the length (electrode spacing 80mm, coating width 10mm) to ensure good ohmic contact. The sample was placed in a constant temperature drying oven at 100±2℃, and a constant DC voltage (field strength set to 5V / cm) was applied to both electrodes for 1000 hours. Sheet resistance changes were recorded every 24 hours using an online four-probe monitoring device (the heating power was briefly disconnected during measurement and restored after measurement). After the test, the initial sheet resistance R0 and the final sheet resistance R... 1000 Calculate the rate of change of resistance = (R) 1000 -R0) / R0×100%.

[0111] (5) High and low temperature cycling resistance change rate (100 cycles): The sample with the cut and prepared electrodes was placed in a high and low temperature alternating test chamber. The single cycle program was as follows: cooling from room temperature (23℃) to -40℃ at a rate of 3℃ / min and holding for 30min; then heating to 80℃ at a rate of 3℃ / min and holding for 30min; then cooling back to room temperature at a rate of 3℃ / min. This cycle was repeated 100 times. After the cycle was completed, the sample was taken out and placed at room temperature for 2 hours. The sheet resistance was measured and compared with the initial sheet resistance to calculate the resistance change rate.

[0112] Example 1: PET flexible substrate ZTO transparent electrothermal material (no transition layer, no protective layer) (1) Substrate pretreatment: A 100μm thick PET film was cut into rolls 1.0m wide and 500m long. The cut PET film rolls were then mounted onto the unwinding mechanism of a roll-to-roll device. The substrate sequentially passed through an ultrasonic cleaning tank and a plasma treatment chamber. The ultrasonic cleaning solution was a 1:1 volume ratio of deionized water and anhydrous ethanol, with an ultrasonic power of 150W and an ultrasonic treatment time (substrate residence time in the cleaning tank) of 15 minutes. After cleaning, the substrate passed through an air knife drying section to remove the surface liquid film. The substrate then entered the plasma treatment chamber for plasma surface treatment under a pure argon atmosphere (99.999% purity) with an argon flow rate of 15 sccm, a radio frequency (13.56MHz) treatment power of 80W, and a treatment time of 4 minutes (substrate residence time in the plasma chamber). After treatment, the substrate was immediately transferred to the sputtering chamber in a low-dew-point dry air protection section, with an interval of approximately 3 minutes.

[0113] (2) Pre-splash cleaning: A ZTO target (ZnO:SnO2=7:3, density 96%, purity 99.95%) was mounted at the target position of the first sputtering station in the roll-to-roll magnetron sputtering equipment. The length direction of the target (1.8m) was perpendicular to the width direction of the substrate (1.0m), and the sputtering distance was set to 10cm. The sputtering chamber was first evacuated to 3.0×10⁻⁶ by a mechanical pump and a molecular pump. -4 After Pa, high-purity argon gas (99.999% purity, flow rate 25 sccm) is introduced, and the target material is pre-sputtered and cleaned for 8 minutes using a DC pulse power supply of 250W. The material generated during pre-sputtering is collected by a baffle and does not deposit on the substrate.

[0114] (3) Sputter deposition of ZTO thin films: After pre-sputtering cleaning, open the baffle and introduce a mixture of argon and oxygen into the sputtering chamber at a flow rate of 40 sccm and 3 sccm. Adjust the throttle valve opening to stabilize the vacuum level in the sputtering chamber at 2.5 × 10⁻⁶. -3 Pa. Turn on the DC pulse sputtering power supply for the target, power density 3.5 W / cm³. 2 (Corresponding to approximately 7.4kW total power), the substrate is driven by an unwinding mechanism to pass through the sputtering area at a constant speed of 1.2m / min, with a sputtering distance of 10cm. The substrate temperature is maintained at 40±5℃ by a back-side cooling roller. Under these conditions, a ZTO transparent electrothermal film with a nominal thickness of 100nm is deposited on a PET substrate (the thickness is calculated using the product of sputtering power, substrate speed, and target-substrate distance, and verified offline by an optical profilometer; thickness uniformity ≤±5nm).

