EP1272437A1

EP1272437A1 - Substrate comprising a thick film consisting of an inorganic gel, glass, vitroceramic or ceramic material, a method for the production of the same and the use thereof

Info

Publication number: EP1272437A1
Application number: EP01931595A
Authority: EP
Inventors: Anette Berni; Andreas Frantzen; Axel Kalleder; Martin Mennig; Navin Suyal; Helmut Schmidt
Original assignee: Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH
Current assignee: LEIBNIZ-INSTITUT fur NEUE MATERIALIEN GEMEINNUETZ
Priority date: 2000-04-14
Filing date: 2001-04-12
Publication date: 2003-01-08
Also published as: DE10018697A1; WO2001079127A1; JP2003531087A; KR20020093905A; US20030059540A1; AU2001258332A1; CA2405942A1

Abstract

Method for the production of substrates comprising a layer consisting of inorganic gel, glass, vitroceramic or ceramic material, according to which a coating composition containing nanoscalar particles and water-soluble organic flexibilizers is applied to the substrate and is thermally treated. Said method allows transparent thick films which are devoid of cracks to be obtained. The coated substrates are particularly suitable for use as optical, optoelectronic, electronic, micromechanical or dirt-repellent components.

Description

Substrates with a thick layer of inorganic gel, glass, glass ceramic or ceramic material, process for their production and their use

The present invention relates to a substrate with at least one thick layer of inorganic gel, glass, glass ceramic or ceramic material, a method for producing substrates with at least one layer of inorganic gel, glass, glass ceramic or ceramic material and their use, e.g. in optics, optoelectronics or electronics.

Si0 ₂ layers and doped SiO ₂ layers with a layer thickness in the μm range are suitable for different applications in the field of optics and optoelectronics. SiO ₂ layers with layer thicknesses in the μm range are used as dielectric insulation layers on silicon for semiconductor production. Another focus is the production of sufficiently thick buffer layers on silicon for the production of integrated optical components. SiO ₂ layers doped with different ions are used in the production of passive and active planar optical waveguides.

Thick SiO ₂ layers in the μm range are generally produced using thermal oxidation or flame hydrolysis. Both methods are very costly and time-consuming. A 10-15 μm thick SiO ₂ layer is required for buffer layers for the production of planar waveguides. For the production of materials with dopings for matching the refractive index, such as Pb, P, Al, or dopings for the production of active materials such as He, the problem arises that flame hydrolysis cannot achieve sufficiently high doping concentrations.

The sol-gel process represents an alternative to the production of thick SiO ₂ layers and doped SiO ₂ layers. The sol-gel process can be used to easily incorporate suitable ions for the production of reinforcing materials.

In comparison to the conventional synthesis methods, one obtains homogeneous Materials with high doping concentrations. The sol-gel process thus offers an alternative to the production of these components. Up to now, however, it has not been possible to produce compacted, high-purity SiO ₂ layers or doped SiO ₂ layers with layer thicknesses in the μm range on silicon or SiO ₂ as the substrate material without cracks.

When inorganic sol-gel layers are formed, the evaporation of the solvents during the sol-gel transition and, in the further course, the thermal treatment leads to the compression and burning out of the remaining organic matter, and the collapse of the resulting pores, which causes the coating to shrink the chemical bond to the substrate can only occur in a direction perpendicular to the surface.

This results in mechanical stresses in the coating and at the interface to the substrate, which, in addition to the shrinkage of the compacting coating, are also determined by the thermal expansion of the substrate and coating during the heating or cooling process. The experts are aware that these tensions increase with the layer thickness, so that there is a limit of approximately less than 1 μm for all known layer systems. Crack-free single coatings cannot be formed for thicker coatings.

Tetraethoxysilane (TEOS) in ethanol, which has been hydrolyzed with aqueous hydrochloric acid or water, is frequently used as the starting material for sol-gel SiO ₂ layers on silicon wafers and on glass substrates. It was only possible to achieve maximum layer thicknesses of 400 nm or coarse porous layers were obtained which are unusable for optical applications because of their porosity.

By Williams et al., Proc. SPIE-Int. Soc. Opt. Eng. (1994), 2288 (Sol-Gel-Optics III), 55-56, describes the production of SiO ₂ layers starting from colloidal SiO ₂ sol which has been mixed with polysiloxanes. The layer thickness that the after drying at 150 ° C., compacted crack-free layers were obtained, were between 100 nm and 1 μm.

