Air-space encapsulated dielectric nanopillars for planar optical devices

Abstract

Embodiments described herein relate to flat optical devices and methods of forming flat optical devices. One embodiment includes a substrate having a first arrangement of a first plurality of pillars formed thereon. The first arrangement of the first plurality of pillars includes pillars having a height h and a lateral distance d, and a gap g corresponding to the distance between adjacent pillars of the first plurality of pillars. The aspect ratio of the gap g to the height h is between about 1:1 and about 1:20. A first encapsulation layer is disposed over the first arrangement of the first plurality of pillars. The first encapsulation layer has a refractive index between about 1.0 and about 1.5. The first encapsulation layer, the substrate, and each of the pillars of the first arrangement define a first space therebetween. The refractive index of the first space is between about 1.0 and about 1.5.

Description

[Technical field]

[0001] background Field FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to optical devices. More particularly, embodiments described herein relate to flat optical devices and methods of forming flat optical devices. [Background technology]

[0002] 2. Description of Related Art A flat optical device includes a configuration of pillars with in-plane dimensions less than half the design wavelength of light and out-of-plane dimensions on the order of the design wavelength or greater. A flat optical device may be comprised of a single or multiple layers of nanostructured pillars. The pillars of a flat optical device need to be encapsulated to act as a protective layer as well as a spacer layer between successive layers of a multi-layer configuration. However, for nanostructured flat optical devices, it is often difficult to fill high aspect ratio openings, resulting in non-uniform gap filling. Furthermore, encapsulation of the pillars increases the height of the pillars and therefore the overall thickness of the flat optical device. Increasing the total thickness of the flat optical device reduces transmission efficiency and increases manufacturing complexity and cost. Therefore, what is needed in the art are improved flat optical devices and methods of forming flat optical devices. Summary of the Invention

[0003] overview In one embodiment, an apparatus is provided. The apparatus includes a substrate. The substrate has a first arrangement of a first plurality of pillars formed thereon. The first arrangement of the first plurality of pillars includes pillars having a height h and a lateral distance d, and a gap g corresponding to a distance between adjacent pillars of the first plurality of pillars. An aspect ratio of the gap g to the height h is between about 1:1 and about 1:20. A first encapsulation layer is disposed over the first arrangement of the first plurality of pillars. The first encapsulation layer has a refractive index between about 1.0 and about 1.5. The first encapsulation layer, the substrate, and each pillar of the first arrangement define a first space therebetween. The first space has a refractive index between about 1.0 and about 1.5.

[0004] In one embodiment, an apparatus is provided. The apparatus includes a substrate. The substrate has a first configuration of a first plurality of pillars formed thereon. The first configuration of the first plurality of pillars includes pillars having a height h and a lateral distance d, and a gap g corresponding to a distance between adjacent pillars of the first plurality of pillars. An aspect ratio of the gap g to the height h is between about 1:1 and about 1:20, the gap g being comprised of a silica-containing aerogel material having nanoscale porosity within the silica-containing material, the silica-containing aerogel material having a gap fill portion disposed within the gap g having the aspect ratio. A first encapsulation layer is disposed over the first configuration of the first plurality of pillars. The first encapsulation layer has a refractive index of about 1.0 to about 1.5. The first encapsulation layer, the substrate, and each pillar of the first configuration define a first space therebetween. The first space has a refractive index of about 1.0 to about 1.5.

[0005] In yet another embodiment, a method is provided. A first configuration of a first plurality of pillars includes pillars having a height h and a lateral distance d, and a gap g corresponding to a distance between adjacent pillars of the first plurality of pillars. An aspect ratio of the gap g to the height h is between about 1:1 and about 1:20. A silica-containing aerogel material is deposited. The deposition of the silica-containing aerogel material includes a silica-containing aerogel material formation process for forming nanoscale porosity in the silica-containing aerogel material. The silica-containing aerogel material has a gap fill portion disposed within the gap g having the aspect ratio, an encapsulation portion disposed on the gap fill portion, and the first configuration of the first plurality of pillars.

