Optical metasurface films

Abstract

To provide optical metasurface polymeric films.SOLUTION: An optical metasurface film includes: a flexible polymeric film having a first major surface; a patterned polymer layer having a first surface proximate to the first major surface of the flexible polymeric film and having a second nanostructured surface opposite the first surface; and a refractive index contrast layer containing a refractive index contrast material adjacent to the nanostructured surface of the patterned polymer layer forming a nanostructured bilayer with a nanostructured interface. The nanostructured bilayer acts locally on the amplitude, phase, polarization of light or on a combination thereof, and imparts a light phase shift that varies as a function of the position of the nanostructured bilayer on the flexible polymeric film. The light phase shift of the nanostructured bilayer defines a predetermined operative phase profile of the optical metasurface film.SELECTED DRAWING: Figure 1

Description

Background Art

[0001] Metamaterials are synthetic composite materials having nanostructural features on at least one surface. When the nanostructural features are selected to have at least one dimension smaller than the wavelength of light impinging on the surface, the metamaterials can exhibit properties not readily obtainable using conventional materials and techniques. Metamaterials can have simple surface structures, such as single or few-pattern layers, or more complex surface structures, such as stacked pattern layers, often aligned with each other, such that the individual nanostructural features interact electromagnetically with the radiation impinging thereon according to the design of the features. Metamaterials having single or few-pattern layers are called metasurfaces. Metasurfaces having nanostructured surfaces have recently found applications in optics, biosensing, semiconductors, and other electronic devices.

[0002] Metasurfaces are formed, for example, on rigid surfaces using electron beam lithography and atomic layer deposition. These materials are formed on substrates having a limited surface area. These materials are formed on wafer substrates having a diameter of 300 mm or less.

[0003] There are mainly two types of metasurfaces, namely, geometric phase metasurfaces and propagation phase metasurfaces. Geometric phase metasurfaces induce a phase change of light through spatially rotated identical nanostructures in which the individual nanostructures function as half-wave plates. Propagation phase metasurfaces induce a phase change of light using linear birefringent nanostructures having different lateral dimensions at each spatial position. These two methods can also be used in combination.

Summary of the Invention

[0004] The flexible substrate can be formed on a flexible substrate. The flexible substrate may be, for example, a large-sized substrate having a lateral dimension of more than 300 mm. These flexible substrate can be formed using highly accurate roll-to-roll processing.

[0005] The flexible substrate includes a flexible polymer film having a first major surface, a patterned polymer layer having a first surface adjacent to the first major surface of the flexible polymer film and a second nanostructured surface on the opposite side of the first surface, and a refractive index contrast layer including a refractive index contrast material adjacent to the nanostructured surface of the patterned polymer layer forming a nanostructured bilayer having a nanostructured interface. The nanostructured bilayer locally acts on the amplitude, phase, polarization of light, or a combination thereof, and provides a phase change of light that varies as a function of the position of the nanostructured bilayer of the flexible polymer film. The phase change of light of the nanostructured bilayer defines a predetermined operating phase profile of the flexible substrate.

[0006] The nanostructured bilayer may locally act on the amplitude of light. The nanostructured bilayer may locally act on the phase of light. The nanostructured bilayer may locally act on the polarization of light.

[0007] The nanostructured bilayer can be defined by a solid material. The nanostructured bilayer can be formed of a solid material. The nanostructured bilayer can be formed of a polymer material.

[0008] The nanostructured bilayer can further include an etching stop layer that separates the patterned polymer layer from the first major surface of the flexible polymer film.

[0009] The refractive index contrast material can have a first refractive index value, and the patterned polymer layer has a second refractive index value that is at least 0.25, or 0.5, or 0.75, or 1.0, or 1.4 different from the first refractive index value.

[0010] The nanostructured bilayer can be defined by a plurality of nanostructures embedded in the refractive index contrast layer. The nanostructures forming the nanostructured surface can have an aspect ratio of at least about 1:1, about 2:1, about 5:1, about 10:1, or about 15:1. The nanostructures forming the nanostructured surface can preferably have an aspect ratio in the range of about 2:1 to about 20:1, or in the range of about 4:1 to about 15:1.

[0011] The nanostructures forming the nanostructured surface can define tapered sidewalls having an angle in the range of about 1 to 10°, about 2 to 10°, about 3 to 10°, about 4 to 10°, about 1 to 6°, about 2 to 6°, or about 3 to 6°, or about 2 to 4°. The nanostructures forming the nanostructured surface can define tapered sidewalls having an angle in the range of about 0 to 10°, about 0 to 6°, about 0 to 3°, about 0 to 2°, about 0 to 1°, or 0°.

[0012] The refractive index contrast material may include a metal oxide or a metal nitride. The refractive index contrast material may include at least one of titanium, zirconium, tantalum, hafnium, niobium, zinc, or cerium; titanium oxide, zirconium oxide, tantalum oxide, hafnium oxide, niobium oxide, zinc oxide, or cerium oxide; titanium nitride, zirconium nitride, tantalum nitride, hafnium nitride, niobium nitride, zinc nitride, or cerium nitride; titanium sulfide, zirconium sulfide, tantalum sulfide, hafnium sulfide, niobium sulfide, zinc sulfide, or cerium sulfide; or a combination thereof.

[0013] The patterned polymer layer may include a fluoropolymer, a (meth)acrylate (co)polymer, or a silica-containing polymer. The patterned polymer layer may include a fluoroacrylate, and the refractive index contrast material may include titanium dioxide. The patterned polymer layer may include a (meth)acrylate, and the refractive index contrast material may include titanium dioxide.

[0014] The compliant polymer film may have an average thickness in the range of about 5 μm to about 300 μm. The nanostructures forming the nanostructured surface may have a height in the range of 5 μm or less, or about 100 nm to about 3000 nm, or about 500 nm to about 1500 nm.

[0015] The nanostructures forming the nanostructured surface have an average pitch (center-to-center distance between adjacent nanostructures) that is sub-wavelength with respect to the shortest wavelength included in the interrogating electromagnetic radiation. For an optical metasurface acting in the visible spectral range, the nanostructures forming the nanostructured surface may have an average pitch of 600 nm or less, or 500 nm or less, or 400 nm or less. For an optical metasurface acting in the visible spectral range, the nanostructures forming the nanostructured surface preferably may have an average pitch in the range of 50 nm to 600 nm, or 100 nm to 500 nm, or 200 nm to 400 nm.

