Patent Application
20240061153
This patent application claims the priority of German patent application 10 2022 120 892.3, filed Aug. 18, 2022, the disclosure content of which is hereby incorporated by reference.
The present application relates to a reflection-reducing layer system with an electrically conductive surface and a method for producing a reflection-reducing layer system.
To achieve reflection-reducing properties of transparent components, coatings based on interference filters are used in optical systems, for example, for which oxide layers with different refractive indices can be deposited on top of each other. However, such coatings do not provide any shielding against static or low-frequency electric fields.
Embodiments provide a layer system that is characterized by reflection-reducing properties with simultaneously high transmission and is suitable for shielding against static or low-frequency electric fields. Further embodiments provide a method with which a reflection-reducing layer system can be produced simply and reliably.
Embodiments provide a reflection-reducing layer system.
According to at least one embodiment of the reflection-reducing layer system, the reflection-reducing layer system is arranged on a substrate.
The term “substrate” generally refers to an element that is to be provided with a reflection-reducing coating. For example, the substrate is transparent or partially transparent. For example, the substrate has a transmission of at least 70% or of at least 80% in a target wavelength range of the reflection reducing coating. For example, the substrate is a glass substrate or a plastic substrate. For example, the substrate is an optical or optoelectronic component or part thereof, or a precursor to an optical or optoelectronic component to be produced.
According to at least one embodiment of the reflection-reducing layer system, a surface of the reflection-reducing layer system facing away from the substrate is electrically conductive. In particular, the electrically conductive surface terminates the reflection-reducing layer system as viewed in a vertical direction, i.e. perpendicular to a main surface of the substrate. The surface forms an interface with an ambient medium, for example a gas such as air. The reflection-reducing layer system thus provides an exposed electrically conductive surface accessible for external electrical contacting.
According to at least one embodiment of the reflection-reducing layer system, a nanostructure with a plurality of pillars arranged side by side is arranged between the substrate and the surface. The nanostructure can provide an antireflection property on its own or in combination with further components of the layer system, in particular in combination with further layers arranged on and/or under the nanostructure.
In at least one embodiment of the reflection-reducing layer system, the layer system is arranged on a substrate, wherein a surface of the layer system facing away from the substrate is electrically conductive and a nanostructure having a plurality of pillars arranged side by side is arranged between the substrate and the surface.
By means of the nanostructure, an effective refractive index can be achieved which is significantly lower than the refractive index of a homogeneous layer of the same material. The reflection at the surface of the layer system can thus be specifically adjusted, for example with regard to a spectrally broadband antireflection property and/or a good antireflection property over a large angular range. If appropriate, this can be done in conjunction with further layers between the substrate and the nanostructure. Furthermore, the layer system provides an electrically conductive surface which is accessible for external electrical contacting. For example, the electrically conductive surface can be connected to a ground potential. The layer system thus combines an anti-reflective property with the possibility of achieving shielding against static or low-frequency electric fields. Furthermore, the layer system can be characterized by a high transmission. For example, the transmission in a target wavelength range is at least 80% or at least 90%. In particular, the total transmission through the reflection reducing layer system and the substrate may be greater than or equal to the transmission through the substrate without the reflection reducing layer system. Thus, the reflection-reducing layer system may be transmission enhancing or at least transmission maintaining for the substrate.
According to at least one embodiment of the reflection-reducing layer system, an electrically conductive layer is arranged between the substrate and the nanostructure. The electrically conductive layer is, for example, a homogeneous, unstructured layer. For example, the nanostructure is immediately adjacent to the electrically conductive layer. In other words, viewed from the nanostructure in the direction of the substrate, at least the layer closest to it is electrically conductive. Other layers closer to the substrate, if any, may also be electrically insulating. For example, in gaps between the pillars, a layer forming the surface of the reflection-reducing layer system is electrically conductively connected to the underlying homogeneous electrically conductive layer directly or via an intermediate layer.
For example, the electrically conductive layer has a thickness of at most 400 nm or at most 200 nm or at most 100 nm or at most 50 nm and/or at least 5 nm or at least 10 nm. The thickness of the electrically conductive layer can also be selected, in particular, with regard to an optical layer thickness that is favorable for the reflection-reducing property of the layer system.
According to at least one embodiment of the reflection-reducing layer system, the electrically conductive layer is electrically conductively connected to the surface of the layer system. Via the electrically conductive layer, the electrical conductivity can be increased parallel to the surface of the layer system. Electrically insulating material can be arranged between the electrically conductive layer and the surface. In this case, the electrically insulating material is expediently present only in places so that there is electrical contact between the electrically conductive layer and the surface.
