Patent ID: 12216243

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

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 of about 1.0 to 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 of about 1.0 to about 1.5.

FIG.1Ais a schematic, perspective view of a flat optical device100having at least one layer stack101A,101B.FIG.1Bis a schematic, cross-sectional view of the layer stack101A.FIG.1Cis a schematic, top view of an arrangement of pillars104of the layer stack101A. The flat optical device100includes at least one layer stack101A,101B. While aspects of the devices and methods described herein may be discussed in reference to the layer stack101A, it is to be understood that aspects of the devices and methods described herein are similarly applicable to the layer stack101B. Reference numerals may be omitted for the arrangement of the layer stack101B for clarity in the Figures provided herein.

In one embodiment, which can be combined with other embodiments described herein, the flat optical device100is a single layer stack flat optical device that includes the layer stack101A. In another embodiment, which can be combined with other embodiments described herein, the flat optical device100is a multi-layer stack optical device that includes the layer stack101A and one or more layer stacks101B. The layer stack101A includes an arrangement of a plurality of pillars104A disposed on a surface of the substrate102and an encapsulation layer106A. In the embodiment of the multi-layer stack optical device, the first layer stack of the one or more layer stacks101B is disposed over the layer stack101A. In one embodiment, which can be combined with other embodiments described herein, the first layer stack of the layer stacks101B includes an arrangement of a plurality of pillars104B disposed on the encapsulation layer106A. In another embodiment, which can be combined with other embodiments described herein, the arrangement of a plurality of pillars104B of the first layer stack of the layer stacks101B is disposed on a spacer layer (not shown) disposed on the encapsulation layer106A. In embodiments including the spacer layer, the spacer layer is operable to provide support for the arrangement of the plurality of pillars104B, and is of a specified thickness according to the optical functionality of the flat optical device100.

The arrangement of the plurality of pillars104A,104B includes pillars104A,104B having a height h and a lateral distance d. The height h of the pillars104A is defined as the distance from the surface of the substrate102to the encapsulation layer106A. The height h of the pillars104B is defined as the distance from the encapsulation layer106A and a spacer layer (not shown) disposed on the encapsulation layer106A to the encapsulation layer106B. In another embodiment, which can be combined with other embodiments described herein, the cross-section of the pillars104A,104B is square and/or rectangular and the lateral distance d of the pillars104A,104B corresponds to a width of the pillars104A,104B. In another embodiment, which can be combined with other embodiments described herein, the cross-section of the pillars104A,104B is circular and the lateral distance d of the pillars104A,104B corresponds to a diameter of the pillars104A,104B. The gap g is a distance between adjacent pillars of the pillars104A,104B. In one embodiment, each of the arrangement of the plurality of pillars104A,104B has an aspect ratio (g:h) between about 1:1.5 and about 1:10. In another embodiment, each of the arrangement of the plurality of pillars104A,104B has an aspect ratio (g:h) between about 1:1.5 and about 1:2.5. In yet another embodiment, each of the arrangement of the plurality of pillars104A,104B has an aspect ratio (g:h) between about 1:1 and about 1:20.

The lateral distance d and the gap g are less than half of a 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 in the UV region to near-infrared region (i.e., from about 300 nm to about 1500 nm). Therefore, 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 pillar of the plurality of pillars104A 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 additional pillars of the plurality of pillars104A. In one embodiment, which can be combined with other embodiments described herein, the gap g of each of the adjacent pillars of the plurality of pillars104A 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 that the gap g of additional sets of adjacent pillars of the plurality of pillars104A. In some embodiments, which can be combined with other embodiments described herein, the arrangement of the plurality of pillars104B corresponds to (i.e., matches) the arrangement of the plurality of pillars104A. In other embodiments, which can be combined with other embodiments described herein, the arrangement of the plurality of pillars104B does not correspond to the arrangement of the plurality of pillars104A.

