UV-curable precursor solution for depositing titanium-containing mixed metal oxide films, and optical elements formed by liquid-phase deposition of metal oxide films.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-07-24
- Publication Date
- 2026-08-14
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Figure 2026527491000001_ABST
Abstract
Description
[Technical Field]
[0001] Cross-reference of related applications This application claims priority to U.S. Provisional Patent Application No. 63 / 515,322, filed on 24 July 2023, entitled "UV-curable precursor solution for deposition of oxide coatings containing titanium, lanthanum, and tellurium," and U.S. Provisional Patent Application No. 63 / 517,078, filed on 1 August 2023, entitled "Volume holographic lattice for metal oxide thin films by liquid-phase deposition." The contents of both of these U.S. Provisional Patent Applications are incorporated herein by reference as part of this Specification. [Background technology]
[0002] Titanium oxide is commonly used as an optical material, such as in diffractive optical elements. This application is at least in part due to the relatively high refractive index of TiO2 and its low light absorption coefficient across the entire visible spectrum. [Overview of the project] [Problems that the invention aims to solve]
[0003] This summary is provided to introduce some of the concepts that will be explained in more detail in the detailed description. This summary is not intended to identify any major or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to embodiments that resolve any or all of the defects described in any part of this disclosure. [Means for solving the problem]
[0004] Examples of acid-stabilized precursor solutions for forming crack-free titanium oxide films with minimal cracking are disclosed. One example provides a method for forming a titanium oxide film by liquid-phase deposition. This method includes the step of coating a substrate with an aqueous solution of the acid-stabilized precursor to form a film. The aqueous solution of the acid-stabilized precursor contains titanium ions, one or more other metal ions, a photodegradable and / or thermally degradable ligand, and an acid. This method further includes the step of exposing the film to heat or light, one or more of the two.
[0005] Examples relating to optical elements formed by liquid-phase deposition of metal oxide films are also disclosed. In one example, a method for forming a metal oxide film is provided, which comprises the step of coating a substrate with an acid-stabilized precursor solution to form a film, the acid-stabilized precursor solution comprising metal ions, a photodegradable and / or thermally degradable ligand, and an acid. The method further comprises the steps of UV curing a first region of the film and not UV curing a second region of the film, and heating the film.
[0006] Brief explanation of the drawing Figure 1 is a flowchart illustrating an example of a method for forming a titanium-containing oxide film using an acid-stabilized precursor solution.
[0007] Figure 2 is a cross-sectional view of an example of a waveguide containing an optical element with a titanium-containing oxide film.
[0008] Figure 3 is a top view of an example of a titanium oxide film formed on a waveguide with a surface having multiple cracks, showing that cracks occur in the oxide film during hardening.
[0009] Figure 4 is a top view of an example of a titanium / lanthanum / aluminum oxide film formed on a waveguide with a cracked surface, showing relatively fewer cracks than the example in Figure 3.
[0010] Figure 5 is a top view of an example of a titanium / lanthanum / tellurium oxide film formed on a waveguide with a cracked surface, showing that no cracks have occurred.
[0011] Figure 6 is a flow chart of an example of a method for forming an inorganic film and a holographic lattice by liquid-phase precipitation of an acid-stabilized precursor solution.
[0012] Figures 7A to 7D schematically show examples of structures that can be formed by the method in Figure 6.
[0013] Figures 8 to 11 are graphs showing the refractive indices of the UV-cured and non-UV-cured portions of a film on various substrates.
[0014] Figure 12 is an example plot showing the absorption of the membrane as the Te concentration increases.
[0015] Detailed explanation Liquid-phase deposition can be used to form metal oxide films. Such films can be used as coatings for optical elements. For example, feature areas can be formed on a substrate. A film can be formed on the substrate surface by a spin-on deposition method, thereby filling the feature areas with a precursor solution. The film is then cured. Examples of curing methods include UV curing, thermal curing, laser curing, and particle beam curing. The curing process helps remove solvents and volatile substances from the film and forms a metal ion-oxygen network.
[0016] However, as solvents and volatile substances are released from the film, the film may shrink during curing. This can lead to cracking in some cases. For example, when forming a titanium oxide film on a waveguide surface with raised regions and gaps between them, the titanium oxide film may crack during curing and shrinking. In some cases, adding metal oxide nanoparticles (e.g., TiO2 nanoparticles) to the precursor solution can reduce shrinkage during the curing process. However, even oxide films containing titanium nanoparticles may crack during curing.
[0017] Therefore, we disclose an example of using an acid-stabilized metal oxide precursor solution to form a titanium-containing oxide film with minimal or no cracking by liquid-phase deposition. Briefly, in the liquid-phase deposition process, a substrate is coated with the acid-stabilized precursor solution to form a film. In some examples, the acid-stabilized precursor solution contains titanium ions and one or more other metal ions. Examples of other metal ions include [list of other metal ions]. The acid-stabilized precursor solution further contains a photodegradable and / or thermally degradable ligand and an acid. In some examples, the acid-stabilized precursor solution further contains a component that slows the evaporation of the solvent, such as a polyol (an alcohol having two or more hydroxyl groups (e.g., a diol)). The precursor solution may be stable for relatively long periods (e.g., several weeks, several months, or several years in various examples). After coating the substrate, the film is exposed to one or more of light and / or heat. This causes the film to harden and form an oxide film.
[0018] Because the precursor solution contains one or more additional metal ions other than titanium, the oxide film may be more amorphous (i.e., glassy) than the titanium oxide film. In other words, the presence of different metal species can help suppress the crystallization of the oxide film compared to a TiO2 film cured under similar conditions. This can help reduce the occurrence of cracks during the curing process compared to examples without such metal species. In some cases, a substantially crack-free oxide film can be formed. In some such examples, a crack-free titanium-containing oxide film can be produced by liquid-phase deposition using an acid-stabilized precursor solution containing titanium ions, lanthanum ions, and one or more of tellurium ions, bismuth ions, tin ions, or antimony ions. Because cracks can scatter light, a substantially crack-free oxide film can provide better optical performance than an oxide film with a relatively high density of cracks. Therefore, using the acid-stabilized precursor solutions described herein may help in forming optical element films that have better performance than optical elements formed using other precursor solutions.