[0006] BRIEF DESCRIPTION OF THE DRAWINGS So that the above-mentioned features of the present disclosure can be understood in detail, a more particular description of the present disclosure briefly summarized above can be made by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings depict only exemplary embodiments, and therefore should not be considered as limiting the scope of the present disclosure, which may also admit of other equally effective embodiments. [Brief description of the drawings]

[0007] [Figure 1A] 1 is a schematic perspective view of a flat optical device according to embodiments described herein; [Figure 1B] 1 is a schematic cross-sectional view of a layer stack according to embodiments described herein; [Figure 1C] 2A-2C are schematic top view illustrations of pillar arrangements of layer stacks according to embodiments described herein; [Fig. 1D-F] 1D-F are schematic cross-sectional views of layer stacks according to embodiments described herein. [Diagram 2] FIG. 2 is a flow diagram of a method for forming a flat optical device according to embodiments described herein. [Figure 3A-D] 3A-3D are schematic cross-sectional views of a substrate during a method of forming a planar optical device according to embodiments described herein. [Figure 4A]FIG. 2 is a flow diagram of a method for forming a flat optical device according to embodiments described herein. [Figure 4B] FIG. 2 is a flow diagram of a method for forming a flat optical device according to embodiments described herein. [Figure 5A-D] 5A-5D are schematic cross-sectional views of a substrate during a method of forming a planar optical device according to embodiments described herein. [Figure 5E-G] 5E-5G are schematic cross-sectional views of a substrate during a method of forming a planar optical device according to embodiments described herein. [Figure 6] FIG. 2 is a flow diagram of a method for forming a flat optical device according to embodiments described herein. [Figure 7A-C] 7A-7C are schematic cross-sectional views of a substrate during a method of forming a planar optical device according to embodiments described herein. [Figure 8] FIG. 2 is a flow diagram of a method for forming a flat optical device according to embodiments described herein. [Figure 9A-B] 9A and 9B are schematic cross-sectional views of a substrate during a method of forming a flat optical device according to embodiments described herein.

[0008] For ease of understanding, wherever possible, the same reference numerals have been used to designate identical elements that are common to several figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Detailed Description SUMMARY OF THE DISCLOSURE Embodiments described herein relate to flat optical devices and methods of forming flat optical devices. One embodiment includes a substrate having a first arrangement of a first plurality of pillars formed thereon. The first arrangement of the first plurality of pillars includes pillars having a height h and a lateral distance d, and a gap g corresponding to a distance between adjacent pillars of the first plurality of pillars. An aspect ratio of the gap g to the height h is between about 1:1 and about 1:20. A first encapsulation layer is disposed over the first arrangement of the first plurality of pillars. The first encapsulation layer has a refractive index between about 1.0 and about 1.5. The first encapsulation layer, the substrate, and each of the pillars of the first arrangement define a first space therebetween. The first space has a refractive index between about 1.0 and about 1.5.

[0010] FIG. 1A is a schematic perspective view of a flat optical device 100 having at least one layer stack 101A, 101B. FIG. 1B is a schematic cross-sectional view of the layer stack 101A. FIG. 1C is a schematic top view of an arrangement of pillars 104 of the layer stack 101A. The flat optical device 100 includes at least one layer stack 101A, 101B. Although aspects of the apparatus and methods described herein may be described with reference to the layer stack 101A, it should be understood that aspects of the apparatus and methods described herein are equally applicable to the layer stack 101B. For clarity of the figures provided herein, reference numbers may be omitted for the arrangement of the layer stack 101B.

