Electrothermal film with low resistance and high transparency and preparation method thereof

Abstract

The invention discloses an electrothermal film with low resistance and high transparency and a preparation method thereof. The electrothermal film comprises a substrate layer, a heating layer and an anti-reflection layer arranged between the substrate layer and the heating layer. The anti-reflection layer is a multi-layer film system formed by alternately stacking at least one high-refractive-index material layer and at least one low-refractive-index material layer. By introducing the optical anti-reflection layer and utilizing the principle of destructive interference of light, the technical contradiction that the visible light transmittance is reduced inevitably when the thickness of a traditional semiconductor heating film is increased to realize low resistance is effectively solved. By adopting the electrothermal film provided by the invention, the visible light transmittance can still be greater than or equal to 90% under the condition that the sheet resistance is less than or equal to 25 ohm / sq, low resistance and high transparency are realized at the same time, and the electrothermal film is particularly suitable for the fields with strict performance requirements, such as vehicle-mounted glass demisting and the like. The invention further provides a corresponding magnetron sputtering preparation method.

Description

Technical Field

[0001] This invention relates to the field of electrothermal film technology, and in particular to a semiconductor electrothermal film with both low resistance and high optical transmittance, and a method for preparing the same. Background Technology

[0002] Electrothermal films are components that convert electrical energy into heat energy. Due to their advantages such as uniform heating, rapid temperature rise, and thin and lightweight structure, they are widely used in building heating, vehicle defogging, and smart wearable devices. Among these, transparent electrothermal films, which can achieve heating while maintaining the optical transparency of the substrate, have unique application value.

[0003] Currently, the heating layer of transparent electrothermal films typically uses transparent conductive oxide (TCO) thin films, such as indium tin oxide (ITO) films, fabricated on transparent substrates (such as PET films or glass) through processes like magnetron sputtering. However, existing semiconductor transparent electrothermal films have an inherent technical contradiction: the sheet resistance of the film is closely related to its thickness. In some applications requiring low voltage (such as the 12V or 24V commonly used in automotive systems), the electrothermal film needs to have a low sheet resistance (e.g., less than 25Ω / □) to obtain sufficient heating power. The most direct way to reduce sheet resistance is to increase the thickness of the semiconductor heating layer. However, as the thickness of the heating layer increases, its absorption and reflection of visible light also increase, resulting in a significant decrease in the visible light transmittance of the entire electrothermal film. For example, for traditional ITO films, if the sheet resistance is to be reduced from 100Ω / □ to 20Ω / □, the thickness needs to be increased several times. This usually causes the visible light transmittance to drop sharply from about 85% to below 70%, which cannot meet the stringent requirements for high transparency (e.g., greater than 90%) for applications such as automotive windshields.

[0004] Therefore, how to provide an electrothermal film that can combine low resistance and high optical transmittance has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide an electrothermal film with both low resistance and high optical transmittance and its preparation method, so as to solve the technical problem that it is difficult to balance the resistance and transparency of semiconductor electrothermal films in the prior art.

[0006] To achieve the above objectives, the present invention provides an electrothermal film, comprising a substrate layer and a heating layer disposed on the substrate layer, and further comprising an antireflection layer disposed between the substrate layer and the heating layer; the antireflection layer is a multilayer film system formed by alternating stacking of at least one high refractive index material layer and at least one low refractive index material layer.

[0007] As can be seen, this invention innovatively introduces a multilayer optical film system composed of alternating layers of high and low refractive index materials as an antireflection layer between the substrate layer and the heating layer. Utilizing the principle of destructive optical interference, it effectively suppresses the reflection of visible light at the interface, offsetting the light absorption and reflection losses caused by the thicker heating layer. This structure allows the heating layer to maintain extremely high visible light transmittance while achieving the thickness required for extremely low sheet resistance, thus successfully resolving the technical contradiction of the incompatibility between low resistance and high transparency in existing technologies, achieving a comprehensive performance that combines the advantages of both. Furthermore, this antireflection layer, as an intermediate transition layer, also helps improve the adhesion between the heating layer and the substrate layer, enhancing the structural stability and durability of the entire film system. More importantly, by introducing a flexibly designable optical antireflection layer, this invention decouples the design of electrical properties (determined by the heating layer) and optical properties (mainly regulated by the antireflection layer) to a certain extent, providing a new and more flexible design approach for the development of high-performance transparent electrothermal films.