[0115] (4) Annealing treatment: The substrate deposited in step (3) is fed online into the annealing furnace section. The annealing furnace is filled with air (natural convection), the annealing temperature is 130±5℃, and the annealing time is 45min (the time the substrate stays in the constant temperature section of the furnace). After annealing, the substrate is naturally cooled to below 40℃ through the cooling section and then wound up by the winding mechanism.

[0116] The cross-sectional structure of the transparent electrothermal material prepared in this embodiment is as follows: Figure 1 As shown: It includes a PET flexible substrate 1 and a ZTO transparent electrothermal film 2 disposed thereon.

[0117] Example 2: ZTO transparent electrothermal material with PI flexible substrate and silicon oxide transition layer (1) Substrate pretreatment: The 80 μm thick PI film was cut into rolls 1.0 m wide and 300 m long. Pretreatment was performed according to the conditions of ultrasonic cleaning (ultrasonic power adjusted to 120 W, ultrasonic time 20 min) and plasma treatment (treatment power adjusted to 100 W, treatment time 5 min) in step (1) of Example 1. After treatment, the film was immediately transferred to the sputtering chamber.

[0118] (2) Pre-splash cleaning: The ZTO target (ZnO:SnO2=8:2, density 97%, purity 99.98%) was pre-sputtered and cleaned according to the pre-sputtering cleaning conditions in step (2) of Example 1. The pre-sputtering power was adjusted to 280W and the time was 10min.

[0119] (3) Deposition of silicon oxide transition layer: After pre-sputtering cleaning, a silicon target (99.999% purity) is installed at the first sputtering station (upstream) of the sputtering chamber. Pure argon gas (99.999% purity, flow rate 30 sccm) is introduced, and a small amount of oxygen (flow rate 0.5 sccm) is introduced to compensate for the oxygen content of silicon oxide during reactive sputtering, maintaining a vacuum of 2.0 × 10⁻⁶. -3 Pa. Using an RF power supply at a power density of 2.5 W / cm². 2 Reactive sputtering was performed at a substrate moving speed of 1.2 m / min to deposit a silicon oxide (SiO2) transition layer with a nominal thickness of 12 nm on the PI film surface. The actual thickness of this transition layer was calculated from the deposition rate calibration curve and confirmed by periodic random checks on a substrate using an ellipsometry.

[0120] (4) Sputter deposition of ZTO thin films: The substrate continues to the second sputtering station (downstream), where the ZTO target (ZnO:SnO2=8:2) has already undergone pre-sputtering cleaning. The same sputtering atmosphere (argon 40 sccm, oxygen 3 sccm) and vacuum level (2.5 × 10⁻⁶) as in step (3) of Example 1 are used. -3 Pa), power density (3.5 W / cm³) 2 Based on the target area, the total power was adjusted and the sputtering distance (10cm) was kept at 1.2m / min. A ZTO transparent electrothermal film with a nominal thickness of 80nm was deposited.

[0121] (5) Annealing treatment: Annealing was performed according to the conditions of step (4) in Example 1. The annealing temperature was set to 140°C and the time was 40 min, taking into account the temperature resistance of the PI substrate.

[0122] The cross-sectional structure of the transparent electrothermal material prepared in this embodiment is as follows: Figure 2As shown: It includes a PI flexible substrate 1, a silicon oxide transition layer 3, and a ZTO transparent electrothermal film 2.

[0123] Example 3: ZTO transparent electrothermal material with rigid glass substrate (1) Substrate pretreatment: Plain soda-lime glass (1mm thick, polished, surface roughness 0.03μm) was selected and cut into 500mm×500mm sheets. A glass substrate carrier was placed on a roll-to-roll machine for continuous transport. The glass substrate was sequentially subjected to ultrasonic cleaning and plasma treatment. The ultrasonic cleaning solution was a 1:1 volume ratio of deionized water and anhydrous ethanol, with an ultrasonic power of 120W and a duration of 20 minutes. After cleaning, the substrate was dried with an air knife. Plasma treatment was performed under a pure argon atmosphere at a flow rate of 15 sccm, an RF power of 100W, and a treatment time of 5 minutes. Immediately after treatment, the substrate was transferred to the sputtering chamber.