[0011] In one embodiment that can be combined with other embodiments described herein, the flat optical device 100 is a single-layer stack flat optical device including a layer stack 101A. In another embodiment that can be combined with other embodiments described herein, the flat optical device 100 is a multi-layer stack optical device including one or more layer stacks 101A and a layer stack 101B. The layer stack 101A includes a configuration of multiple pillars 104A arranged on a surface of the substrate 102, and an encapsulation layer 106A. In the multi-layer stack optical device embodiment, a first layer stack of the one or more layer stacks 101B is arranged on the layer stack 101A. In one embodiment that can be combined with other embodiments described herein, the first layer stack of the layer stack 101B includes a configuration of multiple pillars 104B arranged on the encapsulation layer 106A. In another embodiment that can be combined with other embodiments described herein, the configuration of multiple pillars 104B of the first layer stack of the layer stack 101B is arranged on a spacer layer (not shown) arranged on the encapsulation layer 106A. In embodiments that include a spacer layer, the spacer layer is operable to provide support for the arrangement of pillars 104B and is of a particular thickness according to the optical function of the planar optical device 100.

[0012] The configuration of the plurality of pillars 104A, 104B includes pillars 104A, 104B having a height h and a lateral distance d. The height h of the pillars 104A is defined as the distance from the surface of the substrate 102 to the encapsulation layer 106A. The height h of the pillars 104B is defined as the distance from the encapsulation layer 106A and a spacer layer (not shown) disposed on the encapsulation layer 106A to the encapsulation layer 106B. In another embodiment that can be combined with other embodiments described herein, the cross section of the pillars 104A, 104B is square and / or rectangular, and the lateral distance d of the pillars 104A, 104B corresponds to the width of the pillars 104A, 104B. In another embodiment that can be combined with other embodiments described herein, the cross section of the pillars 104A, 104B is circular, and the lateral distance d of the pillars 104A, 104B corresponds to the diameter of the pillars 104A, 104B. The gap g is the distance between adjacent ones of the pillars 104A, 104B. In one embodiment, each of the configurations of the plurality of pillars 104A, 104B has an aspect ratio (g:h) between about 1:1.5 and about 1:10. In another embodiment, each of the configurations of the plurality of pillars 104A, 104B has an aspect ratio (g:h) between about 1:1.5 and about 1:2.5. In yet another embodiment, each of the configurations of the plurality of pillars 104A, 104B has an aspect ratio (g:h) between about 1:1 and about 1:20.

[0013] The lateral distance d and the gap g are less than half the wavelength of operation. The wavelength of operation corresponds to a wavelength or wavelength range. In one example, the wavelength or wavelength range includes one or more wavelengths from the UV region to the near infrared region (i.e., about 300 nm to about 1500 nm). Thus, for example, at a wavelength of 700 nm, the distance d and the gap g are less than 350 nm. In one embodiment that can be combined with other embodiments described herein, the lateral distance d of each pillar of the plurality of pillars 104A is substantially the same. In another embodiment that can be combined with other embodiments described herein, the lateral distance d of at least one pillar is different from the lateral distance d of additional pillars of the plurality of pillars 104A. In one embodiment that can be combined with other embodiments described herein, the gap g of each adjacent pillar of the plurality of pillars 104A is substantially the same. In another embodiment that can be combined with other embodiments described herein, the gap g of at least one set of adjacent pillars is different from the gap g of the additional set of the plurality of pillars 104A. In some embodiments, which may be combined with other embodiments described herein, the configuration of the plurality of pillars 104B corresponds to (i.e., matches) the configuration of the plurality of pillars 104A. In other embodiments, which may be combined with other embodiments described herein, the configuration of the plurality of pillars 104B does not correspond to the configuration of the plurality of pillars 104A.

[0014] The substrate 102 can be selected to transmit light at the wavelength of operation. In some non-limiting embodiments, the substrate 102 is configured such that the substrate 102 transmits approximately 50%, 60%, 70%, 80%, 90%, 95%, 99% or more of the UV region of the light spectrum. The substrate 102 can be formed from any suitable material, provided that the substrate 102 can adequately transmit light at the wavelength of operation and can serve as a suitable support for at least the placement of the plurality of pillars 104A and the encapsulation layer 106A. In some embodiments that can be combined with other embodiments described herein, the material of the substrate 102 has a relatively low refractive index compared to the refractive index of the material used in each of the pillars 104A, 104B. The substrate selection can include substrates of any suitable material, including, but not limited to, semiconductors, doped semiconductors, amorphous dielectrics, non-amorphous dielectrics, crystalline dielectrics, silicon oxides, polymers, and combinations thereof. In some embodiments that can be combined with other embodiments described herein, the substrate 102 comprises a transparent material. The substrate 102 is transparent with an absorption coefficient of less than 0.001. Examples include, but are not limited to, oxides, sulfides, phosphides, tellurides, and combinations thereof. In one example, the substrate 102 comprises a silica (SiO2)-containing material.

