formulation

Abstract

The present invention relates to a formulation for preparing an optical layer containing a metal oxide. The formulation may exhibit at least one of properties as an advanced material or as a high performance material. The formulation may be used in the nanotechnology process to make semiconductor device / display device application, for example semiconductor chip, or a liquid crystal, quantum dot, OLED display fabricated on a substrate controlled by semiconductors.

Description

[0001]Foreignfiling_text P23-203 - 1 - Formulation Field of the invention The present invention relates to a formulation comprising a metal halide, 5 use of a formulation, method for preparing a formulation, method for preparing a composite, a composite, an optical device and a display device. Background Art Leading edge optical devices typically include optical gratings made from 10 composite materials having a substrate as a support and complex and interlaced patterns thereon, the patterns being made up of different layers or stacks of layers. Usually, the creation of such complex and interlaced patterns demands for structuring processes, which become increasingly challenging with decreasing size of structural dimensions to be prepared. 15 In addition to a wide range of possible uses in various fields of application, such as in spectrometers or in optical storage systems (CD, DVD, etc.), diffractive gratings are the core components of so-called XR devices, usually in the form of glasses. In this context, R stands for the term reality 20 and X denotes different attributes such as, for example, virtual, augmented, mixed and so forth. Hence, diffractive gratings form part of the core of the so-called optical engine in XR devices, specifically in augmented reality and mixed reality glasses. Virtual reality glasses, when built as a head mounted display, are often composed of a conventional liquid crystal (LC) organic 25 light emitting diode (OLED) display being embedded in the device directly in front of the eyes of the user, and thus do not necessarily require diffractive gratings. In contrast, augmented and mixed reality glasses are designed to enable consumers to obtain visual impressions of their environment, at its best as if they would not wear any glasses at all. However, they also make 30 it possible to provide and serve digital information and to also project it into the field of vision of individuals. Additional digital information is gathered from recognizing and analyzing the environment, the individual inspects or Foreignfiling_text P23-203 - 2 - looks at. To convey and project supporting digital information into the eyes of an individual, the augmented or mixed reality glasses are equipped with an information supply unit, which is coupled to an optical waveguide system that transports the optically coded supporting information through it directly 5 to the lens of the glasses. Here, the information passes a diffractive grating which couples the incident light into the lens and splits it according to its angular information and its spectral bands by diffraction. After incoupling of the light, the lens serves as waveguide enabling transport of the light to and into the pupil of an individual. The location of light incoupling is independent 10 of any preferred position and thus of the implication of technical needs. The direction of traversal of light within the lenses is determined by the diffractive grating diffracting or splitting the light. At certain positions in the lens, a second and a third diffractive grating serves for changing the direction of light traversal and thereby enforcing the light to be projected 15 into pupil of the user. The light traversal in the glasses is accomplished by total internal reflection (TIR) of the light, thus bouncing several times between the glass interfaces until reaching another diffractive grating, which changes the internal TIR direction of the light (see Figure 2). The second and third grating are geometrically aligned in different directions 20 with respect to the first and incoupling grating, e. g. by a certain angular distortion of the longitudinal axis, thus allowing to change the direction of propagation of totally internally reflected light. Needless to say, the lens itself or the material of which lenses are made of shall not be absorbing. Otherwise, the supportive information never reaches the pupil of the user or 25 only with strongly depleted light intensity. The process works regardless of the use of reflection or transmission gratings. Usually, the lenses are equipped with both types of gratings to properly guide the light. It should also be mentioned that there are differences in the optical performance of reflection and transmission gratings, which, however, are of no further 30 interest in the context of the current invention. The basic structure of the gratings is very similar, which is more important at this point. Foreignfiling_text P23-203 - 3 - Nevertheless, there are different designs and structures such as surface relief (SR) or volume phase holographic (VPH) gratings to achieve waveguide. Both types are very similar in appearance. In the simplest case, the gratings are mounted onto the surface of a waveguiding material, here 5 the lens. The grating itself is composed of an array of fine structures, mostly trenches of a first material type Material 01 with a refractive index RI 01, however, not limited thereto. The geometrical shape of the trenches may be manifold, from rectangular, over V-shaped trenches, U-shaped and there like. The width, including structures with different widths, the geometrical 10 form of the trenches, their pitch as well as their depth, including different depths, are specially designed to influence the diffraction pattern of the incident light to be diffracted. In case of VPH gratings, the trenches or structures of a first material type 15 (Material 01) having a refractive index (RI 01) are filled by a second material type (Material 02) having a refractive index (RI 02), wherein RI 02 is incrementally different from RI 01 (see Figures 1 and 3). For the sake of completeness, it should be mentioned that Material 01 or Material 02 may be composed of a stack of structured layers, each containing a different 20 material composition with different refractive index, stacked on top of each other, thereby forming Material 01 or Material 02 having an effective or graded refractive index RI 01 or RI 02, respectively. Incidentally, the (effective or graded) refractive indices RI 01 and RI 02 depend on the refractive index of the waveguide or the lens from which the glasses are 25 made of. If a glass lens with high refractive index (n03 > 1.46) is used, the (effective or graded) refractive indices of Material 01 and Material 02 are considered to be higher than that of the lens itself, whereby a RI value of 2.0 can be reached and exceeded. Surface relief (SR) gratings may look similar and may also include a second type of material as a filler for the 30 trenches, but the trenches can also be just air. High performance gratings, especially those of VPH-type, may be manufactured using standard Foreignfiling_text P23-203 - 4 - lithography and deposition techniques known from micro-fabrication such as, for example, the manufacturing of integrated circuits. Such standard techniques typically include physical vapor deposition (PVD) 5 or chemical vapor deposition (CVD) processes and often suffer from incomplete gap filling due to unfavourable deposition and / or layer growth deposition properties including increased deposition and / or growth rates at corners and edges. Such incomplete gap filling results in the formation of voids within the structures to be filled by the PVD- and CVD-materials. In 10 addition to the formation of voids, the surface of the substrate is covered by a PVD and / or CVD layer that is almost as thick as the maximum depth of the deepest structure to be filled by the deposited gap filling material (see Figures 4 and 5). In some applications, however, it may be necessary to expose the surface of the substrate so that it is available for further 15 processing. Consequently, undesired overburden layers from PVD or CVD need to be removed, for example by chemical mechanical planarization (CMP) without harming the original substrate surface underneath. Although CMP is very well established in the process of manufacturing integrated circuits, CMP is a time consuming and costly process and can be seen as a 20 potential economic drawback for mass production of leading-edge optical devices, particularly the mass production of diffractive gratings. It would therefore be desirable to have a solution for an advanced and cost-efficient manufacturing of optical gratings where gap filling does not require CMP (see Figure 6). 25 For that reason, more cost-effective production technology allowing for lower cost of ownership is needed. Foreignfiling_text P23-203 - 5 - Summary of the invention The inventors newly have found that there are still one or more considerable problems for which improvement is desired, as listed below: expanding the parameter space that allows adjusting the optical parameters 5 / optical properties of an obtained optical layer / composite through the combination of at least two metal precursors, optimizing the solid content in a formulation by improving the solubility of metal precursors, changing / optimizing solvents of a formulation, providing a printable formulation for preparing an optical layer / composite containing a material 10 which provides sufficiently high refractive indices after curing, namely after lower temperature curing providing a formulation for fabricating an optical layer / composite which enables to prepare a dense, crack-less or crack-free optical layer and enables to fill up of cavities, trenches or gaps after curing; providing a formulation for preparing an optical layer / composite containing 15 a metal oxide precursor material of a high refractive index material, which is well dispersed in the formulation; simpler and / or cost-efficient method for preparing an optical layer / composite with using the formulation; realizing a more stable formulation, providing suitable formulation for wet printing, namely for spin-coating or ink jetting, realizing continuous inkjet printing. 