The production of thick SiO ₂ layers by means of electrophoresis is described by Nishimori et al., J. Sol-Gel-Sci. Technol. (1996), 7 (3), 211-216. The layers are synthesized from SiO ₂ particles and polyacrylic acid. The layer is applied to stainless steel by means of electrophoretic deposition, sintering is not carried out. Layers produced by means of electrophoresis have the disadvantage that they show a high porosity after densification and are not transparent. Another disadvantage of electrophoretic deposition is that the substrates have to be metallically conductive.

The production of wave-guiding layers is based on inorganic sol-gel materials, with the problem of the low layer thickness arising in all cases. SiO ₂ -Ti0 ₂ layers are discussed as wave-guiding materials. Other doping materials for SiO ₂ layers besides Ti0 ₂ are P ₂ O ₅ and GeO ₂ .

With conventional sol-gel processes, only very thin layers can be achieved, which for many applications, e.g. B. embossing multimode waveguides are not suitable. Thick layers can be obtained in the electrophoretic deposition of pre-compressed SiO ₂ particles on metal substrates, but electrophoretic coating processes are in principle unsuitable for substrates such as those used in optics and optoelectronics (eg Si, glass). In addition, no transparent layers can be obtained as are necessary for optical applications.

The invention was therefore based on the object of developing a method for producing gel, glass or ceramic layers, in particular of SiO ₂ layers and doped SiO ₂ layers, on substrates, by means of which thick layers can be obtained with a coating process, which are crack-free and are particularly suitable for optical or optoelectronic applications. Surprisingly, this could be achieved by a process for producing substrates with at least one layer of inorganic gel, glass, glass ceramic or ceramic material, in which a coating composition comprising nanoscale particles and water-soluble organic flexibilizers is applied to the substrate and heat-treated.

It is particularly surprising that, in the process according to the invention, the layers have a high porosity after the flexibilizer has burned out (for example a refractive index of n _D = 1.22, which corresponds to a porosity of 52%) and with further compaction (for example at about 1100 ° C) below the theoretical Tg, despite high shrinkage (for example approx. 40-50% in thickness), no crack formation, as is known from all other previously known systems. This is apparently due to the agglomerate-free arrangement of the nanoscale particles in the gel layer. The highly porous layers are transparent, which means that the pores contained therein are predominantly or essentially nanopores. Obviously, these nanopores enable crack-free sintering at Tg.

The process according to the invention now makes it possible to produce crack-free thick layers with a thickness of up to several micrometers, which can be sintered to form dense layers by means of thermal compression. On the one hand, the diffusion paths to be covered during sintering are small, so that crack-free compaction is achieved. On the other hand, the layers remain transparent in every stage from the gel to the glass, so that there is the possibility of adjusting the refractive index and / or the dielectric constant via the compression temperature. Layers with thicknesses in the μm range or gel body have always been white. The large pores contained in the prior art layers not only contribute to the scattering of light, but also lead to the formation of cracks when compacted. In contrast to this, they enable the process according to the invention available nanoporous layers the formation of transparent and crack-free layers at every stage.

Any temperature-stable substrate can be used as the substrate. In principle, metal substrates can also be used, but this is not preferred. In contrast, semi-metals and in particular semiconductors are suitable substrates. Preferred substrates are glass substrates such as float glass, borosilicate glass, lead crystal or silica glass, glass ceramic substrates, semiconductor substrates such as optionally doped Si or Ge, or ceramic substrates such as Al ₂ O ₃ , ZrO ₂ or SiO ₂ mixed oxides. Glass and semiconductor substrates, in particular substrates made of silicon or silicon dioxide, are particularly preferred. The silicon can be doped, for example with P, As, Sb and / or B. The silicon dioxide can also be doped. Examples of doping are given below in the description of the nanoscale particles. It can be, for example, silicon wafers or silicon coated with silicon dioxide, as are used in the semiconductor industry and optoelectronics.

Of course, the substrate must be selected so that it survives the necessary thermal treatment. The substrate may have been pretreated, e.g. by structuring or by in particular partial coating, e.g. about printing techniques. Therefore, e.g. there are optical and / or electrical microstructures, e.g. Optical fibers or conductor tracks.

