BE1031181B1 - MULTI-LAYER COATING WITH ADJUSTABLE COLOR - Google Patents

Abstract

The present invention relates to a multi-layer coating comprising a stack of a high refraction layer alternating with a low refraction layer, wherein said low refraction layer comprises 30 to 50 at%. of silicon, from 40 to 70% at. oxygen, from 0 to 30% at. nitrogen, and from 0 to 20% at. of hydrogen and wherein said low refraction layer has a thickness less than 140 nm, wherein said high refraction layer comprises 60 to 100 at%. of silicon, from 0 to 20% at. oxygen, from 0 to 30% at. nitrogen, and from 0 to 40% at. hydrogen, and wherein said high refraction layer comprises a thickness less than 65 nm. The invention also relates to a method of applying a multi-layer coating to a substrate.

Description

1 | BE2022/6067

MULTI-LAYER COATING WITH ADJUSTABLE COLOR

TECHNICAL AREA

The present invention relates to a multi-layer coating comprising a stack of a high refraction layer alternating with a low refraction layer.

In a second aspect, the present invention also relates to a method of applying a multi-layer coating to a substrate.

In another aspect, the present invention also relates to a use of a multi-layer coating.

STATE OF THE ART

The strategy of distributed Bragg reflectors (DBR) to selectively reflect a range of wavelengths is known but mainly used in optical fibers.

US6500251B1 describes a multilayer interference pigment consisting of platelet-shaped titanium dioxide as a carrier material, coated with alternating layers of metal oxides of low and high refractive index, the difference in refractive indices being of at least 0.1, which can be obtained by solidifying and hydrolyzing an aqueous solution of a thermally hydrolyzable titanium compound on an endless belt, detaching the resulting coating layer, coating the resulting platelets with carbon dioxide titanium, with or without drying therebetween, by a wet method with, alternately, a hydrated metal oxide of high refractive index and a hydrated metal oxide of low refractive index by hydrolysis of the compounds of corresponding water-soluble metals, separation, drying and, if desired, calcination of the material obtained.

WO2006088761A2 describes a multi-layer effect pigment including a transparent substrate, a layer of high refractive index material on the substrate, and alternating layers of low refractive index and high refractive index materials on the first layer, the number total layers being an odd number of at least three, all adjacent layers differing in refractive index by at least about 0.2 and at least one of the layers having an optical thickness that is different from all the other layers. The resulting multi-layer effect pigment is not a quarter-wave stack. The present pigment

> BE2022/6067 multi-layer effect can be used in cosmetic products or personal care products.

CN108349792A relates to the surface treatment of supports by coating them, and in particular, to thin film technologies. The purpose of the present invention is to create a simple and reliable optical coating having superior usability and a production technology thereof, which is suitable for low-cost mass production. In the composite optical coating, comprising a multi-layer anti-reflective coating consisting of alternating layers having high and low refractive indices, and a protective coating, the exposed problem is solved by means of a modified adhesive layer made of an amorphous substance having a thickness of 5 to 200 nm formed between the anti-reflective coating and the protective coating. Two variations of the composite optical coating production method are also provided.

SUMMARY OF THE INVENTION

The present invention and embodiments thereof serve to provide a solution to one or more of the above-mentioned disadvantages. To this end, in a first aspect, the present invention relates to a multi-layer coating comprising a stack of a high refraction layer alternating with a low refraction layer according to claim 1.

In order to selectively reflect red light and obtain a red colored substrate by means of the distributed Bragg reflector strategy, a pair of transparent materials with different refractive indices are required. Compounds obtained with a Si target are the most suitable, such as SiO2-Si3N4- a-Si:H. In particular, the SiO2-a-Si:H duo is highly efficient because of the considerable gap in refractive index and because a-Si:H inherently absorbs in the blue region. There is a synergistic effect between interference color and intrinsic color. An advantage of this strategy is that the color shade can be controlled by changing the operational parameters only: the number of layers and their thickness.

Preferred embodiments of the device are shown in any one of claims 2 to 12.

A specific preferred embodiment relates to an invention according to claim 8, 9 and 10. These claims relate to a top layer. A top coat consisting of an anti-reflective layer will significantly reduce

3 BE2022/6067 secondary thoughts. This includes a transparent layer of determined thickness of a material whose refractive index is intermediate between the high refractive index and air. Several candidates were considered, for example the

MoOz, Al2O3, SisN4, SiO,Ny. Al2O3 for example was chosen due to the best refractive index match. Silicon oxynitrides are even more promising since they use a Si target and allow precise adjustment of the refractive index.