[0019] Using the acid-stabilized precursor solution described in the disclosed example, it is possible to form films that are relatively thicker than titanium oxide films while avoiding cracking. Relatively thick metal oxide films may be preferable to relatively thin films in certain applications. For example, when used as a diffractive optical element, a relatively thick film (e.g., 100-1000 nm thick) can increase the photo-interaction within the lattice compared to a lattice formed with a relatively thin film. Another example is holographic components, which require thicker films than other types of components.
[0020] The titanium-containing oxide films disclosed herein can be used in all suitable devices. For example, the oxide film can be used on waveguides. Another example is its use as a light extraction layer in organic light-emitting diode (OLED) display panels. Furthermore, it can be used as an optical cladding or in optical components such as dichroic beam splitters, light diffusers, anti-reflective layers, cold mirrors, and hot mirrors. Examples of optical devices are described in more detail below.
[0021] The titanium-containing oxide films disclosed herein can also be used in thin-film transistors (TFTs). Some TFTs include a dielectric to insulate the gate from the active layer. For example, an indium gallium zinc oxide (IGZO) TFT may include an SiO2 dielectric layer between the gate and the active IGZO layer. The dielectric layer can be formed, for example, by a patterning process or a gap-fill process. Atomic layer deposition (ALD) is typically used for dielectric gap fills. However, voids and seams can occur during ALD gap fills, which can lead to device failure. Furthermore, to avoid or reduce outward diffusion of SiGe, it is advantageous for the film to exhibit atomic-scale smoothness and be deposited at relatively low temperatures. Achieving void-free ALD gap fills at low temperatures can be difficult and costly compared to other deposition techniques.
[0022] Therefore, the disclosed titanium-containing oxide film can be used in a liquid-phase deposition process to form a void-free passivation layer and / or dielectric layer on a TFT at a low temperature (approximately 150°C). In some examples, a film is formed by coating a substrate with an acid-stabilized precursor solution containing titanium ions and one or more other metal ions. This film is cured to form a dielectric layer on the TFT, which contains an oxide film containing titanium and one or more other metal ions. Examples of other metal ions include lanthanum ions, tellurium ions, tin ions, bismuth ions, and antimony ions. Other examples are listed below. In some examples, a pattern is imprinted on the film before curing. In some examples, the liquid-phase deposition process involves forming the film in voids on the substrate. As described above, different metal oxides in the film can reduce the crystallinity level of the oxide film compared to a TiO2 film cured under similar conditions. Reduced crystallinity can reduce cracking during the curing process compared to examples without such metal species. This helps in the formation of a void- and crack-free dielectric layer. Thus, the examples disclosed herein can provide a liquid-phase deposition method for forming dielectric layers of TFTs that is less complex, faster, and less expensive than other methods such as ALD gap filling.
[0023] The exemplary acid-stabilized precursor solution may contain titanium and any other suitable metal ions in any suitable concentration. In some examples, the acid-stabilized precursor solution contains titanium ions and one or more of the following ions: Al, Ga, Bi, Sc, Cu, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, In, Sn, Sb, Hf, Ta, W, Ir, Pt, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Te, Sb, Yb, or Lu. The metal ions may be introduced into the acid-stabilized precursor solution in any suitable way. In some examples, the metal ions are introduced into the acid-stabilized precursor solution in the form of metal chlorides. As an example, solid lanthanum chloride (LaCl3) and solid tellurium chloride (TeCl4) can be added to aqueous titanium chloride (TiCl3) in 3% hydrochloric acid. In other examples, any other suitable compound, such as metal sulfates or metal nitrates, can be used.
[0024] The example acid-stabilized precursor solution may contain any suitable photodegradable and / or pyrodegradable ligand. In some examples, the acid-stabilized precursor solution contains hydrogen peroxide (H2O2). In addition, or instead, formic acid (CH2O2) may be used. In addition, or instead, nitrate ions (NO3) may be used. - ) can be used. The example acid-stabilized precursor solution may omit organic species such as alkoxoligands, thereby allowing precipitation, drying, and curing at lower temperatures than precursor solutions containing organic species. Furthermore, the use of UV-curable ligands such as peroxides, formic acid, or nitrate ions helps to provide precursor solutions that can be cured by exposure to ultraviolet light.
[0025] The exemplary acid-stabilized precursor solutions may contain any suitable acid. Examples include hydrochloric acid (HCl), nitric acid (HNO3), and sulfuric acid (H2SO4). Using an acid in the precursor solution helps to avoid precipitation of metal species. Therefore, the exemplary acid-stabilized precursor solutions described herein may have a relatively long shelf life based on the time of precipitate formation observed.
