Mixed valence sol-gels for high refractive index, transparent optical coatings

Abstract

The technology disclosed herein relates to a sol-gel material comprising at least one metal halide precursor and at least one alcohol. After annealing, the metal in the metal halide is at least in two different oxidation states, and the two oxidation states are stable and transparent to visible light. By producing a mixture of the same metal in multiple oxidation states, which is transparent to visible light, an amorphous state of the sol-gel material is obtained without any significant domain formation, which would otherwise locally distribute stress and result in voids inside the nanograting to be coated. The highly condensed state of the sol-gel has a refractive index value in the range of 1.7-2.2 without sacrificing the recessed feature fill.

Description

[0001] This application is a divisional application of the application with the filing date of January 21, 2023, application number 202380014415.1, and invention title "Hybrid-Valence Sol-Gel for High Refractive Index, Transparent Optical Coatings". Technical Field

[0002] The present disclosure generally relates to a sol-gel material (e.g., a sol-gel overcoating mixture). Background Art

[0003] A sol-gel is a material composed of a solution including a metal oxide precursor, which may have partially or fully condensed into an extended network. After coating the solution and annealing the sol-gel, the precursor ligands and solvents can be thermally removed to fully condense the extended network into an oxide or inorganic film. The condensation process can lead to densification and potentially crystallization. Thus, when applied to a substrate and annealed, sol-gels can be used to fabricate transparent, high refractive index (RI) coatings. Summary of the Invention

[0004] The present disclosure generally relates to a sol-gel material (e.g., a sol-gel overcoating mixture). More specifically, the techniques disclosed herein relate to sol-gel materials that can include at least one metal halide precursor and at least one alcohol. After annealing, the metal in the metal halide can be in at least two oxidation states, both of which are stable and transparent. By producing a mixture of the same metal in multiple oxidation states and a mixture of oxo and chloride ligands that are both transparent to visible light, an amorphous state of the sol-gel material without any distinct domain formation can be obtained, which would otherwise locally distribute stress or shrinkage and cause voiding within the nanogratings to be coated. In this way, a highly condensed state of the sol-gel with an RI value in the range of about 1.7 to about 2.2 can be obtained without sacrificing the filling of the recess features.

[0005] In one embodiment, a tin(II) precursor containing a halide ligand is dissolved in an alcohol or a diol. Upon coating and annealing, the tin(II) mixture is partially oxidized to tin(IV). Both tin(II) and tin(IV) oxides or oxohalides are transparent to visible light, and the mixture of the two oxidation states is also transparent. In addition, regardless of the degree of condensation, when the mixture of tin(II) and tin(IV) oxides or oxohalides is in an amorphous state after annealing, it can condense to produce a coating with an RI value between about 1.7 and about 2.2, and discrete domains are not formed. The ratio of tin(II):tin(IV) can be maintained in the range of about 1:5 to about 4:1 in order to achieve an RI value in the range of about 1.7 to about 2.2 without causing a loss of the ability to fill recessed features (e.g., filling the recessed features of a substrate without voids). Advantageously, the condensation process of the sol-gel material (e.g., the tin(II) / tin(IV) mixture) can be carried out at a temperature below about 300 °C.

[0006] According to a first aspect of the present disclosure, there is provided a sol-gel material for overcoating a surface relief structure, the sol-gel material comprising: a metal halide precursor; and at least one alcohol or diol.

[0007] In some embodiments, the metal halide precursor comprises a source of tin(II) chloride or a source of tin(II) chloride dihydrate.

[0008] In some embodiments, the sol-gel material further comprises a solvent that serves as a source of oxide ligands during the annealing process.

[0009] In some embodiments, after applying an annealing process to the sol-gel material, the sol-gel material comprises at least two different oxidation states of the metal in the metal halide precursor; and at least two different oxidation states of the metal are transparent to visible light.

[0010] In some embodiments, after applying an annealing process to the sol-gel material, the oxohalide composition of the sol-gel material is non-stoichiometric.

[0011] In some embodiments, the metal comprises tin, and at least two different oxidation states of the metal include tin(II) and tin(IV).

[0012] In some embodiments, the sol-gel material is configured to fill recessed features on a substrate in a superconformal fashion without introducing voids caused by complete thermal densification of the sol-gel material.

[0013] In some embodiments, the sol-gel material further comprises a stabilizer, an acid, a base, a peroxide, a surfactant, a crosslinking agent, a softening agent, a toughening agent additive, a solvent, or a combination thereof.

[0014] In some embodiments, the stabilizer comprises ethanolamine, diethanolamine, triethanolamine, a fatty amine, a diamine, a triamine, a polyamine, or a combination thereof.

[0015] In some embodiments, the stabilizer comprises an organic antioxidant, an inorganic antioxidant, or a combination thereof.

[0016] In some embodiments, the sol-gel material further comprises a solvent, which comprises propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol methyl ether acetate, tripropylene glycol monomethyl ether, butyl lactate, propylene carbonate, isopropanol, methanol, water, or a combination thereof.

[0017] In some embodiments, the sol-gel material comprises: 10% - 30% by weight of a tin salt, and 70% - 90% by weight of a solvent mixture.

[0018] In some embodiments, the tin salt comprises: tin(II) chloride, stannous dichloride dihydrate, anhydrous stannous dichloride, or any combination thereof.

[0019] In some embodiments, the solvent mixture comprises: 27% by weight of propylene glycol monomethyl ether, 67% by weight of 1,3-dimethoxy-2-propanol, and 6% by weight of diethylene glycol; 27% by weight of propylene glycol monomethyl ether, 67% by weight of di(propylene glycol) methyl ether, and 6% by weight of diethylene glycol; or 100% by weight of 1,3-dimethoxy-2-propanol.

[0020] According to a second aspect of the present disclosure, there is provided an optical device for a display system, the optical device comprising: a surface relief structure comprising recessed features; and a layer of a sol-gel material that fills the recessed features of the surface relief structure in a conformal manner without voids, wherein the sol-gel material comprises at least two different oxidation states of a metal, and wherein the at least two different oxidation states of the metal are transparent to visible light.

[0021] In some embodiments, the layer of the sol-gel material has an absorption rate of visible light of less than 0.1% / 100nm, and the refractive index of the layer of the sol-gel material is between 1.65 and 2.20.

[0022] In some embodiments, the at least two different oxidation states of the metal comprise tin(II) and tin(IV).

[0023] In some embodiments, the ratio of tin(II) to tin(IV) in the layer of the sol-gel material is between 1:5 and 4:1, and wherein the sol-gel material is in an amorphous state.

[0024] In some embodiments, the surface relief structure includes features characterized by a width between 5 nm and 200 nm and an aspect ratio between 1:1.5 and 1:50.

[0025] According to a third aspect of the present disclosure, there is provided a method of manufacturing an ultraconformal optical coating, the method comprising: depositing a layer of a sol-gel material on a surface relief structure, wherein the sol-gel material comprises: a metal halide precursor; and at least one alcohol or diol; and annealing the layer of the sol-gel material at a temperature below or equal to 300 °C for less than about 10 minutes to ultraconformally fill the surface relief structure with the sol-gel material.

[0026] This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to the appropriate portions of the entire specification of the present disclosure, any or all of the drawings, and each claim. The foregoing, together with other features and examples, will be described in more detail hereinafter in the following specification, claims, and drawings.

[0027] It should be understood that any feature described herein as being suitable for incorporation into one or more aspects, or embodiments, of the present disclosure is intended to be generalizable to any and all aspects and embodiments of the present disclosure. Those skilled in the art can understand other aspects of the present disclosure based on the specification, claims, and drawings of the present disclosure. The foregoing general description and the following detailed description are merely exemplary and explanatory and do not limit the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Exemplary embodiments are described in detail below with reference to the following drawings.

[0029] Figure 1 A simplified block diagram of an example of an artificial reality system environment including a near-eye display according to certain embodiments.

[0030] Figure 2 A perspective view of an example of a near-eye display in the form of a head-mounted display (HMD) device for implementing some examples disclosed herein.

[0031] Figure 3 A perspective view of an example of a near-eye display in the form of glasses for implementing some examples disclosed herein.

[0032] Figure 4Illustrated is an example of an optical see-through augmented reality system including a waveguide display according to certain embodiments.

[0033] Figure 5A Illustrated is an example of a near-eye display device including a waveguide display according to certain embodiments.

[0034] Figure 5B Illustrated is an example of a near-eye display device including a waveguide display according to certain embodiments.

[0035] Figure 6 Illustrated is an example of an inclined grating in a waveguide display according to certain embodiments.

[0036] Figure 7A Illustrated are examples of sol-gel coatings on a flat substrate before and after annealing, where during and after annealing, the sol-gel coating can condense and shrink, resulting in the formation of domains or grains.

[0037] Figure 7B Illustrated is a substrate including recessed features and a sol-gel coating on the recessed features before and after annealing, where domain formation results in voids inside the recessed features.

[0038] Figure 8A Illustrated is a substrate including a sol-gel coating deposited on a substrate before and after annealing, where the sol-gel coating can include a sol-gel material according to certain embodiments disclosed herein.

[0039] Figure 8B Illustrated is a substrate including recessed features and a sol-gel coating on the recessed features before and after annealing, where the sol-gel coating can include a sol-gel material according to certain embodiments disclosed herein, resulting in a void-free conformal filling of the recessed features.

[0040] Figure 9A Shown are the material compositions and properties of Comparative Examples 1-3.

[0041] Figure 9B Shown is a cross-sectional view under a scanning electron microscope (SEM) of an example of a surface relief grating with a coating formed in Comparative Examples 1-3.

[0042] Figure 10A Shown are the material compositions and properties of Working Examples 4-10 according to certain embodiments.

[0043] Figure 10BA cross-sectional view (e.g., via SEM) of an example of a surface relief grating with an overconformal outer coating formed in Working Examples 4-10 according to certain embodiments is shown.

[0044] Figure 11 The material compositions and properties of Working Examples 11-12 according to certain embodiments are shown.

[0045] Figure 12A The material compositions and properties of Working Examples 13-17 according to certain embodiments are shown.

[0046] Figure 12B A cross-sectional view (e.g., via SEM) of an example of a surface relief grating with an overconformal outer coating formed in Working Examples 13-15 and a coating formed in Working Examples 16-17 according to certain embodiments is shown.

[0047] Figure 13 The material compositions and properties of Working Examples 18-20 according to certain embodiments are shown.

[0048] Figure 14 The material compositions and properties of Working Examples 21-22 according to certain embodiments are shown.

[0049] For illustrative purposes only, the drawings depict embodiments of the present disclosure. Those skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods shown may be employed without departing from the principles or advantages of the present disclosure.