The substrate102may be selected to transmit light at the wavelength of operation. Without limitation, in some embodiments, the substrate102is configured such that the substrate102transmits greater than or equal to about 50%, 60%, 70%, 80%, 90%, 95%, 99% of the UV region of the light spectrum. The substrate102may be formed from any suitable material, provided that the substrate102can adequately transmit light of the wavelength of operation and can serve as an adequate support for at least the arrangement of the plurality of pillars104A and the encapsulation layer106A. In some embodiments, which can be combined with other embodiments described herein, the material of substrate102has a refractive index that is relatively low, as compared to the refractive index of materials used in each of the pillars104A,104B. Substrate selection may include substrates of any suitable material, including, but not limited to, semiconductor, doped semiconductor, 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 substrate102includes a transparent material. The substrate102is transparent with an absorption coefficient less than 0.001. Examples may include, but are not limited to, an oxide, sulfide, phosphide, telluride, and combinations thereof. In one example, the substrate102includes silica (SiO2) containing materials.

The pillars104A,104B include materials, not limited to, titanium dioxide (TiO2), zinc oxide (ZnO), tin dioxide (SnO2), aluminum-doped zinc oxide (AZO), fluorine-doped tin oxide (FTO), cadmium stannate (tin oxide) (CTO), zinc stannate (tin oxide) (SnZnO3), and silicon containing materials. The silicon containing materials may include at least one of silicon nitride (Si3N4) or amorphous silicon (a-Si) containing materials. The pillars104A,1046may have a refractive of about 1.8 or greater, and absorption coefficient less than 0.001. In one embodiment, which can be combined with other embodiments described herein, the refractive index of the encapsulation layer106A,106B is about 1.0 to about 1.5. The encapsulation layer106A,106B has an absorption coefficient less than 0.001. In some embodiments, which can be combined with other embodiments described herein, the encapsulation layer106A,106B and the substrate102include substantially the same materials. In one embodiment, the conformal encapsulation layer306A has a thickness of about 2 nm to about 100 nm. In another embodiment, the encapsulation layer106A has a thickness less than 50 μm. In another embodiment, the encapsulation layer306A has a thickness of about 1 μm to about 2 μm.

The materials and dimensions of the encapsulation layer106A,106B are further described in the methods provided herein. Utilization of the materials, dimensions, and processes described herein of the encapsulation layer106A,106B, and the composition of a space108corresponding to the gap g provides for a height h of the pillars104A,104B of about 1500 nm or less. In some embodiments, which can be combined with other embodiments described herein, the height h of the pillars104A,104B is about 500 nm or less. The height h of the pillars104A,104B reduces the thickness110A,110B of the layer stack101A,101B and total thickness of the flat optical device100. The reduced total thickness of the flat optical device100provides for higher transmission efficiency due to impedance matching and device symmetry, as compared to bare optical devices, and reduced manufacturing complexity and cost.

The composition of the space108corresponding to the gap g includes at least one of air, having a refractive index of 1.0 and an absorption coefficient of 0, or a transparent material107(shown inFIGS.1D-1F), having an absorption coefficient less than 0.001. In one embodiment, which can be combined with other embodiments described herein, the refractive index of the transparent material107of the composition of the space108has a refractive index of about 1.0 to about 1.5. In some embodiments, which can be combined with other embodiments described herein, the transparent material107includes one of silica containing materials or non-silica containing materials, such as polymer containing materials, for example, fluoropolymer material. In some embodiments, which can be combined with other embodiments described herein, the transparent material107includes fluorine containing materials, such as aluminum fluoride (AlF3) and magnesium fluoride (MgF2).

As shown inFIG.1D, in one embodiment, which can be combined with other embodiments described herein, the encapsulation layer106A of the layer stack101A includes the transparent material107and the composition of the space108includes air (refractive index of 1.0). In some embodiments of the embodiment ofFIG.1D, the transparent material107has the refractive index of about 1.0 to about 1.5. The height h of the pillars104A decreases as the refractive index of the transparent material107is reduced. One example of the embodiment ofFIG.1Dincludes the layer stack101A ofFIGS.3C,5D, and5F.

