FUNCTIONAL IMPRINTED OPTICAL STRUCTURES FOR OPTICAL DEVICES

Embodiments of the present disclosure include apparatus and methods for optical devices. In one embodiment, a method for forming an optical device generally includes disposing a first material device layer on a substrate, patterning a portion of the first material device layer to form a first plurality of device structures in the first material device layer, disposing a second material device layer on an un-patterned portion of the first device material layer, and patterning the second material device layer to form a second plurality of device structures disposed on the first material device layer.

BACKGROUND

Field

Embodiments of the present disclosure generally relate to optical devices for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide for forming optical device structures having blazed or staircase gratings.

Description of the Related Art

Virtual reality is generally considered to be a computer generated simulated environment in which a user has an apparent physical presence. A virtual reality experience can be generated in 3D and viewed with a head-mounted display (HMD), such as glasses or other wearable display devices that have near-eye display panels as lenses to display a virtual reality environment that replaces an actual environment.

Augmented reality, however, enables an experience in which a user can still see through the display lenses of the glasses or other HMD device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as part of the environment. Augmented reality can include any type of input, such as audio and haptic inputs, as well as virtual images, graphics, and video that enhances or augments the environment that the user experiences. As an emerging technology, there are many challenges and design constraints with augmented reality.

One such challenge is displaying a virtual image overlaid on an ambient environment. Optical devices including waveguide combiners, such as augmented reality waveguide combiners, and flat optical devices, such as metasurfaces, are used to assist in overlaying images. Generated light is propagated through an optical device until the light exits the optical device and is overlaid on the ambient environment. Optical devices may require structures having blazed angles relative to the surface of the optical device substrate. Conventionally, fabricating blazed optical device structures using one or more angled etch tools requires multiple lithographic patterning operations and angled etch steps. The multiple lithographic patterning operations and angled etch steps increase fabrication time and increase cost. Some of the challenges of waveguide display with current grating designs and known materials also include low optical efficiency, stray light, ghost images, and a small Field of View (FOV). In addition, manufacturing current gratings on the same substrate can be a time-consuming process.

Accordingly, what is needed in the art are improved methods of forming optical devices including blazed optical device structures.

SUMMARY

Embodiments of the present disclosure provide a method. The method generally includes disposing a first device material layer over a substrate, the first device material layer being a different material from the substrate and patterning a portion of the first device material layer to form a first plurality of device structures in a top surface of the first device material layer. In some embodiments, the first plurality of device structures comprise a first plurality of gratings and a second plurality of gratings. The method also includes disposing a second device material layer on the top surface of a portion of the first device material layer and patterning the second device material layer with a nanoimprint lithography process to form a second plurality of device structures in the second material layer disposed on the first device material layer. In some embodiments, the second plurality of device structures comprise a third plurality of gratings having a grating depth extending from the top surface of the first device material layer to a top surface of the third plurality of gratings. In some embodiments, the second device material layer comprises an uncured imprintable material for receiving a master stamp of the nanoimprint lithography process. In some embodiments, the third plurality of gratings comprises a plurality of blazed device structures or a plurality of staircase device structures.

In another embodiment of the present disclosure, an optical device is provided. The optical device generally includes a substrate and a first device material layer disposed on the substrate, the first device material layer comprising a material different from the substrate. The optical device also includes a first plurality of device structures formed in a portion of the first device material layer and a second plurality of device structures disposed on an unpatterned portion of the first device material layer. In some embodiments, the first plurality of device structures comprises a first plurality of gratings and a second plurality of gratings. In some embodiments, the first plurality of gratings correspond to a pupil expansion grating of a waveguide combiner and the second plurality of gratings correspond to an output coupling grating of the waveguide combiner. In some embodiments, the second plurality of device structures comprises a third plurality of gratings having a grating depth extending from the top surface of the first device material layer to a top surface of the third plurality of gratings. In some embodiments, the third plurality of gratings correspond to an input coupling grating of a waveguide combiner and comprises a plurality of blazed device structures or a plurality of staircase device structures. In other embodiments, the optical device may also include a metal coating layer disposed on the second plurality of device structures.

DETAILED DESCRIPTION

Embodiments of the present invention generally relate to optical devices for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide apparatus and methods of manufacture for optical devices having imprinted optical device structures disposed on top of a film layer having additional optical device structures integrated therein.