[0026] The exemplary acid-stabilized precursors disclosed may also contain other components to address various challenges faced in certain applications. For example, during the drying process of thick films, the solvent may evaporate before the film components can rearrange into a stable structure. This can lead to cracking. Therefore, one or more components may be added to slow down the evaporation of the solvent during curing. Examples of components that slow down the evaporation of the solvent during curing include polyhydric alcohols (polyols), such as diols. In one experiment, the addition of ethylene glycol to the acid-stabilized precursor solution resulted in films with a thickness of over 400 nm that were virtually crack-free. [Brief explanation of the drawing]
[0027] [Figure 1] Figure 1 is a flowchart illustrating an example of a method for forming a titanium-containing oxide film using an acid-stabilized precursor solution. [Figure 2] Figure 2 is a cross-sectional view of an example of a waveguide containing an optical element with a titanium-containing oxide film. [Figure 3] Figure 3 is a top view of an example of a titanium oxide film formed on a waveguide having a surface with multiple cracks. [Figure 4] Figure 4 is a top view of an example of a titanium / lanthanum / aluminum oxide film formed on a waveguide with a cracked surface. [Figure 5] Figure 5 is a top view of an example of a titanium / lanthanum / tellurium oxide film formed on a waveguide with a cracked surface. [Figure 6] Figure 6 is a flow chart of an example of a method for forming an inorganic film and a holographic lattice by liquid-phase precipitation of an acid-stabilized precursor solution. [Figure 7A] Figure 7A shows the base material 700. [Figure 7B] Figure 7B shows the film 702 deposited on the substrate 700 by, for example, performing step 602 of method 600. [Figure 7C]Figure 7C shows a step in which the first region 704 is cured by exposure to ultraviolet light 706, for example by performing step 620 of method 600. [Figure 7D] Figure 7D shows the substrate 700 after the heating step, for example, by performing step 630 of method 600. [Figure 8] Figure 8 shows a graph of the refractive indices of the UV-cured and non-UV-cured portions of a film on a certain substrate. [Figure 9] Figure 9 shows the graph of the Cauchy equation fitting of the refractive index of the titanium oxide film. [Figure 10] Figure 10 shows the graph 1000 of the Cauchy equation fitting of the refractive index of the third film. [Figure 11] Figure 11 shows graph 1100 of the Cauchy equation fitting of the refractive index of the fourth film. [Figure 12] Figure 12 is an example plot showing the absorption of the membrane as the Te concentration increases. [Examples]
[0028] Figure 1 is a flow chart of an exemplary method 100 for forming a titanium-containing oxide film by liquid-phase deposition. Method 100 includes the step in 102 of forming a film by depositing an acid-stabilized precursor solution on a substrate. The acid-stabilized precursor solution contains titanium ions and one or more other metal ions. The acid-stabilized precursor solution further contains a photodegradable and / or thermally degradable ligand and an acid. Examples of metal ions that can be used in addition to Ti include Al, Ga, Bi, Sc, Cu, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, In, Sn, Sb, Hf, Ta, W, Ir, Pt, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Te, Sb, Yb, or Lu ions.
[0029] In some examples, in 104, the acid-stabilized precursor solution comprises titanium chloride and one or more of lanthanum chloride, bismuth chloride, tin chloride, aluminum chloride, or antimony chloride. Alternatively, or in addition, in some examples, one or more nitrates (e.g., titanium nitrate, lanthanum nitrate, aluminum nitrate, tellurium nitrate), nanoclusters (e.g., Al 13 (OH) 24 (H2O) 24 (NO3) 15), and / or sulfates (e.g., titanium sulfate, lanthanum sulfate, tellurium sulfate) can be used. In some examples, in 106, the acid includes one or more of hydrochloric acid, nitric acid, or sulfuric acid. Furthermore, in some examples, in 108, the photodegradable and / or thermally degradable ligand includes one or more of hydrogen peroxide, formic acid, or nitrate ions. In some examples, in 110, the acid-stabilized precursor solution further includes a polyol. For example, in some examples, the acid-stabilized precursor solution may include one or more of ethylene glycol, propylene glycol, or 1,3-butanediol. In other examples, any other suitable polyol may be used. In some examples, the acid-stabilized precursor solution may further include metal oxide nanoparticles such as TiO2 nanoparticles. Subsequently, method 100 further includes the step in 120 of exposing the film to one or more of heat or light. This hardens the film and forms an oxide film containing titanium and one or more other metal ions. Examples include aluminum, lanthanum, tellurium, bismuth, tin, and / or antimony. In some examples, in 122, method 100 further includes the step of imprinting a pattern on the film before exposing the film to heat or light. In some examples, in 123, method 100 further includes the step of vacuum drying the film before exposing the film to heat or light. In some examples, in 124, exposure of the film to heat includes thermocuring the film at a temperature of 60°C to 650°C. Unless otherwise specified, numerical ranges include endpoints; that is, "X~Y" includes values X and Y. In some examples, films cured at relatively high temperatures (e.g., above 300°C) may have a higher light absorption coefficient in the blue region of the visible spectrum than films cured at relatively low temperatures (e.g., below 300°C). In some examples, in 126, exposure of the film to light includes UV curing of the film. In such examples, UV-curable ligands such as hydrogen peroxide, formic acid, and / or nitrate ions may be used. In such cases, nitric acid can be used to accelerate UV curing. In some cases, exposure of the film to light includes exposure of the film to a laser.In some examples, in 128, method 100 further includes the step of annealing the film after UV curing the film. Annealing can be carried out at any suitable temperature, such as 60°C to 650°C.
[0030] In some examples, in 130, the film is formed on an optical element. In such examples, in 132, the optical element constitutes a waveguide. For example, method 100 may include the step of forming a diffraction grating on the waveguide. In some examples, the waveguide can be incorporated into a near-eye device. In some examples, the film is deposited on a substrate as part of a TFT manufacturing process. In some examples, in 134, the oxide film constitutes a dielectric layer of the TFT. In some examples, in 136, the oxide film constitutes a passivation layer of the TFT.
[0031] Figure 2 is a cross-sectional view of an example of an optical element 200 including an oxide film. The optical element 200 can be formed, for example, using method 100. The optical element 200 is formed on the surface of a substrate 202 having feature portions 204. As shown in Figure 2, the height of the feature portions 204 is approximately 562 nm. In this example, a film is deposited on the substrate 202 using a coating method to fill the gaps 206 between the feature portions 204. The film can be cured, for example, by exposure to heat or light to form the optical element 200.
[0032] Figure 3 is a top view of an example of an oxide film 300 containing titanium atoms. The oxide film 300 is formed between feature portions 304 on the substrate. The oxide film 300 is formed using a precursor solution that does not contain other metal ions. As a result, the oxide film 300 shrinks and cracks during curing. This causes cracks 310 to form in the oxide film 300. These cracks 310 can cause light scattering and device failure.