As shown inFIG.1E, in another embodiment, which can be combined with other embodiments described herein, the encapsulation layer106A of the layer stack101A includes the transparent material107and the composition of the space108includes the transparent material107. In some embodiments of the embodiment ofFIG.1E, the transparent material107has the refractive index of about 1.0 to about 1.5. The height h of the pillars104A decreases as the refractive index of the transparent material107is reduced. For example, in some embodiments, the embodiment ofFIG.1D, with the composition of the space108including air, results in a lower height h. One example of the embodiment ofFIG.1Eincludes the layer stack101A ofFIG.7B.

As shown inFIG.1F, in another embodiment, which can be combined with other embodiments described herein, a conformal encapsulation layer106A is disposed over the plurality of pillars104A. In some embodiments, the conformal encapsulation layer106A fills the space108. In other embodiments, the conformal encapsulation layer106A does not fill the space108such that the composition of the space108includes the transparent material107and air. In addition to the height h of the pillars104A decreasing as the refractive index of the transparent material107is reduced, the composition of the space108including the transparent material107and air may reduce the height h of the pillars104A. In some embodiments of the embodiment ofFIG.1D, the transparent material107has the refractive index of about 1.0 to about 1.5. The height h of the pillars104A decreases as the refractive index of the transparent material107is reduced. One example of the embodiment ofFIG.1Dincludes the layer stack101A ofFIG.9B.

In one embodiment, which can be combined with other embodiments described herein, the transparent material107of the embodiments ofFIGS.1D-1Eincludes one of silica containing materials or non-silica containing materials, such as polymer containing materials, for example, fluoropolymer materials. In another embodiment, which can be combined with other embodiments described herein, the transparent material107of the embodiments ofFIGS.1D-1Eincludes a silica-containing aerogel material. The silica-containing aerogel material includes nanoscale porosities to provide air gaps in the space108. In one embodiment, which can be combined with other embodiments described herein, the silica-containing aerogel material has a porosity, corresponding to the nanoscale air gaps, of about 95% or greater. The nanoscale porosity of the silica-containing aerogel material reduces the refractive index of silica. The reduced refracted index decreases the height h. The silica-containing aerogel material is hydrophobic to protect the pillars104A from external factors.

FIG.2is a flow diagram of a method200of forming a flat optical device100, as shown inFIGS.3A-3D. At operation201, an arrangement of a plurality of pillars104A is formed on the surface of the substrate102. In one embodiment, which can be combined with other embodiments described herein, forming the arrangement of a plurality of pillars104A includes disposing a pillar material301over the surface of the substrate102and removing portions of the pillar material301to form trenches302. The trenches302correspond to the gap g of the pillars104A (including the space108of the flat optical device100), the remaining portions of the trenches correspond to the lateral distance d, and the thickness of the pillar material301corresponds to the height h.

In one embodiment, which can be combined with other embodiments described herein, the pillar material301includes oxides. At optional operation202, a liner304is disposed over the oxide-free pillars104A. The liner304protects the pillars104A from oxidation from disposing an encapsulation layer306A that includes an oxide containing material, such as silica. In one embodiment, which can be combined with other embodiments described herein, the liner304has a refractive index of about 1.0 to about 1.5. In one embodiment, which can be combined with other embodiments described herein, the liner304has a thickness of about 1 nm to about 100 nm. The liner304may be disposed by atomic layer deposition (ALD), such as rapid ALD. In one embodiment, which can be combined with other embodiments described herein, a silica containing liner304is conformably disposed over the pillars104A by an ALD process that includes alternating flows of TMA(AlMe3) and (tButO)3SiOH. Each TMA(AlMe3) and (tButO)3SiOH flow cycle forms a sublayer having a thickness of about 12 nm (greater than 32 monolayers).