The coating composition is, in particular, a coating sol which contains a flexibilizer in the form of a water-soluble organic polymer and / or oligomer and nanoscale particles.

The nanoscale particles are in particular nanoscale inorganic particles.

They are preferably nanoscale non-metal oxide and / or metal oxide particles. The particle size is, for example, in the range from below 100 nm. In particular, the particle sizes are in the range from 1 nm to 40 nm, preferably 5 nm to 20 nm, particularly preferably 8 nm to 12 nm. The size specifications relate to average particle diameters. This material can be used in the form of a powder, but is preferably used in the form of a sol.

Examples of nanoscale particles that can be used are oxides or oxide hydrates of Si, Al, B, Zn, Cd, Ti, Zr, Ce, Sn, Sb, In, La, Fe, Cu, Ta, Nb, V, Mo or W, for example, if appropriate hydrated oxides, such as ZnO, CdO, SiO ₂ , TiO ₂ , ZrO ₂ , CeO ₂ , SnO ₂ , Sb ₂ O ₃ , AIOOH, Al ₂ O ₃ , ln ₂ O ₃₎ La ₂ O ₃ , Fe ₂ O ₃ , Cu ₂ O, Ta ₂ O ₅ , Nb ₂ O ₅ , V ₂ O ₅ , MoO ₃ or WO ₃ , phosphates, silicates, zirconates, aluminates, stannates and corresponding mixed oxides (for example those with a perovskite structure such as BaTiO ₃ and PbTiO ₃ ). These can be used individually or as a mixture of two or more of them. Preferred nanoscale particles are SiO ₂ , CeO ₂ , Al ₂ O ₃ , AIOOH, TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO. SiO _{2 is} very particularly preferably used as a nanoscale particle.

The nanoscale particles can be produced by the known methods. SiO ₂ particles can be produced, for example, via base-catalyzed hydrolysis and condensation of silicon alcoholates or via other known processes for the production of silica sols, for example via the water glass route. Pyrogenic or thermal production processes are also known. Such SiO ₂ particles are commercially available, for example as silica sols. Analogous processes are also known for other oxide particles. Aqueous sols of the nanoscale particles are preferably used, for example aqueous silica sols and in particular colloidal, electrostatically stabilized aqueous silica sols.

In addition to the nanoscale particles, dopants can be used. All glass or ceramic-forming elements are generally suitable as dopants. Examples of glass or ceramic-forming components (in their oxide form) for doping are B ₂ O ₃ , Al ₂ O ₃ , P ₂ O ₅ , GeO ₂ , Bi ₂ O ₃ or oxides of gallium, tin, arsenic, antimony, lead, Niobium and tantalum, network converters, such as alkali and alkaline earth oxides, components which increase the refractive index, such as, for example, PbO, TiO ₂ , ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Tl ₂ 0, optically active components, such as rare earth oxides, for example Er ₂ O ₃ , Yb ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , Ce ₂ O ₃ , Eu ₂ O ₃ , subgroup elements, for example La ₂ O ₃ , Y ₂ 0 ₃ , WO _3> and ln ₂ O ₃ , SnO or SnO ₂ and Sb ₂ O ₃ . In this context, optically active components are understood to mean, in particular, components which are optically active in the sense of photoluminescence in the visible and NIR spectral range or 2-photon absorption processes (upconversion).

The doping is e.g. in concentrations between 0% and 15 mol%, preferably 0% and 10 mol% and particularly preferably 0% and 7.5 mol%, measured on the total oxide content. The doping is e.g. by adding the doping components as water-soluble salts, as alkoxides or as soluble complexes, e.g. Acetylacetonates, acid complexes or amine complexes, to the coating sol and optionally hydrolysis.

