Voided encapsulation dielectric nano-pillars for flat 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 gaps g corresponding to a distance between adjacent pillars of the first plurality of pillars. An aspect ratio of the gaps g to the height h is between about 1 : 1 and about 1 :20. A first encapsulation layer is disposed on the first arrangement 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 arrangement define a first space therebetween. The first space has a refractive index of about 1.0 to about 1.5.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to optical devices. More specifically, the embodiments described herein relate to flat optical devices and methods of forming flat optical devices. BACKGROUND

[0002] Flat optical devices include an arrangement of pillars having in-plane dimensions less than half of a design wavelength of light and out-of-plane dimensions about or greater than the design wavelength. Flat optical devices can be composed of single or multiple layers of nanostructured pillars. The pillars of the flat optical devices require encapsulation to act as a protective layer and as a spacer layer between successive layers of the multiple layer arrangement. However, for nanostructured flat optical devices, filling high aspect ratio openings is generally challenging and can result in non-uniform gap filling. Furthermore, the encapsulation of the pillars increases the height of the pillars, thus increasing the overall thickness of the flat optical device. The increase in the overall 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

[0003] In one embodiment, a device is provided. The device 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 on the first arrangement 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 arrangement define a first space therebetween. The first space has a refractive index of about 1.0 to about 1.5.

[0004] A device is provided. The device 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, wherein the gap g is composed of a silica-containing aerogel material having nanoscale pores in the silica-containing material, the silica-containing aerogel material having a gap-filling portion disposed in the gap g having the aspect ratio. A first encapsulation layer is disposed on the first arrangement 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 arrangement 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 arrangement of a first plurality of pillars includes pillars having a height h and a lateral distance d, and gaps g corresponding to distances between adjacent pillars in the first plurality of pillars. The aspect ratio of the gaps g to the height h is between about 1 : 1 and about 1 :20. A silica-containing aerogel material is deposited. Depositing the silica-containing aerogel material includes a silica-containing aerogel material forming process to form nanoscale pores in the silica-containing aerogel material. The silica-containing aerogel material has a gap-filling portion disposed in the gaps g having the aspect ratio and an encapsulating portion disposed on the gap-filling portion and the first arrangement of the first plurality of pillars. BRIEF DESCRIPTION OF DRAWINGS

[0006] So that the above-recited features of the present disclosure can be understood in detail, a more particular description will be rendered by reference to example implementations, some of which are illustrated in the drawings. It is to be noted, however, that the appended drawings are intended to be exemplary only and should not be construed as limiting the scope of the disclosure in any way.

[0007] Figure 1A is a schematic perspective view of a flat optic according to embodiments described herein.

[0008] Figure 1B is a schematic cross-sectional view of a layer stack according to embodiments described herein.

[0009] Figure 1C is a schematic top view of a pillar arrangement of a layer stack according to embodiments described herein.

[0010] Figures 1D-1F is a schematic cross-sectional view of a layer stack according to embodiments described herein.

[0011] Figure 2 is a flowchart of a method of forming a flat optic according to embodiments described herein.

[0012] Figures 3A-3D is a schematic cross-sectional view of a substrate during a method of forming a flat optic according to embodiments described herein.

[0013] Figure 4A with Figure 4B is a flowchart of a method of forming a flat optic according to embodiments described herein.

[0014] Figures 5A-5G is a schematic cross-sectional view of a substrate during a method of forming a flat optic according to embodiments described herein.

[0015] Figure 6 is a flowchart of a method of forming a flat optical device according to embodiments described herein.

[0016] Figures 7A-7C is a schematic cross-sectional view of a substrate during a method of forming a flat optical device according to embodiments described herein.

[0017] Figure 8 is a flowchart of a method of forming a flat optical device according to embodiments described herein.

[0018] Figure 9A with 9B is a schematic cross-sectional view of a substrate during a method of forming a flat optical device according to embodiments described herein.