[0016] The nanostructures forming the nanostructured surface are separated from each other by a sub-wavelength lateral distance. The nanostructures forming the nanostructured surface may be separated from each other in the range of about 400 nm or less, or about 20 nm to about 400 nm, or about 50 nm to about 300 nm.

[0017] The nanostructures forming the nanostructured surface have a lateral dimension orthogonal to the height of the nanostructured feature that is sub-wavelength. The nanostructures forming the nanostructured surface may have a lateral dimension orthogonal to the height of the nanostructured feature in the range of about 600 nm or less, or about 10 nm to about 400 nm, or about 50 nm to about 350 nm.

[0018] The phase change of light can occur in the visible light wavelength range. The phase change of light can occur in the near-infrared wavelength range. The optical metasurface film can transmit visible light or near-infrared light.

[0019] The nanostructures forming the nanostructured surface can have a varying direction in the case of a geometric phase metasurface that depends on the positions of the individual nanostructures on the flexible polymer film. The nanostructures forming the nanostructured surface can have a varying spatial arrangement that depends on the positions of the individual nanostructures on the flexible polymer film. The nanostructures forming the nanostructured surface can have a varying shape in the case of a propagation phase metasurface that depends on the positions of the individual nanostructures on the flexible polymer film. The nanostructures forming the nanostructured surface can have a varying aspect ratio that depends on the positions of the individual nanostructures on the flexible polymer film.

[0020] The nanostructures forming the nanostructured surface may be geometrically anisotropic with respect to the planar direction. The nanostructures forming the nanostructured surface may be geometrically isotropic with respect to the planar direction.

Brief Description of the Drawings

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BEST MODE FOR CARRYING OUT THE INVENTION

[0035] Optical metasurface polymer films will be described. These optical metasurface polymer films can be formed on a flexible substrate. The flexible substrate may be, for example, a large-sized substrate having a lateral dimension of more than 300 mm. These optical metasurface polymer films can be formed using highly accurate roll-to-roll processing.

[0036] The term "metasurface" refers to a two-dimensional sub-wavelength spacing or arrangement of photonic resonators or cut-off waveguides that perform one or more optical functions. Each arrangement locally acts on one or more physical properties of light, specifically, amplitude, phase, or polarization.

[0037] Representative nano-feature shapes of photonic resonators or cut waveguides include, but are not limited to, rectangles, triangles, trapezoidal prisms, fins, cylindrical and frustum-shaped columns. These features can be arranged in regular or random pitches, directions, and shapes according to the application - functionality and the determined item design.

[0038] The term "nanostructure" refers to features having at least one dimension less than 1 μm.

[0039] The term "aspect ratio" refers to the ratio of the height of a feature to the width of the feature.

[0040] The term "refractive index" refers to the absolute refractive index of a material, which is understood to be the ratio of the speed of electromagnetic radiation in free space to the speed of electromagnetic radiation in the material, and the electromagnetic radiation is green light with a wavelength of about 532 nm. The refractive index can be measured using known methods and is generally measured using an Abbe refractometer.

[0041] The term "flexible polymer film" refers to a polymer film that can be elastically curved with a radius of curvature of 52 mm or less.

[0042] The term "operating phase profile" refers to the phase profile given by the metasurface to the incident electromagnetic radiation. The phase profile is designed to perform a specific optical function.

[0043] The term "thickness of the land area" refers to the height of the structural surface layer between the bottom surface of the structural surface layer and the plane defined by the bottom of the surface feature. It is also called the residual layer or residual area.

[0044] The term "precision land" refers to a structural surface layer having a deterministically controlled land thickness. Two examples are a minimized land that enables a subsequent etching process and a land that defines the height of a feature within a final film. Ideally, when the structural surface enables a subsequent etching process, the thickness of the residual layer is less than the height of the feature. When the land thickness defines the height of the feature within the final film, the land layer thickness ideally has a variation of less than 25% of the thickness of the layer, more preferably less than 10%, and most preferably less than 5%.

[0045] The term "uncontrolled land" refers to a structural surface layer having an arbitrary land thickness. The variation in the layer thickness may exceed 25%.

[0046] Meta-surface polymer films can be formed by any useful nano-replication technique. Nano-replication refers to a continuous thermal or photochemical process for creating a nanostructured surface layer using a cylindrical tool and a roll-shaped polymer carrier film having a thermoplastic (thermal) or ultraviolet curable resin (photochemical) layer. As an example of a nano-replication technique, nanoimprint lithography (NIL) can be mentioned.

[0047] Nanoimprint lithography (NIL) is a high-throughput technique for the patterning of high-precision and low-cost polymer nanostructures. Different from conventional lithography techniques that achieve pattern definition by irradiating a resist layer with photons or electron beams and changing the chemical and physical properties of the resist, NIL relies on the use of a stamp when directly mechanically deforming the resist material. The stamp is made from a master wafer and can be reused at high speed to make many copies of the original pattern.

[0048] Optical applications to direct-view electronic displays (especially, dimming films for high-resolution full-color displays) utilize, for example, substrate transparency, low retardation, high optical efficiency, and low cost per unit area. Since the size of standard wafer substrates (commonly used in NIL) is limited and the unit price is high, it is generally unsuitable for use as a light enhancement element, a diffuser, or a polarizer in direct-view consumer displays. Wafer-level optics are generally classified into micro-optical components with limited dimensions, such as microlens arrays, diffraction gratings, and waveguide optics.

[0049] Large-area display glass panels (larger than 1 m × 1 m) are used for manufacturing display backplanes, but patterning technologies and apparatuses (generally, optical lithography steppers) have limited resolution and cannot create nanostructured features. By using a polymer film substrate having a designed nanostructured surface, it is possible to realize nanopatterned components having dimensions exceeding those of semiconductor wafers, which are actually limited to 300 mm or less in diameter. The nanopatterned polymer film can have dimensions on the order of 1 m in width and 1 km in length or an indefinite length. The polymer film can provide transparency over the visible and near-infrared spectra required for many applications.