The material at the surface of the layer system and/or the electrically conductive layer comprise, for example, a transparent, electrically conductive oxide. Transparent, electrically conductive oxides (TCO) are transparent, electrically conductive materials, usually metal oxides, for example based on indium tin oxide (ITO), zinc oxide, tin oxide or gallium oxide (Ga2O3). In addition to binary metal oxygen compounds, such as ZnO, SnO2 or In2O3 also include ternary metal oxygen compounds, such as Zn2SnO4, CdSnO3, ZnSnO3, MgIn2O4, GaInO3, Zn2In2O5 or In4Sn3O12 or mixtures of different transparent conductive oxides belong to the group of TCOs. Furthermore, it may be possible that the TCOs do not necessarily correspond to a stoichiometric composition and may also be p- or n-doped.
The aforementioned TCO materials are also suitable for further structured, in particular nanostructured or unstructured layers of the reflection-reducing layer system, if appropriate.
According to at least one embodiment of the reflection-reducing layer system, at least some of the pillars have cavities. A lateral extent of the cavities is, for example, more than 10 nm for at least some of the pillars. The cavities may be at least partially completely enclosed. By means of the cavities, a particularly low refractive index can be achieved for the nanostructure.
According to at least one embodiment of the reflection-reducing layer system, the pillars are stochastically randomly distributed over the substrate and/or, at least for some pillars, a center-to-center distance to the closest pillar is between 50 nm and 100 nm, inclusive. During the fabrication of the nanostructure, the formation of the pillars is in particular self-organized. Spaces between adjacent pillars have, at least at some locations, for example, a lateral extent of at least 5 nm or at least 10 nm and/or of at most 60 nm or at most 40 nm. A maximum lateral extent of the pillars is, for example, at least 20 nm and/or at most 60 nm. The respective axes of the pillars may be oblique or perpendicular to the surface of the substrate.
According to at least one embodiment of the reflection-reducing layer system, the pillars have a height-to-width ratio of at least 1.0 or at least 1.5 or at least 2. A height of the pillars, i.e. an extension perpendicular to the surface, is preferably between 40 nm and 300 nm inclusive, particularly preferably between 70 nm and 200 nm inclusive. With a nanostructure having such a height-to-width ratio, scattering losses can be efficiently avoided so that high transmission is achievable.
According to at least one embodiment of the reflection-reducing layer system, the nanostructure has an effective refractive index of at most 1.7 or at most 1.6 or at most 1.3. Alternatively or complementarily, the effective refractive index is, for example, at least 1.05 or at least 1.1. In particular, the effective refractive index of the nanostructure is smaller than the refractive index of the electrically conductive layer, if present, between the substrate and the nanostructure.
According to at least one embodiment of the reflection reducing layer system, a further nanostructure is arranged between the substrate and the nanostructure. For example, the further nanostructure has a higher effective refractive index than the nanostructure. The reflection-reducing property can thus be further promoted. The further nanostructure may be produced largely analogous to the nanostructure or by a different process.
According to at least one embodiment of the reflection reducing layer system, an interference layer sequence is arranged between the substrate and the nanostructure. By combining the nanostructure with the interference layer sequence, the reflection-reducing properties can be adjusted to predetermined requirements with respect to the wavelength range and/or the angular range and/or with respect to the refractive index of the substrate. In particular, the nanostructure can be produced with precisely adjustable layer thickness and effective refractive index, which makes it possible to combine an interference layer sequence with the nanostructure and thus achieve, for example, a particularly broadband antireflection coating.
Furthermore, a method for producing a reflection-reducing layer system is disclosed. The method is particularly suitable for the production of the reflection-reducing layer system described above. Features specified in connection with the reflection-reducing layer system can therefore also be used for the method, and vice versa.
According to at least one embodiment of the method for producing a layer system, the method comprises a step of providing a substrate.
According to at least one embodiment of the method for producing a layer system, the method comprises a step of forming a nanostructure having a plurality of pillars arranged side by side on the substrate.
According to at least one embodiment of the method, a surface of the formed layer system facing away from the substrate is formed electrically conductive. The surface of the layer system can be formed during the formation of the nanostructure or can be formed by an electrically conductive cover layer applied in particular directly to the nanostructure.