[0015] The pillars 104A and 104B may be made of titanium dioxide (TiO2), zinc oxide (ZnO), tin dioxide (SnO2), aluminum doped tin oxide (AZO), fluorine doped tin oxide (FTO), stannic acid (Tin oxide) Kadmiu M( CTO), stannic acid (Tin oxide) sub lead(The pillars 104A, 104B may have a refractive index of about 1.8 or greater and an absorption coefficient of less than 0.001. In one embodiment that may be combined with other embodiments described herein, the encapsulation layers 106A, 106B have a refractive index of about 1.0 to about 1.5. The encapsulation layers 106A, 106B have an absorption coefficient of less than 0.001. In some embodiments that may be combined with other embodiments described herein, the encapsulation layers 106A, 106B and the substrate 102 comprise substantially the same material. In one embodiment, the conformal encapsulation layer 306A has a thickness of about 2 nm to about 100 nm. In another embodiment, the encapsulation layer 106A has a thickness of less than 50 μm. In another embodiment, encapsulation layer 306A has a thickness of about 1 μm to about 2 μm.

[0016] The materials and dimensions of the encapsulation layers 106A, 106B are further described in the methods provided herein. The use of the materials, dimensions, and processes described herein for the encapsulation layers 106A, 106B, and the composition of the space 108 corresponding to the gap g, provides a height h of the pillars 104A, 104B of about 1500 nm or less. In some embodiments, which can be combined with other embodiments described herein, the height h of the pillars 104A, 104B is about 500 nm or less. The height h of the pillars 104A, 104B reduces the thicknesses 110A, 110B of the layer stacks 101A, 101B, and the total thickness of the planar optical device 100. The reduction in the overall thickness of the planar optical device 100 provides higher transmission efficiency and reduced manufacturing complexity and cost due to impedance matching and device symmetry compared to bare optical devices.

[0017] The composition of the space 108 corresponding to the gap g may be air, which has a refractive index of 1.0 and an absorption coefficient of 0, or a transparent material 107 (shown in Figures 1D-1F) with an absorption coefficient of less than 0.001. In one embodiment that may be combined with other embodiments described herein, the refractive index of the transparent material 107 of the composition of the space 108 has a refractive index of about 1.0 to about 1.5. In some embodiments that may be combined with other embodiments described herein, the transparent material 107 comprises one of a silica-containing material or a non-silica-containing material, such as a polymer-containing material, e.g., a fluoropolymer material. In some embodiments that may be combined with other embodiments described herein, the transparent material 107 comprises a fluorine-containing material, such as aluminum fluoride (AlF3) and magnesium fluoride (MgF2).

[0018] In one embodiment, which may be combined with other embodiments described herein, as shown in FIG. 1D, encapsulation layer 106A of layer stack 101A includes transparent material 107 and the composition of space 108 includes air (refractive index 1.0). In some embodiments of the embodiment of FIG. 1D, transparent material 107 has a refractive index between about 1.0 and about 1.5. The height h of pillar 104A decreases as the refractive index of transparent material 107 decreases. An example of the embodiment of FIG. 1D includes layer stack 101A of FIGS. 3C, 5D, and 5F.