[0050] The optical metasurface polymer film utilizes the design of subwavelength structures or features that give a rapid phase change at the interface between the subwavelength structures and the surrounding medium. By arranging these subwavelength structures or features in the polymer film, an operating phase profile of the optical metasurface film is provided. Therefore, a predetermined operating phase profile of the optical metasurface film can be created to determine the arrangement of these subwavelength structures or features in the polymer film.

[0051] The flexible substrate can be, for example, a large-sized substrate having a lateral dimension greater than 300 mm, or greater than about 400 mm, or greater than about 500 mm. The flexible substrate can form a web of indefinite length. These optical metasurface polymer films can be formed using highly accurate roll-to-roll processing. The optical metasurface polymer films will be described. These optical metasurface polymer films can be formed on a flexible substrate.

[0052] The metasurface can utilize the design of subwavelength structures that can impart a sharp phase change at the interface. In particular, the phase gradient (dΦ / dx) along the path on the interface (x → ) leads to the generalized Snell's law of refraction, [Number] where n i and n t are the refractive indices of the incident light and the transmitted light, respectively, θ i and θ t are the angle of incidence and the angle of refraction, and λ 0 is the incident wavelength in vacuum. Therefore, by implementing such a phase discontinuity at the interface, it becomes possible to generate extraordinary refraction.

[0053] There are many ways to design elements that can impart a phase discontinuity to a functional metasurface. Here, as an example of the metasurface design, the approach of Pancharatnam-Berry phase (or geometric phase) is utilized. This enables the use of a single element with different angular directions, and the single element greatly reduces the number of optimization parameters. Furthermore, since the generated phase depends only on the rotation angle of the basic nanostructure, this approach is very robust against manufacturing errors because the rotation angle is a parameter that is generally well controlled in manufacturing compared to the structural dimensions.

[0054] To realize a Pancharatnam-Berry phase metasurface, rectangular TiO having different widths (W), lengths (L), and heights (H) 2Nanofins are formed. Generally, for ease of manufacturing, H is constant across the meta-surface. However, this is not a necessary condition.

[0055] When light propagates in the +Z - direction within the nanofin, it experiences different effective refractive indices in the W - direction and the L - direction respectively. For a given W - size and L - size, the nanofin acts as a half - wave plate (HWP), i.e., linearly polarized light propagating along one principal axis experiences a π phase change with respect to linearly polarized light propagating along the other principal axis.

[0056] Therefore, the nanofin can convert right - circularly polarized light (RCP) (which can be decomposed into two orthogonal linearly polarized states with a relative +π / 2 phase difference) to left - circularly polarized light (LCP) (which can be decomposed into two orthogonal linearly polarized states with a relative -π / 2 phase difference), and vice versa. If the dimensions of the nanofin deviate from the ideal parameters for a half - wave plate, the circularly polarized light is only partially converted in the opposite direction.

[0057] To realize this meta - surface, TiO 2 A parameter sweep of the nanofin dimensions can be performed to find the structural dimensions for an efficient HWP. The sweep can be performed for different dielectric environments where the nanofin is surrounded by either air or various embedded polymers or materials. In addition to nanofins with vertical sidewalls, nanofins with various sidewall taper angles can be utilized to reflect manufacturing constraints defined by direct replication manufacturing routes.

[0058] Using Lumerical's commercially available finite - difference time - domain (FDTD) solver, the characteristics of the nanofin can be simulated and analyzed to determine the optimal nanofin shape that satisfies manufacturing constraints and acts as an HWP. The FDTD solver provides a time - stepping solution of Maxwell's equations with user - specified boundary conditions. The results can be analyzed in the frequency domain after Fourier - transforming the time - domain solution.

[0059] The measurement can be carried out at a wavelength of 532 nm by using a green laser that is located approximately in the center of the visible light and is widely used, which facilitates subsequent measurements.

[0060] The size of the simulation mesh - the interval between individual positions for solving Maxwell's equations at each time step - can be set to 10 nm in each of the x, y, and z dimensions in order to minimize the staircase effect introduced by the Cartesian lattice used in FDTD. The described simulation settings can demonstrate a Pancharatnam-Berry phase TiO 2 nanofin metasurface operating in the visible spectrum.

[0061] To find the optimal nanofin dimensions in different embedding materials, a parameter sweep of different nanofin dimensions and sidewall taper angles can be performed. Assume that the nanofins are embedded in an optical resin. The incident light can be set to be incident from the substrate side with RCP polarization and propagate towards the nanofins. The electric and magnetic field data of the transmitted light can be collected with respect to the wavelength away from the apex of the nanofins. Next, information on the amplitude and polarization of the transmitted light can be obtained by far-field transformation. By comparing the relative phases and amplitudes of the x-polarized and y-polarized transmitted light in the far field with a reference geometry that includes only a quartz substrate without nanofins, the conversion efficiency from RCP to LCP and its transmission amplitude for each nanofin can be measured. For each combination of the embedding material and the sidewall taper angle, the dimensions of the nanofins that most accurately generate the behavior of the HWP and thus result in the highest conversion efficiency for circularly polarized light can be determined.

[0062] FIG. 1 is a cross-sectional schematic view of an exemplary optical metasurface film 100. FIG. 2 illustrates a top view schematic of four representative optical metasurface films. The optical metasurface film can include one or more aspects of the representative optical metasurface films illustrated in FIG. 2. The optical metasurface film illustrated in FIG. 2 is a non-limiting exemplary nanostructure topography.

[0063] The optical metasurface film 100 includes a flexible polymer film 101 having a first major surface, a first surface proximate to the first major surface of the flexible polymer film 101, a patterned polymer layer 103 having a second nanostructured surface opposite to the first surface, and a refractive index contrast layer 104 including a refractive index contrast material adjacent to the nanostructured surface of the patterned polymer layer 103 that forms a nanostructured bilayer 105 having a nanostructured interface 106. The nanostructured bilayer 105 locally acts on the amplitude, phase, or polarization of light, or a combination thereof, and provides a phase change of light that varies as a function of the position of the nanostructured bilayer 105 on the flexible polymer film 101. The phase change of light of the nanostructured bilayer 105 defines a predetermined operating phase profile of the optical metasurface film 100.