20 The inventors aimed to solve one or more of the above-mentioned problems. Then, the present inventors have surprisingly found that one or more of the 25 above-described technical problems can be solved by the features as defined in the claims. Namely, it is found a novel formulation, preferably to be used for preparing an optical layer comprising a metal oxide or to be used for filling one or 30 more trenches of a patterned surface or an uneven surface of a substrate, comprising at least, essentially consisting of or consisting of: a 1stmetal halide represented by any one of formulae (I) to (V); Foreignfiling_text P23-203 - 6 - a 2ndmetal halide represented by any one of formulae (I’) to (V’); and a solvent. M1X12- (I) M2X23 - (II) 5 M3X34 - (III) M4X45- (IV) M5X56 - (V) wherein M1is a divalent metal, preferably M1’is selected from Zn or Sn; M2is a trivalent metal, preferably M2is Bi; 10 M3is a quadrivalent metal selected from Zr, Ti or Hf; M4is a pentavalent metal selected from V, Nb or Ta; M5is Mo or W; and X1, X2, X3, X4, X5, X6are each independently a halogen, preferably X1, X2, X3, X4, X5, X6are each independently selected from F, Cl, Br, I, more 15 preferably X1, X2, X3, X4, X5, X6are Cl. M1’X1’2- (I’) M2’X2’3 - (II’) M3’X3’4 - (III’) M4’X4’5- (IV’) 20 M5’X5’6- (V’) wherein M1’is a divalent metal, preferably M1’is selected from Zn or Sn; M2’is a trivalent metal, preferably M2’is Bi; M3’is a quadrivalent metal selected from Zr, Ti or Hf; M4’is a pentavalent metal selected from V, Nb or Ta; 25 M5’is Mo or W; and X1’, X2’, X3’, X4’, X5’, X6’are each independently a halogen, preferably X1’, X2’, X3’, X4’, X5’, X6’are each independently selected from F, Cl, Br, I, more preferably X1’, X2’, X3’, X4’, X5’, X6’Cl; and said 1stmetal halide and the 2ndmetal halide are different of each other; 30 and the weight ratio of the 2ndmetal halide to the 1stmetal halide is less than 1, preferably in the range from 0.01 to 1. Preferably the total content of the 2nd Foreignfiling_text P23-203 - 7 - metal halide based on the total mass of the 1stmetal halide is in the range from 0.1 to 100wt%. In another aspect, the present invention also relates to use of the 5 formulation of the present invention for preparing a composite, preferably for preparing a layered composite, more preferably for preparing an optical layer or for filling one or more trenches of a patterned surface or an uneven surface of a substrate. 10 In another aspect, the present invention further relates to a method for preparing a formulation of the present invention, comprising at least, essentially consisting of, or consisting of; following step (A): (A) Mixing a 1stmetal halide represented by any one of formulae (I) to (V), a 2ndmetal halide represented by any one of formulae (I’) to (V’) and a 15 solvent. M1X12- (I) M2X23 - (II) M3X34 - (III) M4X45- (IV) 20 M5X56- (V) wherein M1is a divalent metal, preferably M1is Zn or Sn; M2is a trivalent metal, preferably M2is Bi; M3is a quadrivalent metal selected from Ti, Zr or Hf; M4is a pentavalent metal selected from V, Nb or Ta; 25 M5is Mo or W; and X1, X2, X3, X4, X5, X6are each independently a halogen, preferably X1, X2, X3, X4, X5, X6are each independently selected from F, Cl, Br, I, more preferably X1, X2, X3, X4, X5, X6are Cl. M1’X1’2- (I’) 30 M2’X2’3- (II’) M3’X3’4 - (III’) M4’X4’5- (IV’) Foreignfiling_text P23-203 - 8 - M5’X5’6 - (V’) wherein M1’is a divalent metal, preferably M1’is Zn or Sn; M2’is a trivalent metal, preferably M2’is Bi; M3’is a quadrivalent metal selected from Ti, Zr or Hf; 5 M4’is a pentavalent metal selected from V, Nb or Ta; M5’is Mo or W; and X1’, X2’, X3’, X4’, X5’, X6’are each independently a halogen, preferably X1’, X2’, X3’, X4’, X5’, X6’are each independently selected from F, Cl, Br, I, more preferably X1’, X2’, X3’, X4’, X5’, X6’Cl; and 10 said 1stmetal halide and the 2ndmetal halide are different of each other; and the weight ratio of the 2ndmetal halide to the 1stmetal halide is 1 or less, preferably in the range from 0.01 to 1. Preferably the total content of the 2ndmetal halide based on the total mass of the 1stmetal halide is in the range 15 from 0.1 to 100wt%. In another aspect, the present invention further relates to a method for preparing a composite containing a metal oxide, preferably said metal oxide is selected from metal monoxide, metal dioxide and metal pentoxide, or a 20 combination of these; comprising the following steps (a) and (b): (a) providing the formulation of the present invention onto a surface of a substrate, preferably by wet deposition process, more preferably by spin- coating or an area selective printing, preferably said area selective printing is an ink-jetting, even more preferably by ink-jetting; and 25 (b) applying a thermal treatment to the formulation provided on the surface of the substrate to convert at least a part of the metal oxide precursor of the formulation to a metal oxide. Preferably said composite being a layered composite, more preferably said layered composite is an optical layer. 30 In another aspect, the present invention further relates to a composite, preferably being a layered composite, preferably said layered composite is Foreignfiling_text P23-203 - 9 - an optical layer, obtained or obtainable by the method of the present invention. In another aspect, the present invention further relates to a composite, preferably being a layered composite, preferably said layered composite is 5 an optical layer, derived from the formulation of the present invention. In another aspect, the present invention further relates to an optical device comprising the composite of the present invention, and a substrate comprising a patterned surface or an uneven surface. Preferably a gap or 10 trench of said patterned surface or an uneven surface of the substrate is at least partly filled with said composite. Preferably said substrate is a patterned substrate comprising topographical features on the surface thereof. Preferably said composite fills at least a part of a gap of said topographical features, more preferably said composite 15 fills a trench of the patterned substrate. In another aspect, the present invention further relates to a display device comprising at least one functional medium configured to direct and modulate a light or configured to emit light; and the composite of the 20 present invention. Technical effects of the invention The present invention may provide one or more of following effects; expanding the parameter space that allows adjusting the optical parameters 25 / optical properties of an obtained optical layer / composite through the combination of at least two metal precursors, optimizing the solid content in a formulation by improving the solubility of metal precursors, changing / optimizing solvents of a formulation, providing a printable formulation for preparing an optical layer / composite containing a material 30 which provides sufficiently high refractive indices after curing, namely after lower temperature curing providing a formulation for fabricating an optical Foreignfiling_text P23-203 - 10 - layer / composite which enables to prepare a dense, crack-less or crack-free optical layer and enables to fill up of cavities, trenches or gaps after curing; providing a formulation for preparing an optical layer / composite containing a metal oxide precursor material of a high refractive index material, which is 5 well dispersed in the formulation; simpler and / or cost-efficient method for preparing an optical layer / composite with using the formulation; realizing a more stable formulation, providing suitable formulation for wet printing, namely for spin-coating or ink jetting, realizing continuous inkjet printing. 10 Preferred embodiments of the present invention are described hereinafter and in the dependent claims. Brief description of the figures Fig.1: Schematic cross-sectional view of a VPH grating with a Material 01 15 and a Material 02, wherein the refractive index IR 01 of Material 01 is incrementally different to the refractive index IR 02 of Material 02. Fig.2: Schematic cross-sectional view of a VPH grating enabling light diffraction (transmissive case) including propagation of diffracted light within waveguide (e.g. lens) by total internal reflection. 