[0008] Optionally, the sheet resistance of the electrothermal film is less than or equal to 25Ω / □, and the visible light transmittance is greater than or equal to 90%.

[0009] As can be seen, the technical solution of this invention can meet the high transparency requirements of high-end application scenarios while ensuring the low resistance required for low-voltage driving, thus exhibiting significant performance advantages.

[0010] Optionally, the high-refractive-index material layer is selected from one or more of the group consisting of titanium dioxide, niobium pentoxide, silicon nitride, and zirconium oxide.

[0011] It is evident that the aforementioned high refractive index materials exhibit stable optical properties, good compatibility with commonly used fabrication processes, and can reliably construct highly efficient antireflective coating systems.

[0012] Optionally, the low-refractive-index material layer is selected from one or more of the group consisting of silicon dioxide, magnesium fluoride, and aluminum oxide.

[0013] It is evident that by using the aforementioned low-refractive-index material, high transparency is achieved in the visible light band, and the material is readily available, enabling stable anti-reflection effects at a relatively low cost.

[0014] Optionally, the antireflective layer comprises, from the side closest to the substrate to the side closest to the heating layer, a first low-refractive-index material layer, a high-refractive-index material layer, and a second low-refractive-index material layer in sequence.

[0015] It is evident that this three-layer antireflection film design is a classic and efficient antireflection structure, which can achieve excellent antireflection effects in a wide visible light band through reasonable thickness and refractive index matching.

[0016] Optionally, the first low-refractive-index material layer is a silicon dioxide layer with a thickness of 10-20 nanometers, the high-refractive-index material layer is a titanium dioxide layer with a thickness of 40-60 nanometers, and the second low-refractive-index material layer is a magnesium fluoride layer with a thickness of 20-40 nanometers.

[0017] It is evident that by limiting the specific materials and thickness range, an optimized and easily implemented antireflective coating solution is provided, which has strong operability and excellent technical effects.

[0018] Optionally, the heating layer is a metal oxide semiconductor material layer.

[0019] It is evident that metal oxide semiconductor materials possess excellent electrical conductivity and chemical stability, making them an ideal choice for fabricating high-performance heating layers.

[0020] Optionally, it further includes: an electrode layer disposed on the heating layer; and an upper encapsulation layer and a lower encapsulation layer, the upper encapsulation layer covering the electrode layer and the lower encapsulation layer disposed below the substrate layer, to form a structure that completely encapsulates the electrode layer, the heating layer, the antireflection layer and the substrate layer.

[0021] As can be seen, the complete encapsulation structure and electrode layer provide the necessary electrical connection and environmental protection for the practical application of the electrothermal film. The optimized electrode design forms a reliable connection with the heating layer with low resistance, and the encapsulation layer provides comprehensive environmental shielding, ensuring the reliability and durability of the product.

[0022] The present invention also provides a method for preparing an electrothermal film, comprising the following steps: depositing an antireflection layer on a substrate layer, the antireflection layer being a multilayer film system formed by alternating stacking of at least one high refractive index material layer and at least one low refractive index material layer; and depositing a heating layer on the antireflection layer.

[0023] As can be seen, the method has a clear process route, and the electrothermal film structure described in this invention can be accurately constructed by sequentially depositing functional film layers.

[0024] Optionally, both the steps of depositing the antireflection layer and depositing the heating layer are performed using magnetron sputtering.

[0025] It is evident that the magnetron sputtering process produces high-quality films with uniform and controllable thickness, and is suitable for large-scale industrial production, enabling the efficient and stable preparation of electrothermal films that meet design requirements. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with their description, serve to explain the principles of the invention.

[0027] Figure 1 This is a structural exploded view of the electrothermal film provided in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the cross-sectional structure of the electrothermal film provided in an embodiment of the present invention.

[0029] Figure 3 This is a schematic flowchart of the electrothermal film preparation method provided in the embodiments of the present invention.