[0064] The nanostructured bilayer can further include an etching stop layer 102 that separates the patterned polymer layer 103 from the first major surface of the flexible polymer film 101. The etching stop layer can be an etching-resistant layer that is used to define a common etching depth during wet or dry etching processes. The etching stop layer 102 may have a thickness greater than 2 nm and up to about 25 nm at most. The etching stop layer can be formed from metals and their oxides and nitrides including oxides or nitrides of Si, Al, Ti, Zr, Ta, Hf, Nb, Ce, and combinations thereof.

[0065] The nanostructured bilayer may locally act on the amplitude of light. The nanostructured bilayer may locally act on the phase of light. The nanostructured bilayer may locally act on both the amplitude and the phase of light. The nanostructured bilayer may locally act on both the amplitude and the polarization of light. The nanostructured bilayer may locally act on both the phase and the polarization of light.

[0066] The flexible polymer film may be formed from a thermoplastic material. The flexible polymer film may be formed from polyester, copolyester, polycarbonate, polyurethane, poly(methyl methacrylate), polystyrene, polyimide, polyethylene naphthalate, polypropylene, polycycloolefin, preferably polyester and polycarbonate. The flexible polymer film can have a uniform thickness. The flexible polymer film can have an average thickness in the range of about 5 μm to 300 μm. The flexible polymer film can have a uniform thickness in the range of 10 μm to 250 μm, or 25 μm to 125 μm. The flexible polymer film can exhibit an optical retardation.

[0067] The nanostructured bilayer can be defined by a solid material. The nanostructured bilayer may be formed from a solid material. The nanostructured bilayer may be formed from a polymer material.

[0068] The patterned polymer layer may be formed from a thermoplastic material. The patterned polymer layer may be formed from poly(methyl methacrylate), polycarbonate, polypropylene, polyethylene, polystyrene, polyester, polyamide. The patterned polymer layer may be formed from a polymerizable composition containing an acrylate or methacrylate component. The patterned polymer layer may contain a fluoropolymer, a (meth)acrylate (co)polymer, or a silica-containing polymer.

[0069] The refractive index contrast material can have a first refractive index value, and the patterned polymer layer can have a second refractive index value that is at least 0.25 or 0.5 or 0.75 or 1.0 or 1.4 different from the first refractive index value.

[0070] The refractive index contrast material can have a first refractive index value in the range of 1.7 to 2.5. The patterned polymer layer has a second refractive index value in the range of 1.2 to 1.6.

[0071] The refractive index contrast material may include a metal oxide or a metal nitride. The refractive index contrast material may include titanium, zirconium, tantalum, hafnium, niobium, zinc, or cerium; titanium oxide, zirconium oxide, tantalum oxide, hafnium oxide, niobium oxide, zinc oxide, or cerium oxide; titanium nitride, zirconium nitride, tantalum nitride, hafnium nitride, niobium nitride, zinc nitride, or cerium nitride; titanium sulfide, zirconium sulfide, tantalum sulfide, hafnium sulfide, niobium sulfide, zinc sulfide, or cerium sulfide; or at least one of combinations thereof.

[0072] The patterned polymer layer may include fluoroacrylate, and the refractive index contrast material may include titanium dioxide. The patterned polymer layer may include (meth)acrylate, and the refractive index contrast material may include titanium dioxide.

[0073] The nanostructured bilayer can be defined by a plurality of nanostructures embedded in the refractive index contrast layer. The nanostructures forming the nanostructured surface can have an aspect ratio of at least about 1:1, about 2:1, about 5:1, about 10:1, or about 15:1. The nanostructures forming the nanostructured surface can preferably have an aspect ratio in the range of about 2:1 to about 20:1, or in the range of about 4:1 to about 15:1.

[0074] The nanostructures forming the nanostructured surface can define tapered sidewalls having an angle in the range of about 1 to 10°, about 2 to 10°, about 3 to 10°, about 4 to 10°, about 1 to 6°, about 2 to 6°, or about 3 to 6°, or about 2 to 4°. The nanostructures forming the nanostructured surface can define tapered sidewalls having an angle in the range of about 0 to 10°, about 0 to 6°, about 0 to 3°, about 0 to 2°, about 0 to 1°, or 0°.

[0075] The nanostructures forming the nanostructured surface may have a height in the range of 5 μm or less, or about 100 nm to about 3000 nm, or about 500 nm to about 1500 nm.

[0076] The nanostructures forming the nanostructured surface have an average pitch (center-to-center distance between adjacent nanostructures) that is sub-wavelength with respect to the shortest wavelength included in the investigated electromagnetic radiation.

[0077] Regarding the operation of the optical metasurface in the visible spectrum range, the nanostructures forming the nanostructured surface may have an average pitch of 600 nm or less, or 500 nm or less, or 400 nm or less. Regarding the operation of the optical metasurface in the visible spectrum range, the nanostructures forming the nanostructured surface may preferably have an average pitch of 50 nm to 600 nm, or 100 nm to 500 nm, or 200 nm to 400 nm.

[0078] The nanostructures forming the nanostructured surface are separated from each other by a sub-wavelength lateral distance. The nanostructures forming the nanostructured surface may be separated from each other in the range of about 400 nm or less, or about 20 nm to about 400 nm, or about 50 nm to 300 nm, respectively.

[0079] The nanostructures forming the nanostructured surface have a lateral dimension orthogonal to the height of the nanostructure features that is sub-wavelength. The nanostructures forming the nanostructured surface have a lateral dimension orthogonal to the height of the nanostructure features in the range of about 600 nm or less, or about 10 nm to 400 nm, or about 50 nm to 350 nm.

[0080] The phase change of light can occur in the visible light wavelength range. The phase change of light can occur in the near-infrared wavelength range. The optical metasurface film can transmit visible light or near-infrared light.

[0081] The nanostructures forming the nanostructured surface can have a varying direction that depends on the position of the individual nanostructures on the flexible polymer film. The nanostructures forming the nanostructured surface can have a varying spatial arrangement that depends on the position of the individual nanostructures on the flexible polymer film. The nanostructures forming the nanostructured surface can have a varying shape that depends on the position of the individual nanostructures on the flexible polymer film. The nanostructures forming the nanostructured surface can have a varying aspect ratio that depends on the position of the individual nanostructures on the flexible polymer film.

[0082] The nanostructures forming the nanostructured surface may be geometrically anisotropic with respect to the planar direction. The nanostructures forming the nanostructured surface may be geometrically isotropic with respect to the planar direction.