20 Fig.3: Schematic cross-sectional view of a VPH grating providing gaps (trenches) to be filled with a high refractive index material (Material 02), wherein the refractive index of Material 02 is incrementally different form the refractive index of Material 01 flanking the gaps (trenches). Fig.4: Schematic representation of PVD- or CVD-mediated gap filling 25 process and removal of undesired overburden. Fig.5: Schematic representation of PVD- or CVD-mediated gap filling process creating and leaving voids within gaps and deposited layers. Fig.6: Schematic representation of gap filling process using formulations containing inventive metal complex or formulations thereof being converted 30 to metal oxides. List of reference signs Foreignfiling_text P23-203 - 11 - 1. Material 02 with RI 02 2. Material 01 with RI 01 3. Substrate (e.g. glass) 4. Diffraction of incident light represented by broad arrow 5 5. Total internal reflection of light (TIR) 6. Waveguide 7. Structured layer stack with gaps (trenches) 8. Substrate (e.g. glass or silicon) 9. Overburden of material (e.g. high refractive index material or high etch 10 resistant material) 10. Material (e.g. high refractive index material or high etch resistant material) providing gap fill 11. Voids 12. Formulation (e.g. ink) of high refractive index material (e.g. metal oxide 15 precursor) 13. High refractive index material (e.g. metal oxide) providing gap fill with optional concave geometry 14. Overburden layer (optional) 15. Energy 20 Definition of the terms In the context of the present invention, the term “formulation medium” or the plural term “formulation media” as used herein, denote one or more compounds serving as a solvent, suspending agent, carrier and / or matrix 25 for the metal oxide precursor compound and any other component included in the formulation. Formulation media are generally inert compounds that do not react with said metal oxide precursor compounds and said other components. Formulation media may be liquid compounds, solid compounds or mixtures thereof. Typically, formulation media are organic 30 compounds. Foreignfiling_text P23-203 - 12 - The term “surfactant” as used herein, refers to an additive that reduces the surface tension of a given formulation. The term “wetting and dispersion agent” as used herein, refers to an 5 additive that increases the spreading and filling properties of a given formulation. In this way, the tendency of the molecules to adhere to each other is reduced. The term “adhesion promoter” as used herein, refers to an additive that 10 increases the adhesion of a given formulation. The term “polymer matrix” as used herein, refers to an additive that acts as a macromolecular matrix for one or more components of a given formulation. 15 The term “optical device” as used herein, relates to a device containing one or more optical components for forming a light beam including, but not limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. 20 Preferred optical devices in the context of the present invention are waveguides for augmented reality (AR) device, for virtual reality (VR) device and / or for mixed reality (MR) device, or preferred optical devices are augmented reality (AR) glasses, virtual reality (VR) glasses and / or mixed reality (MR) glasses. 25 The term “display device” as used herein, is a kind of an optical device configured to output / present information in visual or tactile form. Examples are Liquid crystal display (LCD), Light emitting diode display (LED display), organic light emitting display (OLED), micro-LED display, quantum dot 30 display (QLED), AR display, VR display, MR display, plasma (PDP) display, electroluminescent (ELD) display. Preferred optical devices in the context of the present invention is AR display, VR display or MR display. Foreignfiling_text P23-203 - 13 - Detailed of the invention The present invention relates to a formulation for preparing an optical layer containing a metal oxide, preferably for preparing a composite, more 5 preferably for preparing a layered composite, comprising at least, essentially consisting of, or consisting of; - a 1stmetal halide represented by any one of formulae (I) to (V), - a 2ndmetal halide represented by any one of formulae (I’) to (V’) and - a solvent. 10 M1X12- (I) M2X23 - (II) M3X34 - (III) M4X45- (IV) M5X56 - (V) 15 wherein M1is a divalent metal, preferably M1is Zn or Sn; M2is a trivalent metal, preferably M2is Bi; M3is a quadrivalent metal selected from Zr, Ti or Hf; M4is a pentavalent metal selected from V, Nb or Ta; M5is Mo or W; and 20 X1, X2, X3, X4, X5, X6are each independently a halogen, preferably X1, X2, X3, X4, X5, X6are each independently selected from F, Cl, Br, I, more preferably X1, X2, X3, X4, X5, X6are Cl. M1’X1’2- (I’) M2’X2’3 - (II’) 25 M3’X3’4 - (III’) M4’X4’5- (IV’) M5’X5’6 - (V’) wherein M1’is a divalent metal, preferably M1’is selected from Zn or Sn; M2’is a trivalent metal, preferably M2’is Bi; 30 M3’is a quadrivalent metal selected from Zr, Ti or Hf; M4’is a pentavalent metal selected from V, Nb or Ta; M5’is Mo or W; and Foreignfiling_text P23-203 - 14 - X1’, X2’, X3’, X4’, X5’, X6’are each independently a halogen, preferably X1’, X2’, X3’, X4’, X5’, X6’are each independently selected from F, Cl, Br, I, more preferably X1’, X2’, X3’, X4’, X5’, X6’Cl; and said 1stmetal halide and the 2ndmetal halide are different of each other; 5 and the weight ratio of the 2ndmetal halide to the 1stmetal halide is less than 1, preferably in the range from 0.01 to 1. Preferably the total content of the 2ndmetal halide based on the total mass of the 1stmetal halide is in the range from 0.1 to 100wt%. 10 - 1stMetal halide According to the present invention, said 1stmetal halide is represented by one of the following chemical formulae (I) – (V); M1X12 - (I) 15 M2X23 - (II) M3X34- (III) M4X45 - (IV) M5X56 - (V) wherein M1is a divalent metal, preferably M1 is Zn or Sn; 20 M2is a trivalent metal, preferably M2is Bi; M3is a quadrivalent metal selected from Zr, Ti or Hf; M4is a pentavalent metal selected from V, Nb or Ta; M5is Mo or W; and X1, X2, X3, X4, X5, X6are each independently a halogen, preferably X1, X2, 25 X3, X4, X5, X6are each independently selected from F, Cl, Br, I, more preferably X1, X2, X3, X4, X5, X6are Cl. As said 1stmetal halide, a publicly known metal halide which falls within one of the above-mentioned chemical formulae can be used. 30 Foreignfiling_text P23-203 - 15 - Examples of 1stmetal halide is W halides, Ta halides, Sn halides, Zr halides, Zn halides, Bi halides, Mo halides, Ti halides, V halides, Hf halides or a combination of any of these. 5 More preferably, said 1stmetal halide is selected from ZnCl2, BiCl3, ZrCl4, TiCl4, HfCl4, TaCl5, NbCl5, VCl5,WCl6,MoCl6or a combination of any of these. - 2ndMetal halide 10 According to the present invention, said 2ndmetal halide is represented by one of the following chemical formulae (I) – (V); M1X12 - (I’) M2’X2’3- (II’) M3’X3’4 - (III’) 15 M4’X4’5 - (IV’) M5’X5’6- (V’) wherein M1’is a divalent metal, preferably M1’is selected from Zn or Sn; M2’is a trivalent metal, preferably M2’is Bi; M3’is a quadrivalent metal selected from Zr, Ti or Hf; 20 M4’is a pentavalent metal selected from V, Nb or Ta; M5’is Mo or W; and X1’, X2’, X3’, X4’, X5’, X6’are each independently a halogen, preferably X1’, X2’, X3’, X4’, X5’, X6’are each independently selected from F, Cl, Br, I, more preferably X1’, X2’, X3’, X4’, X5’, X6’Cl. 25 According to the present invention, said 1stmetal halide and the 2ndmetal halide are different of each other; and the weight ratio of the 2ndmetal halide to the 1stmetal halide is 1 or less, preferably in the range from 0.01 to 1. Preferably the total content of the 2nd30 metal halide based on the total mass of the 1stmetal halide is in the range from 0.1 to 100wt%. Foreignfiling_text P23-203 - 16 - As said 2ndmetal halide, a publicly known metal halide which falls within one of the above-mentioned chemical formulae can be used. Examples of 2ndmetal halide is Sn halides, W halides, Ta halides, Sn 5 halides, Zr halides, Zn halides, Bi halides, Mo halides, Ti halides, V halides, Hf halides or a combination of any of these. More preferably, said 2ndmetal halide precursor is selected from ZnCl2, SnCl2, BiCl3, ZrCl4, TiCl4, HfCl4, TaCl5, NbCl5, VCl5,WCl6,MoCl6or a 10 combination of any of these. According to the present invention, the total content of all metal halide(s) in the formulation is in the range from 0.1 w% to 50 w% based on the total mass of the formulation, preferably it is from 1wt.% to 30wt.%, more 15 preferably from 5 to 20wt.%. It is believed that the above-mentioned total amount of the metal halide precursors based on the total amount of formulation is suitable to realize an improved gap filling or fabricating a thin layer placed directly onto a 20 patterned surface or directly onto an uneven surface of a substrate / under layer. -Solvent According to the present invention, the formulation of the present invention 25 contains a solvent. In a preferred embodiment of the present invention, the solvent is an organic solvent. More preferably said organic solvent is selected from one or more members of the group consisting of ethylene glycol monoalkyl 30 ethers, preferably it is ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether and / or ethylene glycol monobutyl ether; diethylene glycol dialkyl ethers, preferably it is diethylene Foreignfiling_text P23-203 - 17 - glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether and / or diethylene glycol dibutyl ether; propylene glycol monoalkyl ethers, preferably it is propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether and / or propylene glycol 5 monopropyl ether; 1,3-dimethoxy-2-propanol, ethylene glycol alkyl ether acetates, preferably it is methyl cellosolve acetate and / or ethyl cellosolve acetate; propylene glycol alkyl ether acetates, preferably it is propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate and / or propylene glycol monopropyl ether acetate; ketones, 10 preferably it is methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone and / or cyclohexanone; alcohols, preferably it is ethanol, propanol, butanol, hexanol, cyclo hexanol, ethylene glycol, propylene glycol, triethylene glycol and / or glycerin; esters, preferably it is ethyl 3- ethoxypropionate, methyl 3-methoxypropionate and / or ethyl lactate; and 15 cyclic esters, preferably it is gamma-butyro-lactone; preferably said solvent is ethylene glycol monoalkyl ethers, diethylene glycol dialkyl ethers, propylene glycol, ethylene glycol, propylene glycol monoalkyl ethers, ethylene glycol alkyl ether acetates, propylene glycol alkyl ether acetate, more preferably said solvent is selected from propylene glycol alkyl ether 20 acetates, ethylene glycol monoalkyl ethers, propylene glycol and propylene glycol monoalkyl ethers, 1,3-dimethoxy-2-propanol. It is believed that the printing, especially ink jetting of structures is considered as a highly cost-efficient production step. Spin-coating is a 25 convenient method and is preferable to form a uniform thin layer. Thus, suitable solvents of the formulation for spin-coating / inkjet printing the structures or filling up of cavities and structures, is described here. After printing, deposition and fill up of structures, at least a part of the 30 material as the metal halide precursor needs to become converted into the respective metal oxides by any known means know to the persons skilled in the art (thermally, photochemically, etc.). Foreignfiling_text P23-203 - 18 - - Water According to the present invention, the formulation contains water, and the stoichiometric amount of water is in the range from 100 to 400 mol% based 5 on the total amount of metal oxide precursor, preferably the stoichiometric amount of water based on the total amount of the metal oxide precursor is in the range from 150 to 300 mol%, even more preferably from 180 to 270 mol%. 