Due to the principle of doping, there is also the possibility of producing homogeneous μm-thick multi-component glass layers. It was found that the nanoscale particles used, such as the silica sols, in combination with the flexibilizer, for example a PVA binder, provide stable brine and gel layers in both acidic and basic form, so that diverse doping is possible. Homogenization takes place during sintering. Here, too, the nanodispersive state of the (SiO ₂ ) xerogel framework is important in order to achieve a homogeneous element distribution in a short time. Another advantage is that due to the real nanoporosity, complete densification is achieved at Tg. This is the only way to avoid known phase separation processes, especially with low-doped SiO ₂ compositions, which are unavoidable at higher temperatures and often lead to non-transparent coatings. This is particularly important for the production of optically active layers, since phase separation phenomena favor concentration quenching of the emission. Water-soluble organic flexibilizers are also used in the coating composition. These are in particular water-soluble organic polymers and / or oligomers. Water-soluble organic polymers are preferably used, for. B. water-soluble organic binder. They are, for example, polymers and / or oligomers which have polar groups, such as hydroxyl, primary, secondary or tertiary amino, carboxyl or carboxylate groups. Typical examples are polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyvinyl pyridine, polyallylamine, polyacrylic acid, polyvinyl acetate, polymethyl methacrylic acid, starch, gum arabic, other polymeric alcohols, such as, for example, polyethylene-polyvinyl alcohol copolymers, polyethylene glycol, polypropylene glycol and poly (4-vinylphenol). A preferred flexibilizer is polyvinyl alcohol, for example the commercially available Mowiol® 18-88 from Hoechst. Polyvinyl alcohols, for example with an MW of 1200, can also be used. The flexibilizers can be used individually or as a mixture of two or more of them.

In contrast to the solvent, the flexibilizers cannot be distilled off at elevated temperatures either, but are burned out by the heat treatment, i.e. they cannot be vaporized (non-destructively). In particular, they are substances that are solid at room temperature.

In addition to the nanoscale particles and the flexibilizers, the coating composition in particular also contains one or more solvents as the third component. All suitable solvents known to the person skilled in the art can be used. Examples of suitable solvents are water, alcohols, preferably lower aliphatic alcohols, for example C 1 -C ₄ -alcohols, such as methanol, ethanol, 1-propanol, i-propanol and 1-butanol, ketones, preferably lower dialkyl ketones, for example C _r C ₄ Dialkyl ketones, such as acetone and methyl isobutyl ketone, ethers, preferably lower dialkyl ethers, for example C 1 -C 4 dialkyl ethers, such as dioxane and THF, amides, such as dimethylformamide, and acetonitrile. The solvents can be used alone or in their mixtures. Particularly preferred solvents are water, alcohol-water mixtures with alcohol contents between 0% and 90% by volume, mixtures of water and tetrahydrofuran (THF) with THF contents between 0% and 90% by volume, other single-phase mixtures of water and organic solvents such as dioxane, acetone or acetonitrile, a minimum water content of 10% by volume being preferred. Particularly preferred solvents contain at least 10% by volume of water. The water content in the solvent is particularly preferably> 50%, in particular> 90%. Aqueous coating compositions, ie with a minimum water content, are therefore preferably used.

The proportion of solvent in the coating composition largely depends on the coating method chosen. It is e.g. for spray coatings e.g. about 95%, for spin or dip coatings e.g. about 80%, for doctor blade coatings e.g. about 50% and for printing pastes e.g. about 30%.

The coating composition can in principle contain further additives, e.g. Fluorosilane condensates, e.g. are described in EP 587667.

The flexibilizer is processed with the nanoscale particles (and the solvents specified above) to form a coating sol such that this flexibilizer takes over the steric stabilization of the SiO ₂ nanoparticles when the corresponding sol-gel layers dry. As a result, no agglomerates or aggregates are formed when the layers dry, which lead to large pores.

It has proven to be particularly advantageous if the volume ratio between the flexibilizer and the nanoscale particles is selected so that the flexibilizer approximately fills the gaps between the solvent-free particles. Of course, good results can be obtained even if the ratio is not too great. Hence the share of the flexibilizer is preferably selected so that it largely fills the spaces between the nanoparticles after evaporation of the solvent, ie the volume ratio of nanoparticles to flexibilizer is preferably 72:28 to 50:50, particularly preferably 70:30 to 60:40 and in particular 68: 32 to 62:38, e.g. about 65:35.

The layer production can be carried out with all common wet processes. For this purpose the coating composition is applied to the substrate via conventional coating methods, e.g. Dipping, flooding, drawing, pouring, spinning, spraying, spraying, brushing, knife coating, rolling or conventional printing techniques, e.g. with printing pastes. Electrophoretic coating processes are less or not suitable at all because of the disadvantages listed above.

