PATENT DOCUMENT

Publication Number: US-11714212-B1
Application Number: US-202117472454-A
Country: US
Kind Code: B1

Title: Conformal optical coatings for non-planar substrates

Abstract:
Optical coatings for curved or non-planar substrates are disclosed. Optical coatings may include AR (antireflection) coatings or absorbing (“black” optical) coatings. The optical coatings may include a nanostructure layer formed on top of a stack of one or more materials. Both the nanostructure layer and the stack may be deposited on a curved or non-planar substrate using plasma-enhanced atomic layer deposition (PEALD) to provide conformal coating of the substrate. The nanostructure layer may include a mixture of aluminum hydroxide and aluminum oxide hydroxide that is formed by placing a PEALD-deposited aluminum oxide layer in heated deionized water for a predetermined time period. The materials in the stack may be alternated to provide tuning of the optical properties in the optical coating.

Claims:
What is claimed is: 
     
       1. An antireflection optical device, comprising:
 a curved, polymeric substrate; and 
 an antireflection coating formed on a surface of a curved portion of the curved, polymeric substrate, wherein the antireflection coating includes:
 at least one conformal dielectric layer formed on the curved portion of the substrate, wherein each conformal dielectric layer is formed by atomic layer deposition, and wherein the at least one conformal dielectric layer includes a first dielectric layer and a second dielectric layer, and wherein the first dielectric layer has a first index of refraction and the second dielectric layer has a second index of refraction, the first index of refraction being different than the second index of refraction; and 
 an aluminum oxide nanostructure formed directly on a surface of the at least one conformal dielectric layer most distal from the substrate, wherein the aluminum oxide nanostructure includes a mixture of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide. 
 
 
     
     
       2. The device of  claim 1 , wherein the antireflection coating has an average reflectance of at most about 0.05% in a wavelength range of 400 nm to 700 nm at an angle of incidence between 0° and 30° across the surface of the curved, polymeric substrate. 
     
     
       3. The device of  claim 1 , wherein the mixture of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide includes a mixture of Boehmite, Gibbsite, and Bayerite. 
     
     
       4. The device of  claim 1 , wherein the mixture of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide includes crystalline polymorphs of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide. 
     
     
       5. The device of  claim 4 , wherein the crystalline polymorphs include orthorhombic, hexagonal, or monoclinic crystalline structures. 
     
     
       6. The device of  claim 1 , wherein the at least one conformal dielectric layer includes silicon dioxide. 
     
     
       7. The device of  claim 1 , wherein the first index of refraction has a difference of at least about 0.5 from the second index of refraction. 
     
     
       8. An antireflection optical device, comprising:
 a curved, polymeric substrate; 
 at least one dielectric layer formed on a curved portion of the curved, polymeric substrate, wherein each dielectric layer is formed using atomic layer deposition; 
 an adhesion layer between the at least one dielectric layer and the curved, polymeric substrate; and 
 a nanostructure of aluminum oxide formed directly on a surface of the at least one dielectric layer furthest from the substrate, wherein the nanostructure is formed from a layer of aluminum oxide deposited on the at least one dielectric layer that is placed in a heated water-based fluid with a temperature of at least about 50° C. for a time of at least about 5 minutes. 
 
     
     
       9. The device of  claim 8 , wherein the curved, polymeric substrate is an optical lens. 
     
     
       10. The device of  claim 8 , wherein the curved, polymeric substrate has a minimum angle of curvature of at least about 20 degrees on at least a portion of a surface of the substrate. 
     
     
       11. The device of  claim 8 , wherein the at least one dielectric layer includes at least two dielectric layers with at least two different indices of refraction. 
     
     
       12. The device of  claim 8 , wherein the nanostructure is formed from a single layer of aluminum oxide deposited on the at least one dielectric layer using atomic layer deposition. 
     
     
       13. An antireflection optical device, comprising:
 a curved, polymeric substrate; and 
 an antireflection coating formed on a surface of a curved portion of the curved, polymeric substrate, wherein the antireflection coating includes:
 at least one conformal dielectric layer formed on the curved portion of the substrate, wherein each conformal dielectric layer is formed by atomic layer deposition; and 
 an aluminum oxide nanostructure formed directly on a second surface of the at least one dielectric layer that is most distal from the substrate; 
 wherein the antireflection coating has an average reflectance of at most about 0.05% in a wavelength range of 400 nm to 700 nm at an angle of incidence between 0° and 30° across the surface of the curved, polymeric substrate. 
 
 
     
     
       14. The device of  claim 13 , wherein the aluminum oxide nanostructure includes a mixture of Boehmite, Gibbsite, and Bayerite. 
     
     
       15. The device of  claim 13 , wherein the aluminum oxide nanostructure includes a mixture of crystalline polymorphs of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide. 
     
     
       16. The device of  claim 13 , wherein the curved, polymeric substrate is an optical lens. 
     
     
       17. The device of  claim 13 , wherein the at least one dielectric layer includes at least two dielectric layers with at least two different indices of refraction. 
     
     
       18. The device of  claim 13 , wherein the curved, polymeric substrate has a minimum angle of curvature of at least about 20 degrees on at least a portion of a surface of the substrate.