[0019] In another embodiment, which can be combined with other embodiments described herein, as shown in FIG. 1E, the encapsulation layer 106A of the layer stack 101A includes a transparent material 107 and the composition of the space 108 includes the transparent material 107. In some embodiments of the embodiment of FIG. 1E, the transparent material 107 has a refractive index of about 1.0 to about 1.5. The height h of the pillars 104A decreases as the refractive index of the transparent material 107 decreases. For example, in some embodiments, the embodiment of FIG. 1D having the composition of the space 108 including air results in a lower height h. An example of the embodiment of FIG. 1E includes the layer stack 101A of FIG. 7B.

[0020] As shown in FIG. 1F, in another embodiment that can be combined with other embodiments described herein, a conformal encapsulation layer 106A is disposed on the plurality of pillars 104A. In some embodiments, the conformal encapsulation layer 106A fills the space 108. In other embodiments, the conformal encapsulation layer 106A does not fill the space 108 such that the composition of the space 108 includes the transparent material 107 and air. In other embodiments, the conformal encapsulation layer 106A does not fill the space 108 such that the composition of the space 108 includes the transparent material 107 and air. In some embodiments of the embodiment of FIG. 1D, the transparent material 107 has a refractive index of about 1.0 to about 1.5. The height h of the pillars 104A decreases as the refractive index of the transparent material 107 decreases. An example of the embodiment of FIG. 1D includes the layer stack 101A of FIG. 9B.

[0021] In one embodiment that can be combined with other embodiments described herein, the transparent material 107 of the embodiment of Figures 1D-1E includes one of a silica-containing material or a non-silica-containing material, such as a polymer-containing material, such as a fluoropolymer material. In another embodiment that can be combined with other embodiments described herein, the transparent material 107 of the embodiment of Figures 1D-1E includes a silica-containing aerogel material. The silica-containing aerogel material includes nanoscale porosity to provide voids in the space 108. In one embodiment that can be combined with other embodiments described herein, the silica-containing aerogel material has a porosity of about 95% or more corresponding to the nanoscale voids. The nanoscale porosity of the silica-containing aerogel material reduces the refractive index of the silica. The reduced refractive index reduces the height h. The silica-containing aerogel material is hydrophobic to protect the pillars 104A from external factors.

[0022] 2 is a flow diagram of a method 200 of forming a flat optical device 100, as shown in FIGS. 3A-3D. In operation 201, a configuration of pillars 104A is formed on a surface of a substrate 102. In one embodiment, which may be combined with other embodiments described herein, forming the configuration of pillars 104A includes disposing a pillar material 310 on the surface of the substrate 102 and removing a portion of the pillar material 310 to form a trench 302. The trench 302 corresponds to the gap g of the pillars 104A (including the space 108 of the flat optical device 100), the remaining portion of the trench corresponds to the lateral distance d, and the thickness of the pillar material 310 corresponds to the height h.

[0023] In one embodiment that can be combined with other embodiments described herein, the pillar material 310 comprises an oxide. In optional operation 202, a liner 304 is disposed on the oxide-free pillar 104A. The liner 304 protects the pillar 104A from oxidation resulting from the deposition of an encapsulation layer 306A that comprises an oxide-containing material, such as silica. In one embodiment that can be combined with other embodiments described herein, the liner 304 has a refractive index of about 1.0 to about 1.5. In one embodiment that can be combined with other embodiments described herein, the liner 304 has a thickness of about 1 nm to about 100 nm. The liner 304 can be deposited by atomic layer deposition (ALD), such as rapid ALD. In one embodiment that can be combined with other embodiments described herein, the silica-containing liner 304 is conformally deposited on the pillar 104A by an ALD process that includes alternating flows of TMA (AlMe3) and (tButO)3SiOH. Each TMA (AlMe3) and ( t The ButO)SiOH flow cycle produces a sublayer approximately 12 nm thick (more than 32 monolayers).