[0019] To facilitate an understanding of this description, like reference characters are used throughout the disclosure for like elements and features. It should be appreciated that elements and features of one implementation can be readily transposed or substituted into another implementation, as appropriate, without further recitation. DETAILED DESCRIPTION

[0020] 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 gaps g corresponding to a distance between adjacent pillars of the first plurality of pillars. The aspect ratio of the gaps g to the height h is between about 1 : 1 and about 1 :20. A first encapsulation layer is disposed on the first arrangement 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 arrangement define a first space therebetween. The first space has a refractive index of about 1.0 to about 1.5.

[0021] Figure 1A is a schematic perspective view of a flat optical device 100 having at least one layer stack 101 A, 101 B. Figure 1B is a schematic cross-sectional view of a layer stack 101 A. Figure 1C is a schematic top view of an arrangement of pillars 104 of a layer stack 101 A. The flat optical device 100 includes at least one layer stack 101 A, 101 B. While aspects of the devices and methods described herein can be discussed with reference to the layer stack 101 A, it should be understood that aspects of the devices and methods described herein are similarly applicable to the layer stack 101 B. For the sake of clarity, reference characters for the arrangement of the layer stack 101 B in the figures provided herein can be omitted.

[0022] In one embodiment, which can be combined with other embodiments described herein, the flat optic 100 is a single layer stack optic comprising the layer stack 101 A. In another embodiment, which can be combined with other embodiments described herein, the flat optic 100 is a multi-layer stack optic comprising the layer stack 101 A and one or more layer stacks 101 B. The layer stack 101 A comprises an arrangement of a plurality of pillars 104A disposed on a surface of the substrate 102 and an encapsulation layer 106A. In embodiments of the multi-layer stack optic, a first layer stack of the one or more layer stacks 101 B is disposed on the layer stack 101 A. In one embodiment, which can be combined with other embodiments described herein, the first layer stack of the layer stacks 101 B comprises an arrangement of a plurality of pillars 104B disposed on the encapsulation layer 106A. In another embodiment, which can be combined with other embodiments described herein, the arrangement of the plurality of pillars 104B of the first layer stack of the layer stacks 101 B is disposed on a spacer layer (not shown) disposed on the encapsulation layer 106A. In embodiments comprising a spacer layer, the spacer layer can be used to provide support for the arrangement of the plurality of pillars 104B and has a specified thickness depending on the optical function of the flat optic 100.

[0023] The arrangement of the plurality of pillars 104A, 104B comprises 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 the spacer layer (not shown) disposed on the encapsulation layer 106A to the encapsulation layer 106B. In another embodiment, which 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, which 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 pillars 104A, 104B. In one embodiment, the aspect ratio (g:h) of each arrangement of the plurality of pillars 104A, 104B is between about 1 : 1.5 to about 1 : 10. In another embodiment, the aspect ratio (g:h) of each arrangement of the plurality of pillars 104A, 104B is between about 1 : 1.5 to about 1 : 2.5. In yet another embodiment, the aspect ratio (g:h) of each arrangement of the plurality of pillars 104A, 104B is between about 1 : 1 to about 1 : 20.

[0024] The lateral distance d and the gap g are less than half of the operational wavelength. The operational wavelength corresponds to a wavelength or a range of wavelengths. In one example, the wavelength or the range of wavelengths includes one or more wavelengths in the UV region to the near infrared region (i.e., from 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, which can be combined with other embodiments described herein, the lateral distance d of each of the plurality of pillars 104A is substantially the same. In another embodiment, which can be combined with other embodiments described herein, the lateral distance d of at least one pillar is different than the lateral distance d of another pillar of the plurality of pillars 104A. In one embodiment, which 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, which can be combined with other embodiments described herein, the gap g of at least one set of adjacent pillars is different than the gap g of another set of adjacent pillars of the plurality of pillars 104A. In some embodiments, which can be combined with other embodiments described herein, the arrangement of the plurality of pillars 104B corresponds to (i.e., matches) the arrangement of the plurality of pillars 104A. In other embodiments, which can be combined with other embodiments described herein, the arrangement of the plurality of pillars 104B does not correspond to the arrangement of the plurality of pillars 104A.