[0050] In the drawings, like components and / or features may have the same reference numerals. Additionally, various components of the same type may be distinguished by following the reference numeral with a dash and a second numeral that differentiates the similar components. If only the first reference numeral is used in the specification, the description may apply to any one of the similar components having the same first reference numeral, regardless of the second reference numeral. Detailed Description

[0051] The present disclosure generally relates to sol-gel outer coating materials. More specifically, the techniques disclosed herein relate to sol-gel materials that include a mixture of the same metal in multiple oxidation states (e.g., tin(II) and tin(IV)), where all of the oxidation states are transparent and the sol-gel material can remain in an amorphous state without forming any distinct domains. When used for optical coatings, the sol-gel material can reach a highly condensed state with an RI value in the range of about 1.7 - 2.2 without sacrificing the filling of recess features. Various inventive embodiments are described herein, including devices, systems, methods, materials, processes, compositions, etc.

[0052] Artificial reality systems such as head-mounted display (HMD) or heads-up display (HUD) systems typically include a near-eye display configured to present content to a user in front of the user's eyes, such as within about 10-20 mm, via an electronic or optical display. The near-eye display can be in the form of, for example, a head-mounted earphone (headset) or a pair of glasses. The near-eye display can display virtual objects or images of combined reality objects and virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user can view both an image of a virtual object (e.g., a computer-generated image (CGI)) and the surrounding environment, for example, by viewing through transparent display glasses or lenses (commonly referred to as optical see-through).

[0053] An example of an optical see-through AR system can use a waveguide-based optical display, where light of a projected image can be coupled into a waveguide (e.g., a transparent substrate), propagate within the waveguide by total internal reflection, and be coupled out of the waveguide at multiple locations towards the user's eyes. In some embodiments, the light of the projected image can be coupled into or out of the waveguide using a diffractive optical element (grating) that can be transparent to ambient light, and thus can allow light from the surrounding environment to pass through a see-through region of the waveguide to reach the user's eyes without being diffracted. In some embodiments, a surface relief grating including a surface relief structure formed in or deposited on a material layer of a substrate can be used to couple light into or out of the waveguide. An outer coating having a refractive index different from that of the surface relief structure can be formed on the surface relief grating to fill gaps in the surface relief structure and adjust the optical properties of the surface relief structure. The outer coating can need to be superconformal to the surface of the surface relief structure, without voids or bubbles, have a refractive index much higher or much lower than that of the surface relief structure, and have a low absorption rate for visible light. The outer coating can include a dielectric material such as hafnium dioxide, titanium dioxide, tantalum oxide, tungsten oxide, zirconium oxide, gallium sulfide, gallium nitride, gallium phosphide, silicon, or a high refractive index organic material (e.g., a resin).

[0054] According to certain embodiments, an outer coating can be formed on a surface relief grating using sol-gel. Sol-gel is a material that can include a solution containing an oxide precursor and can partially or fully condense into an extended network. After coating and thermal annealing of the sol-gel, the precursor ligands and solvents can be removed to fully condense the extended network into an oxide or inorganic film. The condensation process can result in densification and, in some cases, crystallization. Thus, when applied to a substrate and annealed, sol-gel can be used to fabricate a high refractive index (RI) coating. Sol-gel can be dispensed as a solution and thus can provide improved processability compared to high RI nanocomposites, which can have higher viscosities and reduced material flow. Additionally, since sol-gel does not require the addition of a resin matrix and since annealing can drive out all organic and solvent components from the oxide or inorganic network, sol-gel can also provide the advantage of a high RI coating with improved transparency to visible light compared to nanocomposites that include high RI nanoparticles dispersed in a resin, where the transparency can degrade over time. However, for sol-gel to be used as a grating coating, it is desirable for the coating to penetrate recessed features (gratings, trenches, vias, and through-holes) and maintain a flat surface on top of the coating. In other words, the coating needs to achieve superconformal feature filling. While sol-gel can fill these features prior to annealing and densification, it has been found that densification of typical oxides produces RI values greater than about 1.7, often resulting in voids within nanogratings having feature widths of 5 - 200 nm and aspect ratios (width to depth) of about 1:1.5 to about 1:50.

[0055] During condensation, voids can be generated when the shrinkage stress is unevenly distributed across the film, or when the stress is not applied unidirectionally to prevent pulling out from the nanogratings. It has been found that the stress is locally distributed within domains or grains in the nanogratings, and thus voids can be generated around these domains as the matrix shrinks. Therefore, to avoid the formation of domains or grains, or to allow the shrinkage stress to be globally distributed in the sol-gel coating, a continuous material network needs to be maintained. This can be achieved by keeping the sol-gel material in an amorphous state. However, in most cases, it is unlikely to condense the material to obtain an RI higher than 1.7 without forming discrete domains or inducing a certain degree of crystallization in the sol-gel. In addition, it is desirable to fill the recessed features in a void-free manner without having to increase the organic content in the sol-gel formulation. Surfactants and supporting organic resins can be mixed into the sol-gel to improve feature penetration and fill-retention during shrinkage and to avoid the formation of discrete particles. However, increasing the organic content in the coating generally reduces the transparency of the coating or introduces potential reliability issues. Therefore, novel sol-gel materials are needed, where the sol-gel material is capable of achieving a high RI (e.g., about 1.7 - 2.2) and void-free ultra-conformal filling of recessed features after annealing (e.g., after curing). In addition, to improve the compatibility and practicality of the sol-gel material in industrial manufacturing processes, sol-gel materials that can condense at temperatures below about 300 °C to obtain high RI values are needed.

[0056] Sol-gel coatings are commonly used to form conformal coatings that track the topography of the underlying substrate without recessed features. In most of these applications, the sol-gel coating varies only in two dimensions, but the thickness (the third dimension) is constant (see Barhoum et al., Chem. Mater. 2011, 23, 23, 5177–5184; Yan et al., Electrochimica Acta 2015, 169, 73-81; and Lu et al., Nano Letters 2002, 2, 3, 183–186). Although the shape of the substrate can be complex (i.e., flat, curved, tubular, etc.), the substrate generally does not contain nano-sized recessed features. In the case where the substrate has nano-sized to micro-sized recessed features with a high aspect ratio, it is expected that the sol-gel will delineate the contours of the features and form a conformal coating. If the film thickness is greater than the depth of the recessed feature, it is possible to fill the high aspect ratio feature with an as-deposited film. However, after annealing, the sol-gel material within the nano-sized to micro-sized recessed features with a high aspect ratio can shrink and collapse into microparticles, creating pores or voids. Thus, sol-gel is generally not used for ultra-conformal coatings of high aspect ratio recessed features. In the present disclosure, a sol-gel material capable of ultra-conformally filling high aspect ratio recessed features is disclosed in the case of creating a flat surface on top of the sol-gel coating.

[0057] The annealing temperature for complete densification of the sol-gel coating generally depends on the chemistry of the precursor used and the structure of the target oxide, but the annealing temperature is generally higher than about 500 °C. For example, complete densification of TiO prepared from monomeric precursors is observed at about 600 °C 2Complete densification of the film (see Taherniya et al., Mater. Res. Express 2019, 6, 016417; and Tanski et al., BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES, Vol. 66, No. 2, 2018, DOI: 10.24425 / 119069). The RI is maximized and the film transparency is adjusted using an annealing process (see Blanco et al., Applied Surface Science 2018, 439, 736 - 748; and Gareso et al., 2019 J. Phys.: Conf. Ser. 1242 012037). In many cases, the shrinkage from the initial coating to the fully annealed film is greater than 60%, typically around 90% (see Lodh & Chakraborty, Bandgap Engineering of Sol–Gel Spin-Coated TiO2 Thin Film on Glass Substrate. 2021, DOI: 10.1201 / 9781003047193-2). Thus, films made from sol–gel can have high thickness variations during annealing, and their use in applications for filling recessed features can be accompanied by feature voids due to shrinkage.

[0058] Sol–gels containing multinuclear precursors or precondensed gels can be used to reduce the shrinkage of the film between coating and full annealing. However, the composition of these materials is often unstable and tends to form nanoparticles in solution over time (see Sano et al., ACS Appl. Mater. Interfaces 2020, 12, 40, 44743–44753). In addition, molecular oxide clusters tend to be unstable towards water and molecular oxygen, or they tend to aggregate over time (see Matthews et al., Chem. Commun. 2014, 50, 12815-12823; Coppens et al., Chem. Rev. 2014, 114, 9645-9661; and Rozes et al., Chem. Soc. Rev. 2011, 40, 1006-1030). Once aggregates and nanoparticles are formed, high-quality conformal filling of recessed features may not be achievable without a supporting resin. Thus, the applicability of polyoxo clusters in industrial applications can be severely hindered.

[0059] Titanium oxysulfate-based sol-gels can be used to achieve and maintain recess feature filling throughout the sol-gel annealing process. Sulfate ions can prevent the material from forming particles during condensation, thus avoiding voids. However, titanium oxysulfate-based sol-gels can only allow the optical film to have a maximum RI of about 1.95. For example, when titanium oxysulfate is used as the only precursor in the sol-gel, the maximum RI of the resulting coating is about 1.81. By mixing the titanium oxysulfate precursor with secondary oxytitanyl species or a pre-condensed network from a titanium tetrachloride precursor, the RI can be further increased. The mixing ratio between titanium oxysulfate and the second titanium species can determine the balance between optical properties and recess feature filling ability. However, it can be difficult to increase the RI above 1.95 without causing a loss of recess filling ability. This is because, in a higher ratio of secondary oxytitanyl or titanium tetrachloride precursors, the formation of early particles and voids during shrinkage cannot be avoided.

[0060] Annealing a two-component titanium system at temperatures not higher than 500 °C has the potential to achieve recess feature filling with an RI of up to 2.0. This can be achieved by delaying the formation of domains or grains until the final stage of condensation, so that if any local shrinkage occurs, it will not result in significant voids. However, this performance may not extend to coatings with an RI higher than 2.0, and a processing temperature below 300 °C can only produce coatings with an RI lower than 1.9.

[0061] Therefore, there is a need for sol-gel materials that can be used to produce coatings with superconformal filling of recess features, where the feature width is about 5 - 200 nm, the aspect ratio is about 1:1.5 to 1:50 width to depth, and when the sol-gel is processed at a temperature below about 300 °C, the RI of the sol-gel is between about 1.7 - 2.2.

[0062] The technical solutions disclosed herein provide a sol-gel material that, after annealing, can form a coating having a high RI (e.g., between about 1.7 and 2.2) and can fill nano-scale to micro-scale surface relief structures on a surface in an overconformal manner. In some embodiments, the sol-gel material can include at least one metal halide precursor and at least one alcohol. After annealing, the metal in the metal halide can be in at least two oxidation states, both of which are stable and transparent. By producing a mixture of the same metal in multiple oxidation states and a mixture of oxo- and chloro-ligands that are both transparent to visible light, an amorphous state of the sol-gel material can be obtained without any obvious domain formation, which would otherwise locally distribute stress or shrinkage and cause voids within the nano-gratings to be coated. In this way, a highly condensed state of the sol-gel with an RI value in the range of about 1.7 to about 2.2 can be obtained without sacrificing the filling of recess features.