Description:
PRIORITY CLAIM 
     This application claims the benefit of U.S. Provisional Application No. 63/078,269, filed on Sep. 14, 2020, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments described herein relate to optical coatings. More particularly, embodiments described herein relate to antireflection coatings or absorbing coatings for curved or non-planar substrates such as optical lenses. 
     Description of the Related Art 
     Antireflection (AR) coatings are coated on lenses in many optical devices to reduce reflection on the optical lenses. Reducing the reflection on the optical lenses may improve efficiency of the optical device by reducing light loss due to reflection. An AR coating for a visible range optical lens (e.g., an optical lens used in a visible wavelength range) is typically a multilayer interference coating made of dielectric materials such as inorganic oxides, inorganic fluorides, and/or inorganic nitrides. Such a typical AR coating may be formed by alternating a first material with a high refractive index with a second material with a low refractive index. Examples of high refractive index materials include titanium dioxide (TiO 2 ), niobium oxide (Nb 2 O 5 ), tantalum oxide (Ta 2 O 5 ), zirconium oxide (ZrO 2 ), hafnium oxide (HfO 2 ), and silicon nitride (Si 3 N 4 ). Examples of low refractive index materials include aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), and magnesium fluoride (MgF 2 ). Performance of the AR coating may be dependent on the refractive index of the low refractive index material, especially in the visible range. For example, magnesium fluoride has a low refractive index of 1.38 at 550 nm, which limits the reflectance achievable for visible range AR coatings. 
     Absorbing coatings (which may be referred to as “black” optical coatings”) are non-transparent, non-reflective coatings for surfaces in optical devices. Absorbing coatings may be used on surfaces to prevent glare or other light reflection from interfering with the transmission of light through optical devices. For example, absorbing coatings may be placed on stainless steel surfaces in optical devices to prevent reflection from the stainless steel material. An absorbing coating may have a multilayer interference structure that is similar in structure to an AR coating where the structure includes absorbing materials along with transparent materials. Absorbing materials may include, for example, titanium, tantalum, or silicon-based materials with high absorption in the visible wavelength range. Specific examples of absorbing materials include, but are not limited to, silicon hydride (SiH), titanium nitride (TiN), and titanium aluminum nitride (TiAlN). Transparent materials that may be used in the multilayer interference structure include, but are not limited to, dielectric materials such as silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 ), and aluminum oxide (Al 2 O 3 ). Performance of the absorption coating may be dependent on the absorption properties of the absorbing materials. 
     SUMMARY 
     To provide an optical coating (such as an antireflection (AR) coating) on a curved, polymeric substrate, a conformal coating of dielectric materials is formed on the substrate using atomic layer deposition. The conformal coating may include multiple layers of dielectric material with a top layer of aluminum oxide. In some embodiments, the layers of dielectric material below the top layer of aluminum oxide are stacked dielectric layers that provide tunable optical properties (e.g., index of refraction) depending on the dielectric materials in the stack. The top layer of aluminum oxide is then placed in heated deionized (DI) water for a predetermined time period to transform the aluminum oxide layer into a nanostructure layer. The nanostructure layer may include a mixture of Boehmite, Gibbsite, and Bayerite (e.g., a mixture of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide in different crystalline polymorphs). In certain embodiments, the combination of the stacked dielectric layers and the nanostructure layer provides an AR coating on the curved, polymer substrate with an average reflectance of at most about 0.05% and with little to no angular shift in the spectral performance. 
     To provide an optical coating (such as an absorbing coating) on a non-planar substrate, a conformal coating of inorganic materials is formed on the substrate using atomic layer deposition. The conformal coating may include multiple layers of inorganic material (e.g., a combination of absorbing materials and transparent materials) with a top layer of aluminum oxide. In some embodiments, the layers of inorganic material below the top layer of aluminum oxide are stacked layers that provide tunable optical properties (e.g., lightness value) depending on the materials in the stack. The top layer of aluminum oxide is then placed in heated deionized (DI) water for a predetermined time period to transform the aluminum oxide layer into a nanostructure layer. The nanostructure layer may include a mixture of Boehmite, Gibbsite, and Bayerite (e.g., a mixture of different crystalline polymorphs of aluminum oxide, aluminum hydroxide (which may be Gibbsite or Bayerite), and aluminum oxide hydroxide (which may be Boehmite)). In certain embodiments, the combination of the stacked dielectric layers and the nanostructure layer provides an absorbing coating on the non-planar substrate with an average lightness value of at most about 0.3 over a high range of incidence angles (e.g., from 0° to about 40°). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the methods and apparatus of the embodiments described in this disclosure will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the embodiments described in this disclosure when taken in conjunction with the accompanying drawings in which: 
         FIG.  1    depicts a cross-sectional side-view representation of an example AR (antireflection) coating formed on a curved substrate using physical vapor deposition. 
         FIG.  2    depicts spectral performance of an AR coating deposited using physical vapor deposition as measured at different locations on the surface of a curved substrate. 
         FIG.  3    depicts a cross-sectional side-view representation of an example absorbing coating formed on a flat substrate using PVD. 
         FIG.  4    depicts spectral performance of an absorbing coating as theoretically determined at different angle of incidence on the surface of a substrate. 
         FIG.  5    depicts lightness value theoretically determined versus angle of incidence for an absorbing coating on a substrate. 
         FIG.  6    depicts a cross-sectional side-view representation of an example AR coating formed on a curved substrate using atomic layer deposition. 
         FIG.  7    depicts spectral performance of an AR coating deposited using atomic layer deposition as measured at different locations on the surface of a curved substrate. 
         FIG.  8    depicts spectral performance of an AR coating deposited using atomic layer deposition as theoretically determined at different angle of incidence at the center position on the surface of a curved substrate. 
         FIG.  9    depicts a cross-sectional representation of an antireflection coating formed on a curved substrate, according to some embodiments. 
         FIG.  10    depicts a cross-sectional representation of an embodiment of a flat substrate with an aluminum oxide nanostructure formed on the substrate. 
         FIG.  11    depicts optical modeling of refraction index versus physical thickness for the embodiment depicted in  FIG.  10   . 
         FIG.  12    depicts spectral performance for the embodiment depicted in  FIG.  10    as determined by measurement and optical modeling. 
         FIG.  13    depicts spectral performance determined by theoretical modeling for an embodiment of an AR coating. 
         FIG.  14    depicts the index of refraction versus thickness determined by theoretical modeling for an embodiment of an AR coating. 
         FIG.  15    depicts a cross-sectional representation of a structure having an absorbing coating formed on a non-planar substrate, according to some embodiments. 
         FIG.  16    depicts spectral performance determined by theoretical modeling for an embodiment of an absorbing coating. 
         FIG.  17    depicts a plot of lightness value theoretically determined versus angle of incidence for an embodiment of an absorbing coating. 
         FIG.  18    depicts spectral performance determined by theoretical modeling for an embodiment of an absorbing coating designed for a wavelength range of 400 nm to 1100 nm. 
         FIG.  19    depicts the index of refraction versus thickness determined by theoretical modeling for an embodiment of an absorbing coating designed for a wavelength range of 400 nm to 1100 nm. 
         FIG.  20    depicts spectral performance determined by theoretical modeling for an embodiment of an absorbing coating designed for a wavelength range of 400 nm to 1600 nm. 
         FIG.  21    depicts the index of refraction versus thickness determined by theoretical modeling for an embodiment of an absorbing coating designed for a wavelength range of 400 nm to 1600 nm. 
         FIG.  22    is a flow diagram illustrating a method for forming an AR coating on a substrate, according to some embodiments. 
         FIG.  23    depicts a cross-sectional representation of at least one dielectric layer formed on a substrate using atomic layer deposition, according to some embodiments. 
         FIG.  24    depicts a cross-sectional representation of an aluminum oxide layer formed on a dielectric stack in a structure, according to some embodiments. 
         FIG.  25    depicts a cross-sectional representation of an aluminum oxide layer formed on a dielectric stack in a structure being heated in a water-based fluid, according to some embodiments. 
         FIGS.  26 A-C  depicts examples of molecular structures of Boehmite, Gibbsite and Bayerite. 
         FIG.  27    depicts an example of temperature and pH ranges that may produce different crystalline polymorphs. 
     
    
    