[0025] The substrate 102 can be selected to transmit light at the operational wavelength. Without limitation, in some embodiments, the substrate 102 is configured such that the substrate 102 transmits greater than or equal to about 50%, 60%, 70%, 80%, 90%, 95%, 99% of the UV region of the optical spectrum. The substrate 102 can be formed of any suitable material, so long as the substrate 102 can appropriately transmit light at the operational wavelength and can serve as an appropriate support for at least the arrangement of the plurality of pillars 104A and the encapsulation layer 106A. In some embodiments, which can be combined with other embodiments described herein, the material of the substrate 102 has a relatively low refractive index as compared to the refractive index of the material used in each of the pillars 104A, 104B. 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 oxide, polymers, and combinations thereof. In some embodiments, which can be combined with other embodiments described herein, the substrate 102 includes a transparent material. The substrate 102 is transparent with an absorption coefficient less than 0.001. Examples can include but are not limited to oxides, sulfides, phosphides, tellurides, and combinations thereof. In one example, the substrate 102 includes a material including silicon dioxide (SiO2).

[0026] The pillars 104A, 104B include materials not limited to titanium dioxide (Ti02), zinc oxide (ZnO), tin dioxide (Sn02), aluminum-doped zinc oxide (AZO), fluorine-doped tin oxide (FTO), cadmium stannate (CTO), zinc stannate (SnZn03), and silicon-containing materials. The silicon-containing materials can include at least one of silicon nitride (Si3N4) or amorphous silicon (a-Si). The pillars 104A, 104B can have a refractive index of about 1.8 or greater, and an absorption coefficient less than 0.001. In one embodiment, which can 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 less than 0.001. In some embodiments, which can be combined with other embodiments described herein, the encapsulation layers 106A, 106B and the substrate 102 include 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 less than 50 μm. In another embodiment, the encapsulation layer 306A has a thickness of about 1 μm to about 2 μm.

[0027] The materials and dimensions of the encapsulation layers 106A, 106B are further described in the methods provided herein. With the materials, dimensions, and processing of the encapsulation layers 106A, 106B described herein, and the composition of the space 108 corresponding to the gap g, the height h of the pillars 104A, 104B can be 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 reduction in the height h of the pillars 104A, 104B reduces the thickness 110A, 110B of the layer stack 101A, 101B, and the overall thickness of the flat optical device 100. The reduction in the overall thickness of the flat optical device 100 improves transmission efficiency, and reduces manufacturing complexity and cost, due to impedance matching and device symmetry, as compared to a bare optical device.

[0028] The composition of the space 108 corresponding to the gap g includes air or a transparent material 107 (e.g., Figures 1D-1FOf at least one of the following (shown), air has a refractive index of 1.0 and an absorption coefficient of 0, while the absorption coefficient of transparent material 107 is less than 0.001. In one embodiment that can be combined with other embodiments described herein, the refractive index of transparent material 107 constituting space 108 has a refractive index of about 1.0 to about 1.5. In some embodiments that can be combined with other embodiments described herein, transparent material 107 comprises either a silica-containing material or a silica-free material (e.g., a polymer-containing material, such as a fluoropolymer material). In some embodiments that can be combined with other embodiments described herein, transparent material 107 comprises a fluorinated material, such as aluminum fluoride (AlF3) and magnesium fluoride (MgF2).

[0029] like Figure 1D As shown, in one embodiment that can be combined with other embodiments described herein, the encapsulation layer 106A of the layer stack 101A includes a transparent material 107, and the space 108 comprises air (refractive index 1.0). Figure 1D In some embodiments of the implementation, the refractive index of the transparent material 107 is about 1.0 to about 1.5. The height h of the pillar 104A decreases as the refractive index of the transparent material 107 decreases. Figure 1D An example of an implementation includes Figure 3C , 5D Stacked with 5F layer 101A.

[0030] like Figure 1E As shown, in another embodiment that can be combined with other embodiments described herein, the encapsulation layer 106A of the layer stack 101A includes a transparent material 107, and the space 108 is composed of the transparent material 107. Figure 1E In some embodiments, the refractive index of the transparent material 107 is about 1.0 to about 1.5. The height h of the pillar 104A decreases as the refractive index of the transparent material 107 decreases. For example, in some embodiments, it has a composition that includes a space 108 comprising air. Figure 1D The implementation method results in a lower height h. Figure 1E An example of an implementation method includes Figure 7B The layers are stacked 101A.