[0033] Figure 4 is a top view of an example of another oxide film 400 containing titanium, lanthanum, and aluminum. For example, the oxide film 400 may contain a mixture of titanium oxide, lanthanum oxide, and aluminum oxide, and may be at least partially amorphous. The oxide film 400 is formed between feature portions 404 on the substrate. The oxide film 400 has cracks 410. The oxide film 400 is formed using a precursor solution containing titanium ions, lanthanum ions, and aluminum ions. As a result, the titanium-containing oxide film 400 is more amorphous and exhibits relatively less cracking than the example in Figure 3. Therefore, including lanthanum ions and aluminum ions in the acid-stabilized precursor solution may help reduce the occurrence of cracking during the liquid-phase deposition of the titanium-containing oxide film.
[0034] Figure 5 is a top view of an example of another oxide film 500 containing titanium, lanthanum, and tellurium. For example, the oxide film 500 may contain a mixture of titanium dioxide, lanthanum oxide, and tellurium oxide, and may be at least partially amorphous. The film 500 was formed by a coating method of a precursor solution containing 3 mL of TiCl3·3HCl (30%) (aqueous solution) + 1 g of TeCl4 (solid) + 1 g of LaCl3 (solid) + 1 mL of H2O2 (aqueous solution) (30%). This film was thermally cured at a temperature of 200°C. The oxide film 500 (light-colored portion) is formed between the feature portions 504 (dark-colored portion) on the substrate. The oxide film 500 is formed using a precursor solution according to the example described herein, which contains titanium ions, lanthanum ions, tellurium ions, a photodegradable and / or thermally degradable ligand, and an acid. As a result, the oxide film 500 does not crack during curing. This is because, by including lanthanum and tellurium in the titanium-containing oxide film, it is possible to form an oxide film that is more amorphous and less prone to cracking than oxide films that do not contain these metal ions. As described above, the exemplary acid-stabilized precursor solution disclosed can be used to form diffractive optical elements. Diffractive optical elements can be used to direct light in optical systems. Examples of diffractive optical elements include diffraction relief gratings and volume holographic gratings. By incorporating these into, for example, a waveguide combiner, it is possible to synthesize real-world images and displayed images. Such waveguide combiners can be used in virtual reality systems and augmented reality systems.
[0035] Volume holographic gratings are typically formed using organic photopolymers. They can be created by superimposing wavefronts to produce interference fringe patterns, which are then recorded on a holographic medium. A volume holographic grating can also be formed by creating fringe patterns on a holographic medium using laser light. Such gratings can be used, for example, in diffraction waveguides.
[0036] However, organic films can degrade over time. For example, UV irradiation or oxidation can cause organic films to absorb blue light and exhibit a yellowish tint. Organic films can also become brittle over time. Furthermore, organic polymers have a relatively low dynamic range of refractive index, for example, Δn ≤ 0.04. The dynamic range Δn refers to the difference in refractive index values between different materials. A lower dynamic range results in relatively lower diffraction efficiency (less diffracted light). Organic films may also have relatively high haze (i.e., light scattering), which can sometimes exceed 0.2%. Finally, organic films suffer from self-exchange problems caused by heat, which can lead to a decrease in dynamic range.
[0037] Accordingly, examples relating to the use of metal oxide films as holographic media and the formation of diffractive optical elements by liquid-phase deposition of metal oxide films are disclosed. A metal oxide film that has been UV-cured and heated has a different refractive index than a metal oxide film heated without UV curing, due to differences in film density. UV exposure removes organic matter from that region and increases the density of the exposed region. After heating, the UV-exposed portion of the film becomes denser and has a higher refractive index than the unexposed region. In the unexposed region, organic matter is simultaneously burned off during hard baking. As a result, the film does not become as dense and has a lower refractive index.
[0038] Thus, holographic data can be recorded on a metal oxide film using ultraviolet light, and / or a holographic optical element can be formed, and the film can then be cured by heating. Briefly, an inorganic precursor solution is deposited on a substrate using a liquid-phase deposition method to form a film. The precursor solution contains metal ions, an acid, and a photodegradable and / or thermally degradable ligand as described above. Holograms are recorded on the film by ultraviolet laser curing. Due to interference fringes, the ultraviolet laser light cures a first region of the film, increasing its density, but does not cure the other second region of the film. Next, the film is baked. When the film is baked, the refractive indices of the first and second regions change. Because the density of the first region increases due to ultraviolet curing, its refractive index is different from that of the annealed second region. In this way, holograms can be recorded using this method. In some examples, holographic data can be recorded on a metal oxide film. In some examples, ultraviolet laser interference fringe patterns can be recorded on a metal oxide film to form a volume holographic grating. This can be used, for example, to form a diffraction grating on a waveguide.
[0039] The disclosed exemplary metal oxide films can have a higher dynamic range, excellent durability, and low haze than organic films. Further, the metal oxide films are characterized by being less prone to yellowing than some organic films. The holographic media can include any suitable metal oxides, such as metal oxides deposited using the acid-stabilized precursor solutions according to the examples disclosed herein. As described below, in some examples, a refractive index dynamic range of 0.10 or more can be achieved for the ultraviolet-curable and non-ultraviolet-curable portions of the metal oxide film. Further, the dynamic range may be expanded by vacuum drying the film before ultraviolet curing. Further, the refractive index can be made relatively large compared to the refractive index of organic films (e.g., 1.7 < n < 2.5). For example, Group IV oxides (e.g., TiO2, ZrO2, HfO2, etc.) can provide such refractive indices and low light absorption coefficients across the visible spectrum. A volume holographic grating including a metal oxide film formed according to the disclosed examples can have a higher diffraction efficiency than an organic film. Thereby, in a waveguide system, excellent performance can be obtained with a thinner film than an organic film.