     Although the embodiments disclosed herein are susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are described herein in detail. It should be understood, however, that drawings and detailed description thereto are not intended to limit the scope of the claims to the particular forms disclosed. On the contrary, this application is intended to cover all modifications, equivalents and alternatives falling within the spirit and scope of the disclosure of the present application as defined by the appended claims. 
     This disclosure includes references to “one embodiment,” “a particular embodiment,” “some embodiments,” “various embodiments,” or “an embodiment.” The appearances of the phrases “in one embodiment,” “in a particular embodiment,” “in some embodiments,” “in various embodiments,” or “in an embodiment” do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure. 
     Within this disclosure, different entities (which may variously be referred to as “units,” “circuits,” other components, etc.) may be described or claimed as “configured” to perform one or more tasks or operations. This formulation—[entity] configured to [perform one or more tasks]—is used herein to refer to structure (i.e., something physical, such as an electronic circuit). More specifically, this formulation is used to indicate that this structure is arranged to perform the one or more tasks during operation. A structure can be said to be “configured to” perform some task even if the structure is not currently being operated. A “credit distribution circuit configured to distribute credits to a plurality of processor cores” is intended to cover, for example, an integrated circuit that has circuitry that performs this function during operation, even if the integrated circuit in question is not currently being used (e.g., a power supply is not connected to it). Thus, an entity described or recited as “configured to” perform some task refers to something physical, such as a device, circuit, memory storing program instructions executable to implement the task, etc. This phrase is not used herein to refer to something intangible. 
     The term “configured to” is not intended to mean “configurable to.” An unprogrammed FPGA, for example, would not be considered to be “configured to” perform some specific function, although it may be “configurable to” perform that function after programming. 
     Reciting in the appended claims that a structure is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. § 112(f) for that claim element. Accordingly, none of the claims in this application as filed are intended to be interpreted as having means-plus-function elements. Should Applicant wish to invoke Section 112(f) during prosecution, it will recite claim elements using the “means for” [performing a function] construct. 
     As used herein, the term “based on” is used to describe one or more factors that affect a determination. This term does not foreclose the possibility that additional factors may affect the determination. That is, a determination may be solely based on specified factors or based on the specified factors as well as other, unspecified factors. Consider the phrase “determine A based on B.” This phrase specifies that B is a factor that is used to determine A or that affects the determination of A. This phrase does not foreclose that the determination of A may also be based on some other factor, such as C. This phrase is also intended to cover an embodiment in which A is determined based solely on B. As used herein, the phrase “based on” is synonymous with the phrase “based at least in part on.” 
     As used herein, the phrase “in response to” describes one or more factors that trigger an effect. This phrase does not foreclose the possibility that additional factors may affect or otherwise trigger the effect. That is, an effect may be solely in response to those factors, or may be in response to the specified factors as well as other, unspecified factors. Consider the phrase “perform A in response to B.” This phrase specifies that B is a factor that triggers the performance of A. This phrase does not foreclose that performing A may also be in response to some other factor, such as C. This phrase is also intended to cover an embodiment in which A is performed solely in response to B. 
     As used herein, the terms “first,” “second,” etc. are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.), unless stated otherwise. For example, in a register file having eight registers, the terms “first register” and “second register” can be used to refer to any two of the eight registers, and not, for example, just logical registers 0 and 1. 
     When used in the claims, the term “or” is used as an inclusive or and not as an exclusive or. For example, the phrase “at least one of x, y, or z” means any one of x, y, and z, as well as any combination thereof 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the disclosed embodiments. One having ordinary skill in the art, however, should recognize that aspects of disclosed embodiments might be practiced without these specific details. In some instances, well-known circuits, structures, signals, computer program instruction, and techniques have not been shown in detail to avoid obscuring the disclosed embodiments. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present disclosure describes various techniques for forming AR coatings or absorbing coatings on optical lenses. A widely used current method for coating surfaces with optical coatings (e.g., AR coatings or absorbing coatings) is physical vapor deposition (PVD). PVD may include, for example, evaporation or sputtering of the materials for the optical coating onto a surface (e.g., a surface of an optical lens). One example of a PVD process is an electron beam (E-beam) deposition process. Optical coatings deposited using PVD, however, are non-conforming to the surface, which can be problematic with curved or non-planar substrates. For example, on curved or non-planar substrates, layer thickness of an optical coating deposited by PVD is dependent on the angle of vapor incidence during the PVD process. Such angle dependency may produce non-uniformity in the thickness of the optical coating that results in non-uniformity in the reflectance spectrum across the surface of the curved or non-planar substrate. 
     Atomic layer deposition (ALD) is another method that has been proposed to coat surfaces with optical coatings. An ALD process may be capable of coating a conformable optical coating on a curved or non-planar substrate. Thermal ALD processes are typically operated, however, at temperatures that are not suitable for plastic lens substrates. Recent developments in plasma-enhanced ALD (PEALD), however, have reduced ALD process temperatures into ranges suitable for plastic lens substrates (e.g., processing temperatures below about 100° C.). 
     Another method that has been proposed for optical coatings is forming a nanostructure material on flat substrates or glass substrates. The nanostructure material is formed by depositing a layer of dielectric material (e.g., aluminum oxide) on the flat substrate by PVD (e.g., electron beam (E-beam) deposition) followed by submerging the deposited layer in hot water for a period of time. The submersion transforms the single layer of aluminum oxide into a nanostructure that may include Gibbsite (aluminum hydroxide) and Boehmite (aluminum oxide hydroxide). 
     Such a nanostructure material may achieve a lower average reflectance for an AR coating than AR coatings formed by PVD or ALD (e.g., about 0.15% average reflectance as measured over 400 nm to 700 nm, from 0° to 30° angle of incidence). The nanostructure material, however, may not be tunable for different refraction indices or wavelengths and controlling the spectral performance may be difficult. Additionally, any variations or non-uniformity in the thickness of the layer deposited by PVD may adversely affect the optical performance of the subsequently formed nanostructure material. For example, variations or non-uniformity in the thickness of the PVD layer (e.g., variations of at least 10% in thickness) may actually cause reduction in the optical performance of the layer subsequent to the hot water treatment. In some instances, placing such a non-uniform layer in the hot water treatment may also create more non-uniformity in the layer. 
       FIG.  1    depicts a cross-sectional side-view representation of an embodiment of an AR coating formed on a curved substrate using PVD. In  FIG.  1   , AR coating  100  is formed on curved substrate  102  using PVD. AR coating  100  includes layers of first dielectric material  104  alternating with layers of second dielectric material  106  deposited using PVD processes to form each of the layers. As shown in  FIG.  1   , because of the curved surface of substrate  102 , the layers of first dielectric material  104  and second dielectric material  106  deposited using PVD may be non-uniform in thickness across the surface of the substrate. 
     The non-uniformity in the thickness of the layers of first dielectric material  104  and second dielectric material  106  may cause non-uniformity in the reflectance spectrum of the AR coating.  FIG.  2    depicts spectral performance of AR coating  100  measured at different locations on the surface of substrate  102 . The different locations on the surface of substrate  102  are shown by the arrows in  FIG.  1   , which indicate different angles from center (perpendicular to substrate).  FIG.  2    depicts spectral performance measured by reflectance (in %) at different wavelengths between 380 nm and 780 nm. As shown in  FIG.  2   , the spectral performance of AR coating  100  is non-uniform across the surface of substrate  102 . The non-uniformity in the reflectance spectrum (as shown by the spectral performance shown in  FIG.  2   ) may limit the average reflectance achievable for AR coatings deposited by PVD to average reflectances of about 0.7% or higher (as measured over 400 nm to 700 nm, from 0° to 30° angle of incidence). 
     Absorbing coatings deposited using PVD processes may have similar issues with thickness uniformity across the surface. As absorbing coatings are typically deposited on surfaces with changing topographies (e.g., angle changes, height changes, three-dimensional structures, etc.), PVD deposition of absorbing coatings may be difficult to have uniform thickness on such non-planar surfaces. 
     In some embodiments, multilayer absorbing coatings deposited on flat surfaces using PVD processes have a change in performance based on angle of incidence (AOI) on the surface.  FIG.  3    depicts a cross-sectional side-view representation of an embodiment of an absorbing coating formed on a flat substrate using PVD. In  FIG.  3   , absorbing coating  300  is formed on flat substrate  302  using PVD. Absorbing coating  300  includes layers of first dielectric material  304  alternating with layers of second dielectric material  306  deposited using PVD processes to form each of the layers. 