[0063] In the following description, for purposes of explanation, specific details are set forth in order to provide a thorough understanding of examples of the present disclosure. However, it will be apparent that the various examples may be practiced without these specific details. For example, devices, systems, structures, components, methods, and other elements may be shown as components in block diagram form in order not to obscure the examples with unnecessary detail. In other instances, well-known devices, processes, systems, structures, and techniques have been shown without unnecessary detail in order not to obscure the examples. The drawings and description are not intended to be restrictive. The terms and expressions used in this disclosure are used as descriptive terms and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents or portions of the features shown and described. The word "example" as used herein means "serving as an example, instance, or illustration". Any embodiment or design described herein as an "example" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

[0064] Figure 1 A simplified block diagram of an example of an artificial reality system environment 100 including a near-eye display 120 according to a particular embodiment. Figure 1 The artificial reality system environment 100 shown therein can include a near-eye display 120, an optional external imaging device 150, and an optional input / output interface 140, each of which can be coupled to an optional console 110. Although Figure 1FIG. 0 shows an example of an artificial reality system environment 100 that includes a near-eye display 120, an external imaging device 150, and an input / output interface 140, but any number of these components can be included in the artificial reality system environment 100, or any one of the components can be omitted. For example, there can be multiple near-eye displays 120, which are monitored by one or more external imaging devices 150 that communicate with the console 110. In some configurations, the artificial reality system environment 100 can exclude the external imaging device 150, the optional input / output interface 140, and the optional console 110. In alternative configurations, different or additional components can be included in the artificial reality system environment 100.

[0065] The near-eye display 120 can be a head-mounted display that presents content to a user. Examples of content presented by the near-eye display 120 include one or more of images, videos, audio, or any combination thereof. In some embodiments, the audio can be presented via an external device (e.g., speakers and / or headphones), which receives audio information from the near-eye display 120, the console 110, or both and presents audio data based on the audio information. The near-eye display 120 can include one or more rigid bodies that can be rigidly or non-rigidly coupled to each other. A rigid coupling between the rigid bodies can cause the coupled rigid bodies to act as a single rigid entity. A non-rigid coupling between the rigid bodies can allow the rigid bodies to move relative to each other. In various embodiments, the near-eye display 120 can be implemented in any suitable size specification, including a pair of glasses. The following Figure 2 and Figure 3 further describes some embodiments of the near-eye display 120. Additionally, in various embodiments, the functionality described herein can be used in a head-mounted transceiver that combines images of the external environment of the near-eye display 120 and artificial reality content (e.g., computer-generated images). Thus, the near-eye display 120 can enhance the image of the physical, real-world environment external to the near-eye display 120 with generated content (e.g., images, videos, or sounds) to present augmented reality to the user.

[0066] In various embodiments, the near-eye display 120 may include one or more of display electronics 122, display optics 124, and an eye tracking unit 130. In some embodiments, the near-eye display 120 may further include one or more locators 126, one or more position sensors 128, and an inertial measurement unit (IMU) 132. In various embodiments, the near-eye display 120 may omit any one of the eye tracking unit 130, the locator 126, the position sensor 128, and the IMU 132, or include additional elements. Additionally, in some embodiments, the near-eye display 120 may include an element that combines the functions of the various elements described in conjunction with Figure 1 the elements described herein.

[0067] The display electronics 122 may display an image to a user or facilitate the display of an image to the user based on data received from, for example, the console 110. In various embodiments, the display electronics 122 may include one or more display panels, such as a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, a micro light emitting diode (μLED) display, an active-matrix OLED display (AMOLED), a transparent OLED display (TOLED), or some other display. For example, in one implementation of the near-eye display 120, the display electronics 122 may include a front TOLED panel, a rear display panel, and optical components (e.g., an attenuator, a polarizer, or a diffractive or spectral film) between the front display panel and the rear display panel. The display electronics 122 may include pixels to emit light of a primary color (such as red, green, blue, white, or yellow). In some implementations, the display electronics 122 may display a three-dimensional (3D) image through a stereoscopic effect generated by a two-dimensional panel to create a subjective perception of image depth. For example, the display electronics 122 may include a left display and a right display positioned in front of the user's left and right eyes, respectively. The left display and the right display may present copies of an image that are horizontally offset relative to each other to create a stereoscopic effect (i.e., the user viewing the image perceives image depth).

[0068] In some embodiments, the display optical device 124 may optically display image content (e.g., using optical waveguides and couplers) or magnify the image light received from the display electronics 122, correct optical errors associated with the image light, and present the corrected image light to a user of the near-eye display 120. In various embodiments, the display optical device 124 may include one or more optical elements, such as, for example, a substrate, an optical waveguide, a hole, a Fresnel lens, a convex lens, a concave lens, a filter, an input / output coupler, or any other suitable optical element that may affect the image light emitted from the display electronics 122. The display optical device 124 may include a combination of different optical elements and mechanical couplers that maintain the relative spacing and orientation of the optical elements in the combination. One or more of the optical elements in the display optical device 124 may have an optical coating, such as an anti-reflection coating, a reflective coating, a filter coating, or a combination of different optical coatings.

[0069] The magnification of the image light by the display optical device 124 may allow the display electronics 122 to be physically smaller, lighter, and consume less power compared to a larger display. Additionally, the magnification may increase the field of view of the displayed content. The amount of magnification of the image light by the display optical device 124 may be changed by adjusting, adding, or removing optical elements from the display optical device 124. In some embodiments, the display optical device 124 may project the displayed image onto one or more image planes that may be farther from the user's eyes than the near-eye display 120.

[0070] The display optical device 124 may also be designed to correct one or more types of optical errors, such as two-dimensional optical errors, three-dimensional optical errors, or any combination thereof. Two-dimensional errors may include optical aberrations that occur in two dimensions. Example types of two-dimensional errors may include barrel distortion, pincushion distortion, longitudinal chromatic aberration, and lateral chromatic aberration. Three-dimensional errors may include optical errors that occur in three dimensions. Example types of three-dimensional errors may include spherical aberration, coma aberration, field curvature, and astigmatism.

[0071] The locator 126 can be an object positioned at specific locations on the near-eye display 120 relative to each other and relative to a reference point on the near-eye display 120. In some embodiments, the console 110 can identify the locator 126 in an image captured by the external imaging device 150 to determine the position, orientation, or both of the artificial reality headset. The locator 126 can be an LED, a corner cube reflector, a reflective marker, a light source that contrasts with the environment in which the near-eye display 120 operates, or any combination thereof. In embodiments where the locator 126 is an active component (e.g., an LED or other type of light-emitting device), the locator 126 can emit light in the visible band (e.g., from about 380 nm to 750 nm), in the infrared (IR) band (e.g., from about 750 nm to 1 mm), in the ultraviolet band (e.g., from about 10 nm to about 380 nm), in another part of the electromagnetic spectrum, or in any combination of parts of the electromagnetic spectrum.

[0072] The external imaging device 150 can include one or more cameras, one or more video cameras, any other device capable of capturing an image including one or more of the locators 126, or any combination thereof. Additionally, the external imaging device 150 can include one or more filters (e.g., for increasing the signal-to-noise ratio). The external imaging device 150 can be configured to detect light emitted or reflected from the locator 126 in the field of view of the external imaging device 150. In embodiments where the locator 126 includes passive elements (e.g., a retroreflector), the external imaging device 150 can include a light source that illuminates some or all of the locators 126, which can retroreflect the light back to the light source in the external imaging device 150. Slow calibration data can be communicated from the external imaging device 150 to the console 110, and the external imaging device 150 can receive one or more calibration parameters from the console 110 to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, sensor temperature, shutter speed, or aperture).

[0073] The position sensor 128 can generate one or more measurement signals in response to movement of the near-eye display 120. Examples of the position sensor 128 can include accelerometers, gyroscopes, magnetometers, other motion detection or error correction sensors, or any combination thereof. For example, in some embodiments, the position sensor 128 can include multiple accelerometers to measure translational motion (e.g., forward / backward, up / down, or left / right), and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, or roll). In some embodiments, the various position sensors can be oriented orthogonally to each other.

[0074] The IMU 132 can be an electronic device that generates fast calibration data based on measurement signals received from one or more of the position sensors 128. The position sensors 128 can be located external to the IMU 132, within the IMU 132, or any combination thereof. Based on one or more measurement signals from one or more position sensors 128, the IMU 132 can generate fast calibration data that indicates an estimated position of the near-eye display 120 relative to an initial position of the near-eye display 120. For example, the IMU 132 can integrate measurement signals received from an accelerometer over time to estimate a velocity vector, and integrate the velocity vector over time to determine an estimated position of a reference point on the near-eye display 120. Alternatively, the IMU 132 can provide sampled measurement signals to the console 110, which can determine the fast calibration data. Although a reference point can generally be defined as a point in space, in various embodiments, the reference point can also be defined as a point within the near-eye display 120 (e.g., the center of the IMU 132).

[0075] The eye tracking unit 130 can include one or more eye tracking systems. Eye tracking can refer to determining the position of an eye relative to the near-eye display 120, including the orientation and position of the eye. The eye tracking system can include an imaging system to image one or more eyes, and can optionally include a light emitter that can generate light directed towards the eye such that light reflected by the eye can be captured by the imaging system. For example, the eye tracking unit 130 can include an incoherent or coherent light source (e.g., a laser diode) that emits light in the visible or infrared spectrum, and a camera that captures light reflected by the user's eye. As another example, the eye tracking unit 130 can capture reflected radio waves emitted by a micro radar unit. The eye tracking unit 130 can use a low-power light emitter that emits light at frequencies and intensities that do not damage the eye or cause physical discomfort. The eye tracking unit 130 can be arranged to increase the contrast of the eye image captured by the eye tracking unit 130 while reducing the total power consumed by the eye tracking unit 130 (e.g., reducing the power consumed by the light emitter and imaging system included in the eye tracking unit 130). For example, in some embodiments, the eye tracking unit 130 can consume less than 100 milliwatts of power.

[0076] The near-eye display 120 can use the orientation of the eyes to, for example, determine the user's inter-pupillary distance (IPD), determine the gaze direction, introduce depth cues (e.g., using image blur outside the user's line of sight), gather insights about user interactions in VR media (e.g., the time spent on any particular subject, object, or frame that varies based on the exposed stimuli), some other functions partially based on the orientation of at least one of the user's eyes, or any combination thereof. Since the orientations of both of the user's eyes can be determined, the eye tracking unit 130 can be able to determine where the user is looking. For example, determining the user's gaze direction can include determining the convergence point based on the determined orientations of the user's left and right eyes. The convergence point can be the point where the two fovea axes of the user's eyes intersect. The direction of the user's gaze can be the direction of the line passing through the midpoint between the convergence point and the pupils of the user's eyes.