[0031] like Figure 1FAs shown in FIG. 1, in another embodiment, which 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 spaces 108. In other embodiments, the conformal encapsulation layer 106A does not fill the spaces 108, such that the composition of the spaces 108 includes the transparent material 107 and air. The composition of the spaces 108 including the transparent material 107 and air can reduce the height h of the pillars 104A, in addition to reducing the height h of the pillars 104A as the refractive index of the transparent material 107 is reduced. In some embodiments of the embodiments of the embodiments of FIG. 1, the refractive index of the transparent material 107 is about 1.0 to about 1.5. The height h of the pillars 104A is reduced as the refractive index of the transparent material 107 is reduced. Figure 1D In some embodiments of the embodiments of the embodiments of FIG. 1, the refractive index of the transparent material 107 is about 1.0 to about 1.5. The height h of the pillars 104A is reduced as the refractive index of the transparent material 107 is reduced. Figure 1D An example of the embodiments of FIG. 1 includes Figure 9B the layer stack 101A of FIG. 1.

[0032] In one embodiment, which can be combined with other embodiments described herein, Figures 1D-1E The transparent material 107 of the embodiments of FIG. 1 includes one of a silica-containing material or a silica-free material (e.g., a polymer-containing material, such as a fluoropolymer-containing material). In another embodiment, which can be combined with other embodiments described herein, Figures 1D-1E The transparent material 107 of the embodiments of FIG. 1 includes a silica-containing aerogel material. The silica-containing aerogel material includes nanoscale porosity to provide air gaps in the spaces 108. In one embodiment, which can be combined with other embodiments described herein, the silica-containing aerogel material has a porosity of about 95% or greater corresponding to nanoscale air gaps. 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.

[0033] Figure 2 is a method 200 of forming a flat optic 100 as shown in Figures 3A-3D is a flowchart of a method 200 of forming a flat optic 100 as shown in FIG. 1. At operation 201, an arrangement of a plurality of pillars 104A is formed on a surface of a substrate 102. In one embodiment, which can be combined with other embodiments described herein, the step of forming the arrangement of the plurality of pillars 104A includes disposing a pillar material 301 over the surface of the substrate 102 and removing a portion of the pillar material 301 to form a trench 302. The trench 302 corresponds to the gap g of the pillars 104A (including the spaces 108 of the flat optic 100), the remaining portion of the trench corresponds to the lateral distance d, and the thickness of the pillar material 301 corresponds to the height h.

[0034] In one embodiment that can be combined with other embodiments described herein, the pillar material 301 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 from an encapsulation layer 306A comprising an oxide-containing material, such as silicon dioxide. In one embodiment that can be combined with other embodiments described herein, the refractive index of the liner 304 is from about 1.0 to about 1.5. In one embodiment that can be combined with other embodiments described herein, the thickness of the liner 304 is from about 1 nm to about 100 nm. The liner 304 can be disposed by atomic layer deposition (ALD) (e.g., fast ALD). In one embodiment that can be combined with other embodiments described herein, the silicon dioxide-containing liner 304 is disposed by comprising TMA (AlMe3) and ( t The alternating flow of ButO)3SiOH is conformally disposed on the support 104A by ALD treatment. Each TMA (AlMe3) and ( t The flow cycle of ButO)3SiOH forms a sublayer with a thickness of approximately 12 nm (greater than 32 monolayers).

[0035] In operation 203, an encapsulation layer 306A corresponding to encapsulation layer 106A is disposed on pillar 104A. The encapsulation layer 306A may be disposed via, but is not limited to, chemical vapor deposition (CVD), plasma-enhanced CVD (PECVD), ALD, rapid ALD, spraying, or spin coating. In one embodiment, which may be combined with other embodiments described herein, the thickness of encapsulation layer 306A is from about 1 μm to about 10 μm. In another embodiment, which may be combined with other embodiments described herein, the thickness of encapsulation layer 306A is from about 1 μm to about 2 μm. Operations 201-203 form a single-layer stacked flat optical device 100 including layer stack 101A. In operation 204, operations 201-203 are repeated at least once to form a multilayer stacked 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 a plurality of pillars 104B, and encapsulation layer 306B. The arrangement of multiple pillars 104B formed by operation 201 is disposed on one of the encapsulation layer 306A and the spacer layer (not shown) disposed on the encapsulation layer 306A.