[0083] FIG. 3 illustrates a cross-sectional schematic view of an exemplary method for forming an exemplary optical metasurface film.

[0084] This manufacturing route utilizes a hard mask layer that also functions as a second etch stop layer. Including the hard mask layer has four beneficial effects. First, etching of the thin hard mask layer does not require high aspect ratio resist features, thus reducing or eliminating the need for substantially zero land resist replication processing. Second, the nano-replication resist material can be an acrylate resin formulation rather than a silicon-rich hybrid material. Third, the hard mask etching process enables the formation of deep vias with vertical sidewalls (important for application to optical metasurfaces). Finally, the deposition process of the hard mask layer forms a well-adhered inorganic layer with good wettability to the nano-replication resin layer, enabling the use of a low refractive index pattern transfer layer (e.g., fluoroacrylate).

[0085] A polymer support film and an input roll for nano-replication processing including an etching stop layer, a precision pattern transfer layer, and a hard mask layer are utilized. A process such as roll-to-roll nanoimprint lithography (R2R NIL) is required to form an etching resist layer with a substantially zero land structure in the first processing step, but the land control can be relaxed. Since the structure is etched throughout the thickness of the pattern transfer layer, the layer thickness ultimately defines the height of the feature portion of the final product. This process is important for both the uniformity of the feature height and the absolute feature height in the surface features of the final product (e.g., for applications to metasurfaces), and is useful in the case of an optical element having a low refractive index organic layer and a high refractive index metal oxide backfill layer.

[0086] The material used for the pattern transfer layer can be utilized as either a low refractive index material or a high refractive index material of the embedded optical element.

[0087] A film including a polymer support film, an etching stop layer, a precision pattern transfer layer, and a hard mask layer 410 is used as an input roll for R2R NIL or continuous casting and continuous curing (Process 4A, "R2R NIL"). The nano-replicated film 420 is etched by reactive ion etching (RIE) until the upper surface of the hard mask layer is exposed (Process 4B, "breakthrough etching") to generate an intermediate 430. Some resin residues may remain after this step and can be removed by any additional RIE process (Process 4C). The hard mask pattern intermediate 440 is further etched by a second RIE process using a second etching chemistry until the pattern transfer layer is completely etched to the etching stop layer (Process 4D). The etched nano-patterned film with hard mask residues 450 is planarized with a high refractive index backfill to form an embedded nano-patterned optical film 460 (Process 4E), or can be subjected to different etching conditions to remove the hard mask residues to form an unfilled nano-patterned optical film 470 (Process 4F). Finally, the unfilled nano-patterned optical film 470 can be planarized with a high refractive index backfill to form an embedded nano-patterned optical film 370.

Example

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Table 1

[0089] Example 1. A functional blazed diffraction grating fabricated by a four-layer method with less residual transfer on PETg

Table 2

[0090] Step a: Replication of the nano-feature template film Compound 01 with 0.5% AEBP was supplied to the die and a 5-mil polycarbonate membrane via a peristaltic pump. The membrane coated with resin was sandwiched between round nickel sleeves with a nanoscale pattern welded and controlled at 140°F Fahrenheit. The feature had side surfaces in the range of 100 nm to 350 nm and a height of 200 nm. It had a nominal vertical draft of zero. While in contact with the nickel sleeve, the membrane coated with resin was exposed to radiation from two fusion lamps operating at 142 W / cm. Next, the nanostructured membrane was peeled off from the round nickel sleeve. The process was continuously carried out at 25 fpm for over 1000 feet. Figure 4 is a 50kX top image of the replicated features on the nano-replicated resist transfer membrane, showing the sample area.

[0091] Step b: Peeling process of the nano-feature template membrane The touring membrane from step a was peeled using PECVD. First, the membrane was prepared by flowing O 2 into the chamber at 500 cfpm with a plasma output of 2000 W at 30 fpm.

[0092] Next, the membrane was treated with HMDSO at 30 fpm and 1000 W. Figure 5 is a 50kX perspective view image of the peeled replicated features.

[0093] Step c: Coating of acrylate on the template membrane The peeled touring membrane (b) was die-coated at 10 fpm with a solution of 13% compound 03, 1% compound 05, 43% MEK, and 43% Dowanol PM. The coating was pre-cured with a UV-LED system operating at 0.2 Amps within 30 seconds of the coating. A very thin residual layer was desired so that the thickness of the residual layer could be controlled between 0 and 500 nm with the accuracy of the jig using a pre-measured coating method. This coating method uses a solution that is at least 50% solvent.

[0094] Process d: Drying of acrylate on the touring film The solvent was evaporated from the film (c) in a 40-foot free span. The solvent was dried without using heat or convection to prevent disturbance of the wet film.

[0095] Process e: Preparation of a three-layer film (laminated to the acrylate-coated template film) Since this film is part of the final structure, a PET-g film is selected because of its low in-plane retardation determined by the optical design. This PET-g film is described in FIG. 2 of Application WO2019032635A1. FIG. 2 is a side view of a four-layer film having an ADBC layer configuration. The film includes the following layers within the configuration, namely, an alignment layer A, a bonding layer D, a release layer B, and an isotropic layer C. Here, the alignment layer A is polyester (PET), the bonding layer D is a linear triblock copolymer of styrene and ethylene / butylene (G1645 of Kraton Corp), the release layer B is a mixture of polypropylene (PP9074MED of Exxon Mobil) and a linear triblock copolymer of styrene and ethylene / butylene (G1645 of Kraton Corp), and the isotropic layer C is PETg (Eastar GN071 of Eastman Corp). The configuration of this film provides additional properties that control where the first separation of the layers occurs, in this case between layer B and layer C.

[0096] SiAlOx is O at 1.5 mtorr 2Deposited by dual-cathode AC reactive sputtering from a 90% Si / 10% Al target in an Ar atmosphere and at a plasma power of 16 kW. The coating rate reached a thickness coating of 25 nm at 16 fpm. The acrylate was deposited by the vapor deposition process disclosed in U.S. Patent No. 9,302,291. A mixture of 88% SR833, 4% Compound 02, 4% Dynasilan 1189, and 4% Irgacure 184 as a photoinitiator for polymerization was fed into an evaporator, and a stable stream of vapor passed through a coating die and reached a cooled substrate moving at 24 fpm, where the mixture condensed and was immediately cured by either ultraviolet light or a low-voltage electron beam. Compound 02 and Dynasilan were used to promote adhesion between SiAlOx and the acrylate. The final thickness of the acrylate layer was 1100 nm. Another 25-nm layer of SiAlOx was deposited on top of the acrylate layer in the same manner as the first layer.