[0077] The input / output interface 140 can be a device that allows the user to send action requests to the console 110. An action request can be a request to perform a particular action. For example, the action request can be to start or end an application or to perform a particular action within an application. The input / output interface 140 can include one or more input devices. Example input devices can include a keyboard, a mouse, a game controller, gloves, buttons, a touch screen, or any other suitable device for receiving an action request and communicating the received action request to the console 110. The action request received by the input / output interface 140 can be communicated to the console 110, which can perform the action corresponding to the requested action. In some embodiments, the input / output interface 140 can provide haptic feedback to the user according to instructions received from the console 110. For example, the input / output interface 140 can provide haptic feedback when an action request is received, or when the console 110 has performed the requested action and communicated instructions to the input / output interface 140. In some embodiments, an external imaging device 150 can be used to track the input / output interface 140, such as tracking a controller (which can include, for example, an IR light source) or the position or orientation of the user's hand, to determine the user's movement. In some embodiments, the near-eye display 120 can include one or more imaging devices to track the input / output interface 140, such as tracking a controller or the position or orientation of the user's hand, to determine the user's movement.

[0078] The console 110 can provide content to the near-eye display 120 for presentation to the user according to information received from one or more of the external imaging device 150, the near-eye display 120, and the input / output interface 140. In Figure 1In the example shown, the console 110 can include an application store 112, a headset tracking module 114, an artificial reality engine 116, and an eye tracking module 118. Some implementations of the console 110 can include different or additional modules than those described in conjunction with Figure 1 The functions described further below can be distributed among the components of the console 110 in ways different from those described herein.

[0079] In some implementations, the console 110 can include a processor and a non-transitory computer-readable storage medium storing instructions executable by the processor. The processor can include multiple processing units that execute instructions in parallel. The non-transitory computer-readable storage medium can be any memory, such as a hard disk drive, removable memory, or solid-state drive (e.g., flash memory or dynamic random access memory (DRAM)). In various implementations, the modules of the console 110 described in conjunction with Figure 1 can be encoded as instructions in the non-transitory computer-readable storage medium that, when executed by the processor, cause the processor to perform the functions described further below.

[0080] The application store 112 can store one or more applications executed by the console 110. The applications can include a set of instructions that, when executed by the processor, generate content for presentation to the user. The content generated by the applications can respond to input received from the user via eye movements or from the input / output interface 140. Examples of applications can include: game applications, conferencing applications, video playback applications, or other suitable applications.

[0081] The headset tracking module 114 can use slow calibration information from the external imaging device 150 to track the movement of the near-eye display 120. For example, the headset tracking module 114 can use the locator and the model of the near-eye display 120 observed from the slow calibration information to determine the reference point position of the near-eye display 120. The headset tracking module 114 can also use the position information from the fast calibration information to determine the position of the reference point of the near-eye display 120. Additionally, in some implementations, the headset tracking module 114 can use portions of the fast calibration information, slow calibration information, or any combination thereof to predict the future position of the near-eye display 120. The headset tracking module 114 can provide the estimated position or the predicted future position of the near-eye display 120 to the artificial reality engine 116.

[0082] The artificial reality engine 116 may execute applications within the artificial reality system environment 100 and receive position information of the near-eye display 120, acceleration information of the near-eye display 120, velocity information of the near-eye display 120, predicted future positions of the near-eye display 120, or any combination thereof from the head-mounted transceiver tracking module 114. The artificial reality engine 116 may also receive estimated eye position and orientation information from the eye tracking module 118. Based on the received information, the artificial reality engine 116 may determine content to be provided to the near-eye display 120 for presentation to the user. For example, if the received information indicates that the user has looked left, the artificial reality engine 116 may generate content for the near-eye display 120 that reflects the user's eye movement in the virtual environment. Additionally, the artificial reality engine 116 may perform in-application actions on the console 110 in response to an action request received from the input / output interface 140 and provide feedback to the user indicating that the action has been performed. The feedback may be visual or auditory feedback via the near-eye display 120 or tactile feedback via the input / output interface 140.

[0083] The eye tracking module 118 may receive eye tracking data from the eye tracking unit 130 and determine the position of the user's eyes based on the eye tracking data. The position of the eyes may include the orientation, position, or both of the eyes relative to the near-eye display 120 or any of its components. Since the axis of rotation of the eyes changes depending on the position of the eyes in their sockets, determining the position of the eyes in their sockets may allow the eye tracking module 118 to more accurately determine the orientation of the eyes.

[0084] Figure 2 A perspective view of an example of a near-eye display in the form of an HMD device 200 for implementing some of the examples disclosed herein. The HMD device 200 may be part of, for example, a VR system, an AR system, an MR system, or any combination thereof. The HMD device 200 may include a body 220 and a headband 230. Figure 2 The bottom side 223, front side 225, and left side 227 of the body 220 are shown in the perspective view. The headband 230 may have an adjustable or extendable length. There may be sufficient space between the body 220 of the HMD device 200 and the headband 230 to allow a user to mount the HMD device 200 onto the user's head. In various embodiments, the HMD device 200 may include additional, fewer, or different components. For example, in some embodiments, the HMD device 200 may include temple arms and temple tips as shown, for example, below Figure 3 instead of the headband 230.

[0085] The HMD device 200 can present media to a user, the media including virtual and / or augmented views of a physical, real-world environment with computer-generated elements. Examples of media presented by the HMD device 200 can include images (e.g., two-dimensional (2D) or three-dimensional (3D) images), videos (e.g., 2D or 3D videos), audio, or any combination thereof. The images and videos can be presented to each eye of the user by one or more display components ( Figure 2 not shown) enclosed within the body 220 of the HDM device 200. In various embodiments, the one or more display components can include a single electronic display panel or multiple electronic display panels (e.g., one display panel for each eye of the user). Examples of electronic display panels can include, for example, LCD, OLED displays, ILED displays, μLED displays, AMOLED, TOLED, some other display, or any combination thereof. The HMD device 200 can include two eyebox regions.

[0086] In some embodiments, the HMD device 200 can include various sensors (not shown), such as depth sensors, motion sensors, position sensors, and eye-tracking sensors. Some of these sensors can use structured light patterns for sensing. In some embodiments, the HMD device 200 can include an input / output interface for communicating with a console. In some embodiments, the HMD device 200 can include a virtual reality engine (not shown) that is capable of executing applications within the HDM device 200 and receiving depth information, position information, acceleration information, velocity information, predicted future positions, or any combination thereof of the HDM device 200 from various sensors. In some embodiments, the information received by the virtual reality engine can be used to generate signals (e.g., display instructions) for one or more display components. In some embodiments, the HMD device 200 can include locators (not shown, such as locator 126) positioned at fixed locations on the body 220 relative to each other and relative to a reference point. Each locator can emit light detectable by an external imaging device.

[0087] Figure 3 A perspective view of an example of a near-eye display 300 in the form of a pair of glasses for implementing some examples disclosed herein. The near-eye display 300 can be Figure 1 a specific implementation of the near-eye display 120 and can be configured to operate as a virtual reality display, an augmented reality display, and / or a mixed reality display. The near-eye display 300 can include a frame 305 and a display 310. The display 310 can be configured to present content to the user. In some embodiments, the display 310 can include display electronics and / or display optics. For example, as referred to aboveFigure 1 As described for the near-eye display 120, the display 310 may include an LCD display panel, an LED display panel, or an optical display panel (e.g., a waveguide display assembly).

[0088] The near-eye display 300 may also include various sensors 350a, 350b, 350c, 350d, and 350e on or within the frame 305. In some embodiments, the sensors 350a - 350e may include one or more depth sensors, motion sensors, position sensors, inertial sensors, or ambient light sensors. In some embodiments, the sensors 350a - 350e may include one or more image sensors configured to generate image data representing different fields of view in different directions. In some embodiments, the sensors 350a - 350e may be used as input devices to control or affect the display content of the near-eye display 300, and / or to provide an interactive VR / AR / MR experience to a user of the near-eye display 300. In some embodiments, the sensors 350a - 350e may also be used for stereoscopic imaging.

[0089] In some embodiments, the near-eye display 300 may also include one or more illuminators 330 to project light into the physical environment. The projected light may be associated with different frequency bands (e.g., visible light, infrared light, or ultraviolet light) and may be used for various purposes. For example, the illuminator 330 may project light into a dark environment (or an environment with low-intensity infrared light, ultraviolet light, etc.) to assist the sensors 350a - 350e in capturing images of different objects within the dark environment. In some embodiments, the illuminator 330 may be used to project a specific light pattern onto an object within the environment. In some embodiments, the illuminator 330 may be used as a locator, such as the locator 126 described above with respect to Figure 1 the locator 126.

[0090] In some embodiments, the near-eye display 300 may also include a high-resolution camera 340. The camera 340 may capture an image of the physical environment within the field of view. The captured image may be processed by, for example, a virtual reality engine (e.g., Figure 1 the artificial reality engine 116) to add virtual objects to the captured image or modify physical objects in the captured image, and the processed image may be displayed by the display 310 to the user for AR or MR applications.

[0091] Figure 4FIG. 0 shows an example of an optical see-through augmented reality system 400 including a waveguide display according to certain embodiments. The augmented reality system 400 can include a projector 410 and a combiner 415. The projector 410 can include a light source or image source 412 and projector optics 414. In some embodiments, the light source or image source 412 can include one or more micro-LED devices as described above. In some embodiments, the image source 412 can include a plurality of pixels that display virtual objects, such as an LCD display panel or an LED display panel. In some embodiments, the image source 412 can include a light source that generates coherent light or partially coherent light. For example, the image source 412 can include a laser diode, a vertical cavity surface emitting laser, an LED, and / or a micro-LED as described above. In some embodiments, the image source 412 can include a plurality of light sources (e.g., an array of micro-LEDs as described above), each of which emits monochromatic image light corresponding to a primary color (e.g., red, green, or blue). In some embodiments, the image source 412 can include three two-dimensional arrays of micro-LEDs, where each two-dimensional array of micro-LEDs can include micro-LEDs configured to emit light of a primary color (e.g., red, green, or blue). In some embodiments, the image source 412 can include an optical pattern generator, such as a spatial light modulator. The projector optics 414 can include one or more optical components that can condition the light from the image source 412, such as expanding, collimating, scanning, or projecting the light from the image source 412 onto the combiner 415. The one or more optical components can include, for example, one or more lenses, liquid lenses, mirrors, apertures, and / or gratings. For example, in some embodiments, the image source 412 can include one or more one-dimensional arrays or elongated two-dimensional arrays of micro-LEDs, and the projector optics 414 can include one or more one-dimensional scanners (e.g., micromirrors or prisms) configured to scan the one-dimensional array or elongated two-dimensional array of micro-LEDs to generate an image frame. In some embodiments, the projector optics 414 can include a liquid lens (e.g., a liquid crystal lens) having a plurality of electrodes that allows scanning of the light from the image source 412.

