Metal complexes and formulations for preparing metal oxide optical layers

Abstract

The present invention relates to metal complexes, formulations comprising the metal complexes, and methods for preparing metal oxide optical layers using the formulations and metal complexes, the resulting metal oxide optical layers being particularly suitable for use in optical devices such as, for example, augmented reality (AR) and / or virtual reality (VR) devices.

Description

[Technical Field]

[0001] The present invention relates to metal complexes, formulations, and methods for preparing metal oxide optical layers. The metal complexes, formulations, and methods according to the present invention are particularly suitable for preparing metal oxide optical layers for optical applications or devices, such as, for example, diffraction gratings for augmented reality (AR) and / or virtual reality (VR) devices. The metal oxide optical layers exhibit favorable optical properties, such as (a) a high refractive index (RI) of greater than 1.7, preferably greater than 2.0, at wavelengths of 520 nm or less and low absorption (light loss), (b) favorable mechanical properties, such as low shrinkage, (c) favorable coating properties, such as dense layers and smooth surface structures, and / or (d) favorable filling properties, such as uniform filling of topographical features on patterned substrates.

[0002] Embodiments of the present invention enable the preparation of metal oxide optical layers on the surfaces of both patterned and unpatterned substrates. Metal oxide optical layers contain metal oxides embedded in a cured matrix. The layers can be formed into various structures, such as layers covering the surface of unpatterned substrates and / or filling topographical features, such as gaps, on the surface of patterned substrates, thereby providing highly refractive optical structures. In particular, embodiments of the present invention enable the preparation of advanced optical gap filling with low overburden, thereby avoiding typical problems that arise when layer deposition or gap filling is performed by physical vapor deposition (PVD) or chemical vapor deposition (CVD) techniques, such as incomplete or excessive gap filling due to unfavorable deposition and layer growth characteristics, such as reduced or increased deposition or growth rates at corners and edges, thereby enabling easy and cost-effective mass production of complex optical devices.

[0003] Embodiments of the present invention are particularly suitable for preparing metal oxide optical layers with high refractive index for optical devices such as, for example, diffraction gratings in AR and / or VR devices.

[0004] Finally, the present invention provides an optical device, preferably an AR and / or VR device, comprising a metal oxide optical layer obtainable by the method according to the present invention. [Background technology]

[0005] State-of-the-art optical devices typically include optical gratings made from composite materials with a substrate as a support and a complex interlaced pattern thereon, the pattern being composed of different layers or stacks of layers. The creation of such complex interlaced patterns usually requires a structuring process, which becomes increasingly difficult as the size of the prepared structure dimensions decreases.

[0006] In addition to their wide range of potential uses in various application areas, such as spectroscopy or optical storage systems (CDs, DVDs, etc.), diffraction gratings are a core component of so-called XR devices, which are primarily made of glass. In this context, R stands for "reality," while X denotes different attributes, such as virtual, augmented, or composite. Thus, diffraction gratings form part of the core of the so-called optical engine in XR devices, specifically augmented reality and mixed reality glasses. Virtual reality glasses, when constructed as head-mounted displays, often consist of conventional liquid crystal (LC) organic light-emitting diode (OLED) displays embedded in the device and therefore do not necessarily require a diffraction grating. In contrast, augmented reality and mixed reality glasses are designed to enable consumers to obtain the best visual impression of their environment, as if they were not wearing glasses at all. However, they also allow for the provision and support of digital information and the projection of it into an individual's field of vision. Additional digital information is collected from recognizing and analyzing the environment, allowing the individual to examine or view their current view. To transmit supporting digital information and project it into an individual's eye, augmented reality or mixed reality glasses include an information supply unit coupled to an optical waveguide system that transmits optically encoded supporting information directly to the glasses' lenses. Here, the information passes through a diffraction grating that couples incident light into the lens and splits it according to its angular information and its spectral band by diffraction. After light incoupling, the lens functions as a waveguide that allows light to be transmitted to and within the individual's pupil. The location of the light incoupling is independent of any preferred location and, therefore, independent of the influence of technical needs. The transverse direction of light within the lens is determined by the diffraction grating, which diffracts or splits the light. At specific locations within the lens, second and third diffraction gratings function to change the transverse direction of the light, thereby projecting it into the user's pupil. Light traversal within the glasses is achieved by total internal reflection (TIR) ​​of light, which bounces several times between glass interfaces until it reaches another diffraction grating that changes the internal TIR direction of the light (see Figure 2).The second and third gratings can be geometrically aligned in different directions relative to the first and incoupling gratings, for example, by a specific angular distortion of the longitudinal axis, thus changing the propagation direction of the totally internally reflected light. Needless to say, the lens itself or the material from which it is made must not be absorbing. Otherwise, the auxiliary information will not reach the user's pupil, or will only reach it with a significantly reduced light intensity. This process works regardless of whether a reflective or transmissive grating is used. Typically, lenses are equipped with both types of gratings to properly guide the light. It should also be noted that there are differences in the optical performance of reflective and transmissive gratings, but these are not of any further importance in the context of the present invention. The basic structure of the gratings is very similar, which is more important in this regard.

[0007] Nevertheless, there are different designs and structures for achieving waveguides, such as surface relief (SR) or volume phase holographic (VPH) gratings. Both types are very similar in appearance. In the simplest case, the grating is somehow attached to the surface of a waveguide material, here a lens. The grating itself consists of an array of microstructures, primarily, but not exclusively, trenches of a first material type, Material01, with a refractive index RI01. The trench geometries can range from rectangular to V-shaped trenches, U-shaped trenches, etc. The width, including structures with different widths, the geometry of the trenches, their pitch, as well as their depth, including different depths, are specifically designed to affect the diffraction pattern of the diffracted incident light.

[0008] In the case of SR gratings (SRGs), trenches or structures of a first material type (Material O1) with a refractive index (RI01) are filled with a second material type (Material O2) with a refractive index (RI02), where RI02 is incrementally different from RI01 (see Figures 1 and 3). For completeness, it should be mentioned that Material O1 or Material O2 may be composed of a stack of structured layers, each containing different material compositions with different refractive indices, stacked on top of each other, thereby forming Material O1 or Material O2 with an effective or graded refractive index RI01 or RI02, respectively. Note that the (effective or graded) refractive indices RI01 and RI02 depend on the refractive index of the waveguide or lens material of the eyeglasses. When glass lenses with a high refractive index (n03 > 1.46) are used, the (effective or graded) refractive indices of Material O1 and Material O2 are considered higher than the refractive index of the lens itself, thereby allowing an RI value of 2.0 to be reached or exceeded. High performance gratings, particularly SR type high performance gratings, can be fabricated using standard lithography and deposition techniques known from microfabrication, for example, integrated circuit manufacturing.

[0009] Such standard techniques typically involve physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes and often suffer from incomplete gap filling due to unfavorable deposition and / or layer growth characteristics, including increased deposition and / or growth rates at corners and edges. Such incomplete gap filling results in the formation of voids within the structures filled by the PVD and CVD materials. In addition to the formation of voids, the surface of the substrate is covered by a PVD and / or CVD layer that is approximately as thick as the maximum depth of the deepest structure filled by the deposited gap-fill material (see FIGS. 4 and 5). However, depending on the application, it may be necessary to expose the surface of the substrate and make it available for further processing. As a result, the undesired overburden layer from PVD or CVD must be removed, for example, by chemical mechanical planarization (CMP), without harming the underlying original substrate surface. While CMP is very well established in integrated circuit manufacturing processes, CMP is a time-consuming and expensive process that can be considered a potential economic drawback for the mass production of cutting-edge optical devices, particularly diffraction gratings. Therefore, it is desirable to have a solution for advanced, cost-effective fabrication of optical gratings where gap filling does not require CMP (see FIG. 6).

[0010] The present invention addresses various shortcomings of the techniques for preparing optical gratings for state-of-the-art optical devices as described above, with a focus on improved optical properties, improved mechanical properties, improved coating properties, and improved filling properties.

[0011] Object of the invention It is an object of the present invention to provide metal complexes, formulations, and methods for preparing metal oxide optical layers, which are particularly suitable for optical applications and can be used in optical devices, such as, for example, diffraction gratings for AR and / or VR devices. The resulting metal oxide optical layers exhibit favorable optical properties, such as (a) a high refractive index (RI) greater than 1.7, preferably greater than 2.0, at wavelengths of 520 nm or less and low absorption (light loss), (b) favorable mechanical properties, such as low shrinkage, (c) favorable coating properties, such as dense layers and smooth surface structures, and / or (d) favorable filling properties, such as uniform filling of topographical features on patterned substrates.