[0040] As disclosed, in the liquid phase deposition of metal oxide films, various precursor solutions can be formed and used. In some examples, the acid-stabilized precursor aqueous solution according to the present disclosure can include one or more Group 4 or Group 13 ions referring to the groups of the periodic table of elements, and one or more other ions from Group 1 and / or Group 2 and / or Group 3, and / or Group 4, and / or Group 5, and / or Group 13 and / or Group 14 and / or Group 15 and / or F block ions. Specific examples include TiO2, Al x Ti y O n 、Al w Ti x La y Bi z O n Te x Ti y O n 、Nb x Ti y O nTiO2 / TiO2 nanoparticle composites, other metal oxide / metal oxide nanoparticle composites, ZrO2, Zr x Ti y O n Ce x Ti y O n , La x Ti y O n Li x La y Ti z O nz Li x Bi y Ti z O n Nb w La x Li y Ti z O n , and Al v Nb w La x Li y Ti z O n Examples include metal oxides containing Ti, La, and one or more of Te, Bi, or Sb (e.g., La x Te y Ti z O n , La x Bi y Ti z O n , and La x S y Ti z O n Examples include:
[0041] The metal oxide films prepared using the disclosed exemplary acid-stabilized precursor solutions may be used for a wide variety of applications. Examples include optical films, energy storage, semiconductor devices, photonic integrated circuits (PICs), and biomedical devices. As more specific examples, the TiO2 and mixed metal oxide / TiO2 acid-stabilized precursor solutions according to the disclosed examples can be used to deposit titanium oxide films that have high thermal stability (exceeding 800 °C), high light transmittance (exceeding 90% at 550 nm), and an adjustable refractive index (1.7 < n < 2.5). By controlling the composition and post-deposition treatment, the refractive index and light transmittance can be adjusted.
[0042] The disclosed exemplary precursor solutions may be deposited on a substrate by any suitable method. Examples include spin coating, dip coating, doctor blade, spray coating, electrodeposition, and printing methods (e.g., jet printing, screen printing, etc.). The disclosed exemplary precursor solutions can be formed from a variety of different metal-containing compounds. For example, a precursor solution for forming a TiO2 film can be formed from titanium-containing species such as TiO2, TiCl 3 ·xHCl (x = 0 to 200), and / or TiCl4(l). The precursor solutions according to the present disclosure may be aqueous and / or may contain other suitable solvents.
[0043] Acid-stabilized precursor solutions for forming holographic recording media (e.g., for manufacturing diffractive optical elements) can contain all suitable metal ions at all suitable concentrations. In some examples, the metal ions include one or more ions from Al, Ga, Bi, Sc, Cu, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, In, Sn, Sb, Hf, Ta, W, Ir, Pt, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Te, Sb, Yb, or Lu. In some examples, the acid-stabilized precursor solution includes one or more group 4 or group 13 ions and one or more other ions from group 1 and / or group 2 and / or group 3, and / or group 4 and / or group 5, and / or group 13 and / or group 14 and / or group 15 and / or F block ions. In some examples, the acid-stabilized precursor solution contains Ti and Te. In some examples, the acid-stabilized precursor solution contains Ti, La, and one or more of Te, Bi, or Sb ions. In some examples, the acid-stabilized precursor solution contains Ti, La, and Al. In some examples, the acid-stabilized precursor solution contains Te, Bi, or Sn ions. Specific examples include TiO2 and Al. x Ti y O n Te x Ti y O n Nb x Ti y O n TiO2 / TiO2 nanoparticle composites, other metal oxide / metal oxide nanoparticle composites, ZrO2, Zr x Ti y O n Ce x Ti y O n , La x Ti y O n Li x La y Ti z O nz Li x Bi y Ti z O n, Nb w La x Li y Ti z O n , and Al v Nb w La x Li y Ti z O n etc. can be mentioned. Furthermore, metal oxides containing Ti, La, and one or more of Sn, Te, Bi, and Sb (e.g., La x Te y Ti z O n , La x Bi y Ti z O n , and La x ]>Sb y Ti z O n etc.) can also be mentioned.
[0044] Metal ions can be introduced into the acid-stabilized precursor solution in all appropriate forms. In some examples, the metal ions are introduced into the acid-stabilized precursor solution as metal chlorides. As an example, solid lanthanum chloride (LaCl3) and solid tellurium chloride (TeCl3) can be added to an aqueous solution of titanium chloride (TiCl3) in 3% hydrochloric acid. In other examples, all other appropriate compounds such as metal sulfates or metal nitrates can be used.
[0045] As described above, the acid-stabilized precursor solution can contain a photodegradable and / or thermodegradable ligand. The term "photodegradable and / or thermodegradable ligand" refers to a ligand that decomposes when exposed to light (e.g., ultraviolet light) and / or sufficient heat (e.g., a temperature of 60°C to 650°C), or leaves a film formed by the precursor solution. Examples of photodegradable and / or thermodegradable ligands include oxygen-containing ligands that contribute to the formation of a metal ion-oxygen network. Examples of photodegradable and / or thermodegradable ligands include hydrogen peroxide, formic acid, and nitrate ions.
[0046] To enable curing using ultraviolet laser light, the precursor solution according to this disclosure may contain an ultraviolet-curable ligand. For example, hydrogen peroxide can be used as the ultraviolet-curable ligand. In other examples, other suitable ultraviolet-curable ligands may be used. Examples include other peroxides (e.g., lithium peroxide, sodium peroxide, etc.), formic acid or other carboxylic acids, and nitrate ions. The use of an ultraviolet-curable ligand allows for changes in film density, enabling the encoding of holograms into metal oxide films using ultraviolet laser light. Furthermore, the exemplary acid-stabilized precursor solution can be deposited, dried, and cured at lower temperatures than precursor solutions containing organic species, as it can omit organic species such as alkoxoligands. In some examples, the precursor solution may contain one or more ligands in addition to the ultraviolet-curable ligand.