[0030] Explanation of reference numerals in the attached diagram: 1. Upper encapsulation layer; 2. Electrode layer; 3. Heating layer; 4. Antireflection layer; 5. Substrate layer; 6. Lower encapsulation layer. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

[0032] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0033] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0034] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0035] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0036] This invention provides an innovative transparent electrothermal film structure. Its core concept is to solve the technical problem that semiconductor heating films inevitably lead to a decrease in transparency when pursuing low resistance by introducing a specially designed optical anti-reflection layer into the traditional "substrate + heating layer" structure.

[0037] Please see Figure 1 and Figure 2 , Figure 1 and Figure 2 An exploded view and a cross-sectional view of the electrothermal film in one embodiment of the present invention are shown. The electrothermal film includes, from top to bottom, an upper encapsulation layer 1, an electrode layer 2, a heating layer 3, an antireflection layer 4, a substrate layer 5, and a lower encapsulation layer 6.

[0038] The substrate 5 is the carrier of the entire film system, and is typically made of a flexible or rigid material with good optical transparency and a certain mechanical strength. In a preferred embodiment, the substrate 5 can be made of polyethylene terephthalate (PET) film or polyvinyl butyral (PVB) film, which are transparent, flexible and cost-effective.

[0039] The antireflective layer 4 is directly disposed on the upper surface of the substrate layer 5, and it is the core innovation of this invention. The antireflective layer 4 is not a single material layer, but a multilayer film system composed of alternating stacked thin films of materials with different optical refractive indices. Specifically, it consists of at least one high-refractive-index material layer and at least one low-refractive-index material layer. The refractive index (n) of the high-refractive-index material is typically above 2.0, and optional materials include, but are not limited to, titanium dioxide (TiO2, n≈2.3-2.5), niobium pentoxide (Nb2O5, n≈2.2-2.3), silicon nitride (Si3N4, n≈2.0-2.1), or zirconium oxide (ZrO2, n≈2.0-2.1). The refractive index of the low-refractive-index material is typically below 1.7, and optional materials include, but are not limited to, silicon dioxide (SiO2, n≈1.46), magnesium fluoride (MgF2, n≈1.38), or aluminum oxide (Al2O3, n≈1.63). By precisely controlling the selection, thickness, and stacking order of each layer of material, and utilizing the interference effect generated when light propagates at the interface of different media, the reflection loss of visible light at the film system interface can be minimized, thereby significantly improving the light transmittance of the entire electrothermal film. Furthermore, this multilayer film structure, serving as a transition between the base layer and the heating layer, effectively alleviates potential stress problems due to material differences between the two layers through its material properties and multi-interface structure, and enhances interlayer adhesion.

[0040] The heating layer 3 is disposed on top of the antireflection layer 4. The heating layer 3 is the core component for realizing the electrothermal conversion function, and is typically made of a metal oxide semiconductor material with good conductivity, such as indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO). To achieve efficient heating under low-voltage drive, the heating layer 3 needs to have a low sheet resistance, which usually means that a relatively thick film layer needs to be fabricated. It is precisely because of the presence of the antireflection layer 4 that the entire electrothermal film can maintain high transparency even though the heating layer 3 is relatively thick.

[0041] Electrode layer 2 is disposed in a specific area of ​​heating layer 3 (usually the two side edges) for connecting an external power source and uniformly introducing current into heating layer 3. Electrode layer 2 can be made of a material with excellent conductivity, such as silver paste electrodes prepared by screen printing, or metal electrodes (such as copper, aluminum, etc.) prepared by processes such as evaporation or sputtering.

[0042] The working principle of the electrothermal film of this invention is based on Joule's law. Specifically, when an external power source applies a voltage to the heating layer 3 through the electrode layer 2, current flows through the heating layer 3, which has a certain resistivity. The heating mechanism is as follows: The metal oxide semiconductor material (such as indium tin oxide) used in the heating layer 3 contains a large number of freely moving charge carriers (mainly electrons) due to intrinsic material defects (such as oxygen vacancies) or elemental doping (such as tin replacing indium). Under the action of an external electric field, these charge carriers move directionally and accelerate, forming a macroscopic current. During this movement, the charge carriers collide frequently with atoms in the material's crystal lattice, transferring their kinetic energy to the lattice through these collisions, thus intensifying lattice vibrations. This intensification of lattice vibrations at the microscopic level manifests macroscopically as an increase in the overall temperature of the material, thereby radiating energy outwards in the form of heat. Since the heating layer 3 itself acts as a resistive load, the current flowing through this layer overcomes the resistance and does work, thus efficiently converting electrical energy into heat energy.