[0012] It is a further object of the present invention to provide methods that allow for the easy and cost-effective preparation of metal complexes, formulations, and metal oxide optical layers.

[0013] It is a further object of the present invention to enable the preparation of metal oxide optical layers on the surface of both patterned and unpatterned substrates. The metal oxide layers can form a variety of structures, such as, for example, a layer covering the surface of an unpatterned substrate and / or a filler covering topographical features, such as, for example, gaps, on the surface of a patterned substrate, thereby providing highly refractive optical structures.

[0014] It is therefore an object of the present invention to provide metal complexes, formulations and methods for preparing metal oxide optical layers, which make it possible to obtain a high degree of optical gap filling at a low overburden, thus enabling easy and cost-effective mass production of complex optical devices.

[0015] It is a further object of the present invention to provide metal complexes, formulations, and methods for preparing metal oxide optical layers, which avoid typical problems that arise when layer deposition or gap filling is performed by PVD or CVD techniques, such as unfavorable deposition and layer growth characteristics, such as incomplete or excessive gap filling due to reduced or increased deposition or growth rates at corners and edges.

[0016] It is an object of the present invention that the metal complexes and formulations are particularly suitable for the preparation of metal oxide optical layers with high refractive index and at the same time low absorption (light loss) for optical devices such as, for example, diffraction gratings in AR and / or VR devices.

[0017] Finally, it is an object of the present invention to provide an optical device, preferably an AR and / or VR device, comprising a metal oxide optical layer obtainable by the method according to the invention and thereby exhibiting the beneficial effects mentioned above. Summary of the Invention

[0018] The present inventors have surprisingly found that the above object is achieved by the following embodiments. A metal complex, one or more, preferably two or more metals M selected from the list consisting of V, Nb, and Ta, preferably Nb; and one or more ligands L, which are organic ligands comprising ester groups, preferably carboxylic acid ester groups, and carboxylic acid groups, and which are optionally deprotonated.

[0019] (i) a metal complex according to the present invention as a metal oxide precursor; (ii) an epoxy resin mixture; (iii) a photoinitiator.

[0020] A method for preparing a metal oxide optical layer, comprising the following steps (a) to (c): (a) providing a formulation according to the present invention; (b) applying the formulation to a surface of a substrate; (c) converting the formulation onto the surface of the substrate into a metal oxide optical layer.

[0021] Finally, there is provided an optical device comprising a metal oxide optical layer obtainable or obtainable by a method according to the invention, the optical device being preferably an augmented reality (AR) and / or virtual reality (VR) device.

[0022] Preferred embodiments of the invention are described below and set out in the dependent claims. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic cross-sectional view of an SR grating having material 01 and material 02, where the refractive index IR01 of material 01 is incrementally different from the refractive index IR02 of material 02. [Figure 2] Schematic cross-section of an SR grating, which allows for optical diffraction (in transmission) including propagation of diffracted light within a waveguide (e.g., a lens) by total internal reflection. [Figure 3] FIG. 1 is a schematic cross-sectional view of an SR grating providing gaps (trenches) that are filled with a high refractive index material (material 02), where the refractive index of material 02 is incrementally different from the refractive index of material 01 adjacent to the gaps (trenches). [Figure 4] Schematic of a PVD or CVD mediated gap filling process and removal of unwanted overburden. [Figure 5] Schematic of a PVD or CVD mediated gap-fill process that creates and leaves voids in the gap and deposited layer. [Figure 6] Schematic of a gap-filling process using a formulation containing a metal complex of the present invention or the formulation being converted to a metal oxide. [Figure 7] SEM cross section of a substrate showing surface feature filling of spin-coated 5 / 5% (w / w) Nb citraconate / epoxy mixture A after pre-baking at 100°C for 1 minute, followed by UV curing with 365 nm light for 20 minutes and baking at 350°C for 10 minutes, as described in Example 1. [Figure 8]SEM cross section of a substrate showing surface feature filling of a spin-coated Nb citraconic acid 5% (w / w) solution in PGME annealed at 300° C. for 10 minutes as described in Example 1. [Figure 9] SEM cross-sections of substrates showing the surface feature filling behavior of Nb citraconate / epoxy mixture A at various mix ratios and bake temperatures, as described in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0024] definition As used herein, the term "metal complex" refers to a coordination complex consisting of one or more central metal atoms or ions forming one or more coordination centers and a surrounding arrangement of binding molecules or ions as ligands containing one or more electron pairs that can be shared with the metal. In a metal complex, the metal atom or ion typically acts as a Lewis acid, while the ligand typically acts as a Lewis base. Metal complexes can be neutral, positively charged, or negatively charged. Charged metal complexes are sometimes referred to as complex ions.

[0025] As used herein, the term "metal-organic complex" refers to a class of metal complexes containing a metal and organic ligands that impart solubility or volatility in organic solvents. Compounds with these properties find a variety of applications in materials science for metalorganic vapor deposition (MOCVD) or sol-gel processing. The specific term "metal-organic complex" refers to metal-containing compounds that lack a direct metal-carbon bond but contain organic ligands. Metal alkoxides, metal carboxylates, metal β-diketonates, metal dialkylamides, and metal phosphine complexes are representative members of this class.

[0026] As used herein, the term "ligand" refers to an ion or neutral molecule (with one or more functional groups) that binds to a central metal atom or ion to form a metal complex. Bonding with the metal generally involves the formal donation of one or more of the ligand's electron pairs, often via a Lewis base. The nature of the metal-ligand bond can range from covalent to ionic. Furthermore, the metal-ligand bond order can range from 1 to 3. Ligands are typically considered Lewis bases, although Lewis acid ligands are known to be involved in rare cases. Ligands are classified as L or X (or a combination thereof) depending on the number of electrons they provide to bond between the ligand and the central atom. L ligands donate two electrons from their lone pair, resulting in a coordinate covalent bond. X ligands donate one electron and the central atom donates the other, thereby forming a regular covalent bond.

[0027] As used herein, the term "alkyl" or "alkyl group" refers to a straight-chain, branched-chain, cyclic, or bridged-cyclic alkyl group that forms part of the structure of a compound and is attached via a carbon atom. The alkyl group may contain one or more heteroatoms selected from N, O, S, and P. The alkyl group may be unsubstituted or substituted, and is preferably -C(O)R v , -C(O)OR v , -NR v R w , -OR v , -R x , -CN, -F, and -Cl, wherein R v =H, C3-C10 aryl or C1-C10 alkyl, R w =H, C3-C10 aryl or C1-C10 alkyl, and R x = C3-C10 aryl or C1-C10 alkyl, preferably R v =H, methyl, ethyl, propyl, or phenyl, R w =H, methyl, ethyl, propyl, or phenyl, and R x= phenyl. The alkyl group may contain one or more functional groups, preferably selected from the list consisting of a carbon-carbon double bond, a carbon-carbon triple bond, an amide, a carbamate, a carbonate, a carboxylic acid, an ester, an ether, a secondary or tertiary amine, and a keto. An alkyl group connecting two adjacent structural units in a compound is called an "alkylene group."

[0028] As used herein, the term "aryl" or "aryl group" refers to a monocyclic or polycyclic aromatic group that forms part of the structure of a compound. A polycyclic aromatic group contains two or more linked aromatic ring systems fixed in a plane. An aryl group may be (i) a hydrocarbon aryl group or (ii) a heteroatom-containing aryl group, also known as a heteroaryl group. A hydrocarbon aryl group contains an aromatic ring structure consisting of carbon atoms, while a heteroaryl group contains an aromatic ring structure that further contains one or more heteroatoms selected from N, O, S, and P. An aryl group may be unsubstituted or substituted, and is preferably -C(O)R v , -C(O)OR v , -NR v R w , -OR v , -R x , -CN, -F, and -Cl, wherein R v =H, C3-C10 aryl or C1-C10 alkyl, R w =H, C3-C10 aryl or C1-C10 alkyl, and R x = C3-C10 aryl or C1-C10 alkyl, preferably R v =H, methyl, ethyl, propyl, or phenyl, R w =H, methyl, ethyl, propyl, or phenyl, and R x = methyl, ethyl, propyl, or phenyl.

[0029] As used herein, the term "fluorene epoxy resin" refers to a compound having both a fluorene group and an epoxy group.

[0030] As used herein, the term "acrylate epoxy resin" refers to a compound that has both acrylate and epoxy groups, thereby providing crosslinking functionality. Acrylate epoxy resins are so-called dual-reactive compounds that contain a first reactive group (acrylate group) and a second reactive group (epoxy group).