10 -Additives In some embodiments of the present invention, the formulation may optionally comprise one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices. Or, in some embodiments, the formulation of the present invention does not 15 comprise any additives. In a preferred embodiment of the present invention, the formulation is an ink formulation being suitable for inkjet printing. Typical requirements for ink formulations are surface tensions in the range from 20 mN / m to 30 mN / m 20 and viscosities in the range from 5 mPa·s to 30 mPa·s. -Use In another aspect, the present invention also relates to use of the formulation of the present invention for preparing an optical layer containing 25 a metal oxide, preferably for preparing a composite, more preferably for preparing a layered composite. The present invention may also relate to use of the formulation of the present invention for preparing an encapsulation layer of an electronic device. 30 -Method for preparing a formulation Foreignfiling_text P23-203 - 19 - In another aspect, the present invention also relates to a method for preparing a formulation of the present invention, containing at least, essentially consisting of or consisting of, the following steps; following step (A): 5 (A) Mixing a 1stmetal halide represented by any one of formulae (I) to (V), a 2ndmetal halide represented by any one of formulae (I’) to (V’) and a solvent. M1X12 - (I) M2X23- (II) 10 M3X34- (III) M4X45 - (IV) M5X56 - (V) wherein M1is a divalent metal, preferably M1is selected from Zn or Sn; M2is a trivalent metal, preferably M2is Bi; 15 M3is a quadrivalent metal selected from Ti, Zr or Hf; M4is a pentavalent metal selected from V, Nb or Ta; M5is Mo or W; and X1, X2, X3, X4, X5, X6are each independently a halogen, preferably X1, X2, X3, X4, X5, X6are each independently selected from F, Cl, Br, I, more 20 preferably X1, X2, X3, X4, X5, X6are Cl. M1’X1’2 - (I’) M2’X2’3- (II’) M3’X3’4- (III’) M4’X4’5 - (IV’) 25 M5’X5’6 - (V’) wherein M1’is a divalent metal, preferably M1’is Zn; M2’is a trivalent metal, preferably M2’is Bi; M3’is a quadrivalent metal selected from Ti, Zr or Hf; M4’is a pentavalent metal selected from V, Nb or Ta; 30 M5’is Mo or W; and Foreignfiling_text P23-203 - 20 - X1’, X2’, X3’, X4’, X5’, X6’are each independently a halogen, preferably X1’, X2’, X3’, X4’, X5’, X6’are each independently selected from F, Cl, Br, I, more preferably X1’, X2’, X3’, X4’, X5’, X6’Cl; and said 1stmetal halide and the 2ndmetal halide are different of each other; 5 and the weight ratio of the 2ndmetal halide to the 1stmetal halide is 1 or less, preferably in the range from 0.01 to 1. Preferably the total content of the 2ndmetal halide based on the total mass of the 1stmetal halide is in the range from 0.1 to 100wt%. 10 -Method for preparing a composite containing a metal oxide In another aspect, the present invention also relates to a method for preparing a composite containing a metal oxide, preferably said metal oxide is selected from metal monoxide, metal dioxide or metal pentoxide, or a 15 combination of these; comprising at least the following steps (a) and (b): (a) providing the formulation of the present invention onto a surface of a substrate or a surface of an under layer placed on a substrate, preferably by wet deposition process, more preferably by spin-coating or ink-jetting, even more preferably by ink-jetting; and 20 (b) applying a thermal treatment to the formulation provided on the surface of the substrate or on the surface of the underlayer placed on the substrate to convert at least a part of the metal oxide precursor of the formulation to a metal oxide. Preferably said composite being a layered composite, more preferably said 25 layered composite is an optical layer. -Step (a) According to the present invention, said formulation may preferably be provided onto a surface of a substrate or a surface of an underlayer by wet 30 deposition process. Said wet deposition process is drop casting, coating, or printing. A more preferred coating method is spin-coating, spray coating, slit coating, or slot-die coating. A more preferred printing method is flexo Foreignfiling_text P23-203 - 21 - printing, gravure printing, inkjet printing, EHD printing, offset printing, or screen printing. Furthermore, preferred printing method is spray coating and inkjet printing and the most preferred one is inkjet printing. 5 Thus, in a preferred embodiment, the formulation is applied onto a surface of a substrate or a surface of an underlayer by spin-coating or ink-jetting in step (a). From a viewpoint of cost effectiveness, ink-jetting can preferably be used. 10 In a preferred embodiment of the present invention, the formulation provided in step (a) of the method is an ink formulation being suitable for inkjet printing. Typical requirements for ink formulations are surface tensions in the range from 20 mN / m to 30 mN / m and viscosities in the range from 5 mPa·s to 30 mPa·s. 15 Depending on the specific problem to be solved, the formulation needs to be deposited either as a homogeneous, dense and thin layer covering the entire surface of the substrate or the entire surface of an underlayer by a coating method or the formulation needs to be deposited locally in a 20 structured manner, thus requiring for a printing method. Both, coating and printing methods require formulations to be formulated in an adequate manner to comply with the physico-chemical needs of the respective coating and printing method as well as to comply with certain needs regarding the surface of the substrate to be coated or printed. 25 In a preferred embodiment of the method of the present invention, the surface of the substrate is pre-treated by a surface cleaning process. Preferred surface cleaning processes are silicon wafer cleaning processes such as described in W. Kern, The Evolution of Silicon Wafer Cleaning 30 Technology, J. Electrochem. Soc., Vol.137, 6, 1990, 1887-1892 and in New Process Technologies for Microelectronics, RCA Review 1970, 31, 2, 185-454. Such silicon wafer cleaning processes include wet cleaning Foreignfiling_text P23-203 - 22 - process involving cleaning solvents (e.g., isopropanol (IPA)); wet etching processes involving hydrogen peroxide solutions (e.g., piranha solution, SC1, and SC2), choline solutions, or HF solutions; dry etching processes involving chemical vapor etching, UV / ozone treatments or glow discharge 5 techniques (e.g., O2 plasma etching); and mechanical processes involving brush scrubbing, fluid jet or ultrasonic techniques (sonification). The surface of the substrate can also be pre-treated by salinization or an atomic layer deposition (ALD) process. The pre-treatment of the surface of the substrate serves to modify the hydrophobicity / hydrophilicity of the surface. This can 10 improve the adhesion and filling characteristics of the optical metal oxide layer on the surface of the substrate. In a more preferred embodiment, a wet cleaning process involving cleaning solvents (e.g., isopropanol (IPA)) is combined with one or more of a wet 15 etching process involving hydrogen peroxide solutions (e.g., piranha solution, SC1, and SC2), choline solutions, or HF solutions; dry etching process involving chemical vapor etching, UV / ozone treatments or glow discharge techniques (e.g., O2 plasma etching); and mechanical process involving brush scrubbing, fluid jet or ultrasonic techniques (sonification). 20 In a most preferred embodiment, a wet cleaning process involving cleaning solvents (e.g., isopropanol (IPA)) is combined with a mechanical process involving brush scrubbing, fluid jet or ultrasonic techniques (sonification) and with a wet etching process involving hydrogen peroxide solutions (e.g., 25 piranha solution, SC1, and SC2), choline solutions, or HF solutions; Thus, in a preferable embodiment, in step (a), the formulation is applied to a surface of a substrate or to a surface of an underlayer by spin-coating or ink-jetting. 30 In a preferable embodiment, the formulation is at least partly converted on the surface of the substrate or the surface of an underlayer to a composite, Foreignfiling_text P23-203 - 23 - wherein said composite contains a metal oxide, preferably selected from metal monoxide, metal dioxide and / or metal pentoxide; and a metal oxide precursor. 5 In a preferable embodiment, the substrate is a patterned substrate comprising topographical features on the surface thereof. Said patterned structure of the substrate can be an underlayer placed over the substrate (e.g., an underlayer of a semiconducting device). 