[0036] Figure 4A Is formed as Figures 5A-5E The flowchart of method 400A for the flat optical device 100 shown. Figure 4B Is formed as Figures 5A-5EA flowchart of the method 400B of the flat optical device 100 is shown. In operations 401A, 401B of the method 400A and the method 400B, the arrangement of the plurality of pillars 104A is formed on the surface of the substrate 102 as described in operation 201 of the method 200. In operation 402A, the sacrificial material 504A to be removed is deposited in the trench 302. In one embodiment, which can be combined with other embodiments described herein, the sacrificial material 504A is deposited by hot-wire CVD (HWCVD), PECVD, or inductively coupled (ICPCVD). In operation 402B, the gap fill material 504B to be reduced in area is deposited in the trench 302.

[0037] In operations 403A, 403B, the 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 fill material 504B. Disposing the encapsulation layer 306A can include, but is not limited to, non-flow chemical vapor deposition (CVD), ALD, rapid ALD, PECVD, spray, or spin coating. In operation 404A, the sacrificial material 504A is removed. In one embodiment, which can be combined with other embodiments described herein, the sacrificial material is removed via thermal annealing. In operation 404B, the gap fill material 504B reduces the area 506 in the space 108 such that the gap g includes the gap fill material 504B having the center air gap 503 disposed in the area 506. In one embodiment, which can be combined with other embodiments described herein, the gap fill material 504B is reduced via thermal curing (e.g., thermal curing), chemical reduction, and UV treatment (e.g., UV curing). The operations 401A-404A, 401B-404B form a single layer stack flat optical device 100 including the layer stack 101A. In operations 405A, 405B, the operations 401A-404A, 401B-404B are repeated at least once to form a multi-layer stack optical device having the layer stack 101A and at least one layer stack 101B. The layer stack 101B includes at least the encapsulation layer 306A, the arrangement of the plurality of pillars 104B, and the encapsulation layer 306B.

[0038] Figure 6 is formed as Figures 7A-7CA flowchart of the method 600 of the flat optic 100 is shown. At operation 601, an arrangement of a plurality of pillars 104A is formed on a surface of a substrate 102, as described in operation 201 of the method 200. At 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 optic 100 comprising a layer stack 101A. A gap-filling portion 704A of the silica-containing aerogel material 702A is disposed in the trench 302 corresponding to the gap g of the pillars 104A (including the space 108 of the flat optic 100). An encapsulation portion 706A of the silica-containing aerogel material 702A is disposed on the plurality of pillars 104A and the gap-filling portion 704A. The encapsulation portion 706B corresponds to the encapsulation layer 306B.

[0039] At operation 603, operations 601 and 602 are repeated at least once to form a multi-layer stack optic having the layer stack 101A and at least one layer stack 101B. The layer stack 101B includes at least the encapsulation layer 306A, an arrangement of a plurality of pillars 104B, and the encapsulation layer 306B. The arrangement of the plurality of pillars 104B formed via operation 601 is disposed on one of the encapsulation layer 306A and a spacer layer (not shown) disposed on the encapsulation layer 306A. An encapsulation portion 706B of the silica-containing aerogel material 702B corresponds to the encapsulation layer 306B. A gap-filling portion 704B of the silica-containing aerogel material 702B is disposed in the trench 302. In one embodiment, which can be combined with other embodiments described herein, the encapsulation layers 306A, 306B (i.e., the encapsulation portions 706A, 706B) have a thickness of about 1 pm to about 2 pm. The silica-containing aerogel has a refractive index of about 1.0 to about 1.10 and a transmission coefficient of less than 0.001. The silica-containing aerogel material includes nanoscale porosity to provide an air gap in the space 108. In one embodiment, which can be combined with other embodiments described herein, the silica-containing aerogel material has a porosity of about 95% or greater corresponding to the nanoscale air gap. The nanoscale porosity of the silica-containing aerogel material reduces the refractive index of the solid silica.