In one embodiment, the optical device is a waveguide combiner with a high-index film disposed on a substrate and a plurality of device structures integrated in/formed in a top surface of a portion of the high-index film. The optical device also includes a plurality of device structures disposed on top of the high-index film on the substrate. In some embodiments, the plurality of device structures disposed on top of the high-index film comprise blazed device structures or staircase device structures configured for coupling and directing light towards the optical device structures integrated in the high-index film. Compared with conventional waveguides, various embodiments discussed herein can advantageously provide higher coupling efficiency, better image quality (e.g., lower ghosting, higher uniformity, etc.), and a simpler manufacturing process.

In one embodiment, the method utilizes an imprint lithography process in combination with other forming techniques, such as lithography patterning and etch processes to form the optical device. In some embodiments, the method uses conventional lithography patterning and etch processes to form the plurality of device structures in the high-index film, and the imprint lithography process to form the plurality of blazed device structures or the plurality of staircase device structures on the high-index film without multiple lithographic patterning steps and angled etch steps. Using imprint lithography in combination with other techniques for forming optical devices using the methods and implementations discussed herein can provide a means for fabricating optical devices with high throughput while also reducing costs.

FIG.1Aillustrates a perspective, frontal view of an optical device100. It is to be understood that the optical device100described below is an exemplary optical device. In one embodiment, which can be combined with other embodiments described herein, the optical device100is a waveguide combiner, such as an augmented reality waveguide combiner. In another embodiment, which can be combined with other embodiments described herein, the optical device100is a flat optical device, such as a meta surface. The optical device100includes a first plurality of device structures102and a second plurality of device structures104disposed on a substrate101. In an embodiment, the first plurality of device structures102is integrated in and/or formed in a portion of a first device material layer108disposed on the substrate101. In an embodiment, the second plurality of device structures104is formed in a second device material layer110disposed on a top surface of a remaining portion of the first device material layer108separate from the first plurality of device structures102. The first and second plurality of device structures102,104may be nanostructures having sub-micron dimensions, e.g., nano-sized dimensions, such as critical dimensions less than 1 μm.

In one embodiment, which can be combined with other embodiments described herein, regions of the first plurality of device structures102correspond to one or more gratings112, such as a first grating112A and a second grating112B. In another embodiment, which can be combined with other embodiments described herein, regions of the second plurality of device structures104correspond to a third grating114. In one embodiment, which can be combined with other embodiments described herein, the optical device100is a waveguide combiner that includes at least the first grating112A corresponding to an intermediate or pupil expansion grating and the second grating112B corresponding to an output coupling grating. The waveguide combiner according to the embodiment, which can be combined with other embodiments described herein, may include the third grating114corresponding to an input coupling grating.

A material of the substrate101includes, but is not limited to, one or more of silicon (Si), silicon dioxide (SiO2), germanium (Ge), silicon germanium (SiGe), sapphire, silicon carbide (SiC), lithium niobium oxide (LiNbOx) and high-index transparent materials such as high-refractive-index glass. For example, the substrate101includes glass doped with a heavy dopant such as lanthanum (La), zirconium (Zr), zinc (Zn), and the like. The substrate101may include other suitable materials, including, but not limited to, amorphous dielectrics, non-amorphous dielectrics, crystalline dielectrics, silicon oxide, polymers, and combinations thereof. In some examples, which can be combined with other embodiments described herein, the substrate101includes a transparent material. Suitable examples may include an oxide, sulfide, phosphide, telluride or combinations thereof.

The materials of the substrate101may further have rollable and flexible properties. In one example, the material of the substrate101includes, but is not limited to, materials having a refractive index between about 1.5 and about 2.4. For example, the substrate101may be a doped high index substrate having a refractive index between about 1.7 and about 2.4.

The first device material layer108can be disposed over a top surface of an optical device substrate, for example, by a film deposition method on the substrate101if present. Any suitable method for deposition of the first device material layer108can be used. Examples of suitable thin film deposition methods include a physical vapor deposition (PVD) process (e.g., ion beam sputtering, magnetron sputtering, e-beam evaporation), a chemical vapor deposition (CVD) process, a plasma enhanced chemical vapor deposition (PECVD) process, an atomic layer deposition (ALD) process, an inkjet printing process, or a three-dimensional (3D) printing process.