[0024] In operation 203, an encapsulation layer 306A corresponding to the encapsulation layer 106A is disposed on the pillar 104A. The deposition of the encapsulation layer 306A may include, but is not limited to, chemical vapor deposition (CSD), plasma enhanced chemical vapor deposition (PE CVD), ALD, rapid ALD, spray coating, or spin coating. In one embodiment that can be combined with other embodiments described herein, the encapsulation layer 306A has a thickness of about 1 μm to about 10 μm. In another embodiment that can be combined with other embodiments described herein, the encapsulation layer 306A has a thickness of about 1 μm to about 2 μm. Operations 201-203 form a single layer stack planar optical device 100 including the layer stack 101A. In operation 204, at least operations 201-203 are repeated at least once to form a multi-stack optical device having the layer stack 101A and at least one layer stack 101B. Layer stack 101B includes at least encapsulation layer 306A, an arrangement of multiple pillars 104B, and encapsulation layer 306B. The arrangement of multiple pillars 104B formed via operation 201 is disposed in one of encapsulation layers 306A, and a spacer layer (not shown) is disposed in encapsulation layer 306A.

[0025] FIG. 4A is a flow diagram of a method 400A for forming a flat optical device 100, as shown in FIGS. 5A-5E. FIG. 4B is a flow diagram of a method 400B for forming a flat optical device 100, as shown in FIGS. 5A-5E. In operations 401A, 401B of methods 400A and 400B, a configuration of a plurality of pillars 104A is formed on a surface of a substrate 102, as described in operation 201 of method 200. In operation 402A, a sacrificial material 504A to be removed is deposited in the trench 302. In an embodiment that can be combined with other embodiments described herein, the sacrificial material 504A is deposited by hot wire CVD (HWCVD), PE CVD, or inductively coupled plasma CVD (ICPCVD). In operation 402B, an area-reducing gap-filling material 504B is deposited in the trench 302.

[0026] In operations 403A, 403B, an encapsulation layer 306A corresponding to the encapsulation layer 106A is disposed on the pillars 104A and one of the sacrificial material 504A and the gap-filling material 504B. The disposition of the encapsulation layer 306A may include, but is not limited to, no-flow chemical vapor deposition (CVD), ALD, rapid ALD, PECVD, spray coating, or spin coating. In operation 404A, the sacrificial material 504A is removed. In an embodiment that can be combined with other embodiments described herein, the sacrificial material is removed by thermal annealing. In operation 404B, the gap-filling material 504B is reduced by an area 506 in the space 108, so that the gap g includes the gap-filling material 504B with a central void 503 disposed in the area 506. In an embodiment that can be combined with other embodiments described herein, the gap-filling material 504B is reduced by a thermal cure, such as a thermal cure, a chemical reduction, and a UV treatment, such as a UV cure. Operations 401A-404A, 401B-404B form a single layer stack planar optical device 100 including layer stack 101A. In operations 405A, 405B, operations 401A-404A, 401B-404B are repeated at least one time to form a multi-stack optical device having layer stack 101A and at least one layer stack 101B. Layer stack 101B includes at least encapsulation layer 306A, an arrangement of multiple pillars 104B, and encapsulation layer 306B.

[0027] FIG. 6 is a flow diagram of a method 600 for forming a flat optical device 100, as shown in FIGS. 7A-7C. In operation 601, a configuration of a plurality of pillars 104A is formed on a surface of a substrate 102, as described in operation 201 of method 200. In operation 602, a silica-containing aerogel material 702A is disposed on the plurality of pillars 104A. Operations 601 and 602 form a single layer stack flat optical device 100 including layer stack 101A. A gap-filling portion 704A of the silica-containing aerogel material 702A is disposed in a trench 302 corresponding to a gap g of the pillar 104A (including space 108 of the flat optical device 100). An encapsulating portion 706A of the silica-containing aerogel material 702A is disposed on the plurality of pillars 104A and the gap-filling portion 704A. The encapsulating portion 706B corresponds to an encapsulating layer 306B.