       FIG.  4    depicts spectral performance of absorbing coating  300  as theoretically determined at different angle of incidence on the surface of substrate  302 . The different angles of incidence are 0°, 10°, 20°, 30°, 40°, and 50° where the light is incident on the surface of substrate  302  (shown in  FIG.  3   ).  FIG.  4    depicts the spectral performance theoretically determined by reflectance (in %) at different wavelengths between 380 nm and 780 nm. As shown in  FIG.  4   , the reflectance varies based on the angle of incidence and there is angular shift in the wavelength range as the angle of incidence increases. Additionally, at higher angles of incidence (e.g., greater than 40°), the reflectance increases and the angular shift also continues to increase. 
       FIG.  5    depicts the lightness value (L*) theoretically determined versus angle of incidence for absorbing coating  300  on substrate  302 . As used herein, the term “lightness value (L*)” refers to the L* value from the  1976  CIELAB color space. In some instances, the lightness value may be referred to as relative luminance. As shown in  FIG.  5   , the lightness value increases dramatically at angles of incidence above about 30° or 40°. Thus, high absorbance performance (as measured by lightness value) may be difficult to achieve across a wide range of angles (e.g., L* may be only in a high performing range for angles lower than about 40°). 
     In some embodiments, ALD (atomic layer deposition) may be used to form an optical coating on a substrate.  FIG.  6    depicts a cross-sectional side-view representation of an embodiment of an AR coating formed on a curved substrate using ALD. In  FIG.  6   , AR coating  600  is formed on curved substrate  102  using ALD. AR coating  600  includes layers of first dielectric material  602  alternating with layers of second dielectric material  604  deposited using ALD processes to form each of the layers. As shown in  FIG.  6   , the layers of first dielectric material  602  and second dielectric material  604  conform to the surface of substrate  102 . The ALD processes used to form first dielectric material  602  and second dielectric material  604  may, however, be limited to dielectric materials that have limited ranges of optical indices of refraction. Thus, it may be difficult to achieve low average reflectances (e.g., average reflectances below about 0.3% as measured over 400 nm to 700 nm, from 0° to 30° angle of incidence) for AR coatings deposited using only ALD. 
       FIG.  7    depicts spectral performance of AR coating  600  measured at different locations on the surface of substrate  102 . The different locations on the surface of substrate  102  are shown by the arrows in  FIG.  6   , which indicate different angles from center (perpendicular to substrate).  FIG.  7    depicts spectral performance measured by reflectance (in %) at different wavelengths between 380 nm and 780 nm. As shown in  FIG.  7   , the wavelength range for low reflectance by AR coating  600  may be between about 400 nm and about 600 nm. 
       FIG.  8    depicts spectral performance of AR coating  600  as theoretically determined at different angle of incidence at the center position on the surface of substrate  102 . The different angles of incidence are 0°, 10°, 20°, and 30° where the light is incident at the center position on the surface of substrate  102  (shown in  FIG.  6   ).  FIG.  8    depicts the spectral performance theoretically determined by reflectance (in %) at different wavelengths between 380 nm and 780 nm. As shown in  FIG.  8   , the reflectance varies based on the angle of incidence and there is angular shift in the wavelength range as the angle of incidence increases. Additionally, at higher angles of incidence (e.g., greater than) 30°, the variance in reflectance may become more pronounced and the angular shift may also continue to increase. 
     In certain embodiments, as described herein, an optical coating is formed using a combination of ALD-deposited dielectric layers and a nanostructure material. Forming an optical coating using a combination of ALD-deposited dielectric layers and a nanostructure material may improve spectral performance of the optical coating compared to individual spectral performances of ALD-deposited dielectric layers or a nanostructure material. For example, the combination of ALD-deposited dielectric layers and the nanostructure material may lower the average reflectance of an AR coating compared to individual average reflectances of ALD-deposited AR coatings or a nanostructure material AR coating. Angular dependence of spectral performance may also be reduced by the combination of ALD-deposited dielectric layers and the nanostructure material. Absorbing properties for absorbing coatings may also be improved by the combination of ALD-deposited dielectric layers and the nanostructure material. 
       FIG.  9    depicts a cross-sectional representation of a structure having an antireflection coating formed on a curved substrate, according to some embodiments. Structure  900  includes substrate  901 . In certain embodiments, substrate  901  is an optical lens. For example, substrate  901  may be an optical lens used in a camera or other optical device. In certain embodiments, substrate  901  is a polymeric substrate. Polymeric substrates may include, but not be limited to, cyclic olefin polymer substrates, cyclic olefin copolymer substrates, and thermoplastic substrates (such as poly(methyl methacrylate)(PMMA)). 
     In the depicted embodiment, substrate  901  is a curved planar substrate (e.g., the substrate is a non-planar or non-flat substrate). As used herein, a curved substrate includes a substrate where at least a portion of at least one surface of the substrate has a minimum angle of curvature. In certain embodiments, the minimum angle of curvature is at least about 20 degrees. The curvature of upper portion  902  or lower portion  904  may, however vary. For example, portions with a minimum angle of curvature of at least about 10 degrees or at least about 15 degrees may be contemplated for some embodiments. The curvature of portions of substrate  901  may vary based on, for example, properties (e.g., optical properties) of the substrate. For example, in some embodiments, optical lenses may have different curvatures implemented for different uses in an optical device such as providing different optical properties in the optical device. 
     In certain embodiments, as shown in  FIG.  9   , substrate  901  has two curved portions, curved upper portion  902  on upper surface  901 A of the substrate and curved lower portion  904  on lower surface  901 B of the substrate. In some embodiments, substrate  901  may include a surface that has one or more curved portions in combination with one or more flat portions along the surface. For example, as shown in the depicted embodiment, upper surface  901 A of substrate  901  includes curved upper portion  902  along with two small, flat portions  906  and lower surface  901 B includes curved lower portion  904  along with two flat portions  908 . For embodiments with multiple curved portions on the surface of a substrate, the angles of curvature in the multiple curved portions on the surface may be the same for each curved portion or may vary between the curved portions. 
     In certain embodiments, AR (antireflection) coating  910  is formed on substrate  901 . As shown in  FIG.  9   , AR coating  910  is formed on both upper surface  901 A and lower surface  901 B of substrate  901 . Other embodiments may be contemplated where AR coating  910  is formed on only upper surface  901 A or on only lower surface  901 B. 
     In the depicted embodiment, AR coating  910  includes dielectric stack  912  and nanostructure layer  914  formed on substrate  901 . In certain embodiments, dielectric stack  912  includes one or more dielectric layers (e.g., layers of dielectric material). Dielectric material utilized for the dielectric layers in dielectric stack  912  may include, but not be limited to, silicon oxides, silicon nitrides, transition metal oxides, and alkaline earth fluorides. Examples of these dielectric materials include, but are not limited to, titanium dioxide (TiO 2 ), niobium oxide (Nb 2 O 5 ), tantalum oxide (Ta 2 O 5 ), zirconium oxide (ZrO 2 ), hafnium oxide (HfO 2 ), silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), and magnesium fluoride (MgF 2 ). In certain embodiments, the dielectric layers are formed using a plasma-enhanced atomic layer deposition (PEALD) process, as described herein. An individual dielectric layer may be formed according to a PEALD process for the individual dielectric material in the layer. In some embodiments, the dielectric layers are formed using another ALD process. For example, thermal ALD processes that operate in low-temperature ranges below about 100° C. may be used to form the dielectric layers. 
     In some embodiments, as shown in  FIG.  9   , dielectric stack  912  includes multiple layers of dielectric material to form an interference coating. The interference coating may include alternating layers of dielectric material where the layers alternate between a high index of refraction material and a low index of refraction material. In such embodiments, the refractive index of the low refractive index material may determine the spectral performance of dielectric stack  912 . High refractive index materials that may be used in dielectric stack  912  include, but are not limited to, titanium dioxide, niobium oxide, tantalum oxide, zirconium oxide, hafnium oxide, and silicon nitride. Low refractive index materials that may be used in dielectric stack  912  include, but are not limited to, aluminum oxide, silicon dioxide, and magnesium fluoride. In some embodiments, the difference in index of refraction between the low index material and the high index material is at least about 0.5. Other embodiments may be contemplated with the difference index of refraction being at least about 0.3, at least about 0.4, or at least about 0.6. The difference in index of refraction may range up to about 2.0 or higher depending on the dielectric materials used in the alternating layers. 
     In one embodiment, as shown in  FIG.  9   , dielectric stack  912  includes three layers of dielectric material (e.g., dielectric layers  912 A,  912 B,  912 C). In certain embodiments, dielectric layer  912 A is an adhesion layer for dielectric stack  912 . For example, dielectric layer  912 A may be an aluminum oxide (Al 2 O 3 ) adhesion layer. The adhesion layer may be used to provide adhesion to substrate  901  that maintains adhesion between the dielectric layers and the substrate under typical operating conditions (e.g., typical operating temperatures). 