In some embodiments, which can be combined with other embodiments described herein, the first device material layer108includes material different from the material of the substrate101. In some embodiments, which can be combined with other embodiments described herein, the first device material layer108includes but is not limited to, one or more of silicon oxycarbide (SiOC), titanium dioxide (TiO2), silicon dioxide (SiO2), vanadium (IV) oxide (VOx), aluminum oxide (Al2O3), aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), tin dioxide (SnO2), zinc oxide (ZnO), tantalum pentoxide (Ta2O5), silicon nitride (Si3N4), zirconium dioxide (ZrO2), niobium oxide (Nb2O5), cadmium stannate (Cd2SnO4), or silicon carbon-nitride (SiCN) containing materials. In some embodiments, which can be combined with other embodiments described herein, the material of the first device material layer108may have a refractive index between about 1.5 and about 2.65. In other embodiments, which can be combined with other embodiments described herein, the first device material layer108may have a refractive index between about 3.5 and about 4.0.

In some embodiments, which can be combined with other embodiments described herein, the second device material layer110comprises an uncured patternable material layer for receiving an imprint pattern of a nanoimprint process to form the second plurality of device structures104. In some embodiments, the second device material layer110is a patternable polymer or resist material including but not limited to, an UV curable adhesive, a thermoplastic material, or other polymer material. The uncured patternable material can be deposited using deposition techniques, such as, for example, jet deposition (e.g., inkjet deposition), coating, spin-coating, spraying, or other pre-metered coating techniques such as slot-die, doctor blade, knife edge, screen, etc.

FIG.1Billustrates a schematic, cross-sectional view of the optical device100A, according to certain embodiments. In some embodiments, which can be combined with other embodiments described herein, the first plurality of device structures102can include grating device structures having a variety of shapes, such as, for example lines (binary), pillars, slanted lines or pillars, saw-tooth, staircase, blazed, etc. In one embodiment, which can be combined with other embodiments described herein, the first plurality of device structures102includes binary device structures116of a waveguide combiner, such as an augmented reality waveguide combined.

In one embodiment, which can be combined with other embodiments described herein, the second plurality of device structures104are blazed device structures118of a waveguide combiner, as shown inFIG.1B. In other embodiments, the second plurality of optical structures104may be staircase shaped device structures or another shape. In the example shown, the waveguide combiner includes binary device structures116in the first and second gratings112A,112B and blazed device structures118in the third grating114. The third grating114corresponds to an input coupling grating of optical device100configured for coupling incident light into the optical device100and directing the light towards the first grating112A. The first grating112A corresponding to an intermediate or pupil expansion grating of optical device100can propagate the light through the optical device100via total internal reflection. The first grating112A can then direct the light towards the second grating112B corresponding to an output coupling grating of optical device100which can extract and direct the light out of the optical device100and into a viewer's eyes.

In some embodiments, which can be combined with other embodiments described herein, the optical device100includes a metal coating122deposited on the second plurality of device structures104. The metal coating122can be of any suitable shape. In some embodiments, which can be combined with other embodiments, the metal coating122forms a conformal coating over or on the blazed device structures118or the staircase device structures120. In other embodiments, which can be combined with other embodiments, the metal coating122forms a blanket coating or overfills the patterns defined by the blazed device structures118or the staircase device structures120. In some embodiments, which can be combined with other embodiments described herein, the metal coating122comprises, consists of, or consists essentially of one or more metals. The metal coating122includes but is not limited to transparent conducting materials (e.g., indium-tin-oxide (ITO), fluorine doped tin oxide (FTO), or doped zinc oxide), silver, aluminum, gold, or a combination thereof. The metal coating122has a thickness that is greater than the skin depth of the metal in the operating spectrum. In some embodiments, which can be combined with other embodiments described herein, the metal coating122has a thickness of at least about 200 nanometers.

FIG.1Cillustrates a schematic, cross-sectional view of a blazed device structure118, according to certain embodiments of the present disclosure. Each of the blazed device structures118includes a first blazed surface124, a second blazed surface126opposite the first blazed surface124, a top surface128, a bottom surface130opposite the top surface128, a grating depth “h”, a top width “Tw”, a bottom width “Bw,” a grating period, and a linewidth “d” (shown inFIG.1B). The grating depth “h” extending between a top surface127of the first device material layer108and the top surface128, can be from about 10 nanometers to about 500 nanometers; for example, from about 80 nanometers to about 150 nanometers; or from about 20 nanometers to about 70 nanometers. The first blazed surface124forms a blazed angle “A.” The blazed angle A can be from about 50 degrees to about 80 degrees relative to an axis125perpendicular with a top surface127of the first device material layer108, for example, from about 60 degrees to about 70 degrees from the perpendicular axis125. The second blazed surface126forms a blazed angle “B.” The blazed angle B can be from about 0 degrees to about 40 degrees relative to the axis125, for example, from about 10 degrees to about 30 degrees from perpendicular axis125. A top duty cycle is defined as