[0092] The combiner 415 may include an input coupler 430 for coupling light from the projector 410 into the substrate 420 of the combiner 415. The combiner 415 may transmit light in a first wavelength range, such as visible light from about 400 nm to about 650 nm. The input coupler 430 may include a volume holographic grating, a diffractive optical element (DOE) (e.g., a surface relief grating), an inclined surface of the substrate 420, or a refractive coupler (e.g., a wedge or a prism). For example, the input coupler 430 may include a reflective volume Bragg grating or a transmissive volume Bragg grating. The input coupler 430 may have a coupling efficiency greater than 30%, 50%, 75%, 90% or higher for visible light. The light coupled into the substrate 420 may propagate within the substrate 420 by, for example, total internal reflection (TIR). The substrate 420 may be in the form of a lens of a pair of glasses. The substrate 420 may have a flat or curved surface and may include one or more types of dielectric materials or semiconductor materials, such as glass, quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, silicon, SiN, silicon carbide, ceramic, etc. The thickness of the substrate may be in a range, for example, less than about 1 mm to about 10 mm or greater. The substrate 420 may be transparent to visible light.

[0093] The substrate 420 may include or may be coupled to a plurality of output couplers 440, each output coupler configured to extract at least a portion of the light guided by and propagating within the substrate 420 from the substrate 420 and direct the extracted light 460 to the mobile eye socket 495, in which the eye 490 of a user of the augmented reality system 400 may be positioned when using the augmented reality system 400. The plurality of output couplers 440 may replicate the exit pupil to increase the size of the mobile eye socket 495 such that the displayed image is visible in a larger area. Like the input coupler 430, the output coupler 440 may include a grating coupler (e.g., a volume holographic grating or a surface relief grating), other diffractive optical elements, or a prism. For example, the output coupler 440 may include a reflective volume Bragg grating or a transmissive volume Bragg grating. The output coupler 440 may have different coupling (e.g., diffractive) efficiencies at different locations. The substrate 420 may also allow light 450 from the environment in front of the combiner 415 to pass through with little or no loss. The output coupler 440 may also allow light 450 to pass through with little loss. For example, in some embodiments, the output coupler 440 may have a very low diffractive efficiency for light 450 such that the light 450 may refract or otherwise pass through the output coupler 440 with little loss and may thus have a higher intensity compared to the extracted light 460. In some embodiments, the output coupler 440 may have a high diffractive efficiency for light 450 and the light 450 may be diffracted into certain desired directions (i.e., diffraction angles) with little loss. As a result, the user is able to view a combined image of the environment in front of the combiner 415 and the image of the virtual object projected by the projector 410.

[0094] Figure 5AFIG. 0 shows an example of a near-eye display (NED) device 500 that includes a waveguide display 530 according to some embodiments. The NED device 500 can be an example of a near-eye display 120, an augmented reality system 400, or another type of display device. The NED device 500 can include a light source 510, projection optics 520, and a waveguide display 530. The light source 510 can include a plurality of light emitter panels for different colors, such as a set of red light emitter panels 512, a set of green light emitter panels 514, and a set of blue light emitter panels 516. The red light emitters 512 are organized in an array; the green light emitters 514 are organized in an array; and the blue light emitters 516 are organized in an array. The size and pitch of the light emitters in the light source 510 can be very small. For example, the diameter of each light emitter can be less than 2 μm (e.g., about 1.2 μm), and the pitch can be less than 2 μm (e.g., about 1.5 μm). Thus, the number of light emitters in each of the red light emitters 512, green light emitters 514, and blue light emitters 516 can be equal to or greater than the number of pixels in the display image, such as 960×720, 1280×720, 1440×1080, 1920×1080, 2160×1080, or 2560×1080 pixels. Thus, the display image can be generated simultaneously by the light source 510. Scanning elements may not be used in the NED device 500.

[0095] Before reaching the waveguide display 530, the light emitted by the light source 510 can be conditioned by the projection optics 520 that includes a lens array. The projection optics 520 can collimate or focus the light emitted by the light source 510 onto the waveguide display 530, which can include a coupler 532 for coupling the light emitted by the light source 510 into the waveguide display 530. The light coupled into the waveguide display 530 can propagate within the waveguide display 530, e.g., by total internal reflection as described above with respect to Figure 4 The coupler 532 can also couple a portion of the light propagating within the waveguide display 530 out of the waveguide display 530 and toward the user's eye 590.

[0096] Figure 5BFIG. 0 shows an example of a near-eye display (NED) device 550 that includes a waveguide display 580 according to certain embodiments. In some embodiments, the NED device 550 may use a scanning mirror 570 to project light from a light source 540 onto an image field where a user's eye 590 may be located. The NED device 550 may be an example of a near-eye display 120, an augmented reality system 400, or another type of display device. The light source 540 may include one or more rows, or one or more columns, of light emitters of different colors, such as multiple rows of red light emitters 542, multiple rows of green light emitters 544, and multiple rows of blue light emitters 546. For example, the red light emitters 542, green light emitters 544, and blue light emitters 546 may each include N rows, with each row including, for example, 2,560 light emitters (pixels). The red light emitters 542 are organized into an array; the green light emitters 544 are organized into an array; and the blue light emitters 546 are organized into an array. In some embodiments, the light source 540 may include a single row of light emitters for each color. In some embodiments, the light source 540 may include multiple columns of light emitters for each of red, green, and blue, where each column may include, for example, 1,080 light emitters. In some embodiments, the size and / or pitch of the light emitters in the light source 540 may be relatively large (e.g., about 3 - 5 μm), and thus the light source 540 may not include a sufficient number of light emitters for simultaneously generating a full display image. For example, the number of light emitters for a single color may be less than the number of pixels in a display image (e.g., 2,560 × 1,080 pixels). The light emitted by the light source 540 may be a collection of collimated or divergent light beams.

[0097] Before reaching the scanning mirror 570, the light emitted by the light source 540 may be conditioned by various optical components, such as a collimating lens or a freeform optical element 560. The freeform optical element 560 may include, for example, a multi-faceted prism or another light folding element that may direct the light emitted by the light source 540 toward the scanning mirror 570, such as changing the propagation direction of the light emitted by the light source 540 by, for example, about 90° or more. In some embodiments, the freeform optical element 560 may be rotatable to scan the light. The scanning mirror 570 and / or the freeform optical element 560 may reflect and project the light emitted by the light source 540 onto the waveguide display 580, which may include a coupler 582 for coupling the light emitted by the light source 540 into the waveguide display 580. The light coupled into the waveguide display 580 may propagate within the waveguide display 580, for example, by total internal reflection as described above with respect to Figure 4 The coupler 582 may also couple a portion of the light propagating within the waveguide display 580 out of the waveguide display 580 and toward the user's eye 590.

[0098] The scanning mirror 570 may include a microelectromechanical system (MEMS) mirror or any other suitable mirror. The scanning mirror 570 may rotate to scan in one or two dimensions. When the scanning mirror 570 rotates, the light emitted by the light source 540 can be guided to different areas of the waveguide display 580, such that in each scanning cycle, a complete display image can be projected onto the waveguide display 580 and guided by the waveguide display 580 to the user's eye 590. For example, in an embodiment where the light source 540 includes light emitters for all pixels in one or more rows or one or more columns, the scanning mirror 570 can rotate in the column or row direction (e.g., the x or y direction) to scan the image. In an embodiment where the light source 540 includes light emitters for some but not all pixels in one or more rows or one or more columns, the scanning mirror 570 can rotate in both the row and column directions (e.g., both the x direction and the y direction) to project the display image (e.g., using a raster-type scanning pattern).

[0099] The NED device 550 may operate in a predefined display cycle. The display cycle (e.g., display loop) may refer to the duration of scanning or projecting a complete image. For example, the display cycle may be the reciprocal of the desired frame rate. In the NED device 550 including the scanning mirror 570, the display cycle may also be referred to as the scanning cycle or scanning loop. The light generated by the light source 540 may be synchronized with the rotation of the scanning mirror 570. For example, each scanning cycle may include a plurality of scanning steps, where the light source 540 may generate different light patterns in each respective scanning step.

[0100] In each scanning cycle, as the scanning mirror 570 rotates, the display image can be projected onto the waveguide display 580 and the user's eye 590. The actual color value and light intensity (e.g., brightness) of a given pixel position of the display image may be the average of the light beams of three colors (e.g., red, green, and blue) that illuminate the pixel position during the scanning cycle. After completing the scanning cycle, the scanning mirror 570 may return to the initial position to project the light of the first few rows of the next display image, or may rotate in the opposite direction or scanning pattern to project the light of the next display image, where a new set of drive signals may be supplied to the light source 540. When the scanning mirror 570 rotates in each scanning cycle, the same process can be repeated. Thus, different images can be projected onto the user's eye 590 in different scanning cycles.

[0101] Figure 6Shows an example of the tilted grating 620 in the waveguide display 600 according to some embodiments. The tilted grating 620 can be an example of the input coupler 430, the output coupler 440, the coupler 532, or the coupler 582. The tilted grating 620 can be formed on a waveguide 610 such as the substrate 420. The tilted grating 620 can act as a grating coupler for coupling light into or out of the waveguide 610. In some embodiments, the tilted grating 620 can include a one-dimensional periodic structure with a period p. For example, the tilted grating 620 can include a plurality of ridges 622 and slots 624 between the ridges 622. Each period of the tilted grating 620 can include a ridge 622 and a slot 624, and the slot can be an air gap or region filled with a material having a refractive index n g2 The ratio between the width d of the ridge 622 and the grating period p can be referred to as the duty cycle. The tilted grating 620 can have a duty cycle of, for example, from about 10% to about 90% or greater. In some embodiments, the duty cycle can vary from period to period. In some embodiments, the period p of the tilted grating can vary from one region to another on the tilted grating 620, or can vary from one period to another (i.e., chirped) on the tilted grating 620. In some embodiments, the height of the ridge 622 or the depth of the slot 624 can vary from one region to another on the tilted grating 620, or can vary from one period to another on the tilted grating 620. In some embodiments, the tilted grating 620 can include a two-dimensional grating. In some embodiments, the period p, the duty cycle, the height of the ridge 622, and / or the depth of the slot 624 of the tilted grating 620 can vary along the x direction, the y direction, or both.