[0031] As used herein, the term "optical device" refers to a device containing one or more optical components for shaping a light beam, including, but not limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, and optical coatings. Preferred optical devices in the context of the present invention are augmented reality (AR) glasses and / or virtual reality (VR) glasses.

[0032] Preferred Embodiments metal complexes The present invention relates to a metal complex comprising one or more, preferably two or more metals M selected from the list consisting of V, Nb and Ta, preferably Nb, and one or more ligands L which are organic ligands comprising an ester group, preferably a carboxylic acid ester group, and a carboxylic acid group, and which are optionally deprotonated.

[0033] Ester groups are derived from acids (organic or inorganic) in which at least one --OH (hydroxy) group has been replaced by an --O-alkyl (alkoxy) group.

[0034] Preferred are metal complexes comprising one or more metals M selected from the list consisting of V, Nb and Ta, and one or more ligands L which are organic ligands comprising an ester group, preferably a carboxylic acid ester group, and a carboxylic acid group, and which are optionally deprotonated.

[0035] More preferred are metal complexes comprising one or more metals M selected from the list consisting of V, Nb and Ta, and one or more ligands L which are organic ligands comprising a carboxylic acid ester group and a carboxylic acid group, and which are optionally deprotonated.

[0036] Most preferred are metal complexes comprising Nb and one or more ligands L, which are organic ligands comprising carboxylic acid ester groups and carboxylic acid groups, and which are optionally deprotonated.

[0037] Preferably, L is an organic ligand further comprising a carbon-carbon double bond.

[0038] Preferably, L coordinates to one or more metals M via a carboxylic acid group.

[0039] Preferably, the metal complexes according to the invention are polynuclear.

[0040] In a preferred embodiment of the present invention, L is a carboxylic acid group optionally deprotonated, as represented by formula (1): [ka] [In the formula, the curved line represents a divalent hydrocarbon group having from 2 to 20 carbon atoms, preferably from 2 to 10 carbon atoms, more preferably from 3 to 5 carbon atoms, and having one or more carbon-carbon double bonds, preferably one or two carbon-carbon double bonds, more preferably one carbon-carbon double bond; and R is an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms, or an aryl group having 5 to 20 aromatic ring atoms, preferably 5 to 10 aromatic ring atoms, and more preferably 5 or 6 aromatic ring atoms, and may be substituted or unsubstituted.

[0041] Preferably, L is a compound of formula (1), optionally deprotonated at the carboxylic acid group, wherein the curved line represents a divalent hydrocarbon group having 2 to 10 carbon atoms and having one or two carbon-carbon double bonds; and R is an alkyl group having 1 to 10 carbon atoms or an aryl group having 5 to 10 aromatic ring atoms, which may be substituted or unsubstituted.

[0042] More preferably, L is a compound of formula (1) optionally deprotonated at the carboxylic acid group, wherein the curved line represents a divalent hydrocarbon group having 3 to 5 carbon atoms and having one or more carbon-carbon double bonds; and R is an alkyl group having 1 to 5 carbon atoms or an aryl group having 5 or 6 aromatic ring atoms, which may be substituted or unsubstituted.

[0043] In formula (1), the substituted alkyl is —C(O)R v , -C(O)OR v , -NR v R w , -OR v , -R x , -CN, -F, and -Cl, wherein R v =H, C3-C10 aryl or C1-C10 alkyl, R w =H, C3-C10 aryl or C1-C10 alkyl, and R x = C3-C10 aryl or C1-C10 alkyl, preferably R v =H, methyl, ethyl, propyl, or phenyl, R w =H, methyl, ethyl, propyl, or phenyl, and R x = phenyl.

[0044] In formula (1), the alkyl containing one or more functional groups preferably contains one or more functional groups selected from the list consisting of a carbon-carbon double bond, a carbon-carbon triple bond, an amide, a carbamate, a carbonate, a carboxylic acid, an ester, an ether, a secondary or tertiary amine, and a keto.

[0045] In formula (1), the substituted alkyl is —C(O)R v , -C(O)OR v , -NR v R w , -OR v , -R x , -CN, -F, and -Cl, wherein R v =H, C3-C10 aryl or C1-C10 alkyl, R w =H, C3-C10 aryl or C1-C10 alkyl, and R x = C3-C10 aryl or C1-C10 alkyl, preferably R v =H, methyl, ethyl, propyl, or phenyl, R w =H, methyl, ethyl, propyl, or phenyl, and R x = methyl, ethyl, propyl, or phenyl.

[0046] In a more preferred embodiment of the present invention, L is a carboxylic acid group optionally deprotonated, formula (2): [ka] [In the formula, R is an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, or an aryl group having 5 to 20 aromatic ring atoms, preferably 5 to 10 aromatic ring atoms, more preferably 5 or 6 aromatic ring atoms, which may be substituted or unsubstituted; and R 1is H, an alkyl group having 1 to 10 carbon atoms, preferably 1 to 5 carbon atoms, or an aryl group having 5 to 10 aromatic ring atoms, preferably 5 or 6 aromatic ring atoms, which may be substituted or unsubstituted.

[0047] Preferably, L is a compound of formula (2), optionally deprotonated at the carboxylic acid group, wherein R is an alkyl group having 1 to 10 carbon atoms or an aryl group having 5 to 10 aromatic ring atoms, which may be substituted or unsubstituted; and R 1 is H, an alkyl group having 1 to 5 carbon atoms, or an aryl group having 5 or 6 aromatic ring atoms, which may be substituted or unsubstituted.

[0048] More preferably, L is a compound of formula (2), optionally deprotonated at the carboxylic acid group, wherein R is an alkyl group having 1 to 5 carbon atoms or an aryl group having 5 or 6 aromatic ring atoms, which may be substituted or unsubstituted; and R 1 is H, an alkyl group having 1 to 5 carbon atoms, or an aryl group having 5 or 6 aromatic ring atoms, which may be substituted or unsubstituted.

[0049] Particularly preferably, L is a compound of formula (2), optionally deprotonated at the carboxylic acid group, wherein R is methyl, ethyl, or propyl; and R 1 is H, methyl, or phenyl.

[0050] Most preferably, L is a compound of formula (2), optionally deprotonated at the carboxylic acid group: wherein R is ethyl, and R1 is methyl.

[0051] In formula (2), the substituted alkyl is —C(O)R v , -C(O)OR v , -NR v R w , -OR v , -R x , -CN, -F, and -Cl, wherein R v =H, C3-C10 aryl or C1-C10 alkyl, R w =H, C3-C10 aryl or C1-C10 alkyl, and R x = C3-C10 aryl or C1-C10 alkyl, preferably R v =H, methyl, ethyl, propyl, or phenyl, R w =H, methyl, ethyl, propyl, or phenyl, and R x = phenyl.

[0052] In formula (2), the alkyl containing one or more functional groups preferably contains one or more functional groups selected from the list consisting of a carbon-carbon double bond, a carbon-carbon triple bond, an amide, a carbamate, a carbonate, a carboxylic acid, an ester, an ether, a secondary or tertiary amine, and a keto.

[0053] In formula (2), the substituted alkyl is —C(O)R v , -C(O)OR v , -NR v R w , -OR v , -R x , -CN, -F, and -Cl, wherein R v =H, C3-C10 aryl or C1-C10 alkyl, R w =H, C3-C10 aryl or C1-C10 alkyl, and R x = C3-C10 aryl or C1-C10 alkyl, preferably R v =H, methyl, ethyl, propyl, or phenyl, Rw =H, methyl, ethyl, propyl, or phenyl, and R x = methyl, ethyl, propyl, or phenyl.

[0054] The metal M in the metal complex of the present invention is preferably in an oxidation state selected from the list consisting of +I, +II, +III, +IV, and +V, preferably +II, +III, +IV, and +V, more preferably +V.