A further specific preferred embodiment relates to an invention according to claim 11 and 12. These claims relate to a bottom layer. This improvement is desired to get rid of the influence of the substrate and be able to obtain the same result, regardless of the substrate. A highly absorbent black bottom layer is used for this purpose. There are many candidates for this absorbent layer, for example TiAIN. Selective absorption layers can also be used as a bottom layer, for example an intrinsic color layer, to enhance certain colors.

In a second aspect, the present invention relates to a method according to claim 13. More particularly, the present invention comprises a method of applying a multi-layer coating to a substrate.

Preferred embodiments of the method are shown in claim 14.

In a third aspect the present invention relates to a use according to claim 15. The use of the multi-layer coating here provides an advantageous effect of obtaining colored coatings, preferably red coatings.

DESCRIPTION OF FIGURES

The following description of the figures of specific embodiments of the invention is merely exemplary in nature and is not intended to limit the present teachings, their application or uses. Throughout the drawings, corresponding reference numerals indicate parts and points — analogous or corresponding characteristics.

Figure 1 shows a preferred embodiment according to the present invention.

Figure 1 shows the coating layers in a preferred order. Firstly, a substrate is provided, this can include any type of substrate. Above the substrate

4 BE2022/6067 there is a black layer of TiAIN. Above this TiAIN layer is

Vestment provided. The stack contains a layer system of a-Si:H/SiO2.

As a final layer, an anti-reflective top layer made of AI203 provided on top of the stack.

DETAILED DESCRIPTION

The present invention relates to a multi-layer coating comprising a stack of a high refraction layer alternating with a low refraction layer. This invention generally relates to the coating of substrates using physical or chemical vapor deposition, and more particularly to a color-tunable multi-layer coating obtained by a distributed Bragg reflector strategy.

Unless otherwise indicated, all terms used in the disclosure of the invention, including technical and scientific terms, have the meaning generally accepted by those skilled in the art to which this invention belongs. Definitions of terms are included for guidance to better appreciate the teaching of the present invention. “Un”, “une”, “le” and “la” as used herein mean both the singular and the plural, unless the context clearly indicates otherwise. For example, “a compartment” means one or more compartments. —“Comprising”, “comprising”, and “includes” and “consisting of”, as used herein, are synonymous with “include”, “including”, “includes” or “contain”, “containing”, "contains" and are inclusive or open terms that specify the presence of what follows, for example a component, and do not exclude or preclude the presence of additional, known, unmentioned components, features, elements, members, steps in the art or disclosed herein.

Furthermore, the terms first, second, third and the like in the description and in the claims are used to distinguish between similar elements and not necessarily to describe a sequential or chronological order, unless specified. It is understood that the terms so used are interchangeable in appropriate circumstances and that embodiments of the invention described herein may operate in sequences other than those described or illustrated herein.

Citation of numerical ranges by limits includes all numbers and fractions subsumed within that range, as well as the quoted limits.

While the terms "one or more" or "at least one", such as one or more or at least one member(s) of a group of members, is clear per se, by way of further exemplification, the The term includes, among other things, a reference to any one of said members, or to any two or more of said members, such as, for example, any number > 3, > 4, > 5, > 6 or > 7 etc. of said members, and up to all of said members.

The reference throughout this specification to "an embodiment" means that a particular (particular) feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. at least one embodiment of the present invention. Thus, the appearance of the phrase "in one embodiment" in various places throughout this specification does not necessarily always refer to the same embodiment, but may. Furthermore, the particular characteristic points, structures or characteristics may be combined in any suitable manner, as would be apparent to those skilled in the art from this disclosure, in one or more embodiments. Additionally, while some embodiments described herein include some but not other feature points included in other embodiments, the combinations of feature points of different embodiments are intended to be within the scope of the invention. , and to form different embodiments, as those skilled in the art would understand. For example, in the following claims, any of the claimed embodiments may be used in any combination.

According to the invention, the term “thickness” refers to a portion of a layer located substantially perpendicular to its external surface. The thickness may designate a distance from said surface, such as a distance from a point below said surface.

According to the invention, the term “% in atoms”, “% in atomic”, “% in at. » or “% at. ", here and throughout the description, unless otherwise indicated, refers to the proportion of any nuclide in a mixture expressed as a numerical percentage of all atoms of that element present, regardless of their nuclide mass.

According to the invention, the term "refractive index" is a dimensionless number and is a measure of how light propagates through a material. The higher the refractive index, the slower the light travels, causing

6 BE2022/6067 a correspondingly increased change in the direction of light within the material.

In a first aspect, the present invention relates to a multi-layer coating comprising a stack of a high refraction layer alternating with a low refraction layer.