     In some embodiments, dielectric layer  912 B and dielectric layer  912 C may be alternating dielectric material layers formed on dielectric layer  912 A (e.g., the adhesion layer). In such embodiments, dielectric layer  912 B may include a high refraction index dielectric material and dielectric layer  912 C may include a low refraction index material. Thus, dielectric stack  912  may include dielectric layer  912 A (which is aluminum oxide and a low refraction index material), dielectric layer  912 B (which is a high refraction index material such as titanium dioxide), and dielectric layer  912 C (which is a low refraction index material such as silicon dioxide) with the three layers forming an interference coating. 
     While three dielectric layers (e.g., dielectric layers  912 A,  912 B,  912 C) are shown in the embodiment depicted in  FIG.  9   , dielectric stack  912  may include any number of dielectric layers that provide desired optical and/or mechanical properties for AR coating  910 . For example, in one embodiment, dielectric stack  912  may include a single layer of dielectric material in addition to the adhesion layer (such as a single layer of silicon dioxide on an aluminum oxide adhesion layer). Reducing the number of layers in dielectric stack  912  may also improve throughput of process for forming AR coating  910  (e.g., by reducing total process time needed by reducing number of layer depositions). In some embodiments, the number of layers in dielectric stack  912  is varied to provide a desired spectral performance from AR coating  910 . The dielectric materials in the dielectric layers may also be varied to provide variances in indices of refraction in the dielectric layers and produce desired spectral performance from AR coating  910 . 
     In some embodiments, dielectric stack  912  may have a thickness between about 100 nm and about 500 nm. The thickness of dielectric stack  912  may vary based on the number of layers, types of dielectric materials, and desired optical or mechanical properties of the dielectric stack. For example, smaller thicknesses may be contemplated with dielectric stack  912  only having one or two dielectric layers. 
     In the embodiment shown in  FIG.  9   , AR coating  910  includes nanostructure layer  914  formed on dielectric stack  912 . In certain embodiments, nanostructure layer  914  is a nanostructure of aluminum oxide. As described herein, the nanostructure of aluminum oxide may be formed by depositing a layer of aluminum oxide (e.g., using PEALD) on dielectric stack  912  and placing the structure in heated deionized (DI) water for a predetermined time period. Placing the structure in heated DI water for the predetermined time period restructures the PEALD-deposited aluminum oxide to a nanostructure lattice of aluminum oxide (e.g., an aluminum oxide nanostructure). 
     Depositing the layer of aluminum oxide with PEALD may form the layer conformally on dielectric stack  912  and substrate  901 . With the conformal deposition of the PEALD-deposited aluminum oxide on dielectric stack  912  and substrate  901 , nanostructure layer  914  may also be conformal on the dielectric stack and substrate. In some embodiments, dielectric stack  912  includes a top layer of silicon dioxide. Silicon dioxide may be used in the top layer of dielectric stack  912  to provide adhesion between the dielectric stack and nanostructure layer  914  as silicon dioxide and PEALD-deposited aluminum oxide have good adhesion properties with respect to each other. The top layer of silicon dioxide may be dielectric layer  912 C, shown in  FIG.  9   , or another thin layer of silicon dioxide deposited on top of dielectric layer  912 C. 
     In various embodiments, nanostructure layer  914  includes a mixture of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide. For instance, nanostructure layer  914  may include a mixture of crystalline polymorphs (different crystalline structures) of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide. In certain embodiments, the mixture of crystalline polymorphs includes, but is not limited to, a mixture of Boehmite, Gibbsite, and Bayerite. Boehmite includes aluminum oxide hydroxide and may be referred to as γ-aluminum oxide, γ-AlO(OH), or α-AlOOH. Gibbsite includes aluminum hydroxide and may be referred to as γ-aluminum hydroxide (γ-Al(OH) 3 ). Bayerite is a variation of Gibbsite that also includes aluminum hydroxide. In some instances, Bayerite is referred to as α-aluminum hydroxide (α-Al(OH) 3 ) or β-aluminum hydroxide (β-Al(OH)3). 
     Examples of molecular structures of Boehmite, Gibbsite, and Bayerite are shown in  FIGS.  26 A-C , respectively. In various embodiments, Boehmite, Gibbsite, and Bayerite are crystalline polymorphs having different crystalline structures of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide. Examples of different crystalline structures include, but are not limited to, orthorhombic (such as Boehmite), hexagonal (such as Bayerite), and monoclinic (such as Gibbsite). While embodiments disclosed herein describe nanostructure layer  914  as being a mixture of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide or a mixture of Boehmite, Gibbsite, and Bayerite, it should be understood that other crystalline polymorphs of aluminum oxide, aluminum hydroxide, or aluminum oxide hydroxide may also be possible in the nanostructure layer. For example, other crystalline polymorphs may be possible under different processing conditions (e.g., different DI water temperatures and processing times). 
     The relative amounts of Boehmite, Gibbsite, and Bayerite along with the relative amount of aluminum oxide may vary depending on the structure of the aluminum oxide layer prior to treatment in heated DI water as well as the treatment parameters (e.g., temperature of DI water and treatment time in heated DI water). For example, the relative amounts may vary based on the amount of structural impurities in the PEALD-deposited aluminum oxide. Structural impurities may include, for example, non-crystalline impurities or chemical defects in the PEALD-deposited aluminum oxide such as, but not limited to, —OH groups, alkyl groups, and Al(OH) 3  groups. Treatment parameters in the heated DI water may also be varied to vary the amount of restructuring to the different crystalline polymorphs (e.g., Boehmite, Gibbsite, and Bayerite) that occurs in the PEALD-deposited aluminum oxide. 
     In certain embodiments, nanostructure layer  914  has a thickness between about 160 nm and about 260 nm. In some embodiments, nanostructure layer  914  has a thickness between about 170 nm and about 250 nm. In some embodiments, nanostructure layer  914  has a thickness between about 180 nm and about 240 nm. Other embodiments of thicknesses for nanostructure layer  914  may also be contemplated. For example, the thickness nanostructure layer  914  may be dependent on the temperature of DI water and time of treatment in the heated DI water. Typically, higher temperatures generate thinner layers while lower temperatures generate thicker layers. In various embodiments, the thickness of nanostructure layer  914  may be varied to tune the spectral performance (and other properties) of AR coating  910  in structure  900 . For example, thinner thicknesses may be used to shift the spectral performance to lower wavelengths while thicker thicknesses may be used to shift spectral performance to higher wavelengths. As described herein, the thickness of nanostructure layer  914  may also be determined by the thickness of the PEALD-deposited aluminum oxide layer (e.g., aluminum oxide layer  2400 , shown in  FIGS.  24  and  25   ) prior to being treated in heated DI water. 
     As described above, an aluminum oxide nanostructure, such as nanostructure layer  914 , may provide a lower average reflectance than dielectric layers formed by ALD (e.g., PEALD) without the additional heated DI water treatment. As an example,  FIG.  10    depicts a cross-sectional representation of an embodiment of substrate  1000  with aluminum oxide nanostructure  1002  formed on the substrate. In the depicted embodiment, substrate  1000  is a flat substrate. Nanostructure  1002  may be formed by depositing a layer of aluminum oxide by either PVD or ALD (as substrate  1000  is flat, either PVD or ALD may be used to deposit the layer of aluminum oxide) and placing the structure in heated DI water for a predetermined time period. In certain embodiments, as shown in  FIG.  10   , nanostructure  1002  is a “grass-like” structure on substrate  1000 . 
       FIGS.  11  and  12    depict optical modeling results for the embodiment of nanostructure  1002  depicted in  FIG.  10   . For the optical modeling, nanostructure  1002  was formed by depositing aluminum oxide with PVD and placing the structure in heated DI water for 30 minutes at a temperature of 70° C.  FIG.  11    depicts optical modeling of refraction index versus physical thickness for the embodiment of nanostructure  1002  depicted in  FIG.  10   . As shown in  FIG.  11   , nanostructure  1002  has a refraction index that gradually changes from the substrate (shown by arrow  1100  on left of graph) to the incident medium (e.g., air) (shown by arrow  1102  on right of graph) where the nanostructure has a thickness of about 235 nm. 
       FIG.  12    depicts spectral performance for the embodiment of nanostructure  1002  depicted in  FIG.  10    as determined by measurement and optical modeling.  FIG.  12    depicts spectral performance measured at 0° angle of incidence for nanostructure  1002  along with spectral performance modeled for nanostructure  1002  at different angles of incidence. Spectral performance is shown by reflectance (in %) at different wavelengths between 400 nm and 750 nm. Curve  1200  (open dots) is a measurement of reflectance at 0° angle of incidence. Curves  1202 ,  1204 ,  1206 , and  1208  are reflectance determined by modeling at different angles of incidence with curve  1202  at 0° angle of incidence, curve  1204  at 10° angle of incidence, curve  1206  at 20° angle of incidence, and curve  1208  at 30° angle of incidence. As shown in  FIG.  12   , nanostructure  1002  may have a reflectance that averages at about 0.15% with variation in the reflectance between 400 nm and 700 nm. 
     While nanostructure  1002  has improved spectral performance properties over PVD and ALD deposited films (shown by the curves in  FIGS.  2 ,  7 , and  8   ), as shown by the curve in  FIG.  11   , using only nanostructure  1002  on a substrate may not allow for tuning of the refraction index. For example, the refraction index may not be varied outside the range set by the nanostructure (e.g., the limits shown by the curve in  FIG.  11   ), though the range set by the nanostructure can be varied. Further, as shown by the curves in  FIG.  12   , nanostructure  1002  may have some variation in the spectral performance in the wavelength range between 400 nm and 700 nm. The spectral performance may also be affected by the thickness of nanostructure  1002 . For example, reduced thicknesses may shift the low point of reflectance to lower wavelengths and generate a more v-like shape in the spectral performance curve. Increased thicknesses may shift the low point of reflectance to higher wavelengths and also affect the shape of the spectral performance curve. 