[0028] In operation 603, operations 601 and 602 are repeated at least once to form a multi-stack optical device having layer stack 101A and at least one layer stack 101B. Layer stack 101B includes at least encapsulation layer 306A, a configuration of multiple pillars 104B, and encapsulation layer 306B. The configuration of multiple pillars 104B formed via operation 601 is disposed in one of encapsulation layers 306A, and a spacer layer (not shown) is disposed in encapsulation layer 306A. The encapsulation portion 706B of silica-containing aerogel material 702B corresponds to encapsulation layer 306B. The gap-fill portion 704B of silica-containing aerogel material 702B is disposed in trench 302. In one embodiment, which can be combined with other embodiments described herein, encapsulation layers 306A, 306B (i.e., encapsulation portions 706A, 706B) have a thickness of about 1 μm to about 2 μm. The silica-containing aerogel has a refractive index of about 1.0 to about 1.10 and a permeability coefficient of less than 0.001. The silica-containing aerogel material includes nanoscale porosity to provide voids in the space 108. In one embodiment, which may be combined with other embodiments described herein, the silica-containing aerogel material has a porosity of about 95% or greater corresponding to the nanoscale voids. The nanoscale porosity of the silica-containing aerogel material reduces the refractive index of solid silica.

[0029] The silica-containing aerogel material is formed from a silica-containing aerogel material formation process. The formation process includes a precursor preparation process, a deposition process, or a supercritical drying process. The precursor preparation process includes the preparation of a silica sol-gel. The sol (i.e., solution) is prepared by adding a catalyst to a silica precursor solution in a solvent. Examples of silica precursors include, but are not limited to, tetraethylorthosilicate (TEOS), tetramethylorthosilicate (TMOS), methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTMS), methyltriethoxysilane (MTES), Silbond H-5, or polyethoxydisiloxane (PEDS). Examples of catalysts include, but are not limited to, hydrochloric acid (HF), hydrogen chloride (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), oxalic acid (C2H2O4), acetic acid (CH3COOH), trifluoroacetic acid (TFA), or ammonium hydroxide (NH4OH). Examples of solvent precursors include, but are not limited to, methanol, ethanol, and isopropanol. The gel is prepared by aging the solution, which strengthens the solution into a sol-gel by cross-linking. Aging the sol-gel maintains shrinkage during drying to the supercritical drying process.

[0030] The deposition process includes disposing the sol-gel via either spin coating, dip coating, or spray coating. In one embodiment, which can be combined with other embodiments described herein, during the deposition process, the substrate 102 is rotated (i.e., rotated) about the substrate's central axis 103. The substrate 102 is rotated about the central axis 103 such that the aspect ratio of the arrangement of the plurality of pillars 104A, 104B is between about 1:1.5 and about 1:10, between 1:1.5 and 1:2.5, or between about 1:1.1 and about 1:20. The trench 302 is filled with the gap-filling portions 704A, 704B of the silica-containing aerogel material 702A, 702B that are disposed. The rotation speed can vary during the deposition process. In one embodiment, which can be combined with other embodiments described herein, the rotation speed during the formation of the encapsulation portions 706A, 706B is lower than the rotation speed of the gap-filling portions 704A, 704B. The drying process removes the solvent to form a silica-containing aerogel material with nanoscale porosity that provides voids in the space 108. In one embodiment, which can be combined with other embodiments described herein, the drying process includes one or more of, but is not limited to, supercritical CO2 drying, freeze drying, and pressure drying, such as ambient pressure drying.

[0031] FIG. 8 is a flow diagram of a method 800 of forming a flat optical device 100, as shown in FIGS. 9A and 9B. In operation 801, a configuration of a plurality of pillars 104A is formed on a surface of a substrate 102, as described in operation 201 of method 200. In operation 802, a conformal encapsulation layer 306A is disposed on the plurality of pillars 104A. Disposing the conformal encapsulation layer 306A may include, but is not limited to, CVD, PE CVD, ALD, rapid ALD, and thermal oxidation. In one embodiment, the conformal encapsulation layer 306A has a thickness of about 2 nm to about 100 nm. In another embodiment, the encapsulation layer 306A has a thickness of less than 50 μm. In another embodiment, the encapsulation layer 306A has a thickness of about 1 μm to about 2 μm. In one embodiment, which can be combined with other embodiments described herein, the refractive index of the conformal encapsulation layer 306A is about 1.0 to about 1.5.