[0047] Furthermore, in some cases, organic peroxides or acids may be used as photodegradable and / or thermally degradable ligands. However, organic peroxides may require additional safety measures due to their potentially low stability and flammability. Formic acid and hydrogen peroxide offer the further advantage that carbon in the formic acid is converted to CO2 gas during curing of the deposited film, eliminating the need to remove carbon from the organic species by a relatively high-temperature post-deposition heating process. As an example, titanium-containing precursor solutions can be used as metal source / ligand combinations, for example, TiX3(x=Cl - , Br - , I - NO3 - , OOCH - etc.) + H2O2, TiX4(x=Cl - , Br - , I - NO3 - , OOCH - It may include (etc.) + H2O2, or TiOSO4 + H2O2. In some examples, the precursor solution may include a metallic nitrate (e.g., titanium nitrate) or a metallic sulfate (e.g., titanium sulfate).
[0048] Exemplary acid-stabilized precursor solutions can contain any suitable acid. Examples include hydrochloric acid (HCl), nitric acid (HNO3), and sulfuric acid (H2SO4). The use of acid in the precursor solution helps to avoid precipitation of metal species. Therefore, the exemplary acid-stabilized precursor solutions described herein can have a relatively long shelf life based on the observed precipitation time.
[0049] As described above, in some cases, the acid-stabilized precursor solution may contain components that help reduce the rate of solvent evaporation from the film formed using the acid-stabilized precursor solution. In some cases, polyols such as diols can be used to reduce the rate of solvent evaporation from the film of the acid-stabilized precursor solution. Examples of polyols include ethylene glycol ((CH2OH)2), propylene glycol (CH3CH(OH)CH2OH), 1,3-butanediol, and 1,4-butanediol.
[0050] Figure 6 shows an exemplary method 600 for forming a volumetric holographic grid. In method 601, method 600 optionally includes the step of coating the substrate with an anti-reflective coating. When recording a pattern on a holographic medium, the substrate surface may reflect light through the light-transmitting film during curing, causing unwanted curing in parts of the film. This can lead to blurring or ghosting of the pattern. Therefore, to reduce pattern blurring, an anti-reflective coating can be applied to the substrate surface before deposition of the holographic medium and pattern formation. The anti-reflective coating may include, for example, a multilayer dielectric film tuned to the wavelength of light used for recording the hologram.
[0051] In 602, method 600 includes the step of coating a substrate with an acid-stabilized precursor solution to form a film. The acid-stabilized precursor solution comprises a metal ion, a photodegradable and / or thermally degradable ligand, an acid, and optionally a polyol. In some examples, the metal ion comprises one or more ions from Al, Ga, Bi, Sc, Cu, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, In, Sn, Sb, Hf, Ta, W, Ir, Pt, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Te, Sb, Yb, or Lu. In some examples, the acid-stabilized precursor solution comprises one or more Group 4 or Group 13 ions and one or more other ions from Group 1 and / or Group 2 and / or Group 3, and / or Group 4, and / or Group 5, and / or Group 13 and / or Group 14 and / or Group 15 and / or F-block ions.
[0052] In some examples, in 608, the photodegradable and / or pyrodegradable ligand includes one or more of hydrogen peroxide, nitrate ions, or formic acid. In other examples, any other suitable photodegradable and / or pyrodegradable ligand may be used. In some examples, in 610, the acid includes one or more of hydrochloric acid, nitric acid, or sulfuric acid. In other examples, any other suitable acid may be used. In some examples, in 612, the acid-stabilizing precursor optionally further includes one or more polyols such as ethylene glycol, propylene glycol, or 1,3-butanediol. In other examples, any other suitable polyol may be used. Method 600 may optionally include, in 614, a step of vacuum drying the film before proceeding to UV curing, as described below.
[0053] Next, in 620, method 600 further includes the step of UV curing a first region of the film and not UV curing a second region of the film. This increases the density of the first region of the film. In some examples, in 622, method 600 includes the step of curing the first region of the film by constructive interference of ultraviolet laser light. In other examples, a mask can be used. In some such examples, in 624, method 600 includes the step of recording a hologram on the film. In some such examples, in 626, method 100 includes the step of forming a diffraction grating on a waveguide. The diffraction grating can have any suitable orientation. In some examples, the diffraction grating can be oriented perpendicular to the plane of the substrate. In other examples, the diffraction grating can be oriented at a different angle (e.g., oblique) to the plane of the substrate. Next, in 630, method 100 includes the step of heating the film. In some examples, in 632, the film heating step includes heating the film to a temperature of 60°C to 650°C. Heating the film changes the refractive indices of the first and second regions of the film, stabilizing the film (hardening it). Thus, the refractive index of the film does not change further after heating. Heating the film can also expel the solvent (e.g., water) from the film. This can cause shrinkage of the film. In some cases, upon heating, the first region exhibits greater shrinkage than the second region. As described above, due to UV hardening of the first region and increased film density, the refractive index n1 of the first region becomes greater than the refractive index n2 of the second region. The dynamic range Δn of the film is Δn = n1 - n2. In some cases, at 634, the first region of the film has a refractive index at least 0.01 greater than that of the second region. In other words, Δn ≥ 0.01. In some cases, the annealing temperature can be selected to help control the refractive index and / or dynamic range of the metal oxide film. For example, the refractive index can be tuned by electromagnetic radiation (e.g., ultraviolet, laser, IR, X-ray, gamma rays, etc.). In some cases, the dynamic range can be tuned by electromagnetic radiation. Alternatively, or in addition, in some examples, the film density can be adjusted by electromagnetic radiation. In some examples, the refractive indices of the first and second regions can be adjusted by the film composition, drying process, curing temperature, UV exposure time, and / or UV exposure energy.In some cases, the dynamic range can be adjusted by the film composition, drying process, curing temperature, UV exposure time, and / or UV exposure energy.