In at least one embodiment of the method, a substrate is provided and a nanostructure having a plurality of pillars arranged side by side is formed on the substrate, wherein a surface of the formed layer system facing away from the substrate is electrically conductive.
With the method described, a substrate can be provided in a simple and reliable manner with a layer structure that can offer reflection-reducing properties and high transmission on the one hand and the possibility of shielding from static or low-frequency electric fields on the other hand. Furthermore, the method is compatible with conventional manufacturing processes of optical layer systems.
Before forming the nanostructure, an electrically conductive layer is preferably deposited on the substrate.
The formation of the electrically conductive layer and/or the deposition of electrically conductive material on the nanostructure can be carried out by evaporation, for example. This can involve bombardment with noble gas ions. This promotes layer formation at lower temperatures. This is described in the document DE 19752889 C1, the disclosure content of which is hereby explicitly incorporated by reference. Alternatively, other processes can be used, for example sputtering or atomic layer deposition.
According to at least one embodiment of the method, forming the nanostructure comprises forming a nanostructured layer on the substrate. In particular, the nanostructured layer may be formed directly on the electrically conductive layer.
According to at least one embodiment of the method, the nanostructured layer comprises an organic or partially organic material.
The nanostructured layer can be formed, for example, by a plasma process in which an initial layer is first deposited and subsequently ablated in places so that a pillar-like structure is formed. The initial layer can, for example, be applied as a polymer or vapor-deposited as another organic compound.
According to at least one embodiment of the method, the nanostructured layer contains at least one ring-shaped grouping with conjugated nitrogen and carbon atoms. In particular, the nanostructured layer is vacuum-deposited and has, for example, a thickness between 80 nm and woo nm, inclusive. Preferably, the organic material for the nanostructured layer has a molecular structure derivable from purine, pyrimidine or triazine.
Particularly suitable organic materials are those with conjugated C═N groups and derivatives thereof. For example, a suitable material is one from the class of triazines, for example TIC (1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-triones), acetoguanamine (6-methyl-1,3,5-triazine-2,4-diamine), Melamine (2,4,6-triamino-1,3,5-triazine), cyanuric acid (3,5-triazine-2,4,6-triol,2,4,6-trihydroxy-1,3,5-triazines), of purines, such as xanthine (2,6-dihydroxypurine), adenine (7H-purine-6-amine), guanine (2-amino-3,7-dihydropurine-6-one), of pyrimidines, for example uracil (1H-pyrimidine-2,4-dione) or UEE (uracil-5-carboxylic acid ethyl ester), of the imidazoles, for example creatinine (2-amino-1-methyl-2-imidazolin-4-one) or of phenylamines, for example NPB (N,N-di(naphth-1-yl)-N,N′-diphenylbenzidine), TPB (N,N,N′,N′-tetraphenylbenzidine) or TCTA (tris(4-carbazoyl-9-ylphenyl)amine).
Among the class of polymers, acrylates such as polymethyl acrylate (PMMA) or photoresists containing epoxy compounds or acrylates are suitable, for example.
According to at least one embodiment of the method, forming the nanostructure comprises overlaying the nanostructured layer with a layer. The layer is in particular an inorganic layer. The layer may be electrically conductive or electrically insulating.
The deposition of the nanostructure layer, in particular the inorganic layer, can be carried out in such a way that it replicates the structure of the nanostructured layer. In this case, the deposited thickness on the flanks of the pillars and/or between adjacent pillars can also be much thinner than on the tips of the pillars. If the layer is deposited by physical vapor deposition such as vapor deposition or sputtering, it covers the largely perpendicular structures with varying thickness, depending on the angle of the impinging particles. Deviating from this, the coverage can also be conformal, for example by atomic layer deposition. In this case, however, its total thickness is typically limited to a few nanometers.
Advantageously, the thickness of the layer is between 5 nm and 100 nm inclusive, particularly preferably between 15 nm and 80 nm inclusive.
According to at least one embodiment of the method, forming the nanostructure comprises performing a post-treatment in which the nanostructured layer is at least locally decomposed or removed. In other words, the post-treatment completely or partially dissolves out organic components.
The post-treatment involves, for example, a plasma etching process in which a basic shape of the previously formed nanostructure is retained. The geometry and/or the height-to-width ratio of the pillars of the nanostructure thus do not change, or at least not significantly, as a result of the post-treatment.
Alternatively or complementarily, the post-treatment can also be carried out by thermal treatment, for example at a temperature above 70° C.