[0055] In a preferred embodiment of the present invention, the metal complex is represented by the following formula (3): [ka] [In the formula, M is, in each occurrence independently, a metal selected from the list consisting of V, Nb, and Ta, preferably Nb; L, in each occurrence independently, is an organic ligand comprising an ester group, preferably a carboxylic acid ester group, and a carboxylic acid group, optionally deprotonated; A is μ-L - , μ-OH - , μ-OR - , μ-F - μ-Cl - , μ-Br - , or μ-I - R is an alkyl group having 1 to 10 carbon atoms, preferably 1 to 5 carbon atoms, more preferably methyl, ethyl, propyl, butyl, or pentyl; L - is the deprotonated L, B is the bridging ligand μ-O 2- and m is an integer of 1 to 10, preferably 1 to 5, more preferably 1 or 2, and most preferably 1; n is an integer of 5 to 50, preferably 5 to 25, more preferably 5 to 10, and most preferably 5; a is an integer of 0 to 20, preferably 0 to 10, more preferably 0 to 4, and most preferably 0; and b is an integer of 0 to 10, preferably 0 to 5, more preferably 0 or 2, and most preferably 0; However, the following formula is satisfied: n+a+2×b=S×m, where S is the oxidation state value of M, and is preferably selected from 1, 2, 3, 4, and 5, more preferably selected from 2, 3, 4, and 5, and most preferably 5.

[0056] Preferably, the metal complex is represented by formula (3): wherein M is, in each occurrence independently of one another, a metal selected from the list consisting of V, Nb, and Ta, preferably Nb; L, in each occurrence independently, is an organic ligand comprising a carboxylic acid ester group and a carboxylic acid group, and is optionally deprotonated; A is μ-L - , μ-OH - , μ-OR - , μ-F - μ-Cl - , μ-Br - , or μ-I - R is an alkyl group having 1 to 5 carbon atoms; and L - is the deprotonated L, B is the bridging ligand μ-O 2- and m is an integer from 1 to 5, n is an integer from 5 to 25, a is an integer from 0 to 10, and b is an integer from 0 to 5, However, the following formula is satisfied: n+a+2×b=S×m, where S is the oxidation state value of M and is selected from 1, 2, 3, 4, and 5.

[0057] More preferably, the metal complex is represented by formula (3): wherein M is Nb; L, in each occurrence independently, is an organic ligand comprising a carboxylic acid ester group and a carboxylic acid group, and is optionally deprotonated; A is μ-L - , μ-OH - , μ-OR - , μ-F - μ-Cl - , μ-Br - , or μ-I - R is methyl, ethyl, propyl, butyl, or pentyl; L - is the deprotonated L, B is the bridging ligand μ-O 2- and m is 1 or 2; n is an integer from 5 to 10, a is an integer from 0 to 4, and b is an integer from 0 to 2, However, the following formula is satisfied: n+a+2×b=S×m, where S is the oxidation state value of M and is selected from 1, 2, 3, 4, and 5.

[0058] Most preferably, the metal complex has the formula (3a) [ka] [In the formula, M is Nb; L, in each occurrence independently, is an organic ligand comprising a carboxylic acid ester group and a carboxylic acid group, optionally deprotonated; and n is 5].

[0059] compound The present invention further relates to a formulation comprising: (i) a metal complex according to the present invention as a metal oxide precursor; (ii) an epoxy resin mixture; (iii) a photoinitiator.

[0060] Preferred metal complexes that can be used in the formulations according to the invention are described above.

[0061] In a preferred embodiment of the present invention, the weight ratio of (i) the metal complex in the formulation is 0.1% to 50% (w / w), preferably 0.5% to 30% (w / w), more preferably 1% to 10% (w / w), and most preferably 5% (w / w), based on the total mass of the formulation.

[0062] In a preferred embodiment of the present invention, the weight ratio of (ii) the epoxy resin mixture in the formulation is in the range of 0.1% to 50% (w / w), preferably 0.5% to 30% (w / w), more preferably 1% to 10% (w / w), and most preferably 5% (w / w), based on the total mass of the formulation.

[0063] In a particularly preferred embodiment of the present invention, the weight ratios of (i) the metal complex and (ii) the epoxy resin mixture in the formulation are the same and are selected from the range of 1% to 10% (w / w), more preferably 5% (w / w) each.

[0064] In a preferred embodiment of the present invention, the weight ratio (w / w) of (ii) the epoxy resin mixture to (i) the metal complex in the formulation is in the range of 1:1 to 1:2, preferably 1:1.3 to 1:1.8, more preferably 1:1.6 to 1:1.7.

[0065] In a preferred embodiment of the present invention, (ii) the epoxy resin mixture comprises: (ii-1) one or more fluorene epoxy resins; (ii-2) one or more acrylate epoxy resins.

[0066] In a more preferred embodiment of the present invention, (ii) the epoxy resin mixture comprises: (ii-1) two or more kinds of fluorene epoxy resins, (ii-2) one or more acrylate epoxy resins.

[0067] In a particularly preferred embodiment of the present invention, (ii) the epoxy resin mixture comprises: (ii-1) two types of fluorene epoxy resins, (ii-2) one acrylate epoxy resin.

[0068] In the most preferred embodiment of the present invention, (ii) the epoxy resin mixture comprises: (ii-1) two types of fluorene epoxy resins, (ii-2) one type of acrylate epoxy resin.

[0069] Preferably, the (ii-1) fluorene epoxy resin is represented by the following formula (4): [ka] [In the formula, R is a halogen, preferably F or Cl, an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, or an aryl group having 5 to 20 aromatic ring atoms, preferably 5 to 10 aromatic ring atoms, more preferably 5 or 6 aromatic ring atoms; m is an integer of 0 to 4, preferably 0 or 1, more preferably 0; n is an integer of 0 to 4, preferably 0 or 1, more preferably 0; p is an integer of 0 to 10, preferably 1 to 6, more preferably 1 to 3, and most preferably 1; and and q is an integer of 0 to 10, preferably 1 to 6, more preferably 1 to 3, and most preferably 1.

[0070] More preferably, the (ii-1) fluorene epoxy resin is represented by formula (4): wherein R is F, Cl, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 5 to 10 aromatic ring atoms; m is 0 or 1; n is 0 or 1, p is an integer from 1 to 6, and q is an integer of 1 to 6.

[0071] Particularly preferably, (ii-1) the fluorene epoxy resin is represented by formula (4): wherein R is an alkyl group having 1 to 5 carbon atoms or an aryl group having 5 or 6 aromatic ring atoms; m is 0 or 1; n is 0 or 1, p is an integer from 1 to 3, and q is an integer of 1 to 3.

[0072] Most preferably, (ii-1) the fluorene epoxy resin is represented by formula (4): In the formula, m is 0, n is 0, p is 1, and q is 1.

[0073] Preferred (ii-1) fluorene epoxy resins are "OGSOL" (registered trademark) PG 100, EG 200, CG 500, CG 500H, EG 280, and CG 400 (trade names, manufactured by Osaka Gas Chemicals Co., Ltd.).

[0074] Preferably, the (ii-2) acrylate epoxy resin is represented by the following formula (5): [ka] [In the formula, R a is H or an alkyl group having 1 to 5 carbon atoms, preferably H or CH3; R b is a divalent organic group, preferably selected from aromatic, aliphatic, or mixed aromatic and aliphatic groups, preferably having 6 to 20 carbon atoms, more preferably -CH-C(CH)-CH-, most preferably -p-CH-C(CH)-p-CH-; S a is an alkylene group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, optionally substituted with F or OH, and Sb is an alkylene group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms, and may be substituted with F or OH.

[0075] More preferably, the (ii-2) acrylate epoxy resin is represented by formula (5): In the formula, R a is H or an alkyl group having 1 to 5 carbon atoms, preferably H or CH3; R b is a divalent organic group selected from aromatic groups, aliphatic groups, or a mixture of aromatic and aliphatic groups, preferably having 6 to 20 carbon atoms; S a is an alkylene group having 1 to 6 carbon atoms, optionally substituted with F or OH, and S b is an alkylene group having 1 to 6 carbon atoms, which may be substituted with F or OH.

[0076] Particularly preferably, (ii-2) the acrylate epoxy resin is represented by formula (5): In the formula, R a is H or CH3, R b is a mixed aromatic and aliphatic group having 6 to 20 carbon atoms, S a is an alkylene group having 1 to 3 carbon atoms, optionally substituted with OH, and S b is an alkylene group having 1 to 3 carbon atoms, which may be substituted with OH.

[0077] Most preferably, (ii-2) the acrylate epoxy resin is represented by formula (5): In the formula, R 3 is H, R b is -C6H4-C(CH3)2-C6H4-, preferably -p-C6H4-C(CH3)2-p-C6H4-, S ais —CH—CH(OH)—CH—, and S b is -CH2-.

[0078] A preferred (ii-2) acrylate epoxy resin is CN153.

[0079] Preferably, (iii) the photoinitiator is a photoacid generator (PAG) that catalyzes the radiation-induced polymerization of the epoxy resin mixture. Preferred photoacid generators (PAGs) are diazonium salts, iodonium salts, or sulfonium salts, preferably sulfonium salts, more preferably triarylsulfonium salts.