At operation203, an encapsulation layer306A, corresponding to the encapsulation layer106A, is disposed over the pillars104A. Disposing the encapsulation layer306A may include, but is not limited to, chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), ALD, rapid ALD, spray coating, or spin coating. In one embodiment, which can be combined with other embodiments described herein, the encapsulation layer306A has a thickness of about 1 μm to about 10 μm. In another embodiment, which can be combined with other embodiments described herein, the encapsulation layer306A has a thickness of about 1 μm to about 2 μm. Operations201-203form a single layer stack flat optical device100that includes the layer stack101A. At operation204, at least operations201-203are repeated at least once to form a multi-layer stack optical device having the layer stack101A and at least one layer stack101B. The layer stack101B includes at least the encapsulation layer306A, the arrangement of a plurality of pillars104B, and the encapsulation layer306B. The arrangement of a plurality of pillars104B formed via operation201is disposed on one of the encapsulation layer306A and a spacer layer (not shown) disposed on the encapsulation layer306A.

FIG.4Ais a flow diagram of a method400A of forming a flat optical device100, as shown inFIGS.5A-5E.FIG.4Bis a flow diagram of a method400B of forming a flat optical device100, as shown inFIGS.5A-5E. At operation401A,401B of the method400A and the method400B, as described in operation201of the method200, an arrangement of a plurality of pillars104A is formed on the surface of the substrate102. At operation402A, a sacrificial material504A to be removed is deposited in the trenches302. In one embodiment, which can be combined with other embodiments described herein, the sacrificial material504A is deposited by hot-wire CVD (HWCVD), PECVD, or inductively coupled (ICPCVD). At operation402B, a gap-fill material504B to be reduced in area is deposited in the trenches302.

At operation403A,403B, an encapsulation layer306A, corresponding to the encapsulation layer106A, is disposed over the pillars104A and one of the sacrificial material504A and gap-fill material504B. Disposing the encapsulation layer306A may include, but is not limited to, no-flow chemical vapor deposition (CVD), ALD, rapid ALD, PECVD, spray coating, or spin coating. At operation404A, the sacrificial material504A is removed. In one embodiment, which can be combined with other embodiments described herein, the sacrificial material is removed via thermal annealing. At operation404B, the gap-fill material504B is reduced by an area506in the space108such that the gap g includes the gap-fill material504B with a center air gap503disposed in the area506. In one embodiment, which can be combined with other embodiments described herein, the gap-fill material504B is reduced via thermal curing, such thermal curing, chemical reduction, and UV treatment, such as UV curing. Operations401A-404A,401B-404B, form a single layer stack flat optical device100that includes the layer stack101A. At operation405A,405B, operations401A-404A,401B-404B are repeated at least once to form a multi-layer stack optical device having the layer stack101A and at least one layer stack101B. The layer stack101B includes at least the encapsulation layer306A, the arrangement of a plurality of pillars104B, and the encapsulation layer306B.

FIG.6is a flow diagram of a method600of forming a flat optical device100, as shown inFIGS.7A-7C. At operation601, as described in operation201of the method200, an arrangement of a plurality of pillars104A is formed on the surface of the substrate102. At operation602, a silica-containing aerogel material702A is disposed over the plurality of pillars104A. Operations601and602, form a single layer stack flat optical device100that includes the layer stack101A. A gap-fill portion704A, of the silica-containing aerogel material702A, is disposed in the trenches302correspond to the gap g of the pillars104A (including the space108of the flat optical device100). An encapsulate portion706A of the silica-containing aerogel material702A, is disposed over the plurality of pillars104A and the gap-fill portion704A. The encapsulate portion706B corresponds to the encapsulation layer306B.