[0124] (2) Pre-splash cleaning: According to the conditions of step (2) in Example 1, the ZTO target (ZnO:SnO2=6:4, density 95%, purity 99.9%) was pre-sputtered and cleaned with a pre-sputtering power of 250W for 8 minutes.

[0125] (3) Sputter deposition of ZTO thin films: A mixture of argon (40 sccm) and oxygen (4 sccm) was introduced to maintain a vacuum of 3.0 × 10⁻⁶ in the sputtering chamber. - 3 Pa. With a power density of 3.5 W / cm³ 2 Sputtering deposition was performed with a substrate moving speed of 0.8 m / min, a sputtering distance of 10 cm, and the substrate temperature was controlled at 50 °C by a back heating plate, resulting in a ZTO transparent electrothermal film with a nominal thickness of 150 nm.

[0126] (4) Annealing treatment: The deposited substrate is fed into an annealing furnace online and annealed at 140°C for 50 minutes in an air atmosphere. After being naturally cooled to room temperature in the furnace cooling section, it is unloaded.

[0127] Example 4: ZTO transparent electrothermal material on PET flexible substrate with SiO2 protective layer After the ZTO film deposition in step (3) and the annealing in step (4) of Example 1 are completed, the wound substrate is remounted on the roll-to-roll equipment and a protective layer is deposited at the third sputtering station.

[0128] Protective layer deposition process: SiO2 target material (99.99% purity) was used, pure argon gas was introduced into the sputtering chamber (flow rate 28 sccm), and the RF sputtering power was 190W (corresponding to a power density of approximately 2.7W / cm³). 2 The substrate moving speed was 1.8 m / min, the sputtering distance was 10 cm, and a SiO2 protective layer with a nominal thickness of 20 nm was deposited. After the protective layer was deposited, it was annealed again at 120 °C in air for 20 min to relieve the stress of the protective layer.

[0129] The cross-sectional structure of the transparent electrothermal material prepared in this embodiment is as follows: Figure 3 As shown: It includes a PET flexible substrate 1, a ZTO transparent electrothermal film 2, and a SiO2 protective layer 4.

[0130] Example 5: ZTO transparent electrothermal material with PI flexible substrate and silicon oxide transition layer and Al2O3 protective layer Based on steps (3) of Example 2 (depositing a silicon oxide transition layer), (4) of Example 2 (depositing a ZTO thin film), and (5) of Example 2 (annealing), a protective layer deposition step is added: Using an Al2O3 target (99.99% purity), pure argon gas (flow rate 28 sccm) was introduced into the sputtering chamber. The RF sputtering power was 190 W, and the substrate movement speed was 1.8 m / min. An Al2O3 protective layer with a nominal thickness of 15 nm was deposited. After the protective layer was deposited, it was annealed at 130 °C for 20 min in air.

[0131] The cross-sectional structure of the transparent electrothermal material prepared in this embodiment is as follows: Figure 4 As shown: It includes a PI flexible substrate 1, a silicon oxide transition layer 3, a ZTO transparent electrothermal film 2, and an Al2O3 protective layer 4.

[0132] Example 6: ZTO transparent electrothermal material with a PC flexible substrate and SiO2 protective layer Following the process of Example 4, the substrate was replaced with a 125 μm thick PC film. During ZTO film sputtering deposition, the substrate temperature was controlled at 35°C (because the Tg of PC is approximately 145°C, and the heat distortion temperature is approximately 130°C; a lower substrate temperature was controlled to prevent heat distortion accumulation), and the annealing temperature was adjusted to 120°C for 60 minutes. All other conditions were the same as in Example 4.