In a preferred embodiment of the invention, the low refraction layer is based on silica, more preferably the low refraction layer comprises 30 to 50 at%. of silicon, from 40 to 70% at. oxygen, from 0 to 30% at. nitrogen, and 0 to 20% at. of hydrogen, more preferably 30 to 50 at%. of silicon, from 50 to 70% at. oxygen, from 0 to 20% at. nitrogen, and

O0 to 10% at. of hydrogen, more preferably 30 to 50 at%. of silicon and 50 to 70% at. of oxygen. Silica is preferred for its excellent physical, optical and electrical properties. It is stable over a wide range of conditions, non-toxic and widely available. In a further preferred embodiment, the low refraction layer comprises silica or has a chemical composition as described above, and said low refraction layer is porous. More preferably, the low refraction layer has a porosity of at least 0.5%, more preferably at least 1%, more preferably at least 3%, more preferably at least 3%. at least 5%, more preferably at least 10%, more preferably at least 15%, more preferably at least 20%, more preferably at least 25%; as measured by the pore volume relative to the total volume of the low refractive index layer. Advantageously, the porosity makes it possible to modify and precisely adjust the desired refractive index. With an increase in porosity, the percentage of void spaces in the material also increases. Since air has a refractive index of roughly 1.0, this lowers the effective refractive index of SiO.

Changing the porosity of the layers allows the precise adjustment of refractive indices between 1.10 and 1.50.

In a preferred embodiment of the invention, the low refraction layer has a thickness less than 200 nm, more preferably less than 190 nm, more preferably less than 180 nm, more preferably less than 170 nm , more preferably less than 160 nm, more preferably less than 150 nm, more preferably less than 140 nm, more preferably less than 130 nm, more preferably less than 120 nm. In one embodiment

7 BE2022/6067 preferred of the invention, the low refraction layer has a thickness greater than 30 nm, more preferably greater than 40 nm, more preferably greater than 50 nm, more preferably greater than 60 nm, so more preferably greater than 70 nm, more preferably greater than 80 nm, more preferably greater than 90 nm, more preferably greater than 100 nm, more preferably greater than 110 nm. In a further preferred embodiment, the low refraction layer has a thickness between 30 nm and 200 nm, more preferably between 40 and 190 nm, more preferably between 50 and 180 nm, more preferably between 60 and 170 nm, more preferably between 70 and 160 nm, more preferably between 80 and 150 nm, more preferably between 90 and 140 nm, more preferably between 100 and 130 nm, more preferably between 110 and 120nm. The importance of these thicknesses is to cover the entire range of visible light.

In a preferred embodiment of the invention, the high refraction layer comprises 60 to 100 at%. of silicon, from 0 to 20% at. oxygen, from 0 to 30% at. nitrogen, and from 0 to 40% at. hydrogen, more preferably 70 to 100 at%. of silicon, from 0 to 10% at. oxygen, from O to 10% at. nitrogen, and from 0 to 30% at. hydrogen, more preferably 70 to 100 at%. of silicon, and from 0 to 30% at. of hydrogen. A high hydrogen dilution a-Si:H layer can be used as a good quality silicon thin film. In a high hydrogen dilution a-Si:H layer, the concentration of hydrogen atoms is relatively high compared to the concentration of silicon atoms. As a result, there are more Si-H bonds present in the material. These bonds contribute to the stability and electrical properties of the material. Increasing the silicon content in a-Si:H layers can lead to a number of changes in the material's properties. One of the main effects of increasing silicon content is an increase in the number of Si-H bond bonds, which can improve the stability and electrical properties of the material. Additionally, increasing the silicon content can also lead to an improvement in the mechanical properties of the material, such as its strength and hardness. This is because the presence of silicon atoms can help strengthen the material. Increasing the silicon content can also affect the electrical conductivity of the material. Increasing the concentration of Si-H bonds in a-Si:H layers generally has the effect of increasing the optical absorption of the film. This is because Si-H bonds are able to absorb light in the visible and near-infrared regions of the spectrum.

8 BE2022/6067 electromagnetic, leading to an increase in the absorption coefficient of the film. Advantageously, amorphous silicon absorbs the visible portions of the solar spectrum 40 times more efficiently than does monocrystalline silicon, such that a film only about 1 µm thick can absorb 90% of the usable light energy directed towards it. This allows for thin but effective colored PVD coatings while reducing material and processing requirements. Additional advantages are that it can be produced at lower temperatures and can be deposited on a wide range of substrates. An a-Si:H can thus be deposited by plasma-assisted chemical vapor deposition on almost any substrate at temperatures below 230 °C.