10 -Step (b) It is believed that the formulation is at least partly converted in step (b) on the surface of the substrate or on the surface of the underlayer to a metal oxide to form a composite by exposure to thermal treatment. Said composite is preferably a layered composite. And said solvent is usually 15 removed in step (b). Preferred thermal treatment includes exposure to elevated temperature from 50 to 600 °C, preferably it is from 80 to 500°C, more preferably from 100 to 300°C. It is believed that applying a higher temperature such as in 20 the range from 100 - 600°C, preferably 125-450°C, more preferably from 150-250 °C can realize an improved gap fill. It is preferred to use the formulation containing a lower amount of the metal oxide precursor based on the total amount of the formulation in step (a) to 25 realize an improved gap filing, for examples, in the range from 0.1 to 30wt% based on the total amount of the formulation, more preferably in the range from 1 to 20wt%, even more preferably from 5 to 15wt% based on the total amount of the formulation; and applying a higher temperature in step (b) such as in the range from 100 - 600°C, preferably 125-450°C, more 30 preferably from 150-250°C to realize an improved gap fill. Foreignfiling_text P23-203 - 24 - Thermal treatment method in Step (b) is not limited to any specific thermal treatment methods or times. Depending on the type of substrate and formulation, a person skilled in the art can determine suitable thermal treatment methods. 5 In some embodiments of the method for preparing an optical metal oxide layer according to the present invention, a pre-baking step can be applied before step (b) after step (a) to remove the solvent of the formulation. The formulation can also be partly converted on the surface of the substrate to 10 an optical metal oxide layer by pre-baking (soft baking) at a temperature from 40 to 150 °C, preferably from 50 to 120 °C, more preferably from 60 to 100 °C; then, baking of step (b) (hard baking, sintering or annealing) at a temperature from 100 to 600 °C, preferably from 125 to 450 °C, more preferably from 150 to 255 °C is applied. 15 Pre-baking (soft baking) serves the purpose to remove volatile and low boiling components such as, e.g., volatile and low boiling formulation media or additives from the drop casted, coated or printed films. Pre-baking is preferably carried out for a period of 1 to 60 minutes. After pre-baking, 20 layers of substrate adhering films of metal oxide precursor or metal oxide precursor mixtures are obtained. The films may still comprise residual formulation media or additives. In an alternative preferred embodiment of the method for preparing an 25 optical metal oxide layer according to the present invention, pre-baking is omitted so that the formulation is converted in step (b) on the surface of the substrate or on the surface of the under layer to an optical metal oxide layer directly. 30 Baking (hard baking, sintering or annealing) serves the purpose to convert the metal oxide precursor or metal oxide precursor mixture layers on the substrate into a metal oxide layer. Moreover, the final properties of the Foreignfiling_text P23-203 - 25 - metal oxide layer may be adjusted by the baking treatment. Baking is preferably carried out at the time in the range from 1 to 60min, preferably 2 to 20 min, more preferably 3 to 10min. 5 Said Pre-baking and baking (step (b)) may be carried out under ambient atmosphere or atmospheres with increased oxygen content to decompose unwanted organic components, which can lead to a lower activation energy when the composite is formed and is believed to improve the physical- chemical properties of the resulting layered composite material. 10 In a preferred embodiment of the method of present invention, the substrate or the underlayer is patterned comprising topographical features on the surface thereof, and the layered composite, preferably it is an optical layer, forms a coating layer covering the surface of the substrate and filling said 15 topographical features. As a result, the topographical features are filled and levelled by said composition. Preferred topographical features include, for example, gaps, grooves, trenches and vias. Topographical features may be distributed uniformly or 20 non-uniformly over the surface of the substrate. Preferably, they are arranged as an array or grating on the surface of the substrate. It is preferred that the topographical features have different lengths, widths, diameters as well as different aspect ratios. It is preferred that said topographical features have an aspect ratio of 1:20 to 20:1, more preferably 25 1:10 to 10:1. The aspect ratio is defined as width of structure to its height (or depth). From the viewpoint of dimension, the depth of the topographical features is preferably in the range from 10 nm to 10 µm, more preferably 50 nm to 5 µm, and most preferably 100 nm to 1 µm. 30 It is also preferred that the topographical features are inclined at a certain angle, such as an angle from 10 to 80°, preferably from 20 to 60°, more preferably from 30 to 50°, most preferably about 40°. Such inclined Foreignfiling_text P23-203 - 26 - topographical features are also referred to as slanted or blazed topographical features. It may be also necessary to fill topographical features locally with optical 5 metal oxide layer, either completely or to a certain level, but not to cover adjacent surfaces of the substrate, where no topographical features to be filled are available. The substrate is preferably a substrate of an optical device. Preferred 10 substrates are made of inorganic or organic base materials, preferably inorganic base materials. Preferred inorganic base materials contain materials selected from the list consisting of ceramics, glass, fused silica, sapphire, silicon, silicon nitride, quartz, and transparent polymers or resins. The geometry of the substrate is not specifically limited, however, preferred 15 are sheets or wafers. In step (a) of the method, the formulation is applied onto a surface of a substrate or a surface of an underlayer, wherein said surface may be either a surface of a base material of the substrate or a surface of a layer of a 20 material being different from the base material of the substrate, wherein such layer has been formed prior to applying said formulation. In this way, sequences of different layers (layer stacks) can be formed on top of one another. Such layer stacks may be also structured, wherein such 25 structures typically have dimensions on the nanometer scale, at least with respect to diameter, width and / or aspect ratio. Thus, in a preferable embodiment, in step (b), the formulation is at least partly converted on the surface of the substrate to a composite, preferably it 30 is being of a layered composite, by baking it at a temperature from 50 to 400 °C, preferably it is from 80 to 350°C, more preferably from 100 to 300°C. Foreignfiling_text P23-203 - 27 - In a preferred embodiment of the present invention, said thermal treatment of step (b) is applied at the time in the range from 1 to 60min, preferably 2 to 20 min, more preferably 3 to 10min. 5 In some embodiments, the formulation is at least partly converted on the surface of the substrate to a composite during the thermal treatment process of step (b), wherein said composite contains a metal oxide, preferably selected from metal monoxide, dioxide and / or pentoxide; and a 10 metal alkoxide. - Composite In another aspect, the present invention relates to a composite, preferably being a layered composite, preferably said layered composite is an optical 15 layer, obtained or obtainable by the method of the present invention. In another aspect, the present invention relates to a composite, preferably being a layered composite, preferably said layered composite is an optical layer, derived from the formulation of the present invention. 20 In a preferred embodiment of the present invention, the composite comprises at least a metal oxide derived from the metal oxide precursor of the formulation and metal halide precursor as a non-converted part of the formulation used in step (a) of the method. 25 Thus, in some embodiments, the composite comprises at least one metal halide, and a metal oxide derived from said metal halide. Preferably said metal halide is the 1stmetal halide. More preferably, the composite further comprises the 2ndmetal halide and a metal oxide derived from the 2ndmetal 30 halide. Foreignfiling_text P23-203 - 28 - The details of the metal halide precursor is indicated in the section of 1stmetal halide precursor and 2ndmetal halide precursor above. - Optical device 5 The present invention relates to an optical device comprising the composite of the present invention, which is preferably obtainable or obtained by the method of the present invention as described above. It is preferred that the optical device is a device containing one or more 10 optical components for forming a light beam including, but not limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. Preferred optical devices in the context of the present invention are waveguides for augmented reality (AR) device, for virtual reality (VR) device and / or for 15 mixed reality (MR) device, or preferred optical devices are augmented reality (AR) glasses, virtual reality (VR) glasses and / or mixed reality (MR) glasses. - Display device 20 Finally, the present invention relates to a display device comprising at least one functional medium configured to modulate a light or configured to emit light; and the composite, or an optical device of the present invention. Examples of said display device is selected from a Liquid crystal display 25 (LCD), Light emitting diode display (LED display), organic light emitting display (OLED), micro-LED display, quantum dot display (QLED), Augmented Reality (AR) hardware, Virtual Reality (VR) hardware, Mixed Reality (MR) hardware, plasma (PDP) display and an electroluminescent (ELD) display. Said AR, VR and MR hardware are also called as AR, VR 30 and MR display. Preferably said display device is AR hardware, VR hardware or MR hardware. Foreignfiling_text P23-203 - 29 - The present invention is further illustrated by the examples following herein- after which shall in no way be construed as limiting. The skilled person will acknowledge that various modifications, additions and alternations may be made to the invention without departing from the spirit and scope of the 5 invention as defined in the appended claims. Examples - Analytics and measurement methods Ellipsometry is used to determine layer thickness (nm), refractive index (n) 10 (RI) and absorption index (k) of a metal oxide layer. Measurements are performed using an ellipsometer M2000 from J. A. Woolam and three different angles of incidence (65°, 70 ° and 75°). The measurement data is analyzed with software CompleteEase from J. A. Woolam, assuming either full or almost nearly complete transparent behavior above a wavelength of 15 600 nm (at 560nm) and applying B-spline fitting for obtaining refractive indices (n) as well as absorption indices (k). The optical constants are averaged from three to four measured samples each of them providing a different layer thickness either after soft bake or after hard bake or after combined soft and subsequent hard bake. 20 Usually, quartz and / or silicon wafers, both 2 inch in diameter, are used throughout all coating experiments where flat and non-structured carriers for metal oxides are required (e. g. spectroscopic and ellipsometry measurements). 25 SEM images are recorded using either a Mira 3 LMU from Tescan or Sigma 300VP from Carl Zeiss or Supra 35 from Carl Zeiss. Substrate coating, usually wafers, is done using a spin coater (LabSpin 150i) from Suess. The spin coating process using planar substrates is as 30 follows: deposition of 0.5 ml of the coating onto static quartz wafers followed by a spinning interval of 30 seconds at a given spin speed where the acceleration to reach the final spin speed is set to 500 rpm / s². Different Foreignfiling_text P23-203 - 30 - layers and coating thicknesses are achieved using either different spin speeds or different coating formulations having different concentrations of the metal oxide precursor or mixtures of different metal oxide precursors. After spin coating, the coated substrates are subjected to thermal cure on a 5 conventional lab hotplate. Usually, however not limited hereto, the coated layers are baked at 100 °C to 200 °C for between 1 to 10 minutes. Layer baking is performed using high temperature hotplates from Harry Gestigkeit allowing for reaching temperatures of up to 600 °C. Afore-mentioned conditions and parameters apply to all following experimental examples 10 unless other conditions are explicitly mentioned elsewhere. As an alternative film preparation technique, inkjet printing can be used. The formulations can be filled into single-use cartridges (Dimatix Materials Cartridge with a nominal drop weight of 10 pL) and may be printed using a 15 laboratory scale inkjet printing equipment (Dimatix Materials Printer DMP- 2850 or a Pixdro LP50). The temperature of the printhead and the substrate holder can be set to 30°C. Squares of approximately two by two cm are printed with varying resolutions to obtain different film thicknesses. After printing, the substrates are thermally dried and hardbaked. 20 All substrates, unless otherwise noted, were cleaned by immersion in 2- propanol and ultrasonication for ten minutes; successively immersion in deionized water and ultrasonication for ten minutes and drying on a hot plate at 100°C for 10 minutes. Afterwards the substrates were treated in an 25 oxygen plasma oven (450 watt, 5 minutes). Structured substrates, usually silicon wafers, are used as square-shaped dies with edge lengths of 1.5 cm to 2 cm. The wafer dies are cut and cleaved from a parent wafer, typically having a diameter of 12 inch. The 30 structures are created and arranged in a layer stack composed of SiO2 / SiNxdeposited onto the wafer surface. Dimensions of the structures (e. g. cross- section width and length of trenches) referred to the architecture of Foreignfiling_text P23-203 - 31 - Sematech mask 854. Usually, however not limited hereto, the cross- sectional cleaves perpendicular to trench arrays providing a width of 40 nm to 50 nm are used as trench structures of primary interest to investigate their filling behavior by the wet-chemically coated metal oxide precursors 5 and / or metal oxides received upon thermal conversion of the said metal oxide precursors. Besides to aforementioned, cross-sections of arrays of trenches having widths of 100 nm and 150 nm are used to investigate trench filling by metal oxides, too. 10 Structured wafer dies are, unless otherwise mentioned, coated by spin coating. For that purpose, the coating formulation, typically a volume between 0.15 ml to 0.5 ml per die, is pipetted and casted onto wafer’s surface. The formulation is allowed to spread and settle on the surface for one minute followed by a step of distributing and spreading of the 15 formulation over the entire surface of the wafer die at 500 rpm for 30 seconds, followed by a final spin-off step at 2,000 rpm for further 60 seconds. The acceleration of the spin speed is set to 500 rpm / s². The soft bake and hard conditions of structured wafer dies is chosen similar or identical to those already mentioned for flat substrates. 20 All chemicals for synthesis described are purchased from Sigma Aldrich and used without further purification, unless differently mentioned elsewhere.98 % anhydrous SnCl2is used for the experiments described successively. 25 Working example 1: Preparation of formulation 1 Formulation 1: NbCl5 (5wt%), SnCl22H2O (5wt%) nominal solid content dissolved in 90wt% PGME is made. A clear, transparent and colorless solution is achieved which became filtered using 0.2 µm syringe filter to 30 remove any kind of particles and other suspended materials. Working examples 2 - 3: Preparation of formulations 2 and 3 Foreignfiling_text P23-203 - 32 - Formulation 2: NbCl5 (5.6wt%), SnCl22H2O (4.4wt%) nominal solid content dissolved in 90wt% PGME is made. By changing the amount of NbCl5 and SnCl22H2O, Formulation 3: NbCl5(6.3wt%), SnCl22H2O (3.7wt%) nominal solid content dissolved in 90wt% PGME is also made. 5 Working examples 4: Forming a layer Sample 1 (a layer made from Formulation 1, baking temperature 150°C / 5min) is prepared by the following process. Formulation 1 from working example 1 (W.E.1) is spin coated with 2,000 10 rpm onto an O2plasma pretreated Si3N4 / Si substrate having 150nm width trenches on the surface. Then the coated layer is baked at 150°C for 5min. Finally, Sample 1 is obtained. Working examples 5: Forming layers 15 Samples 2 (a layer made from Formulation 1, baking temperature 200°C / 5min), Sample 3 (a layer made from Formulation 1, baking temperature 250°C / 5min) and Sample 4 (a layer made from Formulation 1, baking temperature 300°C / 5min) are made in the same manner as described in working example 4 above except for that the different baking 20 temperature conditions (200°C / 5min for Sample 2, 250°C / 5min for Sample 3, 300°C / 5min for Sample 4) are applied. Working examples 6: Forming layers Samples 5 (a layer made from Formulation 2, baking temperature 25 150°C / 5min), Samples 6 (a layer made from Formulation 2, baking temperature 200°C / 5min), Sample 7 (a layer made from Formulation 2, baking temperature 250°C / 5min) and Sample 8 (a layer made from Formulation 2, baking temperature 300°C / 5min), Samples 9 (a layer made from Formulation 3, baking temperature 150°C / 5min), Samples 10 (a layer 30 made from Formulation 3, baking temperature 200°C / 5min), Sample 11 (a layer made from Formulation 3, baking temperature 250°C / 5min) and Sample 12 (a layer made from Formulation 3, baking temperature Foreignfiling_text P23-203 - 33 - 300°C / 5min) are made in the same manner as described in working example 4 above except for that the different baking temperature conditions and formulations as mentioned in table 1 are used. These show good gap fill properties. 5 Table 1: 10 15 Working examples 6: measurement of layer thickness and refractive index (n) (RI) value 20 The layer thickness and the refractive index value of each samples 1 to 12 are evaluated with using the Ellipsometry. Table 2 shows the results. 25 30 Foreignfiling_text P23-203 - 34 - Table 2 5 10 Working examples 7: Preparation of formulation 4 15 Formulation 4: NbCl5 (5.7wt%), SnCl22H2O (4.3wt%) nominal solid content dissolved in 90wt% PGME is made. Working examples 8: Forming a layer Sample 15 (a layer made from Formulation 4, baking temperature 20 150°C / 5min), Sample 16 (a layer made from Formulation 4, baking temperature 200°C / 5min), Sample 17 (a layer made from Formulation 4, baking temperature 250°C / 5min) are made in the same manner as described in working example 4 above except for that the Formulation 4 is used for forming samples 15, 16 and 17 and baking temperature 25 150°C / 5min for sample 15, 200°C / 5min for forming sample 16 and 250°C / 5min for forming sample 17 are used. The RI values of the obtained samples are measured in the same manner as described in working example 6. Below table 3 shows the results of RI measurements. 30 As mentioned in table 3, higher RI value (around 2.0 or more) can be obtained by applying lower baking temperature (150°C / 5min, 200°C / 5min, 250°C / 5min). These show good gap fill properties. Foreignfiling_text P23-203 - 35 - Table 3 Sample number RI value Sample 15 1.99 Sample 16 2.05 Sample 17 2.07 5 10 15 20 25 30