[0133] Example 7: ZTO transparent electrothermal material with a glass rigid substrate and SiO2 protective layer Following the process combinations of Examples 3 and 4, a ZTO thin film was deposited on a glass substrate (under the conditions of Example 3), followed by annealing, and then a SiO2 protective layer was deposited (under the conditions of Example 4). The annealing temperature after the protective layer deposition was 140°C, and the time was 30 min.

[0134] Example 8: Low-thickness ZTO transparent electrothermal film Following the basic process of Example 1, the ZTO thin film deposition thickness was adjusted to 50 nm. This was achieved by increasing the substrate transfer speed to 2.0 m / min (while other parameters remained unchanged). The sputtering target was ZnO:SnO2 = 7:3, the Ar flow rate was 40 sccm, the O2 flow rate was 3 sccm, and the power density was 3.5 W / cm³. 2 Annealing temperature 130℃, time 45min. Substrate is PET film (100μm).

[0135] Example 9: High-thickness ZTO transparent electrothermal film Referring to the basic process of Example 3, the ZTO thin film deposition thickness was adjusted to 200 nm. This was achieved by reducing the substrate transfer speed to 0.5 m / min (other parameters remained unchanged). The sputtering target was ZnO:SnO2 = 6:4, Ar flow rate was 40 sccm, O2 flow rate was 4 sccm, and power density was 3.5 W / cm³. 2 Annealing temperature 140℃, time 50min. Substrate is glass (1mm).

[0136] Scale settings instructions To illustrate the necessity of the technical features of this invention and the significance of its defined scope, the following comparative examples are provided, comparing deviations in key parameters such as the ZnO:SnO2 molar ratio and oxygen flow rate with existing technologies.

[0137] Comparative Example 1: The molar ratio of ZnO:SnO2 was below the lower limit (5:5). Following the process conditions of Example 1, only the ZTO target was replaced with ZnO:SnO2 = 5:5 (density 95%, purity 99.9%). PET substrate, sputtering deposition thickness 100 nm, Ar flow rate 40 sccm, O2 flow rate 3 sccm, power density 3.5 W / cm³. 2 Annealing temperature 130℃, time 45min.

[0138] Comparative Example 2: The molar ratio of ZnO:SnO2 is higher than the upper limit (9:1). Following the process conditions of Example 1, only the ZTO target material was replaced with ZnO:SnO2 = 9:1 (density 95%, purity 99.9%). All other conditions were the same as in Comparative Example 1.

[0139] Comparative Example 3: Sputtered oxygen flow rate exceeded the upper limit (10 sccm) Referring to the process conditions of Example 1, only the oxygen flow rate during sputtering was adjusted to 10 sccm (O2 ratio approximately 20%), while the argon flow rate was maintained at 40 sccm. All other conditions were the same as in Example 1.

[0140] Comparative Example 4: Sputtering atmosphere was pure argon (O2 flow rate = 0). Referring to the process conditions of Example 1, only the oxygen passage was shut off, and the sputtering atmosphere was pure argon (Ar flow rate 40 sccm). The remaining conditions were the same as in Example 1.

[0141] Comparative Example 5: Existing ITO materials (conventional magnetron sputtering) Commercially available ITO targets (In₂O₃:SnO₂ = 9:1, density 98%, purity 99.99%) were used for deposition on a conventional single-wafer magnetron sputtering system. Sputtering conditions: pure Ar atmosphere (Ar flow rate 50 sccm), sputtering chamber vacuum 3.0 × 10⁻⁶. -3 Pa, DC sputtering power density 3.0 W / cm³ 2 The substrate was not actively heated (it naturally heated to approximately 60°C during deposition due to plasma radiation), the deposition thickness was 100 nm, and it was annealed at 150°C for 30 min in air atmosphere after deposition. The substrate was a PET film (100 μm).

