Surface relief waveguide using high refractive index resist.

Abstract

This disclosure describes an improved drop-on-demand volumetric control technique for dispensing resist onto a substrate that is subsequently imprinted to create patterned optical devices suitable for use in optical applications such as augmented and / or mixed reality systems. The technique enables dispensing of droplets of resist at precise locations on the substrate with precisely controlled droplet volumes that correspond to imprint templates having different zones associated with different total resist volumes. The controlled droplet size and placement also provides substantially less variation in residual film thickness across the surface of the substrate after imprinting compared to previously available techniques. The technique uses a resist with a refractive index close to that of the substrate, reducing optical artifacts in the device.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. patent application Ser. No. 63 / 301,318, entitled “SURFACE RELIEF WAVEGUIDES WITH HIGH REFRACTIVE INDEX RESIST,” filed Jan. 20, 2022, which is incorporated by reference in its entirety.

[0002] The implementations described herein generally relate to systems and methods for the fabrication of surface relief waveguides for eyepieces using fluids having a high refractive index, and optical devices produced thereby. [Background technology]

[0003] background Traditionally, application of resist for nanoimprint replication of waveguides or other optical elements is by spin-coating a solvent-diluted material onto the substrate, which results in a flat, uniform layer across the entire substrate. One advantage of this approach for optical applications is the local uniformity of the material, which can reduce scattering or phase changes of the incident light due to local roughness or height variations. However, replication in fabrication using spin-coating can also result in varying residual film thickness. In particular, steps in residual film thickness from one feature set to another can introduce undesirable optical artifacts, and large residual film thicknesses under small features can result in reduced image uniformity, for example, if the optical element is intended for use in an eyepiece in an augmented and / or mixed reality system. Summary of the Invention [Means for solving the problem]

[0004] overview The present disclosure describes methods and systems for reliable fabrication of high quality surface relief waveguides for eyepieces. Optical features in the surface relief waveguides have high nanofeature fidelity and high uniformity of residual film thickness in areas that may have different requirements for resist volume. Innovative aspects described in the present disclosure include i) the use of a high refractive index nanoimprintable resist with room temperature viscosity and surface tension that allows for volumetrically controlled dispensing of the resist, ii) continuous recirculation of the high refractive index nanoimprintable fluid in the dispensing device to maintain reliable dispensing of the resist through narrow fluidic channels and nozzles, and iii) drop-on-demand dispensing of less than 2 picoliters (pL) of high refractive index nanoimprintable resist to provide a thin, uniform layer with a thickness that can be closely matched by an imprint template with different zones associated with different total resist volumes on a substrate surface. In some implementations, the substrate can be composed of inorganic amorphous materials (e.g., heavy tantalum flint glass TADF55, quartz, etc.), crystalline materials (e.g., LiNbO3, LiTaO3, SiC, etc.), high refractive index polymers (e.g., containing sulfur, aromatic groups, etc.), and / or other polymeric materials such as polycarbonate (PC), polyethylene terephthalate (PET), etc.

[0005] Implementations include a system for manufacturing an optical device including a reservoir configured to store resist, a fluid dispenser including a dispensing mechanism configured to dispense droplets of the resist onto a substrate, a meniscus pump configured to move the resist from the reservoir to the fluid dispenser via a first channel, a fluid pump configured to move resist not dispensed from the fluid dispenser to the reservoir via a second channel, a fluid control device communicatively coupled to the fluid pump and the meniscus pump, the fluid control device configured to control operation of the fluid pump and the meniscus pump to maintain a continuous flow of resist between the reservoir and the fluid dispenser, and an imprint mechanism operative to fabricate the optical device by applying an imprint template to the resist dispensed on the substrate, where applying the imprint template creates a pattern of one or more structures in the resist, the pattern corresponding to the imprint template.

[0006] In some implementations, the system further includes a control module communicatively coupled to the fluid control device, the fluid dispenser, and the imprint mechanism, The control module can be programmed to send signals that control operation of the fluid control device, the fluid dispenser, and the imprint mechanism.

[0007] In some implementations, the resist droplets have a volume of less than 6 picoliters, less than 4 picoliters, or less than 2 picoliters.

[0008] In some implementations, the resist has a refractive index greater than 1.5 or 1.6 for light having a wavelength of 532 nanometers, hi some implementations, the substrate has a refractive index in the range of 1.5 to 2.7.