[0097] Step f: Adhesion promoter on SiAlOx (to promote adhesion of the three-layer sandwich to the low-land pattern acrylate) 7.5 nm of Compound 02 was die-coated on SiAlOx with MEK at 20 fpm. The solvent evaporated, and the film was annealed at 200°F for 1.5 minutes. Next, Compound 02 was cured using a fusion E valve.

[0098] Step g: Lamination The coated touring film was laminated with the SiAlOx + Compound 02 film using a nip of 90 durometer and a water-heated roll set at 170°F at 10 fpm.

[0099] Step h: Peeling The structured acrylate was peeled from the structured HMDSO film and transferred to the SiAlOx film immediately after the water heating roll (web twist was minimized to reduce strain). All films were tensioned at approximately 1 pli while moving at 10 fpm. Figure 6 is a 50kX perspective image of the structured acrylate peeled and transferred to SiAlOx / acrylate / SiAlOx on PETG (low land film). Figure 7 is a 50kX cross-sectional image of the pre-etching or pre-breakthrough. Note that the thickness of the residual layer where the top mask layer of the via is exposed is very thin.

[0100] Steps i and j: Etching of the residual layer and breakthrough of the SiAlOx mask These steps can be performed separately as oxygen etching followed by fluorine etching, or continuously during a single fluorine etching. Here, the fluorine etching path was selected. In this case, reactive ion etching was performed at a pressure of 3 mTorr at a rate of 12.5 ft / min with 7500 watts using 100 sccm of NF3.

[0101] Step k: Breakthrough etching At a base pressure of 0.3 Torr, with 7500 watts, at a rate of 15 ft / min at a pressure of 5.2 mTorr, 700 sccm of O 2 was used for a second reactive ion etching to remove the transfer layer in the cross-section where the mask was removed. Figure 8 is a 50kX top surface image of the nanolithography pattern film after breakthrough etching. Figure 9 is a cross-sectional image of the post-O 2 etching sample.

[0102] Step l: High refractive index backfill The etched high aspect ratio features were processed in a spatial rotary ALD apparatus. TiO 2 was titanium tetraisopropoxide (TTIP) heated to 65°C (passive delivery), and N at 1 torr 2 and O at 0.3 torr 2Deposited using DC plasma discharge (350 mA) in an environment. The chamber and substrate were heated to 80°C. The substrate was fixed to a platen rotating at 30 RPM and exposed to one precursor and plasma per rotation, for a total of 4688 ALD cycles, with a thickness of 217 nm and a refractive index of 2.33 measured at a wavelength of 632 nm to form a TiO 2 layer. Figure 10 is a 50Kx cross-sectional SEM image of a sample backfilled with TiO 2 . In this image, the bright regions are TiO 2 and the dark regions are acrylate resin.

[0103] Analysis of optical images (Figures 11 and 12) The blazed diffraction grating was analyzed using a laser, and the sample was placed between two orthogonal linear polarizers. The blazed diffraction grating metamaterial sample on PET film 1 (DuPont ST504) showed multiple peaks due to an in-plane optical phase difference of δn = 0.048. Spurious points were removed on the low optical phase difference PETg sample (Figure 12). Note that the "ambiguous" points observed in Figure 12 are due to thermal degradation of PETg during ALD coating at 100°C.

[0104] Example 2: Use of a low refractive index compound as a transfer layer The purpose of the low refractive index material is TiO 2By increasing the change in refractive index between the embedded resin, the optical performance is improved. In the production of the three-layer film of Step E, Compound 04, a fluorinated low refractive index material, was used instead of 1100 nm acrylate. The PET film 2 was used instead of PETg, but this is not important for the treatment purpose. A 25 nm SiAlOx-based etching stop was sputtered onto the PET (ST505) film. Next, the etching stop layer was vapor-coated with a layer of 96% Compound 02 and 4% Darocur 1173 with a thickness of about 15 nm. While keeping the back side of the film in contact with a coating drum cooled to 0 °C, a line speed of 65 fpm was maintained. The drum was brought into contact with the back side, and the SiAlOx surface was treated with dc nitrogen plasma at 100 W and a nitrogen pressure of 150 mTorr. Immediately after treatment with nitrogen plasma, the SiAlOx surface was coated with Compound 02 / Darocur 1173 using the organic vapor deposition system and method described in U.S. Patent No. 8658248. The monomer was degassed under vacuum at a pressure of 20 mTorr before coating. This liquid was pumped into the ultrasonic atomizer at a liquid flow rate of 0.1 ml / min using a syringe pump, and a nitrogen gas flow rate of 10 sccm was input into the atomizer. The liquid was flash-evaporated at 250 °C and carried to the SiAlOx surface. The vapor stream condensed on the film surface and was cured by ultraviolet irradiation using a low-pressure mercury arc lamp.

[0105] While remaining under vacuum, the compound 02 / Darocur 1173 layer was vapor coated with an acrylate layer of 97.5% compound 04 and 2.5% Darocur 1173 with a thickness of about 1100 nm. While keeping the back side of the film in contact with a coating drum cooled to 0 °C, a line speed of 12.5 fpm was maintained. The drum was brought into contact with the back side to coat the compound 02 surface with compound 04 / Darocur 1173 using the organic vapor deposition system and method described in U.S. Patent No. 8,658,248. The monomer was degassed under vacuum at a pressure of 20 mTorr prior to coating. The liquid was pumped into an ultrasonic atomizer at a liquid flow rate of 2.05 ml / min using a syringe pump, and a nitrogen gas flow rate of 10 sccm was input into the atomizer. The liquid was flash evaporated at 250 °C and carried to the compound 02 surface. The vapor stream condensed on the film surface and was cured by ultraviolet irradiation using a low-pressure mercury arc lamp.

[0106] A 25 nm thick top etch stop layer of SiAlOx was deposited on a film coated with compound 04 / SiAlOx as described in "Method of Vapor Coating Etch Stop and Transfer Layers".