The refractive index is a measure of how well light travels through a material. The higher the refractive index, the slower the light travels, causing a correspondingly increased change in the direction of the light within the material. For layers, this means that a higher refractive index material can bend light more and allow the thickness of the layer to be thinner. An additional advantage is that a-Si:H can be deposited at very low temperatures.

In a preferred embodiment of the invention, the high refractive index layer has a thickness less than 95 nm, more preferably less than 90 nm, more preferably less than 85 nm, more preferably less than 80 nm, more preferably less than 75 nm, more preferably less than 70 nm, more preferably less than 65 nm, more preferably less than 60 nm, more preferably less than 55 nm. In a preferred embodiment of the invention, the high refraction layer has a thickness greater than 10 nm, more preferably greater than 15 nm, more preferably greater than 20 nm, more preferably greater than 25 nm , more preferably greater than 30 nm, more preferably greater than 35 nm, more preferably greater than 40 nm, more preferably greater than 45 nm, more preferably greater than 50 nm.

In a further preferred embodiment, the high refraction layer has a thickness between 10 nm and 95 nm, more preferably between 15 and 90 nm, more preferably between 20 and 85 nm, more preferably between 25 and 80 nm, more preferably between 30 and 75 nm, more preferably between 35 and 70 nm, more preferably

9 BE2022/6067 between 40 and 65 nm, more preferably between 45 and 60 nm, more preferably between 50 and 55 nm. The importance of these thicknesses is to cover the entire range of visible light. Even more preferably, the high refraction layer has a thickness between 50 nm and 65 nm, these thicknesses are optimal for obtaining a red coating.

In order to selectively reflect red light and obtain a red-colored substrate by means of the distributed Bragg reflector strategy, a pair of transparent materials with different refractive indices are required. Compounds obtained with a target of Si are the most appropriate, such as SiO”,

SisN4, a-Si:H. There is a synergistic effect between interference color and intrinsic color. An advantage of this strategy is that the color shade can be controlled by changing the operational parameters only: the number of layers and their thickness. SiO2 is mainly used as the lower refractive index layer of DBR and can have a low refractive index that can be controlled by its porosity. In particular, the SiO2 and a-Si:H duo is highly efficient due to the considerable difference in refractive index and because a-Si:H inherently absorbs in the blue region.

In a further embodiment the invention also includes a top layer above the stack, preferably the top layer comprises an anti-reflective layer, more preferably the top layer comprises any transparent material which has a refractive index between 1.7 and 1.9, more preferably MoOz, Al2O3, SisN4, Ta2Os, HfO2, SnO2 or SiO,Ny. A topcoat consisting of an anti-reflective layer will significantly reduce secondary reflections. This comprises a transparent layer of determined thickness of a material whose refractive index is intermediate between the high refractive index and air. More preferably, Al2O3 was chosen because of the best refractive index match and because aluminum oxide is inert to acids and alkalis, is very hard, and provides naturally a passivation layer on coated substrates that prevents weathering and environmental corrosion. Al203 coatings can be electrically insulating, chemically inert, highly wear resistant, and stable at elevated temperatures, depending on the crystal phase and deposition temperature. Since not all substrates tolerate high process temperature, a low temperature version and a high temperature version of Al;O3 have been developed. Alumina coatings are also known to have non-sticky properties towards various liquids

10 BE2022/6067 and molten metals due to hydrophobic surface properties. Even more preferably, silicon oxynitrides are chosen as the upper layer. Silicon oxynitrides are even more promising since they use a Si target and allow precise tuning of the refractive index. One of the benefits of using silicon oxynitrides as coatings is their high thermal stability. They can withstand temperatures up to 1200°C or higher, making them useful in high temperature environments. Additionally, silicon oxynitrides have good chemical resistance, meaning they are resistant to attack by many acids and bases. This makes them useful as protective coatings in a variety of applications. Silicon oxynitride coatings also have good electrical insulation properties and can be used to insulate electrical components or to protect against electrical discharge. They can also have a low coefficient of friction, making them useful in applications where low friction is desirable. Silicon oxynitrides can be synthesized through various methods, such as chemical vapor deposition (CVD) or plasma-assisted CVD. They can be used as thin films or bulk materials, and their properties can be tuned by controlling the stoichiometry and microstructure of the material. Some potential applications of silicon oxynitrides include use as protective coatings, in structural materials for high temperature applications, and as insulating layers in electronics.