[0080] A preferred photoacid generator (PAG) is 4-nitrobenzenediazonium tetrafluoroborate, bis(4-tert-butylphenyl)iodonium hexafluorophosphate, bis(4-fluorophenyl)iodonium trifluoromethanesulfonate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroarsenate, diphenyliodonium trifluoromethanesulfonate, 4-isopropyl-4'-methyl-diphenyliodonium tetrakis(pentafluorophenyl)borate, (4-nitrophenyl)(phenyl)iodonium trifluoromethanesulfonate, [3-(trifluoromethyl)phenyl](2,4,6-trimethylphenyl)iodonium trifluoromethanesulfonate, [4-(trifluoromethyl)phenyl](2,4,6-trimethylphenyl)iodonium trifluoromethanesulfonate, (2-methylphenyl)(2,4,6-trimethylphenyl)iodonium trifluoromethanesulfonate, (3-methylphenyl)(2,4,6-trimethylphenyl)iodonium trifluoromethanesulfonate, (4-methylphenyl)(2,4,6-trimethylphenyl)iodonium trifluoromethanesulfonate, cyclopropyldiphenylsulfonium tetrafluoroborate, cyclopropyldiphenylsulfonium tetrakis(pentafluorophenyl)borate, dimethylphenacylsulfonium tetrafluoroborate, dimethylphenacylsulfonium tetrakis(pentafluorophenyl)borate, triphenylsulfonium tetrafluoroborate, triphenylsulfonium bromide, triphenylsulfonium tetrakis(pentafluorophenyl)borate, tri-p-tolylsulfonium hexafluorophosphate, Tri-p-tolylsulfonium trifluoromethanesulfonate, and tri-p-tolylsulfonium tetrakis(pentafluorophenyl)borate.

[0081] A particularly preferred (iii) photoacid generator is CPI-310B, i.e., triphenyl-sulfonium tetrakis(pentafluorophenyl)borate, in which one or more of the three phenyl groups are optionally substituted, the same or different, with preferably straight-chain, branched-chain, or cyclic alkyl and / or aryl groups.

[0082] In a preferred embodiment of the present invention, the formulation further comprises (iv) one or more solvents.

[0083] The medium is selected to improve the application, wetting, deposition properties, filling properties, and / or stability of the formulation. Any solvent can be used in the formulation according to the present invention as long as it dissolves or disperses the components of the formulation. Preferred solvents are selected from water, organic solvents, and mixtures thereof. Preferred organic solvents are alcohols, esters, ketones, lactones, diketones, carboxylic acids, amides, and mixtures thereof. Particularly preferred organic solvents are ethanol, propanol, 1-butanol, 2-butanol, diacetone alcohol, 1-methoxy-2-propanyl acetate (PGMEA), 1-methoxy-2-propanol (PGME), butyl acetate, amyl acetate, cyclohexyl acetate, 3-methoxybutyl acetate, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, cyclopentanone, ethyl-3-ethoxypropanoate, methyl-3-ethoxypropanoate, methyl-3-methoxypropanoate, methyl acetoacetate, ethyl acetoacetate, methyl pivalate, ethyl pivalate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether propanoate, propylene glycol monoethyl ether propanoate, ethylene glycol monomethyl ether, ethyl Examples of suitable ethylene glycol monoethyl ethers include ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 3-methyl-3-methoxybutanol, N-methylpyrrolidone, dimethyl sulfoxide, gamma-butyrolactone, gamma-valerolactone, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, methyl lactate, ethyl lactate, propyl lactate, tetramethylene sulfone, propylene glycol dimethyl ether, dipropylene glycol dimethyl ether, ethylene glycol dimethyl ether or diethylene glycol dimethyl ether, N-ethylpyrrolidone, 2-pyrrolidone, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, terpineol, 3-phenoxytoluene, 4-phenoxytoluene, and anisole.These solvents may be used alone or in combination of two or more.

[0084] In a preferred embodiment of the present invention, the formulation comprises one or more further metal complexes which can act as further metal oxide precursors. In such a case, a mixed metal oxide optical layer can be formed which comprises a metal oxide obtained from a metal complex according to the present invention and a further metal oxide obtained from a further metal complex.

[0085] Preferred further metal complexes comprise one or more trivalent or tetravalent metals, preferably selected from the list consisting of Sc, Y, La, Ti, Zr, Hf and Sn, more preferably one or more tetravalent metals selected from the list consisting of Ti, Zr, Hf and Sn.

[0086] In a preferred embodiment of the present invention, the formulation comprises, in addition to the metal complex, one, two, three, four, or more additional metal complexes, each of which preferably contains a ligand selected from inorganic or organic ligands. Preferred inorganic ligands are halides, phosphoric acid, sulfonic acid, nitric acid, and water, optionally deprotonated. Preferred organic ligands are alcohols, carboxylic acids, cyanates, isocyanates, 1,3-diketones, β-keto acids, β-keto esters, organic phosphonic acids, organic sulfonic acids, oximes, hydroxamic acids, dihydroxybenzenes, hydroxybenzoic acids, dihydroxybenzoic acids, gallic acid, dihydroxynaphthalenes, anthracene diols, hydroxyanthrones, anthracene triols, dithranols, halogenated hydrocarbons, aromatics, heteroaromatics, esters, catechols, coumarins, and derivatives thereof, optionally deprotonated.

[0087] The presence of such additional metal complexes makes it possible to tailor certain properties of the metal oxide optical layers prepared therefrom, such as material hardness, shrinkage, refractive index, transparency, absorbance, and haze suppression.

[0088] Preferably, the weight ratio (w / w) between the metal complex according to the invention and the one or more further metal complexes in the formulation is in the range of 1:100 to 100:1, preferably 1:10 to 10:1, more preferably 1:5 to 5:1.

[0089] The total weight ratio of the metal complex according to the present invention to the further metal complex contained in the formulation is preferably in the range of 0.1% to 50% (w / w), preferably 0.5% to 30% (w / w), more preferably 1% to 10% (w / w), and most preferably 5% (w / w), based on the total mass of the formulation.

[0090] In a preferred embodiment of the invention, the formulation is an ink formulation suitable for inkjet printing. Typical requirements for an ink formulation are a surface tension in the range of 20 mN / m to 30 mN / m, and a viscosity in the range of 5 mPa·s to 10 mPa·s.

[0091] Method for preparing a metal oxide optical layer The present invention further relates to a method for preparing a metal oxide optical layer, the method comprising the following steps: (a) providing a formulation according to the present invention; (b) applying the formulation to a surface of a substrate; (c) converting the formulation into a metal oxide optical layer on the surface of the substrate.

[0092] Preferably, the formulation provided in step (a) is a solution or dispersion comprising one or more solvents. Preferred solvents for the formulation provided in step (a) are the same as those described above for the formulations according to the invention.

[0093] In a preferred embodiment of the present invention, the formulation provided in step (a) is an ink formulation suitable for inkjet printing. Typical requirements for an ink formulation are a surface tension in the range of 20 mN / m to 30 mN / m and a viscosity in the range of 5 mPa·s to 10 mPa·s.

[0094] Preferably, the formulation is applied to the surface of the substrate in step (b) by a deposition method. Preferred deposition methods are drop casting, coating, or printing. More preferred coating methods are spin coating, spray coating, slit coating, or slot die coating. More preferred printing methods are flexographic printing, gravure printing, inkjet printing, EHD printing, offset printing, or screen printing. Most preferred are spray coating and inkjet printing.

[0095] Depending on the specific problem to be solved, the formulation needs to be deposited as a homogeneous, dense thin layer covering the entire surface of the substrate by a coating method, or the formulation needs to be deposited locally in a structured manner, hence the need for a printing method. Both coating and printing methods require the formulation to be formulated in an appropriate manner to suit the physicochemical needs of the respective coating and printing method, as well as the specific needs of the surface of the substrate to be coated or printed.