[0142] Table 1 compares the key process parameters of the examples and comparative examples. Table 1

[0143] See Table 2, which summarizes the performance test data of the above embodiments and comparative examples.

[0144] Table 2 Performance test results of each embodiment and comparative example

[0145] Results Analysis (1) The importance of the proportions: Example 1 (ZnO:SnO2=7:3) exhibits excellent overall performance: 88% transmittance, 25Ω / □ sheet resistance, and a long-term resistance change rate of only 3.2%. In contrast, Comparative Example 1 (5:5) shows a sharp drop in transmittance to 78% and a significant deterioration in electrothermal stability (9.5% resistance change rate over 1000 hours). This is attributed to excessive SnO2 leading to increased lattice distortion, introducing light scattering centers, and increasing the structural instability of the film under thermal conditions. Comparative Example 2 (9:1) shows acceptable transmittance (89%), but its sheet resistance rises to 120Ω / □, failing to meet the conductivity requirements for electrothermal conversion. This is due to insufficient SnO2 doping, resulting in inadequate donor concentration and a sharp decrease in carrier density. These comparative results demonstrate that a ZnO:SnO2 molar ratio of 6:4 to 8:2 is a necessary condition for achieving optimal synergy among transmittance, conductivity, and stability.

[0146] (2) The criticality of oxygen flow rate: Example 1 (O2 = 3 sccm) exhibits excellent long-term stability. Comparative Example 3 (O2 = 10 sccm) shows a sheet resistance as high as 85 Ω / □ and poor stability, indicating that excess oxygen forms acceptor defects at the grain boundaries and surface of the thin film, reducing carrier mobility and concentration. Comparative Example 4 (pure Ar sputtering) has an initial sheet resistance as low as 12 Ω / □, but its long-term resistance change rate reaches 12.5%, and its high-low temperature cycling change rate is 16.0%, indicating that the thin film produced by pure Ar sputtering is in a metastable state. Under service conditions, the oxygen vacancy concentration continuously changes, resulting in severely insufficient resistance stability. These comparative results demonstrate that an oxygen-containing sputtering atmosphere (O2 2–5 sccm) is a necessary technical characteristic for achieving high stability.

[0147] (3) Validity of thickness range: Examples 8 (50 nm) and 9 (200 nm) both verified that acceptable photoelectric performance can be obtained within the thickness range defined by this invention. In Example 8, due to the lower limit of thickness, the sheet resistance increases to 48 Ω / □, and the uniformity decreases slightly, but it is still within the protection range of this invention, with a transmittance of 90%. In Example 9, the thickness is at the upper limit, the sheet resistance is as low as 14 Ω / □, and the transmittance still maintains a satisfactory level of 85%. These two sets of endpoint examples strongly support the rationality and sufficient disclosure of the 50–200 nm thickness range in the claims.

[0148] (4) Comparison of existing technologies: The relative cost of the target material in Comparative Example 5 (ITO material) is 3.2 times that of Example 1, and the long-term resistance change rate is 12.3% (approximately 3.8 times that of Example 1) and the high and low temperature cycling resistance change rate is 15.7% (approximately 2.4 times that of Example 1). This fully demonstrates the technical effect of the present invention in replacing the expensive In system with a low-cost Zn / Sn system while achieving a breakthrough in electrothermal stability.

[0149] (5) The effects of the transition layer and the protective layer: In Examples 2 and 5, due to the introduction of a silicon oxide transition layer, the adhesion reached level 1 (the surface flatness of the PI substrate is lower than that of glass, so the adhesion rating is slightly lower than level 0 for glass substrates). After introducing a protective layer in Examples 4 to 7, while maintaining the light transmittance and sheet resistance basically unchanged, the long-term stability was further improved (the resistance change rate of Example 4 was 3.0% compared to 3.2% in Example 1). In the supplementary wiping test (500 cycles of wiping with a 500g dry cotton cloth), the surfaces of the examples with the protective layer showed no obvious scratches, and the abrasion resistance was significantly better than that of Example 1 without the protective layer, verifying the protective effect of the protective layer.