In particular, the organic components of the nanostructured layer can be completely or at least almost completely removed by the post-treatment. It has turned out that an organic material is particularly suitable as an initial material for the nanostructured layer, even if the layer system to be produced is formed completely or at least almost completely by inorganic material.
According to at least one embodiment of the method, the layer deposited prior to post-treatment is electrically conductive. In particular, the entire material deposited on the nanostructured layer may be electrically conductive. A low electrical resistance can thus be achieved in a simplified manner.
According to at least one embodiment of the method, an electrically conductive cover layer is applied after the post-treatment, wherein the electrically conductive cover layer forms the electrically conductive surface of the layer system to be produced.
The nanostructure fabrication steps can also be performed repeatedly to achieve stacked nanostructures.
Preferably, at least the formation of the nanostructure and the subsequent steps in which coating of the substrate takes place are carried out in a plant in a closed vacuum process. The production of the layer system can thus be carried out particularly efficiently. In particular, all steps in which deposition, structuring or post-treatment takes place can also be carried out in one plant.
Furthermore, the reflection-reducing layer system can be realized in a technically reliable manner using conventional vacuum technology. This also makes the method particularly suitable for mass production.
The layer system and the method are generally suitable for optical components, such as those made of glass or plastic, in particular for lenses, lens arrays, optical windows, miniaturized plastic lenses or micro-optical components or parts thereof, or also for optoelectronic components or parts thereof.
For example, the optical or optoelectronic components can be used for optical lenses, objectives, cameras, for displays or display covers, for indicators, for illumination optics, for shielding windows, for heating elements, for windows for electromagnetic field control, for solar cell technology, for display technology, for windows of cathode ray tubes (CRT for short) or for quantum cells.
The figures are each schematic representations and therefore not necessarily to scale. Rather, various elements, in particular layer thicknesses, may be shown exaggeratedly large for improved representability and/or better understanding.
Identical, similar or similarly acting elements are given the same reference signs in the figures.
In the exemplary embodiment of a reflection-reducing layer system shown in
The reflection-reducing layer system 100 thus provides an externally accessible electrically conductive layer on the surface 10 of the reflection-reducing layer system facing away from the substrate 1. This layer can, for example, be electrically conductively connected to a ground potential and thus be used for shielding against electrostatic or low-frequency electric fields.
The pillars 35 are stochastically randomly distributed over the substrate 1 and, for at least some of the pillars 35, a center-to-center spacing to the nearest pillar 35 is between 50 nm and 100 nm, inclusive. Spaces between adjacent pillars have, at least at some locations, for example, a lateral extent of at least 5 nm or at least 10 nm and/or of at most 60 nm or at most 40 nm. Preferably, the pillars have a height to width ratio of at least 1.0 or at least 1.5 or at least 2.
The production of the nanostructure 3 is explained in more detail in connection with
In the exemplary embodiment illustrated in
By constructing the interference layer sequence 4 in conjunction with the nanostructure 3, a reflection-reducing layer system 100 can be realized that provides an electrically conductive surface 10 while exhibiting low reflection and high transmission for a given wavelength range.
The curve 101 is based on a layer structure in which the first layers 41 are formed of SiO2 and the second layers 42 are formed of Ta2O5. The electrically conductive layer 2 is a 15 nm thick ITO layer. The nanostructure 3 is formed during fabrication from an about 170 nm thick organic layer of melamine, which is converted by plasma etching into a nanostructure having a height of about 90 nm. The layer 32 is an ITO layer with a thickness of 30 nm which is transparent in the visible spectral range and in the near infrared spectral range and conductive. Thus, the pillars 35 of the nanostructure 3 are formed by hollow ITO needles.
The comparison with curve 102 shows that the reflection can be significantly lowered by the nanostructure 3 in the visible spectral range, with the reflection-reducing layer system 100 simultaneously providing an electrically conductive surface 10. Over the entire range from 400 nm to 700 nm, the residual reflection is less than 0.2%. A linear 4-peak measurement of the surface yields a sheet resistance of 300 ohms/square (Ω/□).
Of course, other materials and/or other layer thicknesses can also be used for the layers described. Furthermore, the course of the spectral reflection can be varied within wide limits by suitable selection of the parameters.
The exemplary embodiment shown in
In contrast, a cover layer 38 is arranged on the nanostructure 3, which forms the surface 10 of the reflection-reducing layer system 100. The materials described in connection with the electrically conductive layer 2 and the layer 32, for example a TCO material such as ITO, are particularly suitable for the cover layer 38.