[0040] 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 preparing 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, tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), methyltrimethoxysilane (MTMS), methyltrimethoxysilane (MTES), methyltriethoxysilane (MTES), silbond H-5, or polyethoxydisiloxane (PEDS). Examples of catalysts include, but are not limited to, hydrofluoric acid (HF), hydrogen chloride (HC1), nitric acid (HN03), sulfuric acid (H2S04), 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 can strengthen the solution into a sol-gel by cross-linking. The aging of the sol-gel maintains the shrinkage to supercritical drying.

[0041] The deposition process includes disposing the sol-gel via one of 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., spun) about a central axis 103 of the substrate. The substrate 102 is spun 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, about 1 : 1.5 and about 1 : 2.5, or about 1 : 1.1 and about 1 : 20. The trench 302 is filled by the gap fill portion 704A, 704B of the silica-containing aerogel material 702A, 702B to be disposed. The spin rate can be varied during the deposition process. In one embodiment, which can be combined with other embodiments described herein, the spin speed during formation of the encapsulation portion 706A, 706B is lower than the spin speed of the gap fill portion 704A, 704B. The drying process removes the solvent to form the silica-containing aerogel material having a nanoscale porosity to provide an air gap in the space 108. In one embodiment, which can be combined with other embodiments described herein, the drying process includes, but is not limited to, one or more of supercritical CO2 drying, freeze drying, and pressure drying (e.g., atmospheric drying).

[0042] Figure 8 is formed as Figure 9A and 9BA flowchart of a method 800 of fabricating the flat optical device 100 is shown in FIG. 8. At operation 801, an arrangement of a plurality of pillars 104A is formed on a surface of a substrate 102, as described in operation 201 of method 200. At operation 802, a conformal encapsulation layer 306A is disposed on the plurality of pillars 104A. Disposing the conformal encapsulation layer 306A can include, but is not limited to, CVD, PECVD, 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 μιη. In another embodiment, the encapsulation layer 306A has a thickness of about 1 μιη to about 2 μιη. In one embodiment, which can be combined with other embodiments described herein, the conformal encapsulation layer 306A has a refractive index of about 1.0 to about 1.5.

[0043] In summary, the embodiments described herein provide flat optical devices and methods of forming flat optical devices. One embodiment of an optical device is a single layer stack flat optical device including a layer stack disposed on a surface of a substrate. The layer stack includes a first arrangement of a first plurality of pillars disposed on the surface of the substrate and a first encapsulation layer. Another embodiment of an optical device is a multi-layer stack optical device including a first layer stack and a second layer stack formed thereon. The second layer stack of one or more layer stacks is disposed on the first layer stack. The second layer stack includes a second arrangement 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 materials, dimensions, and processing of the encapsulation layers and the composition of the space corresponding to the gap g described herein provide a height h of the pillars of about 1500 nm or less (in some embodiments, 500 nm or less). The height h of the pillars reduces the thickness of the layer stack and the overall thickness of the flat optical device. The overall thickness of the flat optical device is reduced compared to a bare optical device due to impedance matching and device symmetry, which improves transmission efficiency and reduces manufacturing complexity and cost.

[0044] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure can be devised without departing from the basic scope thereof, and the scope of the present disclosure is determined by the appended claims.

Claims

1. A flat optical device comprising: a substrate having a first arrangement of a first plurality of pillars formed on the substrate, the first arrangement of the first plurality of pillars comprising: a pillar 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; and a first encapsulation layer disposed on the first arrangement of the first plurality of pillars, the first encapsulation layer having an underside surface that contacts a top surface of each pillar of the first plurality of pillars to define a space between the substrate, each pillar of the first plurality of pillars, and the underside surface of the first encapsulation layer, wherein a silica-containing aerogel material having an absorption coefficient less than 0.001 is disposed in each space, the first encapsulation layer having a refractive index of about 1.0 to about 1.

5.

2. The flat optical device of claim 1, wherein the silica-containing aerogel material has nanoscale pores formed in the silica-containing aerogel material.