The top duty cycle can be from about 0% to about 40%, for example, from about 15% to about 35%. In one embodiment, the grating period can be from about 250 nanometers to about 500 nanometers; for example, from about 300 nanometers to about 400 nanometers. A bottom duty cycle is defined as

The bottom duty cycle can be from about 60% to about 100%, for example, from about 70% to about 90%.

In one embodiment, which can be combined with other embodiments described herein, the blazed angles A and/or B of two or more blazed device structures118are different. In another embodiment, which can be combined with other embodiments described herein, the blazed angles A and/or B of two or more blazed device structures118are the same. In one embodiment, which can be combined with other embodiments described herein, the grating depth h of two or more blazed device structures118are different. In another embodiment, which can be combined with other embodiments described herein, the grating depth h of two or more blazed device structures118are the same. In one embodiment, which can be combined with other embodiments described herein, the linewidth d corresponds to the distance between the first blazed surfaces124of adjacent blazed device structures118. In one embodiment, which can be combined with other embodiments described herein, the linewidth d of two or more blazed device structures118are different. In another embodiment, which can be combined with other embodiments described herein, the linewidths d of two or more blazed device structures118are the same.

FIG.1Dillustrates a schematic, cross-sectional view of an optical device100B, according to certain embodiments. In some embodiments, In another embodiment, which can be combined with other embodiments described herein, the second plurality of device structures104are staircase device structures120of a waveguide combiner, as shown inFIG.1D. In the example shown, the waveguide combiner includes the binary device structures116in the first and second gratings112A,112B corresponding to a pupil expansion and an output coupling grating, respectively, of the optical device100. In the example shown, the third grating114corresponding to an input coupling grating of the optical device100are staircase device structures120configured for coupling incident light into the optical device100and directing the light towards the first grating112A.

FIG.1Eillustrates a schematic, cross-sectional view of a staircase device structure120according to certain embodiments of the present disclosure. Each of the staircase device structures120includes a stepped surface132having a plurality of steps134, a sidewall136, a top surface138, a bottom surface140opposite the top surface138, a grating depth “h”, a top width “Tw”, a step width “SW”, a step number “NS”, a bottom width “Bw”, a step depth “SD”, and a linewidth “d.” In some embodiments, the grating depth extending between a top surface of the first device material layer108and the top surface138can be from about 10 nanometers to about 500 nanometers; for example, from about 80 nanometers to about 150 nanometers; or from about 20 nanometers to about 70 nanometers. In some embodiments, the grating depth h corresponds to the height of the sidewall136. In some embodiments, the number of steps Nsof the stepped surface132includes between 2 steps and about 100 steps; such as about 3 steps and about seven 10 steps. In one embodiment, the stepped surface132includes six steps, as illustrated. In one embodiment, the stepped surface132forms a staircase angle “S.” The staircase angle S can be from about 40 degrees to about 80 degrees relative to the axis125perpendicular with the top surface127of the first device material layer108, for example, from about 60 degrees to about 70 degrees from perpendicular axis125.

A top duty cycle of each of the staircase device structures120is defined as

The top duty cycle can be from about 0% to about 40%, for example, from about 15% to about 35%. In one embodiment, the grating period can be from about 200 nanometers to about 400 nanometers; for example, from about 230 nanometers and about 280 nanometers; or from about 300 nanometers and about 370 nanometers. A bottom duty cycle is defined as

The bottom duty cycle can be from about 60% to about 100%, for example, from about 70% to about 90%.

In one embodiment, which can be combined with other embodiments described herein, the step depth SDcorresponds to the distance between a top surface of adjacent steps134in a staircase device structure120. In one embodiment, which can be combined with other embodiments described herein, the step depth Sp of two or more steps134are different. In another embodiment, which can be combined with other embodiments described herein, the step depth Sp of two or more steps134are the same. In one embodiment, which can be combined with other embodiments described herein, the step width SWcorresponds to the width of the top surface of each step134between the top surface138and the bottom surface140of each staircase device structure120. In one embodiment, which can be combined with other embodiments described herein, the step depth SDof two or more steps134are different. In another embodiment, which can be combined with other embodiments described herein, the step depth SDof two or more steps134are the same.