In a preferred embodiment of the invention, the upper layer has a thickness less than 135 nm, more preferably less than 125 nm, more preferably less than 115 nm, more preferably less than 105 nm, more preferably less than 95 nm, more preferably less than 85 nm, more preferably less than 75 nm, more preferably less than 65 nm, more preferably less than 55 nm. In a preferred embodiment of the invention, the high refraction layer has a thickness greater than 10 nm, more preferably greater than 15 nm, more preferably greater than 20 nm, more preferably greater than 25 nm , more preferably greater than 30 nm, more preferably greater than 35 nm, more preferably greater than 40 nm, more preferably greater than 45 nm, more preferably greater than 50 nm. In a further preferred embodiment the high refraction layer has a thickness between 10 nm and 135 nm, more preferably between 15 and 135 nm.

11 BE2022/6067 125 nm, more preferably between 20 and 115 nm, more preferably between 25 and 105 nm, more preferably between 30 and 95 nm, more preferably between 35 and 85 nm, more preferably preferably between 40 and 75 nm, more preferably between 45 and 65 nm, more preferably between 50 and 55 nm. The importance of these thicknesses is to cover the entire range of visible light.

In yet another additional embodiment, the invention comprises a lower layer between said stack and a substrate, preferably said lower layer comprises an absorbent layer. The bottom layer may include a rather standard absorbent layer, such as Ge:Sb»Tes, TiAIN, SisN4, TiAISIN, M-AIN, TiAION. This improvement is desirable to get rid of the influence of the substrate and be able to obtain the same result, regardless of the substrate. Preferably, a highly absorbent black bottom layer is used for this purpose. For example, a TiAlN layer has the notable advantage that it is a highly absorbent layer and includes additional benefits of extreme hardness, excellent resistance to abrasive wear, superior reliability in dry process operations, possibility of reducing lubricants, heat resistance, hard machining, increased hardness, high wear resistance and oxidation resistance. More preferably, any colored layer may act as a bottom layer. A colored bottom layer can be customized to absorb a specific range of wavelengths, allowing them to be tailored to meet the specific needs of the application. Any colored undercoat can be easily applied using standard coating equipment, making it a convenient choice for many types of applications.

The multilayer having the above characteristics is remarkable. As a result of the constructive interference caused by incident and reflected light waves, a brilliant color is observed on the prepared DBR samples in accordance with the increased number of layers in the stack.

In a more preferred embodiment, - the upper layer comprises 30 to 50% at. of silicon, from 0 to 50% at. oxygen, from 0 to 60% at. nitrogen, and 0 to 20% at. hydrogen, more preferably has a thickness between 45 nm and 120 nm; - the high refraction layer is based on silane, more preferably comprising 70 to 100% at. of silicon, from 0 to 10% at. oxygen,

12 BE2022/6067 from 0 to 10% at. nitrogen, and 0 to 30% at. hydrogen, more preferably has a thickness between 25 nm and 65 nm; - The low refraction layer is based on silica, more preferably comprising 30 to 50% at. of silicon, from 50 to 70% at. oxygen, from O to 20% at. nitrogen, and 0 to 10% at. hydrogen, more preferably has a thickness between 55 nm and 140 nm; - The lower layer comprises an absorbent layer, in which said lower layer comprises from 70 to 100% at. of silicon, from 0 to 10% at. oxygen, from 0 to 10% at. nitrogen, and 0 to 30% at. of hydrogen.

This preferred stack of layers is ideal for adjusting the color of a coating, choosing a color from the entire visible range.

In a most preferred embodiment, - The upper layer comprises 30 to 50% at. of silicon, from 0 to 40% at. oxygen, 25 to 60% nitrogen, more preferably 0 to 10% at. hydrogen, more preferably has a thickness between 45 nm and 60 nm; - the high refraction layer is based on silane, more preferably comprising 70 to 100% at. silicon and O at 30% at. hydrogen, more preferably has a thickness between 50 nm and 65 nm; - The low refraction layer is based on silica, more preferably comprising 30 to 50% at. of silicon and 50 to 70% at. oxygen, more preferably has a thickness between 110 and 140 nm; - The lower layer comprises an absorbent layer, in which said lower layer comprises from 70 to 100% at. silicon and O at 30% at. of hydrogen.

This preferred stack of layers is ideal for optimizing the purity of the red color of the coating.

In another preferred embodiment of the invention, the high refractive layer has a refractive index of 2.5 to 4, the low refractive layer has the refractive index of 1.3 to 1.8, and the top layer has refractive index of 1.7 to 2.1.

In another more preferred embodiment of the invention, the high refractive layer has a refractive index of 2.8 to 3.6, the low refractive layer has the refractive index of 1.4 to 1, 7, and the upper layer has the refractive index

13 BE2022/6067 from 1.7 to 1.9. Different layers can be defined using refractive indices. By selecting layers based on their refractive index, the color of the coating can be adjusted as desired.