[0009] In some implementations, the imprint template includes at least two zones having structures of different heights.

[0010] Implementations also include a method for manufacturing an optical device, the method including: operating a fluid dispenser including a dispensing mechanism to dispense droplets of resist onto a substrate; operating a meniscus pump to move resist from a reservoir to the fluid dispenser via a first channel; and operating a fluid pump to move resist not dispensed from the fluid dispenser to the reservoir via a second channel, wherein the fluid pump and the meniscus pump operate to maintain a continuous flow of resist between the reservoir and the fluid dispenser; and operating an imprint mechanism to create the optical device by applying an imprint template to the resist dispensed on the substrate, wherein applying the imprint template creates a pattern of one or more structures in the resist, the pattern corresponding to the imprint template.

[0011] In some implementations, the method further includes etching at least a portion of the optical device to reduce a residual thickness (RLT) of the resist on the substrate, where the etching includes one or more of heating or atmospheric pressure etching.

[0012] In some implementations, the etching further reduces a dimension of at least one structure of the pattern created by applying the imprint template.

[0013] The implementation also includes a waveguide comprising a substrate and a plurality of structures imprinted in a volume of resist dispensed onto the substrate, the resist being comprised of a polymer, the resist having a refractive index in the range of 1.5 to 2.1, and an RLT of the resist in at least a portion of the substrate in the range of 0 nm to 50 nm.

[0014] In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0 nm to 10 nm, 40 nm to 50 nm, 30 nm to 40 nm, 20 nm to 30 nm, or 10 nm to 20 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0 nm to 40 nm, 0 nm to 30 nm, 0 nm to 20 nm, or 0 nm to 10. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 10 nm to 40 nm or 10 nm to 30 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 20 nm to 40 nm.

[0015] In some implementations, the plurality of structures provide one or more optically active zones including one or more of an input coupler, a combination pupil expander, an exit pupil expander, an orthogonal pupil expander, a recycler, or an anti-reflection feature.

[0016] In some implementations, the plurality of structures are imprinted with nanogeometry including one or more of binary features, sloped features, blazed features, sawtooth features, multi-step features, metafeature features, one-dimensional features, two-dimensional features, or three-dimensional features.

[0017] In some implementations, the substrate has a refractive index in the range of 1.5 to 2.7.

[0018] In some implementations, the multiple structures are imprinted on one side of the substrate. In some implementations, the multiple structures are imprinted on both sides of the substrate.

[0019] In some embodiments, dispensing less than 2 pL can be accomplished by gravity without the use of a pump (e.g., without a meniscus pump, a fluid pump, or both). One embodiment includes dispensing a drop of resist onto a substrate, contacting the resist with an imprint template to obtain a pattern of one or more structures in the resist, the pattern corresponding to the imprint template, polymerizing the resist to obtain imprint nanostructures, and separating the imprint template from the imprint nanostructures. The resist has a refractive index in the range of 1.5 to 2.1, a residual film thickness (RLT) of the resist on at least a portion of the substrate is in the range of 0 nm to 50 nm, and the substrate is comprised of an inorganic material.

[0020] Implementations of this embodiment may have one or more of the following features.

[0021] In some implementations, the volume of each drop of resist is less than 6 picoliters, less than 5 picoliters, less than 4 picoliters, less than 3 picoliters, or less than 2 picoliters. In some implementations, the volume of each drop of resist is less than 1 picoliters.

[0022] In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, or 40-50 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0-40 nm, 0-30 nm, 0-20 nm, or 0-10 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 10-40 nm or 10-30 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 20-40 nm.

[0023] In some implementations, the substrate includes glass, LiTaO 3 , LiNbO 3 , SiC, or a combination thereof.

[0024] In some implementations, the resist does not include inorganic nanoparticles, in which case the resist typically has a refractive index in the range of 1.5 to 1.8.

[0025] In some implementations, the resist includes inorganic nanoparticles (e.g., TiO2, ZrO2, or both). The average diameter of the inorganic nanoparticles is typically in the range of 5 nm to 15 nm. The inorganic nanoparticles can comprise about 10 vol% to about 60 vol% of the resist. The resist typically has a refractive index in the range of 1.5 to 2.1.

[0026] In some implementations, the viscosity of the resist is in the range of 5 to 25 centipoise (cP) at 25°C.