As a result of the heat treatment, the coating composition applied to the substrate is dried, the flexibilizing agent is burned out and, if appropriate, the coating is then partially or completely compacted. The drying can also be partially or completely before the heat treatment, e.g. by simply venting. However, the solvent is also suitably removed by the heat treatment.

For the heat treatment, conventional methods, such as. B. heating in the oven or the so-called "Rapid Thermal Annealing" (flash annealer, flame treatment) can be used, the latter especially for compression. For example, the use of radiant heaters such as IR radiators or lasers is also conceivable. The heat treatment is carried out for example under an oxygen-containing or inert atmosphere, for example nitrogen, or air, but other components, such as ammonia, chlorine or carbon tetrachloride, can also be used as the atmosphere, alone or as an additional component. For the removal of the solvent by evaporation and the flexibilizer by burning out, temperatures of up to approx. 450 ° C. are used, for example by tempering in an oven. The compression temperatures depend on the desired degree of residual porosity and on the composition. They are generally in the range from 450 ° C. to 1200 ° C. for glass layers and in the range from 500 ° C. to 2000 ° C. for ceramic layers. Temperature programs are preferably used for the heat treatment, the parameters, such as heating rates, holding temperatures and temperature ranges, being regulated. These are known to the person skilled in the art.

After drying, a gel still containing the flexibilizing agent is obtained, e.g. in the case of higher-boiling solvents, it can also be removed in parallel. After burning out, a gel, more precisely a xerogel, with pores, preferably essentially nanopores, is obtained which essentially no longer contains any organic constituents (carbon-free). This inorganic gel or xerogel can be converted into a glass, glass ceramic or ceramic-like layer by partial or complete compaction. The layers remain transparent at every stage from the gel to the glass. This also gives the possibility of setting the refractive index and / or the dielectric constant via the compression temperature.

Layers with dry layer thicknesses of, for example, 0.1 μm to 30 μm, preferably 5 μm to 20 μm, particularly preferably 8 μm to 12 μm, can be obtained. This applies to both the nanoporous and the dense inorganic layers. According to the invention, surprisingly, even crack-free thick layers, for example with a thickness of more than 1 μm, in particular more than 3 μm or 5 μm or even more than 8 μm, can be obtained, which are moreover transparent and therefore suitable for optical applications. The gel layers after removal of the solvent but not the flexibilizer have, for example, layer thicknesses from 0.5 μm to 200 μm, preferably 5 μm to 50 μm and particularly preferably from 10 μm to 20 μm.

The inorganic layers obtained in the process according to the invention can also be structured, in particular microstructured. The structuring or microstructuring can be carried out in particular for the production of optical or electronic structures. It can take place in the gel layer or in the compressed, partially compressed or non-compressed inorganic layers. The structuring is preferably carried out in the gel state, in particular after removal of the solvent but before removal of the flexibilizing agent. For this purpose, methods known from the prior art, e.g. photolithography, embossing or etching and masking methods, are used. Microstructuring before thermal compression allows the production of particularly thick (8 μm to 20 μm) compacted microstructures.

The coated substrates produced are particularly suitable as optical, optoelectronic, electronic, micromechanical or dirt-repellent components. Typical application examples are passive and active optical waveguides, buffer and cladding layers for passive and active optical waveguides on glass, ceramic and Si substrates, dielectric layers and microstructures on glass, ceramic and silicon substrates for the production of semiconductor components, silicate and alkali silicate layers and microstructures for the thermal and anodic bonding of silicon substrates, optical components, for example gratings and light-scattering structures, microlenses, microcylinder lenses, microfresnel lenses or arrays made of these, microreactors or transparent dirt-repellent microstructures.

The following examples illustrate the invention. A) Preparation of the coating brine

EXAMPLE 1

Synthesis of the SiO ₂ sol

Two different silica sols were used to synthesize the SiO ₂ sols. A silica sol was synthesized beforehand from TEOS with ammonia in ethanol, the process being designed so that after the synthesis the SiO ₂ pond size was 10 nm and the solids content was adjusted to 5.58% by weight (name of this silica sol: KS10 ). The second silica sol used is commercially available (Levasil VPAc 4039, Bayer). To prepare the sol, 75 g of KS10 and 23.25 g of VPAc 4039 are combined and 39.06 g of a 10% strength by weight aqueous solution of the organic binder PVA (Mowiol 18-88, Hoechst) are added to this solution. After stirring at room temperature, a homogeneous mixture is formed. The desired solids content (25% by weight, based on the oxide content of the sol) is achieved by removing solvent by distillation on a rotary evaporator. After concentrating the sol, the pH is adjusted to pH 9-9.5, in which 0.4 g of a 25% NH ₃ solution are added dropwise. Before the coating process, the brine is filtered through syringe filters (1.2 μm).