[0096] In a preferred embodiment of the method for preparing a metal oxide optical layer according to the present invention, the surface of the substrate is pretreated by a surface cleaning process. A preferred surface cleaning process is the silicon wafer cleaning process described in W. Kern, "The Evolution of Silicon Wafer Cleaning Technology," J. Electrochem. Soc., Vol. 137, 6, 1990, 1887-1892, and "New Process Technologies for Microelectronics," RCA Review 1970, 31, 2, 185-454. Such silicon wafer cleaning processes include wet cleaning processes using cleaning solvents (e.g., isopropanol (IPA)); wet etching processes using hydrogen peroxide solutions (e.g., piranha solution, SC1, and SC2), choline solutions, or HF solutions; dry etching processes using chemical vapor etching, UV / ozone treatment, or glow discharge techniques (e.g., O2 plasma etching); and mechanical processes using brush scrubbing, fluid jets, or ultrasonic techniques (sonification). The surface of the substrate can also be pretreated by silanization or atomic layer deposition (ALD) processes. Pretreatment of the surface of the substrate helps to modify the hydrophobicity / hydrophilicity of the surface, which can improve the adhesion and packing properties of the metal oxide optical layer on the substrate surface.

[0097] In more preferred embodiments, a wet cleaning process involving a cleaning solvent (e.g., isopropanol (IPA)) is combined with one or more of the following: a wet etching process involving a hydrogen peroxide solution (e.g., piranha solution, SC1, and SC2), a choline solution, or an HF solution; a dry etching process involving chemical vapor etching, UV / ozone treatment, or glow discharge techniques (e.g., O2 plasma etching); and a mechanical process involving brush scrubbing, a fluid jet, or ultrasonic techniques (sonification).

[0098] In the most preferred embodiment, a wet cleaning process involving a cleaning solvent (e.g., isopropanol (IPA)) is combined with a mechanical process involving brush scrubbing, fluid jets, or ultrasonic techniques (sonification), and a wet etching process involving a hydrogen peroxide solution (e.g., piranha solution, SC1, and SC2), a choline solution, or an HF solution. In a preferred embodiment of the present invention, step (b) of the method for preparing a metal oxide optical layer is carried out once.

[0099] In a preferred embodiment of the present invention, step (b) of the method for preparing a metal oxide optical layer is carried out several times in succession, preferably 2 to 20 times, more preferably 2 to 10 times, most preferably 2, 3, 4 or 5 times.

[0100] In a preferred embodiment of the method for preparing a metal oxide optical layer according to the present invention, the formulation is converted in step I onto the surface of the substrate into a metal oxide optical layer by exposure to radiation, preferably in combination with a heat treatment.

[0101] Preferred exposure to radiation includes exposure to infrared (IR) light, visible (Vis) light, and / or ultraviolet (UV) light. IR light has a wavelength of more than 800 nm. Vis light has a wavelength of 400-800 nm. UV light has a wavelength of less than 400 nm and may include EUV (extreme UV). Exposure to radiation is not limited to any particular irradiation method or time. Those skilled in the art can determine the appropriate irradiation method and time depending on the type of substrate and formulation.

[0102] Preferred heat treatments include exposure to elevated temperatures of up to 400°C, preferably up to 350°C, preferably up to 300°C, more preferably up to 250°C, particularly preferably up to 200°C, and most preferably up to 150°C. The heat treatment is not limited to any particular heat treatment method or time. Depending on the type of substrate and formulation, a person skilled in the art can determine the appropriate heat treatment method and time.

[0103] In a more preferred embodiment of the method for preparing a metal oxide optical layer according to the present invention, in step I, the formulation is converted into a metal oxide optical layer on the surface of the substrate by (c-1) pre-baking (soft baking) at a temperature of 40-150°C, preferably 50-120°C, more preferably 60-100°C, (c-2) exposure to irradiation, preferably UV radiation, and (c-3) baking (hard baking, sintering, or annealing) at a temperature of 100-400°C, preferably 150-350°C, more preferably 200-250°C.

[0104] Pre-baking (soft baking) serves the purpose of removing volatile and low-boiling components, such as volatile and low-boiling solvents or additives, from the drop-cast, coated, or printed film. Pre-baking is preferably carried out for 1 to 10 minutes. After pre-baking, a substrate-adherent film layer of the formulation is obtained. The film may further contain residual solvents or additives.

[0105] In an alternative, more preferred embodiment of the method for preparing a metal oxide optical layer according to the present invention, (c-1) pre-baking can be omitted, so that in step I the formulation is directly converted into a metal oxide optical layer on the surface of the substrate by (c-2) exposure to irradiation, preferably UV radiation, and (c-3) baking (hard baking, sintering, or annealing) at a temperature of 100-400°C, preferably 150-350°C, more preferably 200-250°C.

[0106] Exposure to radiation (curing) serves the purpose of crosslinking the epoxy resin mixture contained in the formulation, thereby producing a polymer matrix that acts as a framework to prevent void formation due to evaporation of the ligands of the metal complex and subsequent shrinkage of the material. Preferred exposure to radiation involves exposure to UV light, preferably UV light having a wavelength of 365 nm, for 1 to 60 minutes, preferably 5 to 30 minutes, more preferably 10 to 20 minutes.

[0107] Firing (hard firing, sintering, or annealing) serves the purpose of converting the formulation onto the substrate into a metal oxide layer. The firing process may also tailor the properties of the final metal oxide layer. Firing is performed for 1 to 60 minutes, preferably 1 to 30 minutes, more preferably 5 to 20 minutes, and most preferably 10 minutes, to achieve a refractive index (RI) greater than 2.0.

[0108] Pre-baking, exposure to radiation, and calcination may be carried out under ambient atmosphere or under an atmosphere with increased oxygen content to decompose undesired organic components, which may result in a lower activation energy when the metal oxide layer is formed.

[0109] In a preferred embodiment of the method for preparing a metal oxide optical layer according to the present invention, the substrate is a patterned substrate with topographical features on its surface, and the metal oxide optical layer forms a coating layer that covers the surface of the substrate and fills the topographical features, so that the topographical features are filled and planarized by the metal oxide optical layer.

[0110] Preferred topographical features include, for example, gaps, grooves, trenches, and vias. The topographical features may be uniformly or non-uniformly distributed across the surface of the substrate. Preferably, they are arranged on the surface of the substrate as an array or grid. The topographical features preferably have different lengths, widths, diameters, and different aspect ratios. The topographical features preferably have an aspect ratio of 1:20 to 20:1, more preferably 1:10 to 10:1. The aspect ratio is defined as the width of the structure relative to its height (or depth). In terms of size, the depth of the topographical features is preferably in the range of 10 nm to 10 μm, more preferably 50 nm to 5 μm, and most preferably 100 nm to 1 μm.

[0111] It is also preferred that the topographical features are tilted at a particular angle, such as an angle of 10 to 80°, preferably 20 to 60°, more preferably 30 to 50°, and most preferably about 40°. Such tilted topographical features are also referred to as beveled or blazed topographical features.

[0112] It may be necessary to locally fill the topographical features completely or to a certain level with the metal oxide optical layer, but not cover adjacent surfaces of the substrate where the topographical features are not available to be filled.

[0113] Therefore, the method for preparing a metal oxide optical layer according to the present invention comprises the following step (d): Preferably, the method further comprises (d) removing a portion of the metal oxide optical layer overlying a topographical feature, thereby obtaining a filled topographical feature, wherein the overburden of the metal oxide optical layer on top of the topographical feature is reduced to an overburden of preferably 0 to 100 nm, more preferably 0 to 50, and most preferably 0 to 20 nm.

[0114] Step (d) is performed after steps (a) to (c) of the method according to the present invention. Preferably, removing the portion of the metal oxide optical layer overlying the topography in step (d) is performed using a surface cleaning process as described above. Preferred surface cleaning processes are those described in W. Kern, *The Evolution of Silicon Wafer Cleaning Technology*, J. Electrochem. Soc., Vol. 137, 6, 1990, 1887-1892, and *New Process Technologies for Microelectronics*, RCA Review 1970, 31, 2, 185-454. Such silicon wafer cleaning processes include wet etching processes using hydrogen peroxide solutions (e.g., piranha solution, SC1, and SC2), choline solutions, or HF solutions; dry etching processes using chemical vapor etching, UV / ozone treatment, or glow discharge techniques (e.g., O2 plasma etching); and mechanical processes using brush scrubbing, fluid jets, or ultrasonic techniques.

[0115] The substrate is preferably a substrate for an optical device. Preferred substrates are made of inorganic or organic-based materials, preferably inorganic-based materials. Preferred inorganic-based materials include materials selected from the list consisting of ceramic, glass, fused silica, sapphire, silicon, silicon nitride, quartz, and transparent polymers or resins. The shape of the substrate is not particularly limited, but is preferably a sheet or wafer.

[0116] In step (b) of the method for preparing a metal oxide optical layer, the formulation is applied onto the surface of a substrate, which may be either the surface of the base material of the substrate or the surface of a layer of a material different from the base material of the substrate, such layer being formed before applying the formulation.