[0027] In some implementations, the surface tension of the resist is in the range of 20 to 60 millinewtons (mN) per meter (m) at 25°C.

[0028] In some implementations, dispensing the droplets of resist includes pumping the resist from a reservoir through a first channel to a fluid dispenser. Some implementations include maintaining a continuous flow of resist between the reservoir and the fluid dispenser. In some implementations, maintaining a continuous flow of resist between the reservoir and the fluid dispenser includes pumping undispensed resist from the fluid dispenser through a second channel to the reservoir.

[0029] In some implementations, dispensing the droplets is performed without pumping the resist (eg, without pumping the resist using a meniscus pump, a fluid pump, or both).

[0030] Other features and advantages of the present application will become apparent from the following detailed description and drawings, and from the claims. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 illustrates an exemplary system for fluid dispensing and imprinting according to an implementation of the present disclosure.

[0032] [Diagram 2] FIG. 2 illustrates a flow diagram of an exemplary fabrication process in accordance with an implementation of the present disclosure.

[0033] [Diagram 3] FIG. 3 illustrates exemplary results of different imprint processes.

[0034] [Figure 4] 4A-4C illustrate exemplary imprint nanostructures according to implementations of the present disclosure.

[0035] [Figure 5-1] 5A-5N show images of various exemplary nanostructure geometries according to implementations of the present disclosure. [Figure 5-2] 5A-5N show images of various exemplary nanostructure geometries according to implementations of the present disclosure.

[0036] [Figure 6A] 6A and 6B illustrate an example eyepiece design according to an implementation of the present disclosure. [Figure 6B] 6A and 6B illustrate an example eyepiece design according to an implementation of the present disclosure.

[0037] [Figure 7] 7A-7E show images of simulated test results for waveguides fabricated using various techniques. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Detailed Description Implementations described herein provide a drop-on-demand, volume-controlled dispensing technique for dispensing fluid onto a substrate with precise control of the volume of the dispensed droplets and the location on the substrate where the droplets are dispensed. The dispensed fluid can then be imprinted to create patterned optical devices suitable for use in augmented reality (AR) and / or mixed reality (MR) systems, and / or other suitable optical applications. The innovative techniques described herein enable the dispensing of droplets of dispense fluid (which may be described as resist, photoresist, or resin) that are of a smaller size than the droplet sizes used in previously available drop-on-demand inkjet techniques. In particular, implementations use droplet sizes of less than 2 picoliters (pL), which provide dispensing of a thin, uniform resist layer with a target volume that can be matched to an imprint template having different zones associated with different total resist volumes suitable for filling the template. The use of smaller droplet sizes also provides substantially less variation in interconnecting residual film thickness (RLT) across the surface of the substrate compared to previously available techniques using larger droplet sizes. Additionally, the techniques described herein use dispensed resists with high refractive indexes that can more closely match the refractive index of the substrate, thus reducing optical artifacts in the fabricated optical devices. Resists with high refractive indexes can also have higher viscosities than those used in previously available techniques. Thus, to ensure reliable dispensing of higher viscosity resists at smaller drop sizes, implementations use resist dispensing systems that provide substantially continuous recirculation of resist fluid. Such recirculation allows the system to operate with fluids of room temperature viscosity and surface tension while maintaining reliable dispensing through narrow fluid channels and nozzles, thus facilitating high throughput manufacturing of high quality optical devices.

[0039] High refractive index materials are typically used as substrate materials for surface relief based diffractive waveguides in AR and / or MR systems. The use of a high refractive index substrate helps support a wide field of view of the virtual image, which can couple into the waveguide(s) and exit the waveguide(s) towards the user's eye. However, the surface relief diffractive features are typically constructed from a material that has a lower refractive index than the substrate (e.g., a refractive index less than 1.6). When used as an optical combiner in an AR / MR system, this refractive index mismatch can lead to undesirable optical artifacts and limit image brightness and overall uniformity, including the user-to-world ratio of image brightness. In one example, for a single-sided design with surface features on one side of the substrate, the user-to-world ratio can increase from 1:1 to 1.25:1 for an increase in resist refractive index from 1.53 to 1.65. The use of a higher refractive index resist as provided by the implementations described herein allows for the use of gratings with higher diffraction efficiency compared to similar gratings with the same nanogeometry, thus allowing for higher values ​​of image brightness and uniformity over a desired eyebox location or range.