In one embodiment, which can be combined with other embodiments described herein, the linewidth d corresponds to the distance between the sidewalls136of adjacent staircase device structures120. In one embodiment, which can be combined with other embodiments described herein, the linewidth d of two or more staircase device structures120are different. In another embodiment, which can be combined with other embodiments described herein, the linewidths d of two or more staircase device structures120are the same. In one embodiment, which can be combined with other embodiments described herein, the staircase angle S of two or more staircase device structures120are different. In another embodiment, which can be combined with other embodiments described herein, the staircase angle S of two or more staircase device structures120are the same. In one embodiment, which can be combined with other embodiments described herein, the grating depth h of two or more staircase device structures120are different. In another embodiment, which can be combined with other embodiments described herein, the grating depth h of two or more staircase device structures120are the same.

FIG.2is a flow diagram of a method200for forming an optical device having a first plurality of device structures102and a second plurality of device structures104, according to certain embodiments.FIGS.3A-3Hare schematic, cross sectional views of an example optical device, such as a waveguide300formed during the performance of the method200. Therefore,FIGS.2and3A-3Hare herein described together for clarity.

WhileFIGS.3A-3Hdepict etching the first device material layer108such that the first plurality of device structures102are disposed on a substrate101, the substrate101may alternatively be directly etched such that the first plurality of device structures102are disposed in the substrate101. In some embodiments, the waveguide300may correspond to the optical device100inFIG.1A, optical device100A inFIG.1B, and/or optical device100B inFIG.1D. In one embodiment, which can be combined with other embodiments described herein, the substrate101may correspond to a substrate of a flat optical device to have the first and second plurality of device structures102,104formed thereon. In another embodiment, which can be combined with other embodiments described herein, the substrate101may correspond to a substrate of a waveguide combiner to have the first and second plurality of device structures102,104formed thereon.

Method200begins at operation201in which a first device material layer108is disposed over the substrate101. As discussed above, in an embodiment, the first device material layer108may be disposed on a top surface of the substrate101by a film deposition process. For example, the first device material layer108may be disposed by one or more of PVD, chemical vapor deposition (CVD), plasma-enhanced CVD (PECVD), flowable CVD (FCVD), atomic layer deposition (ALD), and spin-on processes. The first device material layer108, as discussed herein, can be a high-index material layer.

In operation202, a portion302of the first device material layer108is patterned (etched) to form a first plurality of device structures102in a top surface304of the first device material layer108. In some embodiments, the portion302of the first device material layer108may be patterned via lithographic patterning and a wet or a dry-etch process. In an embodiment, as shown inFIGS.3B and3C, the first plurality of device structures102patterned in the first device material layer108comprises a first grating112A and a second grating112B formed in the first device material layer108. In some embodiments, as discussed herein, the first and second gratings112A,112B can include grating device structures having a variety of shapes, such as, for example lines (binary), pillars, slanted lines or pillars, saw-tooth, staircase, blazed, etc. For example, the first and second gratings112A,112B can include binary vertical device structures, such as binary device structures116shown inFIGS.1B and1D.

In some embodiments, the first grating112A and the second grating112B may be disposed on the waveguide300corresponding to the positioning of a pupil expansion grating and an output coupling grating, respectively. The first grating112A may therefore be configured to distribute and propagate light via total internal reflection along the waveguide300towards the second grating112B. The second grating112B in turn may be configured to outcouple light propagating in the waveguide300into a viewer's eyes. In certain embodiments, which may be combined with other embodiments herein, the first grating112A and the second grating112B are patterned simultaneously in operation202to form the first plurality of device structures102in the portion302of the first device material layer108. In some embodiments, which may be combined with other embodiments herein, the first grating112A and the second grating112B are patterned sequentially in operation202to form the first plurality of device structures102in the portion302of the first device material layer108.

In operation203, a second device material layer110is disposed over the top surface304of an un-patterned portion308of the first device material layer108. As mentioned above, the second device material layer110comprises an uncured imprintable material. In some embodiments, the second device material layer110can be an imprintable polymer or resist material that may be patterned by a nanoimprint process including but not limited to an UV curable adhesive, UV curable resist, thermoplastic material, or other polymer material. The second device material layer110, as discussed herein, can be disposed on the first device material layer108using deposition techniques, such as a jet deposition (e.g., inkjet deposition) process.