[0117] In this way, a sequence of different layers (layer stacks) can be formed on top of one another. Such layer stacks may be structured, and such structures typically have nanometer-scale dimensions, at least in terms of diameter, width and / or aspect ratio.

[0118] Optical Devices Finally, the present invention relates to an optical device comprising a metal oxide optical layer obtainable or obtained by the method for preparing a metal oxide optical layer according to the present invention as described above, preferably an augmented reality (AR) and / or virtual reality (VR) device.

[0119] The present invention is further illustrated by, but not limited to, the following examples. Those skilled in the art will recognize that various modifications, additions, and variations can be made to the present invention without departing from the spirit and scope of the invention, as defined in the appended claims. [Example]

[0120] Analysis and measurement methods Ellipsometry was used to determine the layer thickness, refractive index (n), and absorptivity (k) of the metal oxide layer. Measurements were performed using a J.A. Woolam M2000 ellipsometer at three different angles of incidence (65°, 70°, and 75°). The measurement data were analyzed using J.A. Woolam CompleteEase software, which applied B-spline fitting to obtain the refractive index (n) and absorptivity (k), assuming either complete or near-complete transparency above a wavelength of 600 nm. Optical constants were averaged from three to four measured samples, each of which provided different layer thicknesses after soft baking, hard baking, or a combination of soft baking and subsequent hard baking.

[0121] Optical spectra of any sheet and substrate, coated or uncoated with the metal oxide layer described in this invention, were recorded using an Agilent Cary 7000 UV / Vis / NIR spectrophotometer equipped with a UMA setup. Measurements were performed in dual-beam mode, with a scan speed of 600 nm / min, a spectral bandwidth of 4 nm, and unpolarized light, applying a spectral window of 350 nm to 700 nm. Transmittance measurements were performed at an incidence angle of 6° relative to the surface normal of the sample. The detector was aligned at 180° relative to the incident light. Reflectance measurements were performed at an incidence angle of 6° relative to the surface normal of the sample, with the detector angle being 12° relative to the incident light. The absorption of the sample was calculated using Equation 1, where A represents the absorption of the coated sample, R represents the reflection, and T represents the transmission of the sample.

[0122] A=1-(R+T) Equation 1 Thermogravimetric analysis was carried out on a TA Instruments TGA Q50. In the normal measurement mode, the samples were heated to 950°C in an air atmosphere by applying a heating gradient of 20 K / min.

[0123] The results of the elemental analysis were received as a service from an analytical service provider who performed the measurements according to DIN 51732:2014-07.

[0124] NMR measurement 1 H-NMR was measured using a 500 MHz spectrometer manufactured by Bruker Biospin GmbH.

[0125] SEM images were recorded using either a Tescan Mira3LMU, or a Carl Zeiss Sigma300VP, or a Carl Zeiss Supra35.

[0126] Substrate coating, typically a wafer, was performed using a Suess spin coater (LabSpin150i). The spin coating process with planar substrates was as follows: 0.5 ml of coating was deposited onto a stationary quartz wafer, followed by a 30-second spin interval at a given spin speed, with an acceleration of 500 rpm / s to reach the final spin speed. 2 The temperature was set to 100°C. Different layer and coating thicknesses were achieved using either different spin speeds or different coating formulations with different concentrations of metal oxide precursors or mixtures of different metal oxide precursors. After spin coating, the coated substrate was subjected to a 2-minute pre-bake at 100°C to remove solvent residues, followed by a high-temperature bake, or the layer deposited on the wafer was directly baked at a high temperature for a specified time. Typically, but not exclusively, the coated layer was baked at 150°C, 200°C, 250°C, and 300°C, typically for 5 to 10 minutes. Pre-bake and layer bake were performed using a high-temperature hotplate manufactured by Harry Gestigkeit, which allows temperatures up to 600°C to be reached. The aforementioned conditions and parameters apply to all following experimental examples unless other conditions are explicitly mentioned elsewhere.

[0127] Typically, quartz and / or silicon wafers (both 2 inches in diameter) were used throughout all coating experiments (e.g., spectroscopy and ellipsometry measurements) where a flat, unstructured support for the metal oxide was required.

[0128] The structured substrate, typically a silicon wafer, was used as a square die with an edge length of 1.5 cm to 2 cm. The wafer die was cut and cleaved from a parent wafer, typically with a diameter of 8 inches. The structure was then fabricated using SiO2 / SiN xThe trenches were fabricated and arranged in a layer stack consisting of: (1) a 100 nm thick trench array; (2) a 150 nm thick trench array; (3) a 100 nm thick trench array; (4) a 150 nm thick trench array; (5) a 150 nm thick trench array; (6) a 150 nm thick trench array; (7) a 150 nm thick trench array; (8) a 150 nm thick trench array; (9) a 150 nm thick trench array; (10) a 150 nm thick trench array; (11) a 150 nm thick trench array; (12) a 150 nm thick trench array; (13) a 150 nm thick trench array; (14) a 150 nm thick trench array; (15) a 150 nm thick trench array; (16) a 150 nm thick trench array; (17) a 150 nm thick trench array; (18) a 150 nm thick trench array; (19) a 150 nm thick trench array; (20) a 150 nm thick trench array; (21) a 150 nm thick trench array; (22) a 150 nm thick trench array; (23) a 150 nm thick trench array; (24) a 150 nm thick trench array; (25) a 150 nm thick trench array; (26) a 150 nm thick trench array; (27) a 150 nm thick trench array; (28) a 150 nm thick trench array; (29 ...30) a 150 nm thick trench array; (31) a 150 nm thick trench array; (

[0129] The structured wafer dies were coated by spin coating unless otherwise stated. For that purpose, a volume of coating formulation, typically 0.15 mL to 0.5 mL per die (with a diameter of 0.5 inches to 2 inches), was pipetted and cast onto the surface of the wafer. The formulation was spread and allowed to settle on the surface for 1 minute, followed by a step of distributing and spreading the formulation over the entire surface of the wafer dies at 500 rpm for 30 seconds, followed by a final spin-off step at 2000 rpm for another 60 seconds. The acceleration of the spin speed was 500 rpm / s. 2 The soft bake and hard bake conditions for the structured wafer die were selected to be similar or identical to those already described for the flat substrate.

[0130] All chemicals for the described syntheses were purchased from Sigma Aldrich and used without further purification unless otherwise stated.

[0131] Preparation of Nb citraconate A three-necked glass flask (100 mL) was continuously flushed with N2, and 17.6116 g of citraconic anhydride and 8.160 g of 1-methoxy-2-propanol acetate (PGME) were added to the flask (first solution). The mixture was stirred for 15 minutes under a constant flow of N2. In parallel, a mixture of 28.770 g of 1-methoxy-2-propanyl acetate (PGMEA) and 10 g of niobium ethoxide (second solution) was prepared under an inert atmosphere and added to the first solution flask over 1 hour using a dropping funnel. After the addition of the second solution to the first solution was complete, the reaction mixture was heated to 50 °C for 4 hours under continuous stirring. The mixture was then cooled and filled into a suitable inert amber glass bottle. A small amount of material was removed, the solvent was removed, and the remaining residue was dried in a sample vial until a final pressure of 0.01 mbar was reached. The crude product was analyzed by H-NMR: 6.78 ppm (s, 1H), 5.81 ppm (m, 0.56H), 4.16 ppm (q, 0.56H), 4.10 ppm (q, 0.82H), 3.29 ppm (m, 3.04H), 2.12 ppm (s, 3.36H), 1.98 ppm (m, 2.06H), 1.18 ppm (m, 5.64H).

[0132] Example 1 Formulation 1: Epoxy Mixture A (see Table 1 below) was mixed with 10% (w / w) Nb citraconic acid salt prepared above in PGME at a 1:1 weight ratio, resulting in a final concentration of Epoxy Mixture A and Nb citraconic acid salt of 5% (w / w), respectively, i.e., 5 / 5% (w / w) Nb citraconic acid salt / Epoxy Mixture A.

[0133] Epoxy Mixture A: [Table 1]

[0134] Deposition: 100 μL of Formulation 1 was deposited onto a substrate (18 × 18 mm) with surface features by depositing a 100 μL droplet followed by spin-coating at 2000 rpm for 25 seconds. The coated substrate was then pre-baked at 100 °C for 1 minute. The substrate was then irradiated with a 365°C UV lamp for 20 minutes and then baked at 300 °C for 10 minutes.

[0135] The formulation deposited via the above process fills the surface features.