[0040] Larger RLT and / or RLT uniformity variations, such as those produced using conventional techniques, can also lead to optical artifacts. Thus, implementations described herein also provide higher quality optical devices by enabling the use of smaller resist drop sizes during resist dispensing, leading to less variation in overall RLT uniformity and less variation (if desired) between zones with different feature heights. Implementations described herein provide systems and methods for manufacturing high quality optical devices, enabling the use of high refractive index resist materials that minimize the difference in refractive index between the resist and the substrate, thus reducing undesirable effects resulting from refractive index differences. Implementations also provide fabrication of devices with thin and / or uniform RLT that meet cost and throughput considerations for high volume manufacturing of optical devices.

[0041] As used herein, optically transparent generally refers to a physical property that allows light to pass through a material without being scattered or absorbed. As used herein, high refractive index generally refers to a refractive index (n) greater than 1.5, or greater than 1.6 or 1.7 (e.g., of an imprint polymer resist). In one example, high refractive index refers to an n greater than 1.6 or 1.7 and less than 1.9. In one example, high refractive index refers to an n in the range of 1.5 to 1.8.

[0042] As used herein, total thickness variation (TTV) refers to the difference between the maximum and minimum thickness of a substrate in a series of point measurements across a dimension of the substrate. For substrates with patterned surfaces, TTV refers to an approximation evaluated by ignoring the contribution of pattern features to the thickness. For example, the thickness (or height) of a typical feature on a patterned substrate may be in the range of approximately 10 nanometers (nm) to 150 nm. The thickness depends at least in part on the trench depth of the template, which may vary by 10% (e.g., 1 nm to 15 nm). The TTV of an unpatterned substrate is typically greater than 100 nm and may be in the range of microns. Thus, the additional variation in thickness of a patterned substrate introduced by pattern features is negligibly small and can be ignored as an approximation. Thus, the thickness of a patterned substrate evaluated at a site including a protrusion can be approximated by subtracting a given feature thickness from the evaluated thickness to obtain an adjusted thickness, while the thickness of a patterned substrate evaluated at a site without a protrusion remains unchanged. That is, the adjusted (e.g., reduced) thickness of the feature area and the intrinsic thickness of the unpatterned area can be used to calculate the TTV of the substrate having a patterned surface. The low TTV values ​​described herein result at least in part from the flat optical grade glass substrate polished to meet the desired flatness, as well as the methods described herein for minimizing or reducing non-uniform material shrinkage during curing. Low TTV can also be imparted to inorganic material substrates by extrusion. Low TTV can also be imparted to polymer substrate materials and achieved from mold surfaces during molding (e.g., injection molding, ultraviolet (UV) or thermoforming, extrusion, etc.) of substrates made of high refractive index polymers (e.g., containing sulfur, aromatic groups, etc.) and other polymeric materials such as polycarbonate (PC), polyethylene terephthalate (PET).

[0043] FIG. 1 is a system diagram illustrating an exemplary system 100 for dispensing a fluid (eg, a high refractive index nanoimprint resist) onto a substrate and imprinting the dispensed fluid to create a pattern on the substrate.

[0044] As shown in FIG. 1, the system 100 may include a substrate 102 supported by a stage 104. The substrate 102 may be constructed of any suitable material, such as glass or a polymer. The stage 104 may be configured to support the substrate 102 and stabilize the substrate 102 during fluid dispensing, imprinting, curing, etching, and / or other manufacturing operations. The fluid dispenser 106 is configured to dispense drops (or droplets) of a fluid 120, such as a resist, onto the substrate 102. The fluid dispenser 106 may also be described as one or more print heads. The fluid 120 is held in a reservoir 108, which is connected to the fluid dispenser 106 by one or more channels (e.g., tubes, conduits, etc.) of suitable type, material, and dimensions. The fluid pump 110 operates to circulate the fluid 120 between the reservoir 108 and the fluid dispenser 106. The meniscus pump 112 operates to extract droplets of the fluid 120 from the reservoir 108 , from which the fluid 120 flows to the fluid dispenser 106 .