[0102] The ridge 622 can be made of a material having a refractive index n g1 such as a silicon-containing material (e.g., SiO 2 , Si 3 N 4 , SiC, SiO x N y or amorphous silicon), an organic material (e.g., spin on carbon (SOC) or amorphous carbon layer (ACL) or diamond like carbon (DLC)), or an inorganic metal oxide layer (e.g., TiO x , AlO x , TaO x or HfO x)。Each ridge 622 may include a leading edge 626 having an inclination angle α and a trailing edge 628 having an inclination angle β. In some embodiments, the leading edge 626 and the trailing edge 628 of each ridge 622 may be parallel to each other. In other words, the inclination angle α is approximately equal to the inclination angle β. In some embodiments, the inclination angle α may be different from the inclination angle β. In some embodiments, the inclination angle α may be approximately equal to the inclination angle β. For example, the difference between the inclination angle α and the inclination angle β may be less than 20%, 10%, 5%, 1% or less. In some embodiments, the inclination angles α and β may be in a range of, for example, about 30° or less to about 60% or more.

[0103] In some embodiments, the grooves 624 between the ridges 622 may be externally coated or filled with an outer coating 630. The outer coating 630 may include a material having a refractive index n g2 higher or lower than the refractive index of the material of the ridges 622. For example, in some embodiments, a high refractive index material (such as hafnium dioxide, titanium dioxide, tantalum oxide, tungsten oxide, zirconium oxide, gallium sulfide, gallium nitride, gallium phosphide, silicon, sol-gel), a high refractive index polymer or a combination thereof may be used to fill the grooves 624. In some embodiments, a low refractive index material (such as silica, alumina, porous silica or a fluorinated low refractive index monomer (or polymer)) may be used to fill the grooves 624. As a result, the difference between the refractive index of the ridges and the refractive index of the grooves may be greater than 0.1, 0.2, 0.3, 0.5, 1.0 or higher. In some embodiments, the top surface of the outer coating 630 may be aligned with the top surface of the ridges 622. In some embodiments, the top surface of the outer coating 630 may be above the top surface of the ridges 622.

[0104] In some embodiments, sol-gel may be used to form an outer coating on a surface relief grating. Sol-gel is a material that may include a solution containing an oxide precursor, which may partially or fully condense into an extended network. After coating and annealing of the sol-gel, the precursor ligands and solvents may be removed to fully condense the extended network into an oxide film. The condensation process may result in densification and, in some cases, crystallization. Thus, when applied to a substrate and annealed, sol-gel can be used to fabricate a high refractive index (RI) coating. Sol-gel can be dispensed as a solution and thus can provide improved processability compared to high RI nanocomposites, which have higher viscosities and reduced material flow. Additionally, since sol-gel does not require the addition of a resin matrix and since annealing can expel all organic and solvent components from the oxide network, sol-gel can also provide the advantage of a high RI coating with improved transparency to visible light compared to nanocomposites that include high RI nanoparticles dispersed in a resin, whose transparency may decrease over time.

[0105] Figure 7A and Figure 7B illustrates the challenges that can be posed by existing sol - gels. Figure 7A illustrates an example of a sol - gel coating 702 of an existing sol - gel material on a flat substrate 701 before and after annealing, where the sol - gel coating 702 can condense and shrink during and after annealing. Figure 7B illustrates a substrate 710 including nano - to - micron - sized recessed features 724 (e.g., having a period of about 100 nm and also referred to hereinafter as "recessed features" 724) and a sol - gel coating 720 on the recessed features 724 before and after annealing. As Figure 7B shown, before annealing, if the thickness of the sol - gel coating 720 is greater than the depth of the recessed features 724, it is possible to fill high - aspect - ratio features (e.g., recessed features 724) with an unannealed film (e.g., the sol - gel coating 720 before annealing). However, after annealing (e.g., the condensation process), voids 730 can form in the recessed features 724 due to the shrinkage of the sol - gel and aggregates that can form nanoparticles or microparticles.

[0106] Figure 8A illustrates a substrate including a sol - gel coating 802 deposited on a substrate 801 before and after annealing, where the sol - gel coating 802 can include a sol - gel material according to certain embodiments disclosed herein. In the example shown, the sol - gel material can include a metal precursor in an initial oxidation state (+n) (e.g., before annealing); one or both of an alkoxide and a halide ligand; and an oxidizing environment that oxidizes a portion of the metal precursor to a second oxidation state (+m) during annealing, thereby producing an amorphous mixture of the same metal in at least two different oxidation states after annealing. The amorphous mixture includes a mixture of oxides and / or halide ligands. The sol - gel material can include a mixture in which the oxidizing species is molecular oxygen, hydrogen peroxide, an alcohol, an alkoxide, or a diol. After annealing, the sol - gel material can include a condensed mixture of metals in different oxidation states, where the metals in different oxidation states can be transparent in the presence of one or both of an alkoxide and a halide ligand.

[0107] Figure 8BShows a substrate 810 including nano- to micro-scale recessed features 824 (e.g., having a period of about 100 nm and also referred to hereinafter as "recessed features" 824) and a sol-gel coating 820 on the recessed features before annealing (e.g., sol-gel coating 820-1) and after annealing (e.g., sol-gel coating 820-2), wherein the sol-gel coating 820 can include a sol-gel material according to certain embodiments disclosed herein (e.g., Figure 8A as shown). By producing a mixture of the same metal with multiple oxidation states, where all oxidation states of the metal are transparent and in the case where the mixture includes oxide and / or halide ligands, an amorphous state without any distinct domain formation (e.g., in sol-gel coating layer 820-2) can be obtained, which would otherwise locally distribute stress and cause voids within the nanogrid. This makes it possible to obtain a highly condensed state of the sol-gel with an RI value in the range of 1.7 - 2.2 without sacrificing recessed feature filling.

[0108] In some embodiments, a tin(II) precursor including a halide ligand can be dissolved in an alcohol or a diol. Upon annealing, the tin(II) mixture is partially oxidized to tin(IV). Both tin(II) and tin(IV) oxides or oxohalides are transparent to visible light, and the mixture of the two oxidation states is also transparent. Additionally, regardless of the degree of condensation, the mixture of tin(II) and tin(IV) oxides or oxohalides can be condensed to produce an amorphous coating with an RI value between about 1.7 and about 2.2 without forming discrete domains. The tin(II):tin(IV) ratio can be maintained in the range of about 1:5 to about 4:1 to achieve an RI value in the range of about 1.7 to about 2.2 without causing a loss of recessed feature filling ability. Advantageously, the condensation process of the tin(II) / tin(IV) mixture can be carried out at a temperature below about 300 °C.

[0109] In some embodiments, the sol-gel solution can include at least one tin(II) halide precursor, where the solvent can include one or more alcohols or diols, an optional secondary oxo-donor (such as hydrogen peroxide), and an optional tin(II) stabilizer. In some embodiments, the solution can also contain acids, bases, and / or surfactants. The solvent type or solvent mixture can be adjusted to produce a coating with an RI value between 1.7 and 2.2 after annealing. In some embodiments, the sol-gel material can be coated onto a substrate by applying a solution comprising the sol-gel material to the substrate via spin coating, dip coating, spray coating, inkjet printing, screen printing, or contact printing, and then the substrate with the sol-gel material can be thermally annealed via at least one thermal annealing stage (e.g., annealing at an annealing temperature below 300°C). By applying the sol-gel material disclosed herein, any recessed features (e.g., recessed features of nanometer or micrometer size) in the substrate can be coated in a superconformal and void-free manner even after the film formed from the sol-gel material is fully dense. Specifically, the film is in an amorphous state throughout the condensation process.

[0110] In some embodiments, the sol-gel material can include at least one metal halide precursor and at least one alcohol, and the metal halide is used to form a superconformal optical coating on a surface having nanometer-sized recessed features. Upon thermal annealing, the sol-gel material can produce a metal oxychloride coating, where the metal exists in at least two different oxidation states. After annealing, the resulting sol-gel coating can have a non-stoichiometric oxychloride composition. In some embodiments, in the resulting sol-gel coating, the mixture of different oxidation states of the metal oxychloride is transparent to visible light (e.g., having an absorption rate of <0.1% / 100 nm). In some embodiments, during thermal curing (e.g., annealing), the solvent of the sol-gel material can at least partially act as a source of oxide ligands. Specifically, in the sol-gel material, the metal halide source can be tin(II) chloride. In some embodiments, after the annealing process, the ratio of tin(II) to tin(IV) in the sol-gel material is between 1:5 and 4:1. The ratio can be adjusted by controlling the annealing temperature, solvent consistency, and / or solvent mixture. After the annealing process, the condensed coating is in an amorphous state.

[0111] In some embodiments, when a sol-gel material is coated onto a substrate having recessed features, annealing can be performed at a temperature not higher than 300 °C for less than 10 minutes to obtain a coating with an RI of 1.7 - 2.2. After the annealing process, the sol-gel material can fill the recessed features on the substrate in a superconformal manner without causing voids. In some embodiments, the sol-gel material can optionally include stabilizers, acids, bases, peroxides, surfactants, crosslinkers, toughening agents and toughening agent additives, and / or solvents. In some embodiments, the stabilizer additive can optionally be one of ethanolamine, diethanolamine, triethanolamine, fatty amines, diamines, triamines or polyamines. In some other embodiments, the stabilizer additive can be one or a mixture of organic antioxidants or inorganic antioxidants. In some embodiments, the solvent additive of the sol-gel material can optionally be one or a mixture of the following: propylene glycol monomethyl ether (PGME), dipropylene glycol monomethyl ether (DPGME), propylene glycol methyl ether acetate, tripropylene glycol monomethyl ether, butyl lactate, propylene carbonate, isopropyl alcohol (e.g., 1,3-dimethoxy-2-propanol), methanol and water.

[0112] According to certain embodiments, the method can include applying a sol-gel material made by dissolving or suspending at least one metal chloride precursor in a solvent including at least one alcohol onto a substrate having recessed features, annealing the sol-gel material at a temperature not higher than 300 °C to produce a mixed-valence metal chlorooxide, and achieving superconformal filling of the recessed features with the sol-gel material. In some embodiments, annealing can be performed in a single stage or multiple stages, wherein the single-stage or multi-stage annealing can have an annealing temperature not higher than 300 °C and a total annealing time not longer than 10 minutes. When the sol-gel material is applied to the substrate to superconformally fill the recessed features in the substrate, the recessed features can be gratings, trenches, vias and / or through-holes, with a feature width of 5 - 200 nm and an aspect ratio width:depth of 1:1.5 to 1:50. The final thickness of the coating on the top surface of the coated substrate can be less than 50 nm, and the recessed features can be completely filled with the annealed sol-gel material in a void-free manner. In some embodiments, the sol-gel material can be applied to the substrate to form an optical coating via spin coating, dip coating, spraying, inkjet printing, screen printing or contact printing. The cured (e.g., annealed) sol-gel coating (e.g., the film layer formed from the sol-gel material) can have an RI between 1.65 - 2.20 and a visible light absorption rate of less than 0.1% / 100 nm after coating densification.