[0136] Figure 7 shows the surface feature filling of spin-coated 5 / 5% (w / w) Nb citraconate / epoxy mixture A after pre-baking at 100 °C for 1 minute, followed by UV curing with 365 nm light for 20 minutes and baking at 350 °C for 10 minutes.

[0137] FIG. 8 shows surface feature filling after spin-coating a 5% (w / w) Nb citraconic acid solution in PGME and annealing at 300° C. for 10 minutes.

[0138] The optical properties (ellipsometric measurements) of the formed films prepared using UV curing after baking at different temperatures are shown in Table 2 below.

[0139] [Table 2]

[0140] Example 2 Formulation: Different weight ratios of Nb citraconic acid salt (1:1 in PGME) and epoxy mixture A (see Table 1 above) were prepared, spin-coated, irradiated with a 365 UV lamp for 20 minutes, and then baked for 10 minutes at 150° C., 200° C., or 250° C. The coated films were then tested for gap-filling (on structured substrates), RI, and absorption (on quartz substrates).

[0141] Figure 9 shows the surface feature filling behavior of Nb citraconate + epoxy mixture A at various mix ratios and baking temperatures. The Nb citraconate concentration remains constant at 5% (w / w), and the epoxy mixture A content is varied from 1% (w / w) to 5% (w / w) as shown.

[0142] When the ratio of epoxy mixture A:Nb citraconic acid salt is 3% (w / w):5% (w / w) and the content of epoxy mixture A is higher, uniform gap filling is achieved after baking at 200°C and 250°C.

[0143] From Table 3, it can be seen that for experiments and material weight ratios (3:5 to 5:5) where good filling is achieved, the refractive index n of these films can be tuned from 1.659 to 1.758 by applying different temperatures from 150 °C to 250 °C.

[0144] Table 4 shows the absorptivity k at a wavelength of 460 nm. Low absorption is achieved for the sample calcined at 150°C.

[0145] [Table 3]

[0146] [Table 4]

[0147] Example 3 The following solutions (5% (w / w) each): Ti isopropoxide, Ti butoxide, Nb ethoxide, and Nb citraconic acid salt were spin-coated onto silicon wafers and baked at 350 °C for 10 min. In addition, new formulations based on mixtures of Ti isopropoxide / epoxy mixture A (5 / 5% (w / w)), Ti butoxide / epoxy mixture A (5 / 5% (w / w)), Nb ethoxide / epoxy mixture A (5 / 5% (w / w)), and Nb citraconic acid salt / epoxy mixture A (5 / 5% (w / w)) were coated onto silicon wafers under the same conditions as above. The refractive index and absorptivity of the coated films were measured.

[0148] Measurement of refractive index n and absorption coefficient k Table 5 shows that refractive indices n greater than 2.00 can be achieved using various metal-organic metal oxide precursors. However, all of these materials, except for Nb citraconate, give a significant increase in absorptivity k with the addition of Epoxy Mixture A. Only for Nb citraconate does k decrease when mixed with Epoxy Mixture A.

[0149] [Table 5]

[0150] Since k is proportional to the light loss of the film, only formulations containing Nb citraconate achieve a surprising effect favorable for use in optical coatings, namely, reduced absorption (light loss) when mixed with an epoxy-based resin matrix to improve filling performance.

[0151] List of Reference Numbers 1 Material with RI02 2 Materials with RI0101 3. Substrate (e.g., glass) 4 Diffraction of incident light represented by thick arrows 5 Total Internal Reflection (TIR) ​​of Light 6 Waveguide 7 Structured layer stack with gaps (trench) 8. Substrate (e.g., glass or silicon) 9 Overburden of materials (e.g., high refractive index materials or highly etch-resistant materials) 10. Materials that provide gap filling (e.g., high refractive index materials or highly etch resistant materials) 11. Void 12 Formulations (e.g., inks) of high refractive index materials (e.g., metal oxide precursors) 13 High refractive index materials (e.g., metal oxides) that provide gap filling with arbitrary concave shapes 14 Overburden layer (optional) 15 Energy

Claims

1. A metal complex, one or more, preferably two or more metals M selected from the list consisting of V, Nb, and Ta, preferably Nb; and one or more ligands L, which are organic ligands comprising an ester group and a carboxylic acid group, and which are optionally deprotonated.

2. 2. The metal complex of claim 1, wherein L is an organic ligand further comprising a carbon-carbon double bond.

3. 3. The metal complex according to claim 1, wherein L is coordinated to the one or more metals M via the carboxylic acid group.

4. L is optionally deprotonated at the carboxylic acid group, 【Chemical 1】 [In the formula, The curved line represents a divalent hydrocarbon group having from 2 to 20 carbon atoms and having one or more carbon-carbon double bonds; R is an alkyl group having 1 to 20 carbon atoms or an aryl group having 5 to 20 aromatic ring atoms, and may be substituted or unsubstituted.

5. L is optionally deprotonated at the carboxylic acid group, 【Chemistry 2】 [In the formula, R is an alkyl group having 1 to 20 carbon atoms or an aryl group having 5 to 20 aromatic ring atoms, which may be substituted or unsubstituted; R １ is H, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 5 to 20 aromatic ring atoms, and may be substituted or unsubstituted.

6. The following formula (3) 【Chemistry 3】 [In the formula, M is, in each occurrence independently, a metal selected from the list consisting of V, Nb, and Ta, preferably Nb; L, in each occurrence, independently, is an organic ligand comprising an ester group and a carboxylic acid group, and is optionally deprotonated; A is μ-L － , μ-OH － , μ-OR － , μ-F － μ-Cl － , μ-Br － , or μ-I － R is an alkyl group having 1 to 10 carbon atoms; L － is deprotonated L, B is a bridging ligand μ-O ２－ and m is an integer from 1 to 10, n is an integer from 5 to 50, a is an integer from 0 to 20, and b is an integer from 0 to 10, However, the following formula is satisfied: n+a+2×b=S×m, where S is the oxidation state value of M, and is preferably selected from 1, 2, 3, 4, and 5, more preferably selected from 2, 3, 4, and 5, and most preferably 5.

7. (i) a metal complex according to any one of claims 1 to 6 as a metal oxide precursor; (ii) an epoxy resin mixture; and (iii) a photoinitiator.

8. 8. The formulation of claim 7, wherein the weight ratio of the (i) metal complex in the formulation ranges from 0.1% to 50% (w / w), based on the total mass of the formulation.

9. The (ii) epoxy resin mixture is (ii-1) one or more fluorene epoxy resins; (ii-2) one or more acrylate epoxy resins.

10. The (ii-1) fluorene epoxy resin is represented by the following formula (4): 【Chemistry 4】 [In the formula, R is a halogen, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 5 to 20 aromatic ring atoms; m is an integer from 0 to 4, n is an integer from 0 to 4, p is an integer from 0 to 10, and 10. The compound according to claim 9, wherein q is an integer from 0 to 10.

11. The (ii-2) acrylate epoxy resin is represented by the following formula (5): 【Chemistry 5】 [In the formula, R ａ is H or an alkyl group having 1 to 5 carbon atoms, R ｂ is a divalent organic group, S ａ is an alkylene group having 1 to 10 carbon atoms, optionally substituted with F or OH, and S ｂ is an alkylene group having 1 to 10 carbon atoms, optionally substituted with F or OH.

12. The formulation of any one of claims 7 to 11, further comprising (iv) one or more solvents.

13. 1. A method for preparing a metal oxide optical layer, comprising: (a) providing a formulation according to any one of claims 7 to 12; (b) applying the formulation to a surface of a substrate; (c) converting the formulation into a metal oxide optical layer on the surface of the substrate.

14. The method of claim 13 , wherein in step (b), the formulation is applied to the surface of the substrate by a deposition method.

15. 15. The method of claim 13 or 14, wherein in step (c) the formulation is converted into a metal oxide optical layer on the surface of the substrate by exposure to radiation.

16. 16. The method of any one of claims 13 to 15, wherein in step (c), the formulation is converted into a metal oxide optical layer on the surface of the substrate by (c-1) pre-baking at a temperature of 40 to 150°C, (c-2) exposing to radiation, and (c-3) baking at a temperature of 100 to 400°C.

17. The method of any one of claims 13 to 16, wherein the substrate is a patterned substrate comprising topographical features on the surface thereof.

18. An optical device comprising a metal oxide optical layer, obtainable by the method according to any one of claims 13 to 17, preferably an Augmented Reality (AR) and / or Virtual Reality (VR) device.

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