[0045] The fluid controller 114 is communicatively coupled to the pumps 110 and 112 and can send signals to the pumps 110 and 112 to control their operation and maintain a continuous circulatory flow of the fluid 120 within the system. As discussed herein, the continuous circulatory flow of the fluid 120 allows for reliable dispensing of high refractive index, high viscosity fluids in droplets that are smaller in size compared to conventional techniques. The system 100 can include one or more pressure sensors 116 that measure the pressure of the fluid 120 as it circulates within the system. Although FIG. 1 illustrates an example using two pressure sensors 116(1), 116(2), the system can include any suitable number and type of pressure sensors 116 at any suitable (one or more) location within the system. The fluid controller 114 is communicatively coupled to the pressure sensor(s) 116 and can receive pressure data from the pressure sensor(s) 116 that describes the pressure of the fluid 120 at one or more locations within the system. The fluid control 114 can use the pressure data to control the circulatory flow of the fluid 120 within the system to ensure a substantially continuous circulatory (eg, recirculating) flow.

[0046] In system 100, fluid recirculation can be maintained through the printhead(s) by a combination of a diaphragm-based fluid pump that supplies fluid to the printhead inlet at positive pressure and a meniscus vacuum pump that applies negative pressure to the printhead(s) outlet. Alternatively, a second diaphragm-based fluid pump can be used to apply negative pressure to the outlet. By applying appropriate inlet and outlet pressures, the meniscus pressure at the printhead nozzles and the differential pressure through the head are independently controlled. The meniscus pressure setpoint is selected to prevent both dripping of fluid from the printhead(s) nozzles and sucking air through the nozzles into the printhead(s). The pressure can be set to a value in the range of -10 to -40 mbar. The differential pressure is proportional to the flow rate of resist through the printhead and is set to deliver a flow rate of approximately 50 to 150 milliliters (mL) / min.

[0047] To ensure system reliability, the various hardware elements of the system can be designed with the composition of the particular resist that will be circulating in the system in mind. The composition of the system components that interact with the resist can be important, as some weaker polymeric components can, over time, begin to chemically dissolve and mix with the resist fluid. Thus, more chemically resistant parts (e.g., made of polytetrafluoroethylene (PTFE), nylon, etc.) can be used to ensure that the printhead system, including components involved in fluid recirculation, functions reliably.

[0048] The control module 118 is communicatively coupled to the fluid controller 114 and the fluid dispenser 106 to control their operation. In some implementations, the control module 118 is a computing device including at least one processor and a memory. The memory can store computer programs including instructions that, when executed by the at least one processor, cause the processor(s) to perform operations to control the fluid controller 114, the fluid dispenser 106, and / or other components of the system. The control module 118 may be any suitable type of computing device, such as a personal computer, and may communicate with other computing devices to receive instructions, provide data, etc.

[0049] In some implementations, the system 100 includes a mechanism (not shown) for moving the stage 104 and the substrate 102 along a stage travel direction 122 between multiple stages of a process for manufacturing an optical device. This mechanism may also be controlled by the control module 118. The stage 104 (and the substrate 102) can be moved from a first position where the fluid 120 is dispensed onto the substrate 102 during a first stage of the manufacturing process to a second position. At the second position, the substrate 102 is imprinted using an imprint template 124 that forms the fluid 120 into a desired pattern to create the optical device during the second stage. The imprint template 124 can be manipulated by an imprint mechanism 126 that is controllable by the control module 118. During one of the stages, or during another stage, the fluid 120 may also be cured using light (e.g., UV light), heat, and / or a combination of light and heat. Alternatively, the system may be configured such that dispensing, imprinting, and / or curing of the fluid 120 occur at the same position of the stage 104.

[0050] FIG. 1 illustrates one example of a system 100 including a single fluid dispenser 106, although other implementations are possible. The system may be a single fluid circulation system including multiple fluid dispensers for dispensing resist in parallel to different substrates and / or different portions of a substrate to enable more efficient and higher volume manufacturing. Additionally, the system may include multiple fluid circulation systems for circulating different (e.g., having different refractive indexes) resist fluids and dispensing different resists via different printheads to different regions of a substrate. For example, a first resist having a first refractive index may be dispensed to a combined pupil expander (CPE) region of a substrate, and a second resist having a second refractive index may be dispensed (e.g., in parallel with the first resist) to a different region, such as an in-coupling grating (ICG) or a recycler. Thus, manufacturing may include a single dispense and imprint step that dispenses and imprints multiple resists to different regions. Alternatively, multiple systems may circulate and dispense the same fluid to achieve higher throughput in the manufacturing process.