     Returning to  FIG.  9   , forming nanostructure layer  914  on dielectric stack  912  and substrate  901  may, however, provide significant improvements in the spectral performance in comparison to embodiments that implement only either a nanostructure layer (e.g., nanostructure  1002 ) or a dielectric stack deposited by PEALD.  FIGS.  13  and  14    depict theoretical (optical) modeling results for an example embodiment of AR coating  910  in structure  900  (shown in  FIG.  9   ). For the theoretical modeling of AR coating  910  in FIGS.  10  and  11 , dielectric stack  912  is a dielectric stack with three dielectric layers  912 A,  912 B,  912 C where dielectric layer  912 A is aluminum oxide, dielectric layer  912 B is titanium oxide, and dielectric layer  912 C is silicon dioxide. Nanostructure layer  914  is an aluminum oxide nanostructure formed by depositing a layer of aluminum oxide with a thickness around  40  nm using PEALD and placing the structure with the PEALD-deposited aluminum oxide in heated DI water at a temperature of about 70° C. for about 30 minutes. After the heated DI water treatment, the thickness of nanostructure layer  914  is about 220 nm. 
       FIG.  13    depicts spectral performance determined by theoretical modeling for the above-described embodiment of AR coating  910 . The spectral performance depicted in  FIG.  13    includes spectral performance modeled at different angles of incidence and shown by reflectance (in %) at different wavelengths between 380 nm and 780 nm. Curve  1300  is reflectance modeled at 0° angle of incidence. Curve  1302  is reflectance modeled at 10° angle of incidence. Curve  1304  is reflectance modeled at 20° angle of incidence. Curve  1306  is reflectance modeled at 30° angle of incidence. 
     As shown in  FIG.  13   , AR coating  910  may have a theoretical reflectance that averages at most about 0.05% at wavelengths between 400 nm and 700 nm. Such spectral performance may be beyond what might be expected based on the individual spectral performances of a nanostructure layer (as shown in  FIG.  12   ) and an ALD-deposited dielectric stack (as shown in  FIGS.  7  and  8   ). For example, the theoretical average reflectance for AR coating  910 , shown in  FIG.  13   , is lower than the average reflectance individually of either a nanostructure layer or an ALD-deposited dielectric stack. Additionally, the angular dependence of the spectral performance for AR coating  910  is reduced versus the angular dependence of the spectral performance individually of either a nanostructure layer or an ALD-deposited dielectric stack. For example, at wavelengths between about 400 nm and about 700 nm, there is little to no angular shift in the spectral performance of AR coating  910  (e.g., little to no change in spectral performance based on the angle of incidence). As described herein, AR coating  910  may provide high antireflection performance across a wide range of incidence angles for substrate  901  (e.g., a curved or non-planar polymeric substrate). 
       FIG.  14    depicts the index of refraction versus thickness determined by theoretical modeling for the above-described embodiment of AR coating  910 . The index of refraction for the substrate (e.g., a polymeric substrate) is shown in section  1400 . The index of refraction changes at point  1402  to dielectric layer  912 A (e.g., aluminum oxide) in the PEALD-deposited layers (e.g., dielectric stack  912 ). The index of refraction then changes again in dielectric layer  912 B (e.g., titanium oxide) and dielectric layer  912 C (silicon dioxide). The changes in the index of refraction in dielectric stack  912  is abrupt, as shown in  FIG.  14   , and the changes allow for tuning of the index of refraction in the dielectric stack. For example, by changing materials, thicknesses, and/or number of layers in dielectric stack  912 . 
     The index of refraction gradually changes in nanostructure layer  914  between point  1404  and point  1406 . The gradual change of the index of refraction in nanostructure layer  914  is similar to the gradual change shown of the index of refraction shown in  FIG.  11   . The index of refraction then changes to the index of refraction for the incident medium (e.g., air) in section  1408  at point  1406 . As shown by the curves in  FIGS.  13  and  14   , AR coating  910  has an index of refraction that may be tuned within dielectric stack  912  (e.g., dielectric layers  912 A,  912 B,  912 C) and then gradually changed in nanostructure layer  914  for substrate  901  (e.g., a curved or non-planar polymeric substrate) where the index of refraction also has little to no angular shift across a wide range of incidence. 
       FIG.  15    depicts a cross-sectional representation of a structure having an absorbing coating formed on a non-planar substrate, according to some embodiments. Structure  1500  includes substrate  1501 . In certain embodiments, substrate  1501  is a metal substrate (e.g., a stainless steel substrate). For example, substrate  1501  may be a surface located in a camera or other optical device. Substrate  1501  may be, for example, a surface with reflective properties, which need to be inhibited in the camera or optical device. In certain embodiments, substrate  1501  includes one or more non-planar features. For example, substrate  1501  may include angle changes, height changes, three-dimensional structures, etc. 
     In the depicted embodiment, substrate  1501  includes a curved, non-planar structure (e.g., the structure is non-planar such that a portion of the surface of the substrate is non-flat). As used herein, a curved, non-planar structure includes a structure that causes a surface of a substrate to be non-flat or non-planar. The angles and/or shapes of the non-planar structure may vary. For example, structures may be contemplated with curved angles, rectangular angles, or combinations thereof. 
     In certain embodiments, as shown in  FIG.  15   , substrate  1501  has two curved, non-planar structures, curved upper structure  1502  on upper surface  1501 A of the substrate and curved lower structure  1504  on lower surface  1501 B of the substrate. In some embodiments, substrate  1501  may include a surface that has one or more curved, non-planar structures in combination with one or more flat portions along the surface. For example, as shown in the depicted embodiment, upper surface  1501 A of substrate  1501  includes curved upper structure  1502  along with two small, flat portions  1506  and lower surface  1501 B includes curved lower structure  1504  along with two flat portions  1508 . For embodiments with multiple structures on the surface of a substrate, the angles or shapes in the multiple structures on the surface may be the same for each structure or may vary between the structures. 
     In certain embodiments, absorbing (e.g., “black” optical) coating  1510  is formed on substrate  1501 . As shown in  FIG.  15   , absorbing coating  1510  is formed on both upper surface  1501 A and lower surface  1501 B of substrate  1501 . Other embodiments may be contemplated where absorbing coating  1510  is formed on only upper surface  1501 A or on only lower surface  1501 B. 
     In the depicted embodiment, absorbing coating  1510  includes stack  1512  and nanostructure layer  1514  formed on substrate  1501 . In certain embodiments, stack  1512  includes one or more absorbing material layers in combination with one or more transparent material layers. Absorbing material utilized for the absorbing material layers in stack  1512  may include, but not be limited to, titanium-based materials, tantalum-based materials, and silicon-based materials. Examples of these dielectric materials include, but are not limited to, silicon hydride (SiH), titanium nitride (TiN), and titanium aluminum nitride (TiAlN). Transparent material utilized for the transparent material layers in stack  1512  may include, but not be limited to, silicon oxides and transition metal oxides. Examples of these transparent materials include, but are not limited to, titanium dioxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), and silicon dioxide (SiO 2 ). 
     In certain embodiments, the absorbing material layers and the transparent material layers are formed using a plasma-enhanced atomic layer deposition (PEALD) process, as described herein. An individual absorbing material or transparent material layer may be formed according to a PEALD process for the individual material in the layer. In certain embodiments, absorbing material layers are alternated with transparent material layers in stack  1512 . Thus, the alternating layers include layers that alternate between a high index of refraction material (e.g., an absorbing material) and a low index of refraction material (e.g., a transparent material) to form an interference coating in stack  1512 . For absorbing coating  1510 , the absorbing properties of the high refractive index materials (e.g., the absorbing material layers) may determine the spectral performance of stack  1512 . 
     In one embodiment, as shown in  FIG.  15   , stack  1512  includes four layers of material (e.g., layers  1512 A,  1512 B,  1512 C,  1512 D). In certain embodiments, layer  1512 A is an adhesion layer for stack  1512 . For example, layer  1512 A may be an aluminum oxide, a titanium dioxide, or a titanium nitride adhesion layer. The adhesion layer may be used to provide adhesion to substrate  1501  that maintains adhesion between stack  1512  and the substrate under typical operating conditions (e.g., typical operating temperatures). 
     In some embodiments, layers  1512 B,  1512 C,  1512 D are alternating material layers formed on layer  1512 A (e.g., the adhesion layer). In such embodiments, layer  1512 B may include a low refraction index dielectric material, layer  1512 C may include a high refraction index material, and layer  1512 D may include a low refraction index dielectric material. Thus, stack  1512  may include layer  1512 A (which is titanium nitride and a high refraction index material), layer  1512 B (which is a low refraction index material such as silicon dioxide), layer  1512 C (which is a high refraction index material such as titanium nitride), and layer  1512 D (which is a low refraction index material such as silicon dioxide), with the four layers forming an interference coating. 
     While four layers (e.g., layers  1512 A,  1512 B,  1512 C,  1512 D) are shown in the embodiment depicted in  FIG.  15   , stack  1512  may include any number of layers that provide desired optical and/or mechanical properties for absorbing coating  1510 . For example, in one embodiment, stack  1512  may include a single layer of transparent material in addition to the adhesion layer, which is an absorbing material (such as a single layer of silicon dioxide on a titanium nitride adhesion layer). Examples of stack  1512  having larger numbers of layers are shown in the plots of index of refraction versus thickness shown in  FIGS.  19  and  21   . Reducing the number of layers in stack  1512  may improve the throughput of a process for forming absorbing coating  1510  (e.g., by reducing total process time needed by reducing number of layer depositions) while increasing the number of layers in stack  1512  may improve tuneability of the absorbing coating. In some embodiments, the number of layers in stack  1512  is varied to provide a desired spectral performance from absorbing coating  1510 . The materials in the alternating absorbing and transparent layers may also be varied to provide variances in indices of refraction in the layers and produce desired spectral performance from absorbing coating  1510 . 