Claims

Foreignfiling_text P23-203 - 36 - Claims 1. Formulation, preferably to be used for forming an optical layer comprising a metal oxide, comprising at least a 1stmetal halide represented by any one 5 of formulae (I) to (V), a 2ndmetal halide represented by any one of formulae (I’) to (V’) and a solvent. M1X12 - (I) M2X23 - (II) M3X34- (III) 10 M4X45- (IV) M5X56 - (V) wherein M1is a divalent metal, preferably M1is selected from Zn or Sn; M2is a trivalent metal, preferably M2is Bi; M3is a quadrivalent metal selected from Zr, Ti or Hf; 15 M4is a pentavalent metal selected from V, Nb or Ta; M5is Mo or W; and X1, X2, X3, X4, X5, X6are each independently a halogen, preferably X1, X2, X3, X4, X5, X6are each independently selected from F, Cl, Br, I, more preferably X1, X2, X3, X4, X5, X6are Cl. 20 M1’X1’2- (I’) M2’X2’3 - (II’) M3’X3’4- (III’) M4’X4’5- (IV’) M5’X5’6 - (V’) 25 wherein M1’is a divalent metal, preferably M1’is selected from Zn or Sn; M2’is a trivalent metal, preferably M2’is Bi; M3’is a quadrivalent metal selected from Zr, Ti or Hf; M4’is a pentavalent metal selected from V, Nb or Ta; M5’is Mo or W; and 30 X1’, X2’, X3’, X4’, X5’, X6’are each independently a halogen, preferably X1’, X2’, X3’, X4’, X5’, X6’are each independently selected from F, Cl, Br, I, more preferably X1’, X2’, X3’, X4’, X5’, X6’Cl; andForeignfiling_text P23-203 - 37 - said 1stmetal halide and the 2ndmetal halide are different of each other; and the weight ratio of the 2ndmetal halide to the 1stmetal halide is less than 1, preferably in the range from 0.01 to 1. Preferably the total content of the 2nd5 metal halide based on the total mass of the 1stmetal halide is in the range from 0.1 to 100wt%.