[0113] Examples

[0114] I. Comparative Examples 1 - 3

[0115] Figure 9A Show the material compositions and properties of Comparative Examples 1 - 3. Figure 9B Show cross - sectional views (e.g., via SEM) of embodiments of surface relief gratings with coatings formed in Comparative Examples 1 - 3 under a microscope. As Figure 9A and Figure 9B shown, in Comparative Example 1, titanium(IV) chloride was dissolved in DPGME solvent. The resulting sol - gel was coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano - sized trenches 15 to 100 nm wide and 220 nm deep. Then the substrate was annealed at 150 °C, and the sol - gel coating thickness and RI were measured by ellipsometry. As Figure 9A shown, the RI of the film was found to be 1.64. In addition, a cross - section of the substrate was drawn, and the quality of the trenches filled with the sol - gel was determined via SEM. It was found that the sol - gel did not fill the trenches completely. Instead, the trenches were only partially filled and contained voids. More specifically, regardless of the low condensation level corresponding to the RI value of 1.64, the sol - gel seemed to include aggregates of particles. This result indicates that traditional sol - gel materials cannot remain non - particulate throughout the annealing process, which is related to the inability to achieve super - conformal filling of nano - sized features. In addition, titanium(IV) can be used without forming a mixture with other titanium oxidation states because other available titanium oxidation states are unstable under ambient conditions or are colored in the visible spectrum.

[0116] In Comparative Example 2, hafnium(IV) chloride was dissolved in DPGME solvent. The resulting sol - gel was coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano - sized trenches 15 to 100 nm wide and 220 nm deep. Then the substrate was annealed at 150 °C, and the sol - gel coating thickness and RI were measured by ellipsometry. As Figure 9A shown, the RI of the film was found to be 1.57. In addition, a cross - section of the substrate was drawn, and the quality of the trenches filled with the sol - gel was determined via SEM. It was found that the sol - gel did not fill the trenches completely. Instead, the trenches were only partially filled and contained voids. More specifically, regardless of the low condensation level corresponding to the RI value of 1.57, the sol - gel seemed to include aggregates of particles. This result indicates that traditional sol - gel materials cannot remain non - particulate throughout the annealing process, which is related to the inability to achieve super - conformal filling of nano - sized features. In addition, hafnium(IV) can be used without forming a mixture with other hafnium oxidation states because other available hafnium oxidation states are unstable under ambient conditions or are colored in the visible light spectrum.

[0117] In Comparative Example 3, niobium(V) pentachloride was dissolved in the DPGME solvent. The resulting sol-gel was coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano-sized trenches that were 15 to 100 nm wide and 220 nm deep. The substrate was then annealed at 150 °C, and the sol-gel coating thickness and RI were measured by ellipsometry. As Figure 9A shown, the RI of the film was found to be 1.72. In addition, a cross-section of the substrate was drawn, and the quality of the trenches filled with the sol-gel was determined via SEM. It was found that the sol-gel did not fill the trenches. Instead, the trenches were only partially filled and contained voids. More specifically, regardless of the low condensation level corresponding to the RI value of 1.72, the sol-gel appeared to include aggregates of particles. This result indicates that conventional sol-gel materials cannot remain non-particulate throughout the annealing process, which is related to the inability to achieve superconformal filling of nano-sized features. In addition, niobium(V) can be formed without mixing with other niobium oxidation states because the other available titanium oxidation states are unstable under ambient conditions or are colored in the visible light spectrum.

[0118] II. Working Examples 4-10

[0119] Figure 10A shows the material compositions and properties of Working Examples 4-10, and Figure 10B shows cross-sectional views under a microscope (e.g., SEM) of surface relief gratings with superconformal overcoats formed in Working Examples 4-10 according to certain embodiments. Working Examples 4-10 reveal the relationship between the RI of the coating (e.g., RI between 1.6 - 2.2) and the annealing temperature.

[0120] In Working Examples 4-10, tin(II) dichloride was dissolved in DPGME to achieve a final mass concentration of 10% tin(II) chloride, as Figure 10A shown. The resulting sol-gel was coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano-sized trenches that were 15 to 100 nm wide and 220 nm deep. The substrate was then annealed in the temperature range of 80 - 200 °C, and the thickness and RI of the sol-gel coating were measured by ellipsometry. As Figure 10AAs shown, it was found that the RI of the film varied between 1.59 and 2.12, and the shrinkage of the film increased with increasing annealing temperature. In addition, cross-sections were drawn of the substrate, and the quality of the sol-gel filling of the trenches was determined via SEM. It was found that the sol-gel coating completely penetrated all the trenches and remained within the trenches after annealing and shrinkage. Even in the case of Examples 9-10, where the final coating shrank below the top surface of the nanogratings, the sol-gel still exhibited a superconformal bottom-up filling behavior. Finally, the sol-gel was coated on a fused silica substrate. The substrate was then annealed in the temperature range of 80-200 °C, and the absorbance of the sol-gel coating was measured via spectrophotometry. It was found that in all cases, the absorbance of the film remained less than 0.1%. Overall, these results show that tin(II) precursors containing halide and alcohol ligands can be used to form highly transparent, high-RI coatings with the ability to fill recessed features.

[0121] III. Working Examples 11-12

[0122] Figure 11 Shows the material compositions and properties of Working Examples 11-12 according to certain embodiments. In Working Examples 11-12, stannous dichloride (II) was dissolved in DPGME to achieve a final mass concentration of 10% stannous chloride (II), as Figure 11 shown. The resulting sol-gel was coated on a fused silica substrate. The substrate was then annealed at a temperature of 150 °C or 185 °C. The crystallinity of the coating was determined via X-ray diffraction (XRD). As Figure 11 shown, it was found that neither annealing temperature resulted in any measurable crystallinity. This is consistent with the SEM data of Experiments 8 and 9, in which the sol-gel deposits appeared continuous and amorphous. In addition, the composition of the sol-gel coating was studied via surface X-ray photoelectron spectroscopy (XPS). It was found that in both cases, the material was tin oxychloride with a mixed tin(II) / tin(IV) oxidation state. As Figure 11 shown, the ratio of Sn(II) increased with increasing temperature, which is consistent with the Figure 10A observation that the RI measured in

[0123] IV. Working Examples 13 - 17

[0124] Figure 12A shows the material compositions and properties of Working Examples 13 - 17, and Figure 12B shows an example of a surface relief grating having a superconformal outer coating formed in Working Examples 13 - 15 and a coating formed in Working Examples 16 - 17 in a cross-sectional view under a microscope (e.g., via SEM). In Working Examples 13 - 15, stannous chloride (II) was dissolved in isopropyl alcohol, diethylene glycol, or propylene glycol methyl ether to achieve a final mass concentration of 10% stannous chloride (II), as Figure 12A shown. The resulting sol - gel was coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano-sized trenches that were 15 to 100 nm wide and 220 nm deep. The substrate was then annealed at a temperature of 200 °C, and the RI of the sol - gel was measured via ellipsometry. It was found that the RI varied depending on the solvent selected. The choice of solvent could change the balance between the stannous (II) and stannic (IV) contents, as well as the ability of the solvent to act as an oxygen donor, thereby changing the degree of densification experienced by the film. In addition, cross-sections of the substrate were drawn, and the quality of the trenches filled with the sol - gel was determined via SEM. It was found that the sol - gel coating completely penetrated into all the trenches and remained within the trenches after annealing and shrinkage. All the sol - gel deposits appeared continuous and amorphous. Overall, these results indicate that it is possible to vary the solvent in order to tune the composition and optical properties of the resulting sol - gel coating without sacrificing the ability to fill recessed features.

[0125] In Working Examples 16 - 17, stannous chloride (II) was dissolved in dipropylene glycol butyl ether or diethylene glycol methyl ether to achieve a final mass concentration of 10% stannous chloride (II), as Figure 12AAs shown. The resulting sol-gel was coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano-sized trenches that were 15 to 100 nm wide and 220 nm deep. The substrate was then annealed at a temperature of 200 °C, and the RI of the sol-gel was measured via ellipsometry. It was found that the RI varied depending on the solvent selected, with non-alcoholic diethylene glycol methyl ether producing the highest RI in the set. The choice of solvent can alter the balance between the tin(II) and tin(IV) contents, and non-alcoholic solvents can reduce its oxidation ability, thus increasing the tin(II) content and the resulting RI. In addition, cross-sections of the substrate were drawn, and the quality of the trenches filled with the sol-gel was determined via SEM. It was found that the sol-gel did not fill the trenches completely. Instead, the trenches were only partially filled and contained voids. More specifically, the sol-gel deposits appeared to consist of aggregates of particles. These results show that the choice of solvent has a significant impact on controlling the tin(II) / tin(IV) ratio, altering the composition and densification of the film, and maintaining the amorphous continuous state that is crucial for filling recessed features.

[0126] V. Working Examples 18 - 20

[0127] Figure 13 Shows the material compositions and properties of Working Examples 18 - 20 according to certain embodiments. In Working Examples 18 - 20, stannous chloride (II) was dissolved in propylene glycol methyl ether to achieve a final mass concentration of 10% tin(II) chloride, as Figure 13 shown. The resulting sol-gel was coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano-sized trenches that were 15 to 100 nm wide and 220 nm deep. The substrate was then annealed at a temperature of 120 °C, 200 °C, or via a dual annealing scheme that included an initial temperature of 120 °C and a second temperature of 250 °C. The RI of the sol-gel was then measured via ellipsometry. It was found that the final RI varied depending on the annealing scheme. Specifically, it was found that the dual-annealed samples had a RI more similar to that of the single 120 °C annealed samples compared to the single 250 °C annealed samples. The initial annealing can control the ratio of tin(II) to tin(IV) and the content of oxides and chlorides. Thus, the subsequent annealing at a higher temperature follows a different condensation path compared to a film annealed directly at the same higher temperature. In addition, cross-sections of the substrate were drawn, and the quality of the trenches filled with the sol-gel was determined via SEM. It was found that the sol-gel coating completely penetrated all the trenches and remained within the trenches after annealing and shrinkage. All the sol-gel deposits appeared continuous and amorphous. Overall, these results show that it is possible to vary the annealing scheme in order to regulate the composition and optical properties of the resulting sol-gel coating without sacrificing the ability to fill recessed features.

[0128] VI. Working Examples 21 - 22

[0129] Figure 14 The material compositions and properties of Working Examples 21 - 22 according to certain embodiments are shown. In Working Examples 21 - 22, stannous chloride (II) and monoethanolamine were dissolved in dipropylene glycol methyl ether to achieve final concentrations of 10% and 1% by mass, respectively, as Figure 14 shown. The resulting sol - gel was stored in a refrigerator at - 20 °C for 1 week and then coated on a silicon substrate that had been cleaned with oxygen plasma. The substrate contained nano - sized trenches that were 15 to 100 nm wide and 220 nm deep. The substrate was then annealed at a temperature of 150 or 200 °C. Then the RI of the sol - gel was measured via ellipsometry. It was found that the ethanolamine stabilizer had little effect on the RI, but RI values significantly higher than 2.0 were still obtained. In addition, cross - sections of the substrate were drawn and the quality of the trenches filled with the sol - gel was determined via SEM. It was found that the sol - gel coating completely penetrated all the trenches and remained in the trenches after annealing and shrinkage. All the sol - gel deposits were continuous and amorphous. Finally, the sol - gel was coated on a fused silica substrate. The substrate was then annealed at a temperature of 150 °C or 200 °C and the absorbance of the sol - gel coating was measured via spectrophotometry. It was found that in both cases, the absorbance of the film remained less than 0.1%. Overall, these results indicate that stabilizers can be added to the sol - gel to maintain optical and recess - filling characteristics over time.