EXAMPLE 2

Synthesis of a SiO ₂ sol doped with aluminum oxide

(95 mol% SiO ₂₎ 5 mol% AI ₂ O ₃ )

40 g of 1 molar aqueous HNO ₃ are slowly added dropwise to 100 g of KS10 and the mixture is heated to 60.degree. A solution of 2.01 g (9.8x10 ^"3 mol) of aluminum isopropylate, which was dissolved in 40 ml of tetrahydrofuran, is added dropwise to this solution while warm. Then, 21.28 g of the organic binder PVA (10% by weight) are added % solution in water), followed by distillation of the solvent on a rotary evaporator until a solids content of 10% by weight (based on the oxide content of the sol) is set. Before coating, the sol is filtered through syringe filters to 1.2 μm.

EXAMPLE 3 Synthesis of an SiO ₂ sol doped with Al ₂ O ₃ and PbO. (92.5 mol% SiO ₂ , 5 mol% Al ₂ O ₃ , 2.5 mol% PbO)

40 g of 1 molar aqueous HNO ₃ are slowly added dropwise to 100 g of KS10 and the mixture is heated to 60.degree. A solution of 2.053 g (1, 00x10 ³ mol) aluminum isopropylate, which was dissolved in 40 ml of tetrahydrofuran, is added dropwise to this solution while hot. After cooling to room temperature, 0.832 g (2.51x10 ^"3 mol) of lead nitrate is dissolved in the reaction mixture. 23.02 g of the organic binder PVA (10% strength by weight solution in water) are then added. The distillative removal is then carried out of the solvent on a rotary evaporator until a solids content of 10% by weight (based on the oxide content) has been set in. Before coating, the sol is filtered through syringe filters to 1.2 μm.

EXAMPLE 4

Synthesis of a SiO ₂ sol which is doped with Al ₂ O ₃ and Er ₂ O ₃ . (92.5 mol% SiO ₂ , 5 mol% Al ₂ O ₃₎ 2.5 mol% Er ₂ O ₃ )

40 g of 1 molar aqueous HNO ₃ are slowly added dropwise to 100 g of KS10 and the mixture is heated to 60.degree. A solution of 2.053 g (1.00x10 ^{~ 3} mol) of aluminum isopropylate, which was dissolved in 40 ml of tetrahydrofuran, is added dropwise to this solution while hot. After cooling to room temperature, 2.23 g (5.02x10 ^"3 mol) of erbium nitrate pentahydrate is dissolved in the reaction mixture. 23.28 g of the organic binder PVA (10% strength by weight solution in water) are then added Removal of the solvent by distillation on a rotary evaporator until a solids content of 10% by weight (based on the oxide content) has been set in. Before coating, the sol is filtered through syringe filters to 1.2 μm. EXAMPLE 5

Synthesis of a SiO ₂ sol doped with B ₂ O ₃ . (97.5 mol% Si0 _2l 2.5 mol% B ₂ O ₃ )

40 g of 1 molar aqueous HNO ₃ are slowly added dropwise to 100 g of KS10 and the mixture is heated to 60.degree. After cooling to room temperature, 0.696 g (0.00476 mol) of triethyl borate is dissolved in the reaction mixture. This is followed by the addition of 20.12 g of the organic binder PVA (10% by weight solution in water). The solvent is then removed by distillation on a rotary evaporator until a solids content of 10% by weight (based on the oxide content) has been set. Before coating, the sol is filtered through syringe filters to 1.2 μm.