In operation204, a nanoimprint lithography process is performed to form the second plurality of device structures104in the second device material layer110. Operation204generally includes imprinting a master stamp306into the second device material layer110to form positive waveguide patterns. The master stamp306has a negative waveguide pattern310with an inverse pattern312. The inverse pattern312includes at least one of an inverse grating portion corresponding to the inverse of the third grating114.

In certain embodiments, the positive waveguide pattern includes at least one of a plurality of grating patterns such as waveguide grating patterns corresponding to the third grating114, as shown inFIG.3E. The same master stamp306may be used in subsequent iterations of method200described herein when repeating the fabrication process to form the waveguide300. Use of the same master stamp306to form the positive waveguide patterns of the second plurality of device structures104enables increased efficiency and higher throughput in fabricating the waveguide300due to only needing to manually perform the multiple lithographic patterning steps and angled etch steps to form the master stamp306.

In yet another embodiment, operation204may generally include the patterned second device material layer110being imparted on the un-patterned portion of the first device material layer108by the master stamp306via a printing rather than an imprinting process. The master stamp306may be partially coated with the material of the second device material layer110, wherein master stamp306has the characteristic of causing the second device material layer110to form a desired pattern on the first device material layer108. As the master stamp306is brought into contact with the first device material layer108, the second device material layer110is transferred or printed onto the first device material layer108.

After the second device material layer110is imprinted with the master stamp306, in operation205, the positive waveguide patterns are cured to form the third gratings114of the second plurality of device structures104, as shown inFIG.3F. The curing process performed generally depends on the material of the second device material layer110. For example, in some embodiments, the second device material layer110comprises a UV curable resist and operation205therefore includes exposing the imprinted second device material layer110to radiation, such as infrared (IR) radiation or ultraviolet (UV) radiation. In other embodiments, the second device material layer110comprises a thermally curable material that may be cured by a solvent evaporation curing process. The solvent evaporation curing process may include thermal heating or infrared illumination heating. After the positive waveguide pattern in the second device material layer110is cured, the master stamp306is released.

FIG.3Gillustrates a schematic, cross-sectional view after the master stamp306has been released at operation205. In one embodiment, the master stamp306can be mechanically removed by a machine tool or by hand peeling as master stamp306may be coated with a monolayer of anti-stick surface treatment coating, such as a fluorinated coating. In another embodiment, the master stamp306may comprise a polyvinyl alcohol (PVA) material that is water soluble in order for the master stamp306to be removed by dissolving the master stamp306in water. In yet another embodiment, the master stamp306comprises a rigid backing sheet, such as a sheet of glass, to add mechanical strength to maintain the integrity of the master stamp306during and after release.

In method200, the first and second plurality of device structures102,104may be formed in either order. In some embodiments, after the first device material layer108is disposed over the substrate101in operation201, operations203-204may be performed to form the second plurality of device structures104on a portion of the first device material layer108. After the second device material layer110is patterned, operation202may then be performed to pattern a remaining portion of the first device material layer108not covered by the second device material layer110to form the first plurality of device structures102in the first device material layer108.

At operation206, a metal coating122is disposed over the third gratings114of the second plurality of device structures104as shown inFIG.3H. The metal coating122coats the exposed surfaces of the third gratings114. The metal coating122can be of any suitable shape. In some embodiments, which can be combined with other embodiments, the metal coating122forms a conformal coating over or on the third gratings114. In other embodiments, which can be combined with other embodiments, the metal coating122forms a blanket coating or overfills the patterns defined by the third gratings114. Any suitable deposition method for disposing the metal coating122can be used. For example, suitable film deposition methods for disposing the metal coating122include physical vapor deposition (PVD) (e.g., ion beam sputtering, magnetron sputtering, or e-beam evaporation), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), inkjet printing, or three-dimensional (3D) printing.

As described herein, the third gratings114of the second plurality of device structures104can be configured to incouple incident light into the waveguide300. In some embodiments, the metal coating122may therefore prevent/reduce reflection of the incoupled light from an opposite surface of the third gratings114. In other embodiments, an anti-reflecting coating may be deposited over the second plurality of device structures104instead of the metal coating122. The anti-reflecting coating may comprise a material having a refractive index less than the refractive index of the material of the second plurality of device structures104.