The cover layer 38 is electrically conductively connected to the electrically conductive layer 2. In this exemplary embodiment, the layer 32 can be electrically conductive or electrically insulating. Such a cover layer 38 may also be additionally present in the exemplary embodiment according to
Furthermore, in this exemplary embodiment, in contrast to the exemplary embodiment shown in
In
The resulting reflection is lower than for an uncoated glass substrate (curve 202) in the entire wavelength range from about 600 nm to 1500 nm. At the same time, as
The high transmission is achieved in particular due to a particularly low effective refractive index of the electrically conductive nanostructure 3 of at most 1.4 or at most 1.3. For example, the effective refractive index of the nanostructure 3 is between 1.2 and 1.4 inclusive.
The exemplary embodiment shown in
In contrast, a further nanostructure 5 is arranged between the nanostructure 3 and the substrate 1 instead of an interference layer sequence. The electrically conductive layer 2 is located between the further nanostructure 5 and the nanostructure 3. A further conductive layer 25 is arranged between the further nanostructure 5 and the substrate 1. The further nanostructure 5 and the further electrically conductive layer 25 can be formed similarly to the nanostructure 3 and electrically conductive layer 2, respectively. However, the nanostructure 3 and the further nanostructure 5 may differ from each other, for example, with respect to the effective refractive index, for example, due to a different structuring, for example, with respect to the height in the vertical direction or the extension in the lateral direction, and/or due to different materials. The further nanostructure 5 has further pillars 55 with cavities 56 similar to the nanostructure 3.
In the case that all layers arranged on the substrate 1 are formed by ITO,
As shown in
As illustrated in
As illustrated in
After overlaying with layer 32 as shown in
The post-treatment creates cavities 36 in the pillars 35. By means of the cavities 36, the nanostructure 3 has a particularly low effective refractive index.
The post-treatment can be achieved by a plasma etching process. In this case, the layer to be processed, i.e. the nanostructured layer 31, is covered by an overlying layer, i.e. layer 32, in contrast to the intermediate step shown in
With the described method, the nanostructure 3 can be produced with precisely adjustable and reproducible properties, in particular with regard to the height of the nanostructure 3 and its effective refractive index. This allows the nanostructure 3 to be efficiently combined with the interference layer sequence 4, for example.
Preferably, the same plasma source is always used for all plasma processes. For example, a plasma source of the APS type is suitable, such as a coating system of the SyrusPro series from the manufacturer Bühler Leybold Optics with an ion energy of 80-150 eV.
In particular, at least the steps in which coating of the substrate 1 takes place can be carried out in a plant in a closed vacuum process. The production of the layer system can thus be carried out particularly efficiently. In particular, all steps in which a deposition, structuring or post-treatment is carried out can also be carried out in one plant.
The reflection reducing layer system 100 shown in
Alternatively, as in
Thus, in this exemplary embodiment, a portion of the material is applied over the cavities 36 prior to post-treatment, namely the layer 32, while another portion of the material, namely the cover layer 38, is applied after the post-treatment.
By means of the cover layer 38, the material thickness over the cavities 36 of the nanostructure can be increased. Since the cover layer 38 is applied after the post-treatment, the thickness of the cover layer 38, in particular in contrast to the thickness of the layer 32, has no influence on the method step of the post-treatment. Such a two-step application may therefore also be favorable in the case where the layer 32 and the cover layer 38 are made of the same material. However, the materials may also be different from each other.
In the spaces between the pillars 35, the cover layer 38 is electrically conductively connected to the electrically conductive layer 2. This can take place directly via direct contact between the layers or indirectly via layer 32.
The reflection-reducing layer system wo shown in
With reference to
A further electrically conductive layer is applied to a substrate 1 (
The further nanostructured layer 51 is overlaid with a further layer 52 (
Subsequently, as described in connection with
The deposition of the initial layer 310 in
The method produces a reflection-reducing layer system 100 with two nanostructures stacked on top of each other. These nanostructures each form an effective refractive index which is small compared to the effective refractive index of the electrically conductive layer 2 and the further electrically conductive layer 25. Here, the entire layer sequence formed on the substrate 1 can be electrically conductive, so that particularly low sheet resistances can result.
The exemplary embodiment for a method illustrated in
The invention is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses any new feature as well as any combination of features, which in particular includes any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or the exemplary embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022120892.3 | Aug 2022 | DE | national |