[0054] Figures 7A–7D show schematic cross-sectional views of exemplary structures that can be formed using Method 600. Figure 7A shows a substrate 700. The substrate 700 can include any suitable material capable of forming a volume holographic lattice. In some examples, the substrate 700 includes a waveguide. Figure 7B shows a film 702 deposited on the substrate 700, for example by performing step 602 of Method 600. The film 702 is deposited using an acid-stabilized precursor solution according to examples disclosed herein. The precursor solution comprises a metal ion, a photodegradable and / or thermally degradable ligand, and an acid, and optionally a polyol (e.g., a diol) or other component configured to slow the evaporation rate of the solvent. In some examples, the film 702 is vacuum-dried before curing (not shown in Figures 7A–7D).
[0055] Figure 7C shows the process of curing the first region 704 by exposure to ultraviolet light 706, for example by performing step 620 of method 600. As shown in Figure 7C, the second region 708 is not exposed to ultraviolet light 706. In this example, two wavefronts from the ultraviolet laser form an interference fringe pattern. The first region 704 represents a region of constructive interference. As a result, the first region 704 is UV-cured. The second region 708 represents a region of canceling interference. Therefore, the second region 708 is not UV-cured. In other examples, the pattern may be formed by a mask (not shown in Figure 7).
[0056] Figure 7D shows the substrate 700 after a heating step, for example, by performing step 630 of method 600. The heating step stabilizes (cures) the film 702. Due to UV curing and densification, the first region 704 has a refractive index n1 greater than the refractive index n2 of the second region 708, which is heated but not UV cured. Figure 7D also schematically shows the shrinkage of the first region 704 and the second region 708. As shown, the first region 704 shrinks more than the second region 708. In some examples, the first and second regions may shrink to the same extent.
[0057] In some examples, the film 702 can function as a holographic medium for recording holographic data. In some examples, the film 702 can be used as a diffractive optical element, such as a volume holographic grating on a waveguide. Although illustrated as a vertically oriented grating, in other examples, the grating elements may be oriented obliquely to the substrate 700. In some examples, one or more additional layers may be deposited on the film 702. For example, an additional volume holographic grating can be deposited on the film 702 by repeating method 600. In some examples, two or more volume holographic gratings can be stacked. In some such examples, each volume holographic grating is configured to diffract light of different wavelengths (e.g., red, green, blue) from a display.
[0058] In one experiment, six silicon wafer substrates were cut into approximately 1-inch squares. The substrates were then plasma-treated for 10 minutes. The films were spin-coated in a vacuum chamber at a maximum rotation speed of 3000 rpm and an acceleration of 3000 rpm / second for 60 seconds. The films were coated using precursor solutions according to the examples disclosed herein.
[0059] The mask was fabricated by covering aluminum foil with a 2-inch square piece of glass, stretching it taut with sufficient height between the film and the glass to avoid direct contact and heat transfer, and to reduce reflected light reaching the substrate.
[0060] After spin coating, the substrate is subjected to a load of 5 J / cm². 2The films were cured with ultraviolet light at a specific dose. In this process, half of the film area of each substrate was UV-cured. However, the remaining half of the film area was covered with a mask and therefore not UV-cured, resulting in a lower density. After UV curing, the films were baked in a furnace at 400°C for 15 minutes. In another experiment, the films were baked at 250°C for 10 minutes.
[0061] Figure 8 shows graph 800 of the refractive indices of the UV-cured and non-UV-cured portions of a film on a certain substrate. This film is titanium-aluminum oxide, with a molar percentage of 75% titanium and 25% aluminum. Graph 800 is based on Cauchy's equation:
[0062]
number
[0063] This shows the fitting of refractive index measurements according to the following. This film is 5 J / cm 2 The film was UV-cured at a specific dose and baked at 400°C for 15 minutes. A mask was used to ensure that half of the film area was UV-cured and the other half was not. Fitting revealed that n=1.957 in the UV-cured portion of the film and n=1.913 in the non-UV-cured portion. Therefore, the Δn of this film was 0.044. Furthermore, after baking, the thickness of the UV-cured portion of the film was 98 nm and the thickness of the non-UV-cured portion was 105 nm.
[0064] Figure 9 shows the graph of the Cauchy equation fitting of the refractive index of the titanium oxide film. 2 The film was cured with UV light at a dose (using a mask that covered half of the film area) and baked at 400°C for 15 minutes. Fitting revealed that n=2.278 in the UV-cured portion of the film and n=2.221 in the non-UV-cured portion. Therefore, the Δn of the second film was 0.057. Furthermore, after baking, the thickness of the UV-cured portion of the film was 63 nm and the thickness of the non-UV-cured portion was 67 nm.
[0065] Figure 10 shows the Cauchy equation fitting graph 1000 for the refractive index of the third film. The third film was formed using a precursor solution containing Ti: 33%, Te: 33%, and La: 33% (molar percentages). This film was prepared at 5 J / cm². 2 The film was UV-cured at a specific dose (using a mask that covered half of the film area) and baked at 250°C for 10 minutes. Fitting revealed that n=2.01 in the UV-cured portion of the film and n=1.91 in the non-UV-cured portion. Therefore, the Δn of the third film was 0.10. Furthermore, after baking, the thickness of the UV-cured portion of the film was 115 nm, and the thickness of the non-UV-cured portion was 140 nm.
[0066] Figure 11 shows graph 1100 of the Cauchy equation fitting of the refractive index of the fourth film. The fourth film was formed using a precursor solution containing Ti: 72% and Te: 28% (molar percentages). This film was prepared at 5 J / cm². 2 The film was UV-cured at a specific dose (using a mask that covered half of the film area) and baked at 250°C for 10 minutes. Fitting revealed that n=2.20 in the UV-cured portion of the film and n=2.04 in the non-UV-cured portion. Therefore, the Δn of the second film was 0.16. Furthermore, after baking, the thickness of the UV-cured portion of the film was 95 nm, and the thickness of the non-UV-cured portion was 119 nm.