At operation603, operations601and602are repeated at least once to form a multi-layer stack optical device having the layer stack101A and at least one layer stack101B. The layer stack101B includes at least the encapsulation layer306A, the arrangement of a plurality of pillars104B, and the encapsulation layer306B. The arrangement of a plurality of pillars104B formed via operation601is disposed on one of the encapsulation layer306A and a spacer layer (not shown) disposed on the encapsulation layer306A. The encapsulate portion706B of the silica-containing aerogel material702B corresponds to the encapsulation layer306B. The gap-fill portion704B of the silica-containing aerogel material702B is disposed in the trenches302. In one embodiment, which can be combined with other embodiments described herein, the encapsulation layer306A,306B (i.e., the encapsulate portion706A,706B) has 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 transmission coefficient less than 0.001. The silica-containing aerogel material includes nanoscale porosities to provide air gaps in the space108. In one embodiment, which can be combined with other embodiments described herein, the silica-containing aerogel material has a porosity, corresponding to the nanoscale air gaps, of about 95% or greater. The nanoscale porosity of the silica-containing aerogel material reduces the refractive index of solid silica.

The silica-containing aerogel material is formed from a silica-containing aerogel material formation process. The formation process includes a precursor preparation process, deposition process, or supercritical drying process. The precursor preparation process includes preparing silica sol-gels. The sol (i.e., solution) is prepared by addition of a catalyst to a silica precursor solution in a solvent. Examples of the silica precursor include, but are not limited to, tetraethylorthosilicate (TEOS), tetramethylorthosilicate (TMOS), methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTMS), methyltriethoxysilane (MTES), silbond H-5, or polyethoxydisiloxane (PEDS). Examples of the catalyst include, but are not limited to, hydrofluoric 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 the solvent precursor include, but are not limited to, methanol, ethanol, and isopropanol. The gel is prepared by ageing the solution which strengthens the solution into a sol-gel by crosslinking. The ageing of the sol-gel keeps the shrinkage during drying to the supercritical drying process.

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 substrate102is rotated (i.e., spun) about a central axis103of the substrate. The substrate102is rotated about a central axis103such that the aspect ratio of the arrangements of the plurality of pillars104A,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. Trenches302are filled by the gap-fill portion704A,704B, of the silica-containing aerogel material702A,702B, to be disposed. The rotation rate may be varied during the deposition process. In one embodiment, which can be combined with other embodiments described herein, the rotation rate during the formation of the encapsulate portion706A,706B, is lower that the rotation rate for the gap-fill portion704A,704B. The drying process removes the solvent to form the silica-containing aerogel material having nanoscale porosities providing air gaps in the space108. 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 CO2drying, freeze drying, and pressure drying, such as ambient pressure drying.

FIG.8is a flow diagram of a method800of forming a flat optical device100, as shown inFIGS.9A and9B. At operation801, as described in operation201of the method200, an arrangement of a plurality of pillars104A is formed on the surface of the substrate102. At operation802, a conformal encapsulation layer306A is disposed over the plurality of pillars104A. Disposing the conformal encapsulation layer306A may include, but is not limited to, CVD, PECVD, ALD, rapid ALD, and thermal oxidation. In one embodiment, the conformal encapsulation layer306A has a thickness of about 2 nm to about 100 nm. In another embodiment, the encapsulation layer306A has a thickness less than 50 μm. In another embodiment, the encapsulation layer306A 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 layer306A is about 1.0 to about 1.5.

In summation, embodiments described herein provide flat optical devices and methods of forming flat optical devices. One embodiment of the optical devices is a single layer stack flat optical device that includes one layer stack. The layer stack includes a first arrangement of a first plurality of pillars disposed on a surface of a substrate and a first encapsulation layer. Another embodiment of the optical devices is a multi-layer stack optical device that includes the first layer stack and a second layer stack formed thereover. The second layer stack of the one or more layer stacks is disposed over the first layer stack. The second layer stack includes 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 processes described herein of the encapsulation layers, and the composition of a space corresponding to a gap g provides for a height h of the pillars of about 1500 nm or less, and in some embodiments 500 nm or less. The height h of the pillars reduces the thickness of the layer stacks and total thickness of a flat optical device. The reduced total thickness of the flat optical devices provides for higher transmission efficiency due to impedance matching and device symmetry, as compared to bare optical devices, and reduced manufacturing complexity and cost.

While the foregoing 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, and the scope thereof is determined by the claims that follow.