[0043] The generated heat is then evenly dissipated from the surface of the electrothermal film in the form of thermal radiation and thermal conduction, thereby heating the target object or raising the temperature of the environment. The heating layer 3, as a planar heat source, ensures the uniformity of heat distribution and avoids the local overheating problem that may occur with traditional linear heating elements.

[0044] The upper encapsulation layer 1 and the lower encapsulation layer 6 cover the top and bottom surfaces of the electrothermal film, respectively, serving as encapsulation, protection, and insulation. They completely seal the internal functional layers (electrode layer 2, heating layer 3, antireflective layer 4) and the base layer 5, preventing damage from moisture, oxygen, and mechanical scratches, thus ensuring the long-term operational stability and safety of the electrothermal film. The encapsulation layer material also needs to have high transparency and good insulation properties; materials such as PET and PVB can be selected. Its inner surface can be coated with hot melt adhesive (such as EVA film), and sealing is achieved through a hot-press lamination process.

[0045] The present invention will be further illustrated below with reference to a specific preparation example.

[0046] Example 1 Please see Figure 3 This embodiment provides a method for preparing an electrothermal film that combines low resistance and high transparency. The specific steps are as follows: Step S101: Substrate pretreatment.

[0047] Select a 125-micron-thick PET film as the base layer 5 and clean and remove dust to ensure its surface is clean.

[0048] Step S102: Prepare the antireflection layer by magnetron sputtering.

[0049] The prepared substrate layer 5 is placed into the vacuum chamber of a roll-to-roll magnetron sputtering apparatus. A three-layer antireflection layer 4 is then formed by sequential sputtering.

[0050] First, a silicon target is used to perform reactive sputtering in a mixed atmosphere of argon and oxygen to deposit a silicon dioxide (SiO2) layer with a thickness of 15 nanometers on the substrate layer 5 as the first low refractive index material layer.

[0051] Next, the target was switched to titanium, and reactive sputtering was performed in a mixed atmosphere of argon and oxygen to deposit a 50-nanometer-thick titanium dioxide (TiO2) layer on the silicon dioxide layer as a high refractive index material layer.

[0052] Finally, a magnesium fluoride ceramic target was used to sputter in an argon atmosphere to deposit a 30 nm thick magnesium fluoride (MgF2) layer on the titanium dioxide layer as a second low-refractive-index material layer. This yielded a composite film with a "substrate / SiO2 / TiO2 / MgF2" structure.

[0053] Step S103: Prepare the heating layer by magnetron sputtering.

[0054] In the same vacuum equipment, the heating layer 3 is further sputtered onto the surface of the topmost layer (magnesium fluoride layer) of the antireflection layer 4. Using an indium tin alloy target (indium oxide to tin oxide mass ratio of 90:10), reactive sputtering is performed in an argon and oxygen atmosphere. By controlling the sputtering power and time, a thin film of indium tin oxide (ITO) is deposited, with a thickness sufficient to achieve a sheet resistance of 20 Ω / □.

[0055] Step S104: Prepare the electrode layer.

[0056] The thin film containing the antireflection layer and the heating layer is removed. Conductive silver paste is then printed onto both edges of the heating layer 3 using screen printing technology to form the electrode layer 2. The film is then placed in an oven for drying and curing, ensuring good ohmic contact between the silver paste electrode and the heating layer 3. To facilitate external wiring and further reduce contact resistance, conductive materials such as copper foil can be laminated onto the cured silver paste electrode. The silver paste layer serves as a crucial transition layer, ensuring a low-resistance and stable connection between the main electrode and the heating layer.

[0057] Step S105: Film coating and encapsulation.

[0058] Prepare two PET films with EVA hot melt adhesive coated on their inner surfaces as the upper encapsulation layer 1 and the lower encapsulation layer 6. Place the film with electrodes between the upper and lower encapsulation layers, and perform hot pressing lamination using a roller laminator or vacuum laminator to melt the EVA adhesive and firmly encapsulate all layers together to form the final electrothermal film product.