In a second aspect, the invention relates to a method of applying a multi-layer coating to a substrate, said method comprising the sequential steps of: a. supply of substrate; b. application of an optional bottom layer on top of the substrate;

C. application, layer by layer, above the lower layer or substrate, of a stack of a high refraction layer alternating with a low refraction layer by vapor deposition; d. optionally application of a top layer above

Vestment; wherein said low refraction layer comprises 30 to 50 at%. of silicon, from 40 to 70% at. oxygen, from 0 to 30% at. nitrogen, and 0 to 20% at. of hydrogen and in which said low refraction layer has a thickness less than 140 nm, and in that said high refraction layer comprises from 60 to 100 at%. of silicon, from O to 20% at. oxygen, from 0 to 30% at. nitrogen, and from 0 to 40% at. hydrogen, and wherein said high refraction layer has a thickness less than 75 nm.

In a preferred embodiment of the method, the vapor deposition comprises physical or chemical vapor deposition, preferably plasma-assisted chemical vapor deposition. Vapor deposition techniques offer many advantages compared to wet coatings, such as superior adhesion, absence of chemical waste, easier scaling up to industrial scale. There is therefore an interest in creating red coatings using vapor deposition techniques, and being able to adjust the shade as needed. Vapor deposition processes are used to deposit thin layers of material on a base material, said substrate.

These processes are highly sensitive and must be carried out in a chamber that is isolated from external atmospheric conditions and contaminants at very low pressure inside a vacuum. There are two types of vapor deposition, physical vapor deposition (PVD) and chemical vapor deposition (CVD).

14 BE2022/6067

The thin layer is deposited on a base material, said substrate such as glass or silicon wafers; in theory any material can have a thin layer deposited on its surface. The substrate is essentially a foundation on which the thin layer will be deposited. The design and execution of a vapor deposition process requires careful consideration of materials and equipment to ensure system compatibility. The substrate is then exposed to one or more vaporized sources; the presence of the vapors together with other stimuli will cause the thin layer to be deposited on the surface of the substrate. The type of thin layer that will be deposited is dictated by the chemistry of the vapors. Thin films deposited through processes such as vapor deposition have their own unique properties. These layers are used to reinforce or enhance the original substrate material. The layer can also be used as a constituent part of a composite structure.

This allows materials to be created for a specific application. The properties desired in the final application will dictate the type of layer to be deposited, which requires careful consideration of the materials and operating conditions for the deposition process.

In PVD, the source is a solid material in solid form inside the chamber with the substrate. Through physical processes such as heating or spraying, the solid material forms vapors which will coat the surface of the substrate.

CVP processes are different from PVD processes. Instead of forming vapors from solid material inside the chamber, gases are pumped into the chamber from an external source, which react and cause the thin film to settle. The main difference between PVD and CVD is the medium through which the vapors are generated. In PVD the vapors need to be generated from a solid or liquid source, while in PVD

CVD no new generation is required because the source is already in the vapor phase. There are notable differences in both deposition and material properties between layers deposited with PVD and CVD.

In CVD, the substrate is placed in a vacuum reactor, source gases are pumped into the reactor, which react with the surface of the substrate. This causes a thin layer to settle on the surface. External stimuli such as heat or plasma can be used to initiate or propagate the reaction, which causes the film to settle. A gaseous byproduct will form as a result of the reaction and must be pumped away. There are many different types of

15 BE2022/6067 CVD processes, but they all share the same framework. Within this framework, there is a wide range of variables that can be changed. The processes of

CVD are categorized and classified by the conditions used. For example the pressure inside the reactor, some processes are more sensitive and require a higher vacuum while others are not as critical. For this reason, there are different levels of CVD based on pressure. Another way to differentiate CVD processes is by the stimulus used inside the reactor, most CVD processes will use heat to help the reaction propagate, however some samples will degrade at high temperatures, such as polymers or biological materials. For this reason, another form of stimulus is preferred. This includes plasma-assisted CVD, which involves the conversion of precursors into plasma. CVD allows the preparation of coatings that extend the life of materials, such as the preparation of rust and corrosion resistant metals. Plasma-assisted CVD is an example of a preferred deposition technique in said invention due to their many advantages such as good coating homogeneity, high control over film thickness, high versatility on materials, high adhesion to most substrates and, what's more, these techniques do not use solvents.

In a third aspect, the invention relates to a use of the multilayer coating as a colored coating, preferably as a red coating.

However, it is obvious that the invention is not limited to this application. The method according to the invention can be applied in all kinds of multilayer coatings.

The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended to, nor should be construed as, limiting the scope of the invention.

EXAMPLES

Comparative examples 1-2: A stack with only transparent layers.