[0032] In summary, the embodiments described herein provide a flat optical device and a method of forming a flat optical device. One embodiment of the optical device is a single-layer stack flat optical device including one layer stack. The layer stack includes a first configuration of a first plurality of pillars disposed on a surface of a substrate and a first encapsulation layer. Another embodiment of the optical device is a multi-layer stack optical device including a first layer stack and a second layer stack formed thereon. A second layer stack of the one or more layer stacks is disposed on the first layer stack. The second layer stack includes a second configuration of a second plurality of pillars disposed on one of the first encapsulation layer and a spacer layer disposed on the first encapsulation layer. The composition of the encapsulation layer and the space corresponding to the gap g described herein provides a pillar height h of about 1500 nm or less, and in some embodiments 500 nm or less. The pillar height h reduces the thickness of the layer stack and the total thickness of the flat optical device. The reduced overall thickness of the planar optical device provides higher transmission efficiency and reduced manufacturing complexity and cost due to impedance matching and device symmetry compared to bare optical devices.

[0033] While the above description is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, the scope of the disclosure being determined by the claims that follow.

Claims

1. A substrate; A first arrangement of a first plurality of pillars formed over the substrate, a pillar having a height h and a lateral distance d; and a gap g corresponding to the distance between adjacent pillars of the first plurality of pillars; a first configuration of first plurality of pillars, comprising: an aspect ratio of the gap g to the height h is between 1:1 and 1:20, and the height h is less than or equal to 1500 nm; a first encapsulation layer having a refractive index between 1.0 and 1.5 and a thickness less than 50 micrometers (μm) disposed over the first arrangement of the first plurality of pillars, including over both the pillars and the gaps g; wherein the first encapsulation layer, the substrate, and the pillars of the first configuration each define a first space therebetween, the first space including a central void comprising air and a region of material surrounding the central void, the material being a transparent material having a refractive index between 1.0 and 1.5 and an absorption coefficient less than 0.

001.

2. 10. The apparatus of claim 1, wherein the transparent material comprises a silica-containing aerogel material, the silica-containing aerogel material having nanoscale porosity formed therein.

3. The device of claim 2 , wherein the transparent material and the first encapsulation layer are made of the same material.

4. The device of claim 1 , wherein the transparent material comprises a fluorine-containing material or a silica-containing material.

5. The apparatus of claim 1 , wherein a liner is disposed on the pillar.

6. The apparatus of claim 5 , wherein the liner has a thickness between 1 nanometer (nm) and 200 nm.

7. a second configuration of a second plurality of pillars formed on the first encapsulation layer, a pillar having said height h and said lateral distance d; and a gap g corresponding to the distance between adjacent pillars of the second plurality of pillars; a second configuration of the second plurality of pillars, comprising: an aspect ratio of the gap g to the height h being between 1:1 and 1:20; a second encapsulation layer having a refractive index between 1.0 and 1.5 disposed over the second arrangement of the second plurality of pillars; wherein the second encapsulation layer, the first encapsulation layer, and the pillars of the second configuration each define a second space therebetween having a refractive index of 1.0 to 1.

5.

8. The pillars are made of titanium dioxide (TiO ２ ), zinc oxide (ZnO), tin dioxide (SnO ２ ), aluminum doped zinc oxide (AZO), fluorine doped tin oxide (FTO), cadmium stannate (CTO), zinc stannate (SnZnO ３ 7. The apparatus of claim 1 , further comprising one or more of the following: a silicon-containing material;

9. 9. The apparatus of claim 1, wherein the gap g is less than 350 nanometers (nm).

10. 10. The device of claim 1, wherein the first encapsulation layer has a thickness of 1 micrometer (μm) to 2 micrometers (μm).

11. 11. The device of claim 1, wherein the height h is less than or equal to 500 nm.

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