[0059] Performance comparison test To verify the beneficial effects of the present invention, Comparative Example 1 was prepared. The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that step S102 is omitted, that is, a heating layer of the same thickness as that of Example 1 is directly sputtered onto the PET substrate.

[0060] The performance of the finished products from Example 1 and Comparative Example 1 was tested, and the results are shown in the table below: As can be clearly seen from the data in the table above, with the same heating layer thickness (and therefore the same sheet resistance), Example 1, which added an anti-reflection layer, achieved a visible light transmittance of 92%, far exceeding the 68% of Comparative Example 1 without an anti-reflection layer. This fully demonstrates that the technical solution of the present invention can effectively resolve the contradiction between low resistance and high transparency, achieving significant technological progress.

[0061] It should be noted that although the preferred embodiment of the present invention places the antireflection layer between the substrate layer and the heating layer to most effectively suppress reflection from the high-refractive-index heating layer, those skilled in the art will understand that, in order to achieve antireflection of the overall film system, antireflection structures can also be set at other interfaces, such as on the other side of the substrate layer (i.e., the side facing the air), or above the heating layer (i.e., below the upper encapsulation layer), adding another antireflection film system with a protective function. These variations based on the same inventive concept should all fall within the protection scope of the present invention.

[0062] In summary, this invention successfully achieves low sheet resistance while maintaining high transparency by introducing a multilayer optical antireflection film system composed of alternating high and low refractive index materials into the electrothermal film, thus solving a long-standing technical problem in the prior art. Its ingenious structural design and compatibility with existing processes make it highly practical and promising for future applications.

[0063] While specific embodiments of the invention have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of the invention. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims

1. An electrothermal film, comprising a base layer (5) and a heating layer (3) disposed on the base layer (5), characterized in that, It also includes an anti-reflective layer (4) disposed between the base layer (5) and the heating layer (3); The antireflective layer (4) is a multilayer film system formed by alternating stacking of at least one high refractive index material layer and at least one low refractive index material layer.

2. The electrothermal film according to claim 1, characterized in that, The sheet resistance of the electrothermal film is less than or equal to 25Ω / □, and the visible light transmittance is greater than or equal to 90%.

3. The electrothermal film according to claim 1, characterized in that, The high refractive index material layer is selected from one or more of the following groups: titanium dioxide, niobium pentoxide, silicon nitride, and zirconium oxide.

4. The electrothermal film according to claim 1, characterized in that, The low-refractive-index material layer is selected from one or more of the group consisting of silicon dioxide, magnesium fluoride, and aluminum oxide.

5. The electrothermal film according to claim 1, characterized in that, The antireflective layer (4) consists of a first low-refractive-index material layer, a high-refractive-index material layer, and a second low-refractive-index material layer, from the side closest to the base layer (5) to the side closest to the heating layer (3).

6. The electrothermal film according to claim 5, characterized in that, The first low-refractive-index material layer is a silicon dioxide layer with a thickness of 10-20 nanometers, the high-refractive-index material layer is a titanium dioxide layer with a thickness of 40-60 nanometers, and the second low-refractive-index material layer is a magnesium fluoride layer with a thickness of 20-40 nanometers.

7. The electrothermal film according to claim 1, characterized in that, The heating layer (3) is a metal oxide semiconductor material layer.

8. The electrothermal film according to claim 1, characterized in that, Also includes: Electrode layer (2) disposed on the heating layer (3); The upper encapsulation layer (1) and the lower encapsulation layer (6) are provided, with the upper encapsulation layer (1) covering the electrode layer (2) and the lower encapsulation layer (6) disposed below the substrate layer (5) to form a structure that completely encapsulates the electrode layer (2), the heating layer (3), the anti-reflection layer (4) and the substrate layer (5).

9. A method for preparing an electrothermal film as described in any one of claims 1 to 8, characterized in that, Includes the following steps: An antireflection layer (4) is deposited on the substrate layer (5), the antireflection layer (4) being a multilayer film system formed by alternating stacking of at least one high refractive index material layer and at least one low refractive index material layer; A heating layer (3) is deposited on the anti-reflective layer (4).

10. The preparation method according to claim 9, characterized in that, The steps of depositing to form an antireflection layer (4) and depositing to form a heating layer (3) both employ magnetron sputtering.

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