A distributed Bragg reflector strategy was used to selectively reflect red light and obtain red-colored materials on a substrate. To achieve this effect, several transparent materials with different refractive indices are required.

16 BE2022/6067

The stack includes the layers as given in Table 1.

Table 1: a 3-layer and 5-layer stack.

THE index of 1 layer refraction thickness (nm) composition n

Example: stack of 1 2.8 50-65 TiO2 3 layers 2 1.4 110-140 SiO» 3 2.8 50-65 TiO2

Examplec2: stacking of 1 2.8 50-65 TiO2 layers 2 1.4 110-140 SiO» 3 2.8 50-65 TiO2 4 1.4 110-140 SiO» 5 2.8 50-65 TiO2

The constructive interference design result for high reflectance in the 650-800 nm range with only transparent layers comprising a TiO2/SiO2 system is given in Figure 1. Bragg reflectors are effective in reflecting wavelengths selective, but there is a secondary reflection in the blue region, see figure 1.

Comparative example 3 and example 4: A stack with an a-system

Si:H/SiO2.

A distributed Bragg reflector strategy was used to selectively reflect red light and obtain red-colored materials on a substrate. To achieve this effect, several transparent materials with different refractive indices are required. A stack comprises alternating layers of a-Si:H and SiO> as described in Table 2.

17 BE2022/6067

Table 2: a 1-layer and 5-layer stack.

EE Tndicede 11 refraction layer thickness (nm) composition n - Examplec. 3: 1 3.2 50-65 a-Si:H 1 layer “Example4: 1 32 50-655 a-SEH layer stack 2 1.4 110-140 SiO” 3 3.2 50-65 a-Si: H 4 1.4 110-140 SiO» 5 3.2 50-65 a-Si:H

The results of stacking with an a-Si:H:SiO system are given in Figure 2. With its low bandgap (>2.0 eV), a-Si:H can be used to absorb 5 high energy photons, in conjunction with the distributed Bragg reflector strategy. Except that it tends to reflect most of the blue before it has a chance to absorb it.

Example 5 - 7: A multi-layer stack to provide a red colored coating.

A distributed Bragg reflector strategy was used to selectively reflect red light and obtain red-colored materials on a substrate. To achieve this effect, several transparent materials with different refractive indices are required.

Assume a stack comprising the layers as described in Table 3. All three examples have a Si substrate as the base.

Table 3: multilayer stacking. layer thickness index composition refraction n (nm) _ Example5: 1 32 50-65 a-SiH stacking at 5. layers 2 1.4 110-140 SiO» 3 3.2 50-65 a-Si:H

18 BE2022/6067 4 1.4 110-140 SiO2 3.2 50-60 a-Si:H

Example 6: upper mn 1.7 45-60 Al»O3 layer

AR + 1 3.2 50-65 a-Si:H 5 stack 2 1.4 110-140 SiO2 layers 3 3.2 50-65 a-Si:H 4 1.4 110-140 SiO2 5 3.2 50-65 a-Si:H

Example 7: upper mn 1.7 45-60 Al»O3 layer

AR + 1 3.2 50-65 a-Si:H 5 stack. 2 1.4 110-140 SiO2 layers + layer

LE 3 3.2 50-65 a-Si:H lower 4 1.4 110-140 SiO2 5 3.2 50-65 a-Si:H lower eu layer / / TiAIN

Compounds obtained with a Si target are the most appropriate. In particular, the SiO2-a-Si:H duo proved to be very effective due to the considerable difference in refractive index (1.4 and 3.2), and because the a-Si:H intrinsically absorbs in the 5 blue region. There is a synergistic effect between interference color and intrinsic color.

An advantage of this strategy is that the color shade can be controlled by changing the following operational parameters: the number of layers and their thickness.

Improvement is desired to get rid of the influence of the substrate and be able to achieve the same result regardless of the substrate. For this purpose, a highly absorbent black bottom layer, TiAIN, is used.

The top layer is a topcoat consisting of an anti-reflective layer to significantly reduce secondary reflections, especially in the region

19 BE2022/6067 blue. This includes a transparent layer of determined thickness of a material whose refractive index is intermediate between the high refractive index and air. Al203 was chosen due to the best refractive index match.

The results with 5-layer stacking and the improvements introduced by the black layer and AR are shown in Figure 3.

It can be concluded from the examples provided that optimizing red color purity ideally requires an anti-reflective top layer, a stack of a-Si:H and SiO2 layers, and a bottom layer.