[0150] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A transparent electrothermal film of zinc tin oxide, characterized in that, It contains zinc oxide and tin oxide, wherein the molar ratio of zinc oxide to tin oxide is 6:4 to 8:2, and the thickness of the zinc-tin oxide transparent electrothermal film is 50 to 200 nm.

2. The zinc-tin oxide transparent electrothermal film according to claim 1, characterized in that, The zinc tin oxide transparent electrothermal film has a visible light transmittance of not less than 85% at a wavelength of 550 nm and a sheet resistance of 10 to 50 Ω / □.

3. The zinc-tin oxide transparent electrothermal film according to claim 1 or 2, characterized in that, The resistance change rate of the zinc tin oxide transparent electrothermal film after being energized at a constant temperature of 100°C for 1000 hours does not exceed 5%.

4. The zinc-tin oxide transparent electrothermal film according to claim 1 or 2, characterized in that, The resistance change rate of the zinc tin oxide transparent electrothermal film after 100 temperature cycles from -40°C to 80°C does not exceed 8%.

5. A transparent electrothermal material, characterized in that, The invention includes a substrate and a zinc-tin oxide transparent electrothermal film disposed on the substrate. The zinc-tin oxide transparent electrothermal film comprises zinc oxide and tin oxide, wherein the molar ratio of zinc oxide to tin oxide is 6:4 to 8:2, and the thickness of the zinc-tin oxide transparent electrothermal film is 50 to 200 nm.

6. The transparent electrothermal material according to claim 5, characterized in that, The substrate is a transparent substrate.

7. The transparent electrothermal material according to claim 5, characterized in that, An intermediate functional layer is also provided between the substrate and the zinc tin oxide transparent electrothermal film.

8. The transparent electrothermal material according to claim 7, characterized in that, The intermediate functional layer is a silicon oxide transition layer.

9. The transparent electrothermal material according to any one of claims 5 to 8, characterized in that, The zinc tin oxide transparent electrothermal film also has a protective layer on the side opposite to the substrate, and the protective layer material is selected from SiO2 or Al2O3.

10. A method for preparing a transparent electrothermal material, characterized in that, The roll-to-roll magnetron sputtering process includes the following steps: S1. Provide substrate; S2. The substrate is placed in the sputtering chamber of a roll-to-roll magnetron sputtering device. A zinc tin oxide target is provided in the sputtering chamber. The molar ratio of zinc oxide to tin oxide in the target is 6:4 to 8:

2. Sputtering deposition is performed in an oxygen-containing sputtering atmosphere to deposit a zinc tin oxide thin film on the substrate. S3. Anneal the substrate with the zinc tin oxide film deposited on it in an oxygen-containing atmosphere.

11. The preparation method according to claim 10, characterized in that, The oxygen-containing sputtering atmosphere mentioned in step S2 is a mixture of argon and oxygen.

12. The preparation method according to claim 10, characterized in that, Step S1 also includes surface pretreatment of the substrate; the surface pretreatment includes ultrasonic cleaning and plasma surface treatment.

13. The preparation method according to claim 10, characterized in that, When the substrate is a flexible transparent polymer film, step S2 further includes depositing a silicon oxide transition layer before depositing the zinc tin oxide film.

14. The preparation method according to claim 10, characterized in that, Step S3 is followed by depositing a SiO2 or Al2O3 protective layer on the surface of a zinc tin oxide thin film using magnetron sputtering.

15. The application of the zinc tin oxide transparent electrothermal film according to any one of claims 1 to 4 or the transparent electrothermal material according to any one of claims 5 to 9 in a transparent heating device, wherein the transparent heating device is selected from architectural glass, automobile windshields, high-speed rail windshields, aircraft windshields, electronic display panels, medical transparent diagnostic and treatment equipment, smart home transparent panels or outdoor transparent instruments and equipment.

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