[0107] Etching through the land and SiAlOx mask was performed in one step. Reactive ion etching was performed at a base pressure of 0.5 mTorr using 100 sccm of C6F14, at 7500 watts, at a speed of 4 ft / min, at a pressure of 6.3 mTorr and a base pressure of 0.5 mTorr. Breakthrough etching: at a base pressure of 0.4 Torr, at 7500 watts, at a speed of 6 ft / min, at a pressure of 4.7 mTorr, 275 sccm of O 2 By a second reactive ion etching using O, the transfer layer in the area where the mask was removed was removed. FIG. 13 is a cross-sectional image and a perspective image of the arrangement of the features etched in the compound 04 layer. FIG. 14 is a close-up cross-sectional image of the via etched in the compound 04 layer.

[0108] Example 3 - Results Using the refractive index data, the effect of embedding nanofins in the replica resin was investigated. First, the effect of the embedding medium on the optical properties of nanofins with vertical sidewalls was examined. TiO 2 When the refractive index contrast between the nanofin and the surrounding dielectric environment decreases, the effective refractive index along the major axis of the nanofin - which can be considered a cut - off dielectric waveguide - decreases. Therefore, the ideal height of the nanofin determined for the freestanding nanostructure no longer causes the behavior of a half - wave plate. After passing through the nanofin, the phase difference (Δφ) of the linearly polarized light along the fast axis (φ fast ) and the slow axis (φ slow ) is given by the following equation,

Equation

[0109] When an appropriate nanofin height is selected, good RCP - to - LCP conversion efficiency can be achieved in the embedding of different media. However, in an environment with a high refractive index, since more guided - mode resonances are supported, the conversion - efficiency spectrum decreases more sharply. This effect is expected to be suppressed in the actual metasurface where the nanofins are not perfectly aligned but are rotated with respect to each other.

[0110] Next, the influence of the taper angle on the performance of the embedded nanofins was investigated. By increasing the taper angle of the sidewalls, the height of the nanofins may be truncated when limiting the maximum basic dimension. The taper angle can be limited to 3° and 2°, respectively, to maintain the preferred heights of 1100 nm and 1500 nm. Similar to what was observed with tapered nanofins in air, it is found that the high RCP-to-LCP conversion efficiency can only be achieved with a narrower bandwidth for increasing the taper angle. For the embedded structure, a sidewall taper angle of 2° maintains a conversion efficiency exceeding 50% over the visible spectral range.

[0111] To evaluate the performance of the optimized nanofins on the functional optical surface, the behavior of the nanofins when used in the construction of a Pancharatnam-Berry phase gradient metasurface was investigated. Specifically, six elements were arranged over a long period of Λ while each nanofin rotated counterclockwise by 30° with respect to the adjacent one on the left. Such a metasurface functions as a blazed diffraction grating with a deviation angle given as follows,

Equation

[0112] Full electromagnetic field simulations of a gradient metasurface composed of nanofins with basic dimensions of 120 nm × 300 nm were performed. The nanofins were surrounded by air and had either vertical sidewalls or taper angles of 4° and 8°. The resulting diffraction gratings were 97%, 90%, and 63% for vertical, 4° taper, and 8° taper, respectively. The decrease in efficiency with increasing sidewall taper angle is consistent with previous findings for individual nanofins.

[0113] Based on the results obtained from previous studies, the optical metasurface was designed to examine wafers exploring direct nano-replication (referred to as H1) and nano-imprint lithography (H2) routes.

[0114] The investigation wafer H1 hosts designs H1A and H1B (Table 1), both of which consist of 600 nm high nanofins embedded in a resin with n = 1.52 and having tapered sidewalls at an angle of 4°. Individual nanofins operate as approximately quarter-wave plates due to height limitations imposed by the manufacturing method. This results in a reduction in circular polarization conversion efficiency compared to the ideal case of half-wave plate nanofins. For H1A, a gradient metasurface with a deviation angle of 4.7° was designed. H1B consists of perfectly aligned nanofins to examine manufacturing diversity.

Table 3

[0115] The investigation wafer H2 hosts designs H2A, H2B, and H2C (Table 2). In all designs, straight-wall nanofins with a height of 1100 nm embedded in a resin with a refractive index n = 1.36 are used. H2A consists of nanofins with basic dimensions of 120 nm × 300 nm and functions as a half-wave plate. A blazed diffraction grating with a deviation angle of 4.8° was designed.

[0116] H2B and H2C consist of switchable holograms (a cat / dog and 3M / Harvard logos, respectively) that display different images for orthogonal states of linearly polarized light. In contrast to the periodic patterns used in H1A and H2A, H2B and H2C contain non-repeating patterns of nanofins with various basic dimensions to generate a wide range of local phases through the propagation phase approach. The images are encoded as computer-generated holograms via the Gerchberg-Saxton algorithm.

Table 4

[0117] Tables 3A and 3B show the relative performance of nanofins with basic dimensions close to the optimal half-wave plate nanofins in an embedding medium with a refractive index of 1.36. To compromise on nanofins with basic dimensions of 140 nm × 280 nm and meet the manufacturing limitations that require a minimum feature size of 80 nm, they were arranged in a 420 nm grid. The numerical values in Tables 3A and 3B show the percentage of the relative RCP-to-LCP conversion efficiency at 532 nm when 140 nm × 280 nm is set to 100%. The region of the red box includes the execution of better parameters. However, the said parameters cannot be utilized due to the limitation of the 80 nm feature size. Due to errors of ±20 nm in W (minor axis), ±10 nm in H (major axis), and ±20 nm in height, they perform less than 15% worse than the designed structure.

Table 5

Table 6

[0118] Tables 3A and 3B Sensitivity analysis TiO 2 The nanofins were embedded in an optical resin with an optical refractive index of 1.5. The said figures show the percentage of the relative RCP-to-LCP conversion efficiency when a 140 nm × 280 nm × 600 nm nanofin is set to 100%. Due to errors of ±20 nm in W (minor axis), ±10 nm in L (major axis), and ±20 nm in H (height), they perform less than 15% worse than the designed structure.