Claims (14)

20 BE2022/6067 CLAIMS 1. Multi-layer coating comprising a stack of a layer with a high refractive index alternating with a layer with a low refractive index, in which said low refractive layer comprises from 30 to 50% at. of silicon, from 40 to 70% at. oxygen, from 0 to 30% at. nitrogen, and 0 to 20% at. of hydrogen and in which said low refraction layer has a thickness less than 140 nm characterized in that said high refraction layer is based on silane and comprises from 60 to 100% at. of silicon, from O to 20% at. oxygen, from 0 to 30% at. nitrogen, and from 0 to 40% at. of hydrogen, and in which said high refractive layer has a thickness less than 75 nm, and in which the refractive index of the high refractive layer ranges from 2.5 to 4 and preferably from 2.8 to 3 ,6. 2. Multi-layer coating according to at least one of claim 1, in which the high refraction layer, and comprises: - more preferably from 70 to 100% at. of silicon, from O to 10% at. oxygen, from 0 to 10% at. nitrogen, and from 0 to 30% at. hydrogen; and - most preferably from 70 to 100% at. silicon and O at 30% at. of hydrogen. 3. Multi-layer coating according to at least one of claims 1 to 2, wherein the high refraction layer has a thickness preferably between nm and 75 nm and more preferably between 50 nm and 65 nm. 4. Multi-layer coating according to at least one of claims 1 to 3, in which the refractive index of the low refractive layer ranges from 1.3 to 1.8, preferably from 1.4 to 1.7 . 5. Multi-layer coating according to at least one of claims 1 to 4, in which the low refractive layer is based on silica, and comprises: - more preferably from 30 to 50% at. of silicon, from 50 to 70% at. oxygen, from 0 to 20% at. nitrogen, and 0 to 10% at. hydrogen; and - most preferably 30 to 50% at. of silicon and 50 to 70% at. of oxygen. 21 BE2022/6067 6. Multi-layer coating according to at least one of claims 1 to 5 in which the low refraction layer has a thickness preferably between 55 nm and 140 nm and more preferably between 110 and 140 nm. 7. Multi-layer coating according to at least one of claims 1 to 6, wherein said multi-layer coating further comprises an upper layer above said stack, preferably the upper layer comprises an anti-reflective layer. 8. Multi-layer coating according to claim 7, wherein the upper layer comprises any transparent material which comprises the refractive index of 1.7 to 2.1, preferably 1.7 to 1.9 and preferably the upper layer includes: - from 30 to 50% at. of silicon, from 0 to 50% at. oxygen, 0 to 60% at. nitrogen, and 0 to 20% at. hydrogen; and - more preferably from 30 to 50% at. of silicon, from O to 40% at. oxygen, 25 to 60% nitrogen, and 0 to 10% at. of hydrogen. 9. Multi-layer coating according to at least one of claims 7 to 8 in which the thickness of the upper layer is greater than 45 nm, preferably between 45 nm and 120 nm and more preferably between 45 nm and 60 nm. 10. Multi-layer coating according to at least one of claims 1 to 9, wherein said multi-layer coating further comprising a lower layer between said stack and a substrate, preferably said lower layer comprises an absorbent layer. 11. Multi-layer coating according to claim 10, in which said lower layer comprises: - from 70 to 100% at. of silicon, from 0 to 10% at. oxygen, 0 to 10% at. nitrogen, and 0 to 30% at. hydrogen; and - more preferably a silicone compound which comprises from 70 to 100% at. of silicon and from 0 to 30% at. of hydrogen. 12. Process for applying a multi-layer coating to a substrate, said process comprising the sequential steps of: has. supply of substrate; 22 BE2022/6067 b. application of an optional bottom layer on top of the substrate; vs. application, layer by layer, above the lower layer or the substrate, of a stack of a high refraction layer alternating with a low refraction layer by vapor deposition; d. optionally application of a top layer above the stacking; wherein said low refraction layer comprises 30 to 50 at%. of silicon, from 40 to 70% at. oxygen, from 0 to 30% at. nitrogen, and 0 to 20% at. of hydrogen and in which said low refraction layer has a thickness less than 140 nm, and in that said high refraction layer is based on silane and comprises from 60 to 100% at. silicon, from 0 to 20% at. oxygen, from 0 to 30% at. nitrogen, and from 0 to 40% at. of hydrogen, and in which said high refractive layer has a thickness less than 75 nm, and in which the refractive index of the high refractive layer ranges from 2.5 to 4 and preferably from 2.8 to 3 ,6.. 13. Method for obtaining a multi-layer coating according to claim 12, wherein said vapor deposition comprises physical or chemical vapor deposition, preferably plasma-assisted chemical vapor deposition. 14. Use of the multi-layer coating according to at least one of claims 1 to 11 or of the method according to at least one of claims 12 to 13 to create colored coatings, preferably red coatings.