3. The flat optical device of claim 2, wherein the silica-containing aerogel material is substantially composed of the same material as the first encapsulation layer.

4. The flat optical device of claim 1, wherein the gap g has an air gap disposed in a central opening of the silica-containing aerogel material.

5. The flat optical device of claim 1, wherein a liner is disposed on the pillars.

6. The flat optical device of claim 5, wherein the liner has a thickness of about 1 nm to about 200 nm.

7. The flat optical device of claim 1, further comprising: a second arrangement of a second plurality of pillars formed on the first encapsulation layer, the second arrangement of the second plurality of pillars comprising: a pillar having the height h and the lateral distance d; the gap g corresponding to a distance between adjacent pillars of the second plurality of pillars, and a silica-containing aerogel material having an absorption coefficient less than 0.001 disposed in each gap g; and a second encapsulation layer disposed on the second arrangement of the second plurality of pillars, the second encapsulation layer disposed on a top surface of each pillar of the second plurality of pillars and on the silica-containing aerogel material disposed in each gap g, the second encapsulation layer having the refractive index of about 1.0 to about 1.

5.

8. The flat optical device of claim 1, wherein the pillars comprise one or more of: titanium dioxide (Ti02), zinc oxide (ZnO), tin dioxide (Sn02), aluminum-doped zinc oxide (AZO), fluorine-doped tin oxide (FTO), cadmium stannate (CTO), zinc stannate (SnZn03), or a silicon-containing material.

9. The flat optical device of claim 1, wherein the underside surface is planar on the top surface of each pillar of the first plurality of pillars and on each gap.

10. A flat optical device comprising: a substrate having a first arrangement of a first plurality of pillars formed on the substrate, the first arrangement of the first plurality of pillars comprising: a pillar 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; and a first encapsulation layer disposed on the first arrangement of the first plurality of pillars, the first encapsulation layer having an underside surface that contacts a top surface of each pillar of the first plurality of pillars to define a space between the substrate, each pillar of the first plurality of pillars, and the underside surface of the first encapsulation layer, wherein a silica-containing aerogel material having an absorption coefficient less than 0.001 is disposed in each space, the first encapsulation layer having a refractive index of about 1.0 to about 1.

5. pillars having a height h and a lateral distance d; and gaps g corresponding to a distance between adjacent pillars of the first plurality of pillars, wherein each gap g is composed only of a silica-containing aerogel material having nanoscale pores in the silica-containing aerogel material, the silica-containing aerogel material having: an absorption coefficient less than 0.001; and a first encapsulation layer disposed on the first arrangement of the first plurality of pillars, the first encapsulation layer disposed on a top surface of each pillar of the first plurality of pillars and on the silica-containing aerogel material disposed in each gap g, the first encapsulation layer having a refractive index of about 1.0 to about 1.

5.

11. The flat optical device of claim 10, wherein the gaps are less than 350 nm.

12. The flat optical device of claim 10, wherein the height h is about 1500 nm or less.

13. The flat optical device of claim 10, wherein a thickness of the first encapsulation layer is less than 50 pm.

14. The flat optical device of claim 10, further comprising: a second arrangement of a second plurality of pillars formed on the first encapsulation layer, the second arrangement of the second plurality of pillars comprising: pillars having the height h and the lateral distance d; the gaps g corresponding to a distance between adjacent pillars of the second plurality of pillars, and silica-containing aerogel material having an absorption coefficient less than 0.001 disposed in each gap g; and a second encapsulation layer disposed on the second arrangement of the second plurality of pillars, the second encapsulation layer disposed on a top surface of each pillar of the second plurality of pillars and on the silica-containing aerogel material disposed in each gap g, the second encapsulation layer having the refractive index of about 1.0 to about 1.

5.

15. The flat optical device of claim 10, wherein the pillars comprise one or more of: titanium dioxide (Ti02), zinc oxide (ZnO), tin dioxide (Sn02), aluminum-doped zinc oxide (AZO), fluorine-doped tin oxide (FTO), cadmium stannate (CTO), zinc stannate (SnZn03), or a silicon-containing material.

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