[0067] As described above, according to this disclosure, various metal oxides can be used as holographic films. Examples include titanium dioxide (TiO2), zirconium dioxide (ZrO2), hafnium oxide (HfO2), lithium titanium oxide, strontium titanium oxide, yttrium titanium oxide, titanium zirconium oxide, niobium titanium oxide, aluminum titanium oxide, titanium tin oxide, bismuth titanium oxide, titanium lanthanum oxide, titanium lanthanum telluride oxide, titanium lanthanum bismuth oxide, titanium lanthanum antimony oxide, titanium lanthanum aluminum oxide, cerium titanium oxide, lithium aluminum oxide, aluminum strontium oxide, yttrium aluminum oxide, aluminate niobate, tin aluminum oxide, bismuth aluminum oxide, aluminum lanthanum oxide, lithium lanthanum titanium oxide, and lithium bismuth titanium oxide.
[0068] The recording efficiency of holograms, such as diffractive optical elements, on metal oxide films according to this disclosure can be improved by increasing the amount of light absorbed by the metal oxide film during hologram recording for forming the diffractive optical element. This can be achieved by adding metal ions that absorb more strongly at the wavelength used for hologram recording. Examples of metal ions that can be incorporated into metal oxide films to provide relatively high absorbency compared to other ions include silver, bismuth, indium, tin, antimony, and tellurium. Figure 12 shows an exemplary plot 1200 of a tellurium-doped titanium dioxide (TiO2) film showing the absorbency with increasing Te concentration. As the concentration of Te ions in the precursor solution increases from 0% to 7.5%, 15%, and 30%, the absorbance of light at 400 nm increases.
[0069] Therefore, exemplary acid-stabilized precursor solutions help avoid cracking during liquid-phase deposition of titanium-containing oxide films. In particular, acid-stabilized precursor solutions containing titanium ions, lanthanum ions, and one or more of tellurium ions, bismuth ions, tin ions, or antimony ions can be used to form substantially crack-free oxide films. This can improve the performance of devices that utilize such titanium-containing oxide films as optical elements, such as volumetric holographic gratings. Furthermore, exemplary acid-stabilized precursor solutions can be used to deposit void-free dielectric layers in thin-film transistors. Other applications include high-density data storage, three-dimensional (3D) displays for augmented reality and mixed reality, advanced optical components, enhanced security and anti-counterfeiting features, and improved medical imaging.
[0070] The configurations and methods described herein are illustrative, and these examples should not be interpreted restrictively. Numerous variations, extensions, and omissions are conceivable. All the various steps of the above methods may be performed in the illustrated order, in any other order, in parallel, or omitted. The subject matter of this disclosure includes all novel and non-obvious combinations and partial combinations of the various configurations, methods, properties, and other features disclosed herein, as well as all their equivalents.
Claims
1. This is a method for forming a titanium-containing oxide film by liquid-phase deposition. - The substrate is coated with an aqueous solution of an acid-stabilizing precursor to form a film. The acid-stabilizing precursor aqueous solution comprises a step of comprising titanium ions, one or more other metal ions, a photodegradable and / or thermally degradable ligand, and an acid. - A step of exposing the film to one or more of heat, vacuum, or light, A method of having.
2. The method according to claim 1, wherein the acid-stabilizing precursor solution comprises titanium chloride, lanthanum chloride, and one or more of tellurium chloride, bismuth chloride, tin chloride, or antimony chloride.
3. The method according to claim 1, wherein the acid comprises one or more of hydrochloric acid, nitric acid, or sulfuric acid.
4. The method according to claim 1, wherein the photodegradable and / or thermally degradable ligand comprises one or more of hydrogen peroxide, formic acid, or nitrate ions.
5. The method according to claim 1, wherein the exposure of the film to light includes ultraviolet curing of the film.
6. The method according to claim 5, further comprising annealing the film at a temperature of 60 to 650°C after curing the film with ultraviolet light.
7. The method according to claim 1, wherein the exposure of the film to heat includes thermocuring the film at a temperature of 60 to 650°C.
8. The method according to claim 1, wherein the aqueous solution of the acid-stabilizing precursor further comprises one or more diols.
9. The method according to claim 8, wherein the substrate and the film form an optical element including a waveguide.
10. The method according to claim 9, further comprising the step of imprinting a pattern on the film before exposing the film to heat or light or one or more of the same.
11. The method according to claim 10, wherein the formation of the titanium-containing oxide film includes the formation of a passivation layer in a thin-film transistor.
12. An aqueous solution of an acid-stabilized precursor for forming a titanium-containing oxide film by liquid-phase deposition, comprising titanium ions, one or more other metal ions, a photodegradable and / or thermally degradable ligand, and an acid.
13. The aqueous solution of the acid-stabilized precursor according to claim 12, wherein the one or more other metal ions include one or more of tellurium ions, bismuth ions, tin ions, aluminum ions, or antimony ions.
14. The aqueous solution of the acid-stabilized precursor according to claim 13, wherein the acid contains hydrochloric acid and the photodegradable and / or thermally degradable ligand contains hydrogen peroxide.
15. The aqueous solution of the acid-stabilizing precursor according to claim 12, wherein the acid comprises one or more of hydrochloric acid, nitric acid, or sulfuric acid.
16. The aqueous solution of the acid-stabilized precursor according to claim 12, wherein the photodegradable and / or thermally degradable ligand comprises one or more of hydrogen peroxide, formic acid, or nitrate ions.
17. TiO ２ The aqueous solution of the acid-stabilizing precursor according to claim 12, further comprising nanoparticles.
18. - The substrate is coated with an acid-stabilized precursor solution to form a film. The acid-stabilized precursor solution comprises a metal ion, a photodegradable and / or thermally degradable ligand, and an acid. - A step of curing a first region of the film with ultraviolet light, and not curing a second region of the film with ultraviolet light, - A step of heating the film, A method for forming a metal oxide film having the following properties.
19. The method for forming a diffraction grating according to claim 18.
20. The method according to claim 18, wherein, after heating the film, the refractive index of the first region of the film is at least 0.04 greater than the refractive index of the second region.