[0130] It should be understood that the compositions of the sol - gel materials described above, such as with respect to Figure 8A 、 Figure 8B and Figures 10A - 14 , are for illustrative purposes only. Other suitable compositions may also be used. For example, the sol - gel material may include any tin salt disclosed herein in an amount of 10% - 30% by weight, and any suitable solvent mixture disclosed herein in an amount of 70% - 90% by weight.

[0131] In some embodiments, in addition to or as an alternative to the tin salts disclosed above, the tin salts may further include stannous chloride dihydrate and / or anhydrous stannous chloride. In addition to or as an alternative to the solvent mixture disclosed above, the solvent mixture may include from about 17% to 37% by weight of propylene glycol methyl ether, from about 57% to 77% by weight of 1,3-dimethoxy-2-propanol, and from about 1% to 11% by weight of diethylene glycol. Alternatively, the solvent mixture may include from about 17% to 37% by weight of propylene glycol methyl ether, from about 57% to 77% by weight of di(propylene glycol) methyl ether, and from about 1% to 11% by weight of diethylene glycol. Alternatively, the solvent mixture may include about 100% by weight of 1,3-dimethoxy-2-propanol.

[0132] Embodiments of the present invention may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some way before being presented to a user, and may include, for example, virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and / or derivative thereof. Artificial reality content may include fully generated content or content generated in combination with captured (e.g., real-world) content. Artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of these may be presented in a single channel or in multiple channels (such as stereoscopic video that produces a three-dimensional effect for a viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof for creating content in artificial reality and / or otherwise for use in artificial reality (e.g., to perform activities therein). An artificial reality system that provides artificial reality content may be implemented on a variety of platforms, including a head-mounted display (HMD) connected to a host computer system, a stand-alone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0133] The methods, systems, and devices discussed above are examples. Various embodiments may appropriately omit, replace, or add various procedures or components. For example, in alternative configurations, the described methods may be performed in a different order than described, and / or various stages may be added, omitted, and / or combined. Additionally, features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of embodiments may be combined in a similar manner. Further, technology is evolving, and thus many elements are embodiments that do not limit the scope of the present disclosure to those specific examples.

[0134] Specific details are given in the description to provide a thorough understanding of the embodiments. However, the embodiments may be practiced without these specific details. For example, well-known circuits, processes, systems, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the embodiments. This specification merely provides example embodiments and is not intended to limit the scope, applicability, or configuration of the invention. Instead, the foregoing description of the embodiments will provide those skilled in the art with an enabling description for implementing various embodiments. Various changes may be made to the functionality and arrangement of the elements without departing from the scope of the disclosure defined in the appended claims.

[0135] In addition, some embodiments are described as processes depicted as flowcharts or block diagrams. Although each may describe the operations as a sequential process, multiple operations may be performed in parallel or simultaneously. In addition, the order of the operations may be rearranged. A process may have additional steps not included in the figures. Moreover, embodiments of the method may be implemented by hardware, software, firmware, middleware, microcode, hardware description language, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments for performing the associated tasks may be stored in a computer-readable medium such as a storage medium. The processor may execute the associated tasks.

[0136] It will be apparent to those skilled in the art that substantial variations may be made in accordance with specific requirements. For example, customized or special-purpose hardware may also be used, and / or specific elements may be implemented in hardware, software (including portable software such as applets), or both. In addition, connections to other computing devices (such as network input / output devices) may be used.

[0137] Referring to the accompanying drawings, components that may include a memory may include a non-transitory machine-readable medium. As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any storage medium that participates in providing data that causes a machine to operate in a particular manner. In the embodiments provided above, various machine-readable media may be involved in providing instructions / code to a processing unit and / or other devices for execution. Additionally or alternatively, a machine-readable medium may be used to store and / or carry such instructions / code. In many embodiments, a computer-readable medium is a physical and / or tangible storage medium. Such a medium may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Common forms of computer-readable media include, for example, magnetic and / or optical media, such as a compact disk (CD) or a digital versatile disk (DVD), punched cards, paper tapes, any other physical medium with hole patterns, RAM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), FLASH-EPROM, any other memory chip or cartridge tape, a carrier wave described below, or any other medium from which a computer can read instructions and / or code. A computer program product may include code and / or machine-executable instructions that may represent steps, functions, subroutines, programs, routines, applications (Apps), subroutines, modules, software packages, classes, or any combination of instructions, data structures, or program statements.

[0138] Those skilled in the art will appreciate that any of a variety of different technologies and techniques may be used to represent the information and signals for conveying the messages described herein. For example, throughout the above description, data, instructions, commands, information, signals, bits, symbols, and chips may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0139] As used herein, the terms "and" and "or" can have a variety of meanings, and it is contemplated that these meanings will depend at least in part on the context in which these terms are used. Typically, "or" when used in a related list, such as A, B, or C, means A, B, and C (used herein in an inclusive sense) as well as A, B, or C (used herein in an exclusive sense). In addition, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in the singular, or it can be used to describe some combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example, and the claimed subject matter is not limited to such examples. In addition, if used in a related list, such as A, B, or C, the term "at least one" can be interpreted to mean A, B, C, or a combination of A, B, and / or C, such as AB, AC, BC, AA, ABC, AAB, or AABBCCC.

[0140] In addition, although specific combinations of hardware and software have been used to describe particular embodiments, it should be recognized that other combinations of hardware and software are possible. Some embodiments can be implemented only in hardware, or only in software, or using a combination thereof. In one example, the software can be implemented with a computer program product that includes computer program code or instructions that can be executed by one or more processors to perform any or all of the steps, operations, or processes described in this disclosure, where the computer program can be stored on a non-transitory computer-readable medium. The various processes described herein can be implemented in any combination on the same processor or different processors.

[0141] Where a device, system, component, or module is described as being configured to perform a particular operation or function, such configuration can be achieved, for example, by designing an electronic circuit to perform the operation, by programming a programmable electronic circuit (such as a microprocessor) to perform the operation, such as by executing computer instructions or code, or a processor or core programmed to execute code or instructions stored on a non-transitory storage medium, or any combination thereof. Processes can communicate using a variety of techniques, including but not limited to conventional techniques for inter-process communication, and different pairs of processes can use different techniques, or the same pair of processes can use different techniques at different times.

[0142] Accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive. However, it is apparent that additions, subtractions, deletions, and other modifications and changes can be made without departing from the broader scope set forth in the claims. Thus, although specific embodiments have been described, these are not intended to be limiting. Various modifications and equivalent means are within the scope of the appended claims.

Claims

1. A sol-gel material, the sol-gel material comprises: a metal halide precursor and at least one alcohol and diol, wherein the metal halide precursor comprises a source of tin(II) dichloride dihydrate.

2. The sol-gel material according to claim 1, wherein, the sol-gel material further comprises a solvent that serves as a source of oxide ligands during the annealing process.

3. The sol-gel material according to claim 1 or claim 2, wherein: after applying an annealing process to the sol-gel material, the sol-gel material comprises at least two different oxidation states of the metal in the metal halide precursor; the at least two different oxidation states of the metal are both transparent to visible light; optionally, wherein after applying the annealing process to the sol-gel material, the oxychloride composition of the sol-gel material is non-stoichiometric; optionally, wherein the metal comprises tin, and wherein the at least two different oxidation states of the metal comprise tin(II) and tin(IV).

4. The sol-gel material according to any one of the preceding claims, the sol-gel material further comprises a stabilizer, an acid, a base, a peroxide, a surfactant, a crosslinker, a solvent, or a combination thereof.

5. The sol-gel material according to claim 4, wherein, the stabilizer comprises ethanolamine, diethanolamine, triethanolamine, fatty amine, diamine, triamine, polyamine, or a combination thereof.

6. The sol-gel material according to claim 5, wherein, the stabilizer comprises an organic antioxidant, an inorganic antioxidant, or a combination thereof.

7. The sol-gel material according to any one of the preceding claims, wherein, the sol-gel material further comprises a solvent, the solvent comprises propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol methyl ether acetate, tripropylene glycol monomethyl ether, butyl lactate, propylene carbonate, isopropanol, methanol, water, or a combination thereof.

8. The sol-gel material according to claim 7, wherein, the isopropanol is 1,3-dimethoxy-2-propanol.

9. The sol-gel material according to any one of the preceding claims, wherein, the sol-gel material comprises: 10% - 30% by weight of a tin salt; and 70% - 90% by weight of a solvent mixture; optionally, wherein the tin salt comprises: tin(II) chloride; tin(II) dichloride dihydrate; anhydrous tin(II) chloride; or any combination thereof; optionally, wherein the solvent mixture comprises: 27% by weight of propylene glycol monomethyl ether, 67% by weight of 1,3-dimethoxy-2-propanol, and 6% by weight of diethylene glycol; 27% by weight of propylene glycol monomethyl ether, 67% by weight of di(propylene glycol) methyl ether, and 6% by weight of diethylene glycol; or 100% by weight of 1,3-dimethoxy-2-propanol.

10. A sol-gel material, the sol-gel material comprises: 10% - 30% by weight of a tin salt; and 70% - 90% by weight of a solvent mixture; optionally, wherein the tin salt comprises: Tin(II) chloride; Tin dichloride dihydrate; Anhydrous tin dichloride; or Any combination thereof; wherein the solvent mixture comprises: 27% by weight of propylene glycol methyl ether, 67% by weight of 1,3-dimethoxy-2-propanol, and 6% by weight of diethylene glycol; 27% by weight of propylene glycol methyl ether, 67% by weight of di(propylene glycol) methyl ether, and 6% by weight of diethylene glycol; or 100% by weight of 1,3-dimethoxy-2-propanol.

11. A sol-gel material, the sol-gel material comprises: 10%-30% by weight of a tin salt; and 70%-90% by weight of a solvent mixture; Optionally, wherein the tin salt comprises: Tin(II) chloride; Tin dichloride dihydrate; Anhydrous tin dichloride; or Any combination thereof; wherein the solvent mixture comprises: Approximately 17%-37% by weight of propylene glycol methyl ether, approximately 57%-77% by weight of 1,3-dimethoxy-2-propanol, and approximately 1%-11% by weight of diethylene glycol.

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