Claims

1. An optical metasurface film, a flexible polymeric membrane having a first major surface; a patterned polymeric layer having a first surface adjacent to the first major surface of the flexible polymeric membrane and a second nanostructured surface opposite the first surface; a refractive index contrast layer comprising a refractive index contrast material adjacent to the nanostructured surface of the patterned polymeric layer forming a nanostructured bilayer having a nanostructured interface; the nanostructured bilayer comprising a plurality of nanostructures disposed on the flexible polymeric film, the nanostructured bilayer locally acting on the amplitude, phase, polarization, or a combination thereof, of light to impart a phase change of light that varies as a function of the position of the nanostructured bilayer on the flexible polymeric film, the phase change of light in the nanostructured bilayer defining a predetermined manipulation phase profile of the optical metasurface film.

2. The optical metasurface film of claim 1 , wherein the nanostructured bilayer locally affects the amplitude of light.

3. The optical metasurface film of claim 1 or 2, wherein the nanostructured bilayer locally affects the phase of light.

4. The optical metasurface film of any one of claims 1 to 3, wherein the nanostructured bilayer locally affects the polarization of light.

5. The optical metasurface film of any one of claims 1 to 4, wherein the nanostructured bilayer is defined by a solid material.

6. The optical metasurface film of any one of claims 1 to 5, further comprising an etch stop layer separating the patterned polymer layer from the first major surface of the flexible polymer film.

7. 7. The optical metasurface film of claim 1, wherein the refractive index contrast material has a first refractive index value and the patterned polymer layer has a second refractive index value that differs from the first refractive index value by at least 0.25, or 0.5, or 0.75, or 1.0, or 1.

4.

8. The optical metasurface film of any one of claims 1 to 7, wherein the nanostructured bilayer is defined by a plurality of nanostructures embedded in the refractive index contrast layer.

9. The optical metasurface film of any one of claims 1 to 8, wherein the refractive index contrast material comprises a metal oxide or a metal nitride.

10. 10. The optical metasurface film of claim 1, wherein the refractive index contrast material comprises at least one of titanium, zirconium, tantalum, hafnium, niobium, zinc, or cerium; titanium oxide, zirconium oxide, tantalum oxide, hafnium oxide, niobium oxide, zinc oxide, or cerium oxide; titanium nitride, zirconium nitride, tantalum nitride, hafnium nitride, niobium nitride, zinc nitride, or cerium nitride; titanium sulfide, zirconium sulfide, tantalum sulfide, hafnium sulfide, niobium sulfide, zinc sulfide, or cerium sulfide; or a combination thereof.

11. The optical metasurface film of any one of claims 1 to 10, wherein the patterned polymeric layer comprises a fluoropolymer, a (meth)acrylate (co)polymer, or a silica-containing polymer.

12. The optical metasurface film of any one of claims 1 to 11, wherein the patterned polymeric layer comprises a fluoroacrylate and the refractive index contrast material comprises titanium dioxide.

13. The optical metasurface film of any one of claims 1 to 12, wherein the patterned polymeric layer comprises a (meth)acrylate and the refractive index contrast material comprises titanium dioxide.

14. The optical metasurface film of any one of claims 1 to 13, wherein the nanostructures forming the nanostructured surface have an aspect ratio of at least about 1:1, about 2:1, about 5:1, about 10:1, or about 15:

1.

15. The optical metasurface film of any one of claims 1 to 14, wherein the nanostructures forming the nanostructured surface define tapered sidewalls having an angle in the range of about 1 to 10°, about 2 to 10°, about 3 to 10°, about 4 to 10°, about 1 to 6°, about 2 to 6°, or about 3 to 6°.

16. The optical metasurface film of any one of claims 1 to 15, wherein the nanostructures forming the nanostructured surface define tapered sidewalls having an angle in the range of about 0-10°, about 0-6°, about 0-3°, about 0-2°, about 0-1°, or 0°.

17. The optical metasurface film according to any one of claims 1 to 16, wherein the flexible polymer film has an average thickness in the range of about 5 μm to about 300 μm.

18. The optical metasurface film of any one of claims 1 to 17, wherein the nanostructures forming the nanostructured surface have a height of 5 μm or less, or in the range of about 100 nm to about 3000 nm, or about 500 nm to about 1500 nm.

19. The optical metasurface film of any one of claims 1 to 18, wherein the nanostructures forming the nanostructured surface have an average pitch of 600 nm or less, or 500 nm or less, or 400 nm or less.

20. The optical metasurface film of any one of claims 1 to 19, wherein the nanostructures forming the nanostructured surface are separated from each other by about 400 nm or less, or by about 20 nm to about 400 nm, or by about 50 nm to about 300 nm.

21. 21. The optical metasurface film of any one of claims 1 to 20, wherein the nanostructures forming the nanostructured surface have a lateral dimension orthogonal to the height of the nanostructured features in a range of about 600 nm or less, or about 10 nm to about 400 nm, or about 50 nm to about 350 nm.

22. The optical metasurface film according to any one of claims 1 to 21, wherein the phase change of the light occurs in the visible light wavelength range.

23. The optical metasurface film according to any one of claims 1 to 22, wherein the phase change of the light occurs in the near-infrared wavelength range.

24. The optical metasurface film of any one of claims 1 to 23, wherein the nanostructures forming the nanostructured surface have varying orientations that depend on the position of the individual nanostructures on the flexible polymer film.

25. The optical metasurface film of any one of claims 1 to 24, wherein the nanostructures forming the nanostructured surface have a varying spatial arrangement that depends on the position of the individual nanostructures on the flexible polymer film.

26. The optical metasurface film of any one of claims 1 to 25, wherein the nanostructures forming the nanostructured surface have varying shapes that depend on the position of the individual nanostructures on the flexible polymer film.

27. The optical metasurface film of any one of claims 1 to 26, wherein the nanostructures forming the nanostructured surface have varying aspect ratios that depend on the position of the individual nanostructures on the flexible polymer film.

28. The optical metasurface film according to any one of claims 1 to 27, wherein the optical metasurface film transmits visible light or near-infrared light.

29. The optical metasurface film according to any one of claims 1 to 28, wherein the nanostructures forming the nanostructured surface are geometrically anisotropic with respect to a planar direction.

30. The optical metasurface film according to any one of claims 1 to 29, wherein the nanostructures forming the nanostructured surface are geometrically isotropic with respect to a planar direction.

31. The optical metasurface film of any one of claims 1 to 30, wherein the optical metasurface film has at least one lateral dimension greater than about 300 mm, or greater than about 400 mm, or greater than about 500 mm.

Images