2. Formulation of claim 1, wherein the total content of all metal halide(s) in the formulation is in the range from 0.1 w% to 50 w% based on the total 10 mass of the formulation, preferably it is from 1wt.% to 30wt.%, more preferably from 5 to 20wt.%.

3. Formulation of claim 1 or 2, wherein the solvent is an organic solvent. Preferably said organic solvent is selected from one or more members of 15 the group consisting of ethylene glycol monoalkyl ethers, preferably it is ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether and / or ethylene glycol monobutyl ether; diethylene glycol dialkyl ethers, preferably it is diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether and / or 20 diethylene glycol dibutyl ether; propylene glycol monoalkyl ethers, preferably it is propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether and / or propylene glycol monopropyl ether; 1,3- dimethoxy-2-propanol, ethylene glycol alkyl ether acetates, preferably it is methyl cellosolve acetate and / or ethyl cellosolve acetate; propylene glycol 25 alkyl ether acetates, preferably it is propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate and / or propylene glycol monopropyl ether acetate; ketones, preferably it is methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone and / or cyclohexanone; alcohols, preferably it is ethanol, propanol, butanol, 30 hexanol, cyclo hexanol, ethylene glycol, propylene glycol, triethylene glycol and / or glycerin; esters, preferably it is ethyl 3-ethoxypropionate, methyl 3- methoxypropionate and / or ethyl lactate; and cyclic esters, preferably it isForeignfiling_text P23-203 - 38 - gamma-butyro-lactone; preferably said solvent is ethylene glycol monoalkyl ethers, diethylene glycol dialkyl ethers, propylene glycol, ethylene glycol, propylene glycol monoalkyl ethers, ethylene glycol alkyl ether acetates, propylene glycol alkyl ether acetate, more preferably said solvent is 5 selected from propylene glycol alkyl ether acetates, ethylene glycol monoalkyl ethers, propylene glycol and propylene glycol monoalkyl ethers, 1,3-dimethoxy-2-propanol.

4. Use of the formulation of any one of claims 1 to 3 for preparing a 10 composite, preferably for preparing a layered composite, more preferably for preparing an optical layer or for filling one or more trenches of a patterned surface or an uneven surface of a substrate.

5. Method for preparing the formulation of any one of claims 1 to 3 comprising at least following step (A): 15 (A) Mixing a 1stmetal halide represented by any one of formulae (I) to (V), a 2ndmetal halide represented by any one of formulae (I’) to (V’) and a solvent; M1X12- (I) M2X23- (II) 20 M3X34 - (III) M4X45- (IV) M5X56- (V) wherein M1is a divalent metal, preferably M1is selected from Zn or Sn; M2is a trivalent metal, preferably M2is Bi; 25 M3is a quadrivalent metal selected from Ti, Zr or Hf; M4is a pentavalent metal selected from V, Nb or Ta; M5is Mo or W; and X1, X2, X3, X4, X5, X6are each independently a halogen, preferably X1, X2, X3, X4, X5, X6are each independently selected from F, Cl, Br, I, more 30 preferably X1, X2, X3, X4, X5, X6are Cl. M1’X1’2- (I’)Foreignfiling_text P23-203 - 39 - M2’X2’3 - (II’) M3’X3’4 - (III’) M4’X4’5- (IV’) M5’X5’6 - (V’) 5 wherein M1’is a divalent metal, preferably M1’is Zn; M2’is a trivalent metal, preferably M2’is Bi; M3’is a quadrivalent metal selected from Ti, Zr or Hf; M4’is a pentavalent metal selected from V, Nb or Ta; M5’is Mo or W; and 10 X1’, X2’, X3’, X4’, X5’, X6’are each independently a halogen, preferably X1’, X2’, X3’, X4’, X5’, X6’are each independently selected from F, Cl, Br, I, more preferably X1’, X2’, X3’, X4’, X5’, X6’Cl; and wherein said 1stmetal halide and the 2ndmetal halide are different of each other; and 15 the weight ratio of the 2ndmetal halide to the 1stmetal halide is 1 or less, preferably in the range from 0.01 to 1. Preferably the total content of the 2ndmetal halide based on the total mass of the 1stmetal halide is in the range from 0.1 to 100wt%. 20 6. Method for preparing a composite containing a metal oxide, preferably said metal oxide is selected from metal monoxide, dioxide or pentoxide, or a combination of these; comprising the following steps (a) and (b): (a) providing the formulation of any one of claims 1 to 3 onto a surface of a substrate, preferably by wet deposition process, more preferably by 25 spin-coating or ink-jetting, even more preferably by ink-jetting; and (b) applying a thermal treatment to the formulation provided on the surface of the substrate to convert at least a part of the metal alkoxide of the formulation to a metal oxide. Preferably said composite being a layered composite, more preferably said 30 layered composite is an optical layer.Foreignfiling_text P23-203 - 40 - 7. Method according to claim 6, wherein in step (a) the formulation is applied to a surface of a substrate by spin-coating or ink-jetting.

8. Method according to claim 6 or 7, wherein in step (b), the formulation is 5 at least partly converted on the surface of the substrate to a composite, preferably it is being of a layered composite, by baking it at a temperature from 50 to 400 °C, preferably it is from 80 to 350°C, more preferably from 100 to 300°C. 10 9. Method according to any one of claims 6 to 8, wherein the formulation is at least partly converted on the surface of the substrate to a composite, wherein said composite contains a metal oxide, preferably selected from metal monoxide, dioxide and / or pentoxide; and a metal alkoxide. 15 10. Method according to any one of claims 6 to 9, wherein the substrate is a patterned substrate comprising topographical features on the surface thereof.

11. A composite, preferably being of a layered composite, preferably said 20 layered composite is an optical layer, derived from the formulation of any one of claims 1 to 3.

12. A composite, preferably being of a layered composite, preferably said layered composite is an optical layer, made from the method of any one of 25 claims 6 to 8.

13. The composite of claim 11 or 12, comprises at least one metal halide, and a metal oxide derived from said metal halide. Preferably said metal halide is the 1stmetal halide. More preferably, the composite further 30 comprises the 2ndmetal halide and a metal oxide derived from the 2ndmetal halide.Foreignfiling_text P23-203 - 41 - 14. An optical device comprising the composite of any one of claims 11 to 13, and a substrate comprising a patterned surface or an uneven surface. Preferably a gap or trench of said patterned surface or an uneven surface of the substrate is at least partly filled with said composite. 5 Preferably said substrate is a patterned substrate comprising topographical features on the surface thereof. Preferably said composite fills at least a part of a gap of said topographical features, more preferably said composite fills a trench of the patterned substrate. 10 15. A display device comprising at least one functional medium configured to direct and modulate a light or configured to emit light; and the composite of claim 11 or 13, or an optical device of claim 14. 15 20 25 30

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