EXAMPLE 6

Synthesis of a SiO ₂ sol doped with P ₂ O ₅ . (97.5 mol% SiO ₂ , 5 mol% P ₂ O ₅ )

40 g of 1 molar aqueous HNO ₃ are slowly added dropwise to 100 g of KS10 and the mixture is heated to 60.degree. After cooling to room temperature, 0.694 g (0.00489 mol) of phosphorus pentoxide is dissolved in the reaction mixture. This is followed by the addition of 20.21 g of the organic binder PVA (10% by weight solution in water). The solvent is then removed by distillation on a rotary evaporator until a solids content of 10% by weight (based on the oxide content) has been set. Before coating, the sol is filtered through syringe filters to 1.2 μm. Example 7

Synthesis of a sol for a porous SiO ₂ -CeO ₂ layer (50 mol% SiO ₂ , 50 mol% CeO ₂ )

100 g of KS10 are slowly added dropwise to 6.5 g of 1 molar aqueous HNO ₃ with stirring. Then 40 g of acetate-stabilized, particulate CeO ₂ sol (CeO ₂ ACT, 20% by weight, from AKZO-PQ) are slowly added at room temperature with stirring. Then 37.7 g of the organic flexibilizer PVA-18-88 are added as a 10% strength by weight solution in water. Before coating, this sol is filtered through a syringe filter to 1.2 μm.

B) coating

The sols synthesized as stated above are applied to various substrates, preferably SiO ₂ and silicon, using the customary coating methods (for example spinning, spraying, dipping or knife coating).

C) heat treatment of the layers

The layers are compressed in the muffle furnace in accordance with a specified temperature program. The layers are heated from room temperature to 250 ° C at a heating rate of 0.8 K / min, the temperature is kept at 250 ° C for 1 hour. From 250 ° C is heated at a heating rate of 0.8 K / min to 450 ° C and again held at this temperature for 1 h. The final compression temperature for the undoped SiO ₂ layers is 1100 ° C, which is held for 1 hour. Final compression temperatures of 500 to 1000 ° C lead to porous layers with a correspondingly lower refractive index. The heating rate for compression from 450 to 1100 ° C is 2 K / min. The doped layers are compacted at the same heating rate up to 1000 ° C for 1 h.

Crack-free and transparent layers are obtained in each case.

Claims

1. A process for producing substrates with at least one layer of inorganic gel, glass, glass ceramic or ceramic material, in which a coating composition comprising nanoscale particles and water-soluble organic flexibilizers is applied to the substrate and heat-treated.

2. The method according to claim 1, characterized in that the coating applied to the substrate is partially or completely compressed by heat treatment.

3. The method according to claim 1 or 2, characterized in that the coating applied to the substrate is dried to a gel and structured or the inorganic gel, glass, glass ceramic or ceramic layer is structured.

4. The method according to any one of claims 1 to 3, characterized in that nanoscale non-metal oxide and / or metal oxide particles from the group SiO ₂ , CeO ₂ , Al ₂ O ₃ , AIOOH, TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO or mixtures or mixed oxides thereof are used as nanoscale particles.

5. The method according to any one of claims 1 to 4, characterized in that the coating composition additionally compounds of glass or ceramic-forming elements, network converters, refractive index increasing

Contains components and / or optically active components as dopants.

6. The method according to any one of claims 1 to 6, characterized in that a flexibilizer made of polyvinyl alcohol, polyvinyl pyrrolidone,

Polyacrylamide, polyvinylpyridine, polyallylamine, polyacrylic acid, polyvinyl acetate, Polymethyl methacrylic acid, polyethylene-polyvinyl alcohol copolymers, polyethylene glycol, polypropylene glycol and poly (4-vinylphenol) are used.

7. The method according to any one of claims 1 to 6, characterized in that the coating composition by spraying, dipping,

Spin coating, flooding, knife coating, rolling or printing techniques onto the substrate.

8. The method according to any one of claims 1 to 7, characterized in that one uses a glass, glass ceramic, semiconductor or ceramic substrate.

9. The method according to any one of claims 1 to 8, characterized in that the substrate used is silicon dioxide, silicon, doped silicon dioxide or doped silicon.

10. substrate with at least one thick layer of inorganic gel, glass, glass ceramic or ceramic material, obtainable by the method of one of claims 1 to 9.

11. Substrate according to claim 10, characterized in that the dry layer thickness of the inorganic gel, glass, glass ceramic or ceramic layer is at least 1 μm.

12. Substrate according to claim 10 and 11, characterized in that the inorganic layer is transparent.

13. Use of a substrate according to one of claims 10 to 12 as an optical, optoelectronic, electronic, micromechanical or dirt-repellent component.