     In some embodiments, stack  1512  may have a thickness between about 100 nm and about 1000 nm. The thickness of stack  1512  may vary based on the number of layers, types of absorbing or transparent materials, and desired optical or mechanical properties of the stack. For example, smaller thicknesses may be contemplated with stack  1512  only having one or two dielectric layers. 
     In the embodiment shown in  FIG.  15   , absorbing coating  1510  includes nanostructure layer  1514  formed on stack  1512 . In certain embodiments, nanostructure layer  1514  is a nanostructure of aluminum oxide. In some embodiments, nanostructure layer  1514  is similar in properties to nanostructure layer  914 , shown in  FIG.  9   . For example, as described herein, nanostructure layer  1514  may include a nanostructure of aluminum oxide formed by depositing a layer of aluminum oxide (e.g., using PEALD) on stack  1512  and placing the structure in heated deionized (DI) water for a predetermined time period. Placing the structure in heated DI water for the predetermined time period restructures the PEALD-deposited aluminum oxide to a nanostructure lattice of aluminum oxide (e.g., an aluminum oxide nanostructure). 
     Depositing the layer of aluminum oxide with PEALD may form the layer conformally on stack  1512  and substrate  1501 . With the conformal deposition of the PEALD-deposited aluminum oxide on stack  1512  and substrate  1501 , nanostructure layer  1514  may also be conformal on the stack and substrate. In some embodiments, stack  1512  includes a top layer of silicon dioxide. Silicon dioxide may be used in the top layer of stack  1512  to provide adhesion between the stack and nanostructure layer  1514  as silicon dioxide and PEALD-deposited aluminum oxide have good adhesion properties with respect to each other. The top layer of silicon dioxide may be layer  1512 D, shown in  FIG.  15   , or another thin layer of silicon dioxide deposited on top of layer  1512 D. 
     In certain embodiments, similar to nanostructure layer  914 , nanostructure layer  1514  includes a mixture of aluminum oxide, aluminum hydroxide, and aluminum oxide hydroxide crystalline polymorphs (e.g., a mixture of Boehmite, Gibbsite, and Bayerite). As described above, the relative amounts of crystalline polymorphs along with the relative amount of aluminum oxide may vary depending on the structure of the aluminum oxide layer prior to treatment in heated DI water as well as the treatment parameters. Treatment parameters in the heated DI water may also be varied to vary the amount of restructuring to different crystalline polymorphs (e.g., Boehmite, Gibbsite, and Bayerite) that occurs in the PEALD-deposited aluminum oxide. 
     In certain embodiments, nanostructure layer  1514  has a thickness between about 160 nm and about 260 nm. In some embodiments, nanostructure layer  1514  has a thickness between about 170 nm and about 250 nm. In some embodiments, nanostructure layer  1514  has a thickness between about 180 nm and about 240 nm. Other embodiments of thicknesses for nanostructure layer  1514  may also be contemplated, as described for nanostructure layer  914  above. The thickness of nanostructure layer  1514  may be varied to tune the spectral performance (and other properties) of absorbing coating  1510  in structure  1500 . For example, thinner thicknesses may be used to shift the spectral performance to lower wavelengths (e.g., wavelengths in the visible range, as shown in  FIGS.  18  and  19   ) while thicker thicknesses may be used to shift spectral performance to higher wavelengths (e.g., wavelengths in the near-IR range, as shown in  FIGS.  20  and  21   ). As described herein, the thickness of nanostructure layer  1514  may be determined by the thickness of the PEALD-deposited aluminum oxide layer (e.g., aluminum oxide layer  2400 , shown in  FIGS.  24  and  25   ) prior to being treated in heated DI water. 
     Forming nanostructure layer  1514  on stack  1512  and substrate  1501  may provide improvements in the absorbance properties of absorbing coating  1510  as compared to absorbance properties of a stack of alternating layers of absorbing and transparent materials deposited by PEALD without the nanostructure layer (e.g., the properties of absorbing coating  300 , shown in  FIGS.  3 - 5   ).  FIGS.  16  and  17    depict theoretical (optical) modeling results for an example embodiment of absorbing coating  1510  in structure  1500  (shown in  FIG.  15   ). 
       FIG.  16    depicts spectral performance determined by theoretical modeling for the above-described embodiment of absorbing coating  1510 . The spectral performance depicted in  FIG.  16    includes spectral performance modeled at different angles of incidence and shown by reflectance (in %) at different wavelengths between 380 nm and 780 nm. Curve  1600  is reflectance modeled at 0° angle of incidence. Curve  1602  is reflectance modeled at 10° angle of incidence. Curve  1604  is reflectance modeled at 20° angle of incidence. Curve  1606  is reflectance modeled at 30° angle of incidence. Curve  1608  is reflectance modeled at 40° angle of incidence. Curve  1610  is reflectance modeled at 50° angle of incidence. 
     As shown in  FIG.  16   , absorbing coating  1510  may have a theoretical reflectance that averages at most about 0.05% at wavelengths between 400 nm and 780 nm over all angles of incidence. Additionally, the angular dependence of the spectral performance for absorbing coating  1510  is reduced versus the angular dependence of the spectral performance of a stack of alternating layers of absorbing and transparent materials deposited by PEALD without the nanostructure layer (shown in  FIG.  4   ). 
       FIG.  17    depicts a plot of lightness value theoretically determined versus angle of incidence for an embodiment of absorbing coating  1510 . As shown in  FIG.  17   , absorbing coating  1510  has a low lightness value over a wide range of angles of incidence. For example, absorbing coating  1510  has an average lightness value of less than about 0.3 over angles between about 0° and about 40° while the lightness value remains below about 0.5 at angles of incidence up to about 50°. Thus, the angular dependence of lightness value in absorbing coating  1510  is reduced versus the angular dependence of the lightness value of a stack of alternating layers of absorbing and transparent materials deposited by PEALD without the nanostructure layer (shown in  FIG.  5   ). As described herein, absorbing coating  1510  may provide high absorbing performance across a wide range of incidence angles for substrate  1501  (e.g., a curved or non-planar substrate). 
     Absorbing coating  1510  may also be designed for implementation over different wavelength ranges. For example, absorbing coating  1510  may be designed for visible wavelength ranges and/or near-IR wavelength ranges depending on the utilization of the absorbing coating. Absorbing coating  1510  may be suitable for the different wavelength ranges based on the utilization of nanostructure layer  1514  in the absorbing coating.  FIGS.  18  and  19    depict spectral performance and an index of refraction profile for an embodiment of absorbing coating  1510  designed for a wavelength range of 400 nm to 1100 nm. 
       FIG.  18    depicts spectral performance determined by theoretical modeling for the embodiment of absorbing coating  1510  designed for a wavelength range of 400 nm to 1100 nm. The spectral performance depicted in  FIG.  18    includes spectral performance modeled at different angles of incidence and shown by reflectance (in %) at different wavelengths between 400 nm and 1600 nm. Curve  1800  is reflectance modeled at 0° angle of incidence. Curve  1802  is reflectance modeled at 10° angle of incidence. Curve  1804  is reflectance modeled at 20° angle of incidence. Curve  1806  is reflectance modeled at 30° angle of incidence. Curve  1808  is reflectance modeled at 40° angle of incidence. Curve  1810  is reflectance modeled at 50° angle of incidence. 
     As shown in  FIG.  18   , spectral performance is optimized for the wavelength range of about 400 nm to about 1100 nm. Additionally, there is minimal wavelength dependence and angular dependence of the spectral performance for absorbing coating  1510  over a range of angles of incidence between 0° and about 40°. 
       FIG.  19    depicts the index of refraction versus thickness determined by theoretical modeling for the embodiment of absorbing coating  1510  designed for a wavelength range of 400 nm to 1100 nm. As shown in  FIG.  19   , absorbing coating  1510  includes stack  1512  with a thickness of about 560 nm. Stack  1512  includes the alternating layers of transparent materials and absorbing materials (shown by alternating indices of refraction between 0 nm thickness (point  1900 ) and about 560 nm thickness (point  1902 ). Absorbing coating  1510  includes nanostructure layer  1514  above stack  1512  with a thickness of about 190 nm. Nanostructure layer  1514  includes a gradual change in refraction index between about 560 nm (point  1902 ) and about 750 nm (point  1904 ) in thickness in absorbing coating  1510 . The index of refraction then transitions to air at about 750 nm (point  1904 ). 
       FIGS.  20  and  21    depict spectral performance and an index of refraction profile for an embodiment of absorbing coating  1510  designed for a wavelength range of 400 nm to 1600 nm.  FIG.  20    depicts spectral performance determined by theoretical modeling for the embodiment of absorbing coating  1510  designed for a wavelength range of 400 nm to 1600 nm. The spectral performance depicted in  FIG.  20    includes spectral performance modeled at different angles of incidence and shown by reflectance (in %) at different wavelengths between 400 nm and 1600 nm. Curve  2000  is reflectance modeled at 0° angle of incidence. Curve  2002  is reflectance modeled at 10° angle of incidence. Curve  2004  is reflectance modeled at 20° angle of incidence. Curve  2006  is reflectance modeled at 30° angle of incidence. Curve  2008  is reflectance modeled at 40° angle of incidence. Curve  2010  is reflectance modeled at 50° angle of incidence. 
     As shown in  FIG.  20   , spectral performance is optimized for the wavelength range of about 400 nm to about 1600 nm. Additionally, there is minimal wavelength dependence and angular dependence of the spectral performance for absorbing coating  1510  over a range of angles of incidence between 0° and about 40°. 