FIG.4is a flow diagram of a method400for forming an optical device having a first plurality of device structures102and a second plurality of device structures104, according to certain embodiments. Method400begins at operation401in which a first device material layer108is disposed over the substrate101. The first device material layer108, as discussed herein, can be a high-index material layer.

In operation402, the portion302of the first device material layer108is patterned (etched) to form a first plurality of device structures102in a top surface304of the first device material layer108. In some embodiments, the portion302of the first device material layer108may be patterned via lithographic patterning and a wet or a dry-etch process. In an embodiment, as shown inFIGS.3B and3C, the first plurality of device structures102patterned in the first device material layer108comprises a first grating112A and a second grating112B formed in the first device material layer108. In some embodiments, as discussed herein, the first and second gratings112A,112B can include grating device structures having a variety of shapes, such as, for example lines (binary), pillars, slanted lines or pillars, saw-tooth, staircase, blazed, etc.

In some embodiments, the first grating112A and the second grating112B may be disposed on the waveguide300corresponding to the positioning of a pupil expansion grating and an output coupling grating, respectively. The first grating112A may therefore be configured to distribute and propagate light via total internal reflection along the waveguide300towards the second grating112B. The second grating112B in turn may be configured to outcouple light propagating in the waveguide300into a viewer's eyes. In certain embodiments, which may be combined with other embodiments herein, the first grating112A and the second grating112B are patterned simultaneously in operation202to form the first plurality of device structures102in the portion302of the first device material layer108. In some embodiments, which may be combined with other embodiments herein, the first grating112A and the second grating112B are patterned sequentially in operation402to form the first plurality of device structures102in the portion302of the first device material layer108.

In operation403, a second device material layer110is disposed over the top surface304of an un-patterned portion of the first device material layer108. As mentioned above, the second device material layer110comprises an uncured imprintable material. In some embodiments, the second device material layer110can be an imprintable polymer or resist material that may be patterned by a nanoimprint process including but not limited to, an UV curable adhesive, UV curable resist, thermoplastic material, or other polymer material. The second device material layer110, as discussed herein, can be deposited on the first device material layer108using deposition techniques, such as a jet deposition (e.g., inkjet deposition) process.

In operation404, the second device material layer110is patterned to form the second plurality of device structures104. In some embodiments, the second plurality of device structures104can be configured to incouple incident light into the waveguide300. In an embodiment, the second plurality of device structures104patterned in the second device material layer110comprises a third grating114. In some embodiments, as discussed herein, the third grating114can include grating device structures having blazed device structures as shown inFIG.3G, or staircase device structures as shown inFIGS.1D and1E.

In some embodiments, patterning the second device material layer110in operation404may include a nanoimprint lithography process (as described above in method200). In other embodiments, operation404may include use of one or more angled etch tools and multiple lithographic patterning and angled etch steps to form the third gratings114of the second plurality of device structures104.

At operation405, a metal coating122is formed over the third gratings114of the second plurality of device structures104as shown inFIG.3H. The metal coating122coats the exposed surfaces of the third gratings114. The metal coating122can be of any suitable shape. In some embodiments, which can be combined with other embodiments, the metal coating122forms a conformal coating over or on the third gratings114. In other embodiments, which can be combined with other embodiments, the metal coating122forms a blanket coating or overfills the patterns defined by the third gratings114. Any suitable method for deposition of the metal coating122can be used. Examples of suitable thin film deposition methods include physical vapor deposition (PVD) (e.g., ion beam sputtering, magnetron sputtering, or e-beam evaporation), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), inkjet printing, or three-dimensional (3D) printing.

As described herein, the third gratings114of the second plurality of optical structures104can be configured to incouple incident light into the waveguide300. In some embodiments, the metal coating122may therefore function as a mirror or reflecting surface to reflect portions of the incident light from an opposite surface of the third gratings114into the waveguide, thereby increasing the efficiency of the incoupling of the incident light by the third gratings114.

In summation, disposing the second device material layer110and forming the second plurality of device structures104via nanoimprint lithography before or after forming the first plurality of device structures104in the first device material layer108disposed in the substrate101enables fabrication of the second plurality of device structures104with blazed or staircase device structures with higher efficiency and lower cost. As a result, the method of fabricating the blazed or staircase device structures in the second device material layer110as described herein therefore eliminates the need to use one or more angled etch tools and multiple lithographic patterning steps and angled etch steps as conventionally used to form blazed and/or staircase device structures, resulting in increased efficiency, lower fabrication time, and lower costs.