       FIG.  21    depicts the index of refraction versus thickness determined by theoretical modeling for the embodiment of absorbing coating  1510  designed for a wavelength range of 400 nm to 1600 nm. As shown in  FIG.  20   , absorbing coating  1510  includes stack  1512  with a thickness of about 750 nm. Stack  1512  includes the alternating layers of transparent materials and absorbing materials (shown by alternating indices of refraction between 0 nm thickness (point  2100 ) and about 750 nm thickness (point  2102 ). Absorbing coating  1510  includes nanostructure layer  1514  above stack  1512  with a thickness of about 190 nm. Nanostructure layer  1514  includes a gradual change in refraction index between about 750 nm (point  2102 ) and about 940 nm (point  2104 ) in thickness in absorbing coating  1510 . The index of refraction then transitions to air at about 940 nm (point  2104 ). As shown in  FIGS.  18 - 21   , stack  512  may be tuned (e.g., by varying the number of layers in the stack and/or the indices of refraction in the stack) to provide absorbing properties that are designed for operation over varying wavelength ranges. 
     Example Method for Optical Coatings 
       FIG.  22    is a flow diagram illustrating method  2200  for forming AR coating  910  on substrate  901 , according to some embodiments. While method  2200  is described for an AR coating, it is to be understood that method  2200  may implement for any optical coating described herein based on changing materials of deposition. For example, method  2200  may be implemented to form absorbing coating  1510  on substrate  1501  by forming transparent and absorbing material layers using PEALD on a curved or non-planar substrate in lieu of forming dielectric layers on a curved, polymeric substrate, as described for method  2200 , while forming the nanostructure from a layer of aluminum oxide remains substantially the same in the described method. 
     As shown in  FIG.  22   , at  2202 , in the illustrated embodiment, at least one dielectric layer is formed on substrate  901  using atomic layer deposition.  FIG.  23    depicts a cross-sectional representation of at least one dielectric layer formed on substrate  901  using atomic layer deposition, according to some embodiments. As shown in  FIG.  23   , dielectric stack  912 , which includes dielectric layers  912 A,  912 B, and  912 C is formed on substrate  901  in structure  900 . In certain embodiments, dielectric layers  912 A,  912 B, and  912 C are formed using PEALD (plasma-enhanced atomic layer deposition). Dielectric layers  912 A,  912 B, and  912 C may be formed using different PEALD processes for each of the dielectric layers. The different PEALD processes may be carried out in a single process chamber or single process flow. Using PEALD, dielectric layers  912 A,  912 B, and  912 C may be conformal on substrate  901  (e.g., the dielectric layers conform to the curvature of the substrate and are deposited with substantially uniform thickness across the substrate surfaces). 
     In certain embodiments, the processing temperature is a temperature for the PEALD processes is below the glass transition temperature of substrate  901 . For example, the PEALD processes may have processing temperatures of at most about 90° C. The processing temperatures may vary based on the desired dielectric material and the substrate material being implemented. 
     Returning to  FIG.  22   , after dielectric stack  912  (e.g., the at least one dielectric layer) is formed on substrate  901 , at  2204 , in the illustrated embodiment, a layer of aluminum oxide is formed on the at least one dielectric layer (dielectric stack  912 ).  FIG.  24    depicts a cross-sectional representation of aluminum oxide layer  2400  formed on dielectric stack  912  in structure  900 , according to some embodiments. In certain embodiments, aluminum oxide layer  2400  is formed on dielectric stack  912  using atomic layer deposition (e.g., PEALD). In some embodiments, PEALD of aluminum oxide layer  2400  is carried out in the same process chamber or same process flow as used to form dielectric stack  912 . Using atomic layer deposition, aluminum oxide layer  2400  may be conformally formed on dielectric stack  912  with substantially uniform thickness. The thickness of aluminum oxide layer  2400  may vary between, for example, about 30 nm and about 55 nm. As described above, a uniform thickness of aluminum oxide layer  2400  may inhibit undesirable increases in non-uniformity and reductions in spectral performance of nanostructure layer  914  formed during subsequent processing of the aluminum oxide layer (described below). 
     Returning to  FIG.  22   , after aluminum oxide layer  2400  is formed on dielectric stack  912  and substrate  901 , at  2206 , in the illustrated embodiment, the aluminum oxide layer is heated in a water-based fluid at a temperature of at least about 50° C. for a time of at least about 5 minutes.  FIG.  25    depicts a cross-sectional representation of aluminum oxide layer  2400  formed on dielectric stack  912  in structure  900  being heated in water-based fluid  2500 , according to some embodiments. Aluminum oxide layer  2400  may be heated by placing structure  900  in water-based fluid  2500  for a predetermined period of time to transform aluminum oxide layer  2400  into nanostructure layer  914  (shown in  FIG.  9   ). 
     In certain embodiments, water-based fluid  2500  is deionized (DI) water. Embodiments may also be contemplated where water-based fluid  2500  includes additional additives (e.g., surfactants, reaction inhibitors, reaction accelerators, etc.). In certain embodiments, water-based fluid  2500  (e.g., DI water) is at a temperature between about 50° C. and about 95° C. during heating of structure  900 . In some embodiments, water-based fluid  2500  is at a temperature between about 60° C. and about 95° C. during heating of structure  900 . In various embodiments, the time period for heating structure  900  in water-based fluid  2500  may be between about 5 minutes and about 60 minutes. Typically, the higher the temperature of water-based fluid  2500 , the shorter duration of the time period for structure  900  to be placed in water-based fluid  2500 . For example, as described above, in one embodiment, structure  900  is placed in water-based fluid  2500  at a temperature of about 70° C. for about 30 minutes. Increasing the temperature of water-based fluid  2500  may allow for a reduced time period (e.g., a temperature of about 95° C. for about 5 minutes). Lowering the temperature of water-based fluid  2500  may necessitate increasing the time period (e.g., a temperature of about 60° C. for about 60 minutes or a temperature of about 50° C. for about 90 minutes). The temperature and time period for placing structure  900  in water-based fluid  2500  may also be varied to provide different transformations (e.g., different crystalline polymorph transformations) in aluminum oxide layer  2400  to nanostructure layer  914 . 
     In some embodiments, the pH of water-based fluid  2500  (e.g., DI water) may have an effect on the different transformations (e.g., different crystalline polymorph transformations) in aluminum oxide layer  2400  to nanostructure layer  914 . For instance, Gibbsite may be more likely to form than Bayerite at lower pH values (e.g., pH values below about 7) while Bayerite or other forms of Boehmite (such as pseudo-Boehmite or polycrystalline Boehmite) may be more likely to form at higher pH values (e.g., pH values above about 7).  FIG.  27    depicts an example of temperature and pH ranges that may produce different crystalline polymorphs (Boehmite, Gibbsite, and Bayerite) in nanostructure layer  914  from treatment of aluminum oxide layer  2400 . Based on the example of  FIG.  27   , it should be understood that varying the exposure of aluminum oxide layer  2400  to different temperatures and/or pH conditions may affect the formation of different crystalline structures in nanostructure layer  914 . 
     As described above, nanostructure layer  914  is a “grass-like” or “flower-like” structure after aluminum oxide layer  2400  is placed in the heated DI water (an example of the “grass-like” or “flower-like” is shown by nanostructure  1002 , shown in  FIG.  10   ). Reaction of aluminum oxide layer  2400  with heated DI water also increases the thickness of nanostructure layer  914  compared to aluminum oxide layer  2400 . For example, a 30 nm aluminum oxide layer  2400  may generate nanostructure layer  914  with a thickness of about 160 nm while a 55 nm aluminum oxide layer  2400  may generate nanostructure layer  914  with a thickness of about 240 nm. 
     Forming nanostructure layer  914  with the “grass-like” or “flower-like” structure may be dependent on conformal deposition (by PEALD) of aluminum oxide layer  2400 . The conformal deposition of aluminum oxide layer  2400  may allow uniform reaction with DI water along the surface of the aluminum oxide layer. In addition, aluminum oxide layer  2400  deposited by PEALD may include impurities (e.g., structural impurities) that allow the aluminum oxide layer to chemically react with DI water. Impurities may include, but not be limited to, the presence of —OH groups, alkyl groups, and/or AlOH 3  groups in aluminum oxide layer  2400 , as deposited by PEALD. Without these impurities (e.g., if aluminum oxide layer  2400  is pure crystalline), there may be little to no reaction between aluminum oxide layer  2400  and the heated DI water. 
     Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications. 
     Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of this disclosure. 
     The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.

Metadata:
Filing Date: 20210910
Publication Date: 20230801
Grant Date: 20230801
Priority Date: 20200914
Inventors: GUSTAFSON, TIMOTHY M.
KONISHIIKE, ISAMU
WANG, LIGANG
FUKUZAKI, RYOZO
HALABICA, Andrej
Assignee: APPLE INC
CPC Classifications: [{"code": "C23C16/0272", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/403", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/45536", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/56", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": true, "tree": "[]"}, {"code": "C23C16/0272", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/403", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/45536", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/56", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/118", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": true, "tree": "[]"}, {"code": "C23C16/45536", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/0272", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/118", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/56", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/403", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B1/118", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/115", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/111", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 87472913