[0051] Conventional systems use spin-coating techniques to apply resist to a substrate. In such systems, application of resist for nanoimprint replication of waveguides or other optical elements is accomplished by spin-coating a solvent-diluted material onto the substrate, resulting in a uniform, flat layer across the substrate. This conventional approach is an industrially mature process and offers the advantage of providing excellent local uniformity of the dispensed material. Such uniformity minimizes scattering or phase changes of the incident light due to local roughness or height variations. However, replication in manufacturing using conventional spin-coating techniques also has drawbacks. When the goal is to create target features that are non-uniform (e.g., of varying heights and / or duty cycles), the amount of resist required to fill the template features during the nanoimprint process varies. Because the underlying applied film starts out substantially uniformly distributed, spin-coating can lead to a final film (e.g., after template imprint) with a variety of RLTs, as shown in Figure 3. Large step differences in RLT when moving from one feature set to another introduce undesirable optical artifacts. The large RLT under small features results in poor image uniformity, especially at the temple side. Another manufacturing drawback of spin coating is that more than 95% of the resist solution is wasted, thus significantly increasing the manufacturing cost.

[0052] The implementation applies resist for nanoimprinting using a modified version of a drop-on-demand jet-and-flash imprint lithography (J-FIL) process rather than spin-coating. The J-FIL process locally adapts the volume of fluid to the appropriate volume to fill the feature, thus reducing the large step in RLT from one feature zone to another compared to the step change that results from spin-coating. Conventional J-FIL processes use large drops (e.g., >3 pL) of dispensed material with a refractive index greater than 1.6 and are produced by standard industrial printheads. However, conventional J-FIL processes also have drawbacks. Using this process, the resist drops do not spread to form a uniform local film, thus introducing some local non-uniformity in the imprint fluid thickness where the drops meet. Additionally, due to the digital nature of the conventional J-FIL dispensing process, not all target thicknesses or boundaries can be perfectly matched.

[0053] The implementations described herein are modifications of conventional J-FIL techniques and provide systems and processes that address the problems of conventional J-FIL techniques. The implementations use smaller (e.g., <2 pL) droplets of high-index resist with higher resolution to improve local planarity and further reduce RLT within zones of similar nanofeatures (also described as features, structures, or nanostructures), as well as step heights across transitions between two or more feature zones in an imprinted pattern. In other words, the implementations use smaller droplets of high-index resist to improve local surface planarity (RLTu) and reduce RLT step size at boundaries and / or zone transition regions.

[0054] To achieve sub-2 pL nanoimprinting with high refractive index resist, the techniques described herein use a combination of: 1) a high refractive index (e.g., n>1.6) fluid with rheological properties compatible with a volumetric control dispensing process, 2) fluid recirculation to maintain reliable jetting at the printhead of the fluid dispenser 106 (e.g., printhead) that dispenses the resist, and 3) a multi-nozzle fluid dispenser 106 that can generate sub-2 pL resist droplets and deliver them to the substrate with sufficient precision to provide a nanoimprinting optics with minimal defects.

[0055] To be dispenseable by an inkjet-type dispensing process, a material must typically have a viscosity in the range of 5-25 centipoise (cP) and a surface tension in the range of 20-60 (e.g., 20-40) millinewtons (mN) / meter (m). Many high refractive index components, organic or inorganic, have properties outside that range. In traditional inkjet applications, heating is used to reduce the viscosity of more viscous materials to a jettable viscosity range. However, heating introduces risks of both oxidation and gelation, and is generally undesirable in reactive materials designed to be UV cured. Thus, the implementation uses a high refractive index resist that offers a higher refractive index than competing commercially available materials while having rheological properties that enable inkjet-type dispensing at room temperature.

[0056] Implementations support the use of various suitable types of high refractive index resists. In some implementations, the resist (e.g., fluid 120) is a polymer-based resin with nanoparticles (NPs) of a high refractive index material incorporated therein. Alternatively, the resist can be a polymer-based resin without NPs incorporated therein. The incorporation of NPs may increase the overall refractive index of the material, which provides an advantage in more closely matching the refractive index of the substrate as described herein. However, the incorporation of NPs may also cause Rayleigh scattering of light in the resist. Thus, the choice of using a resist with NPs or a resist that omits NPs may be based on considerations, such as a balance between a higher refractive index and more scattering. For example, a resist with a refractive index of 1.6 or 1.7 and no NPs may provide optimal performance providing a higher refractive index (e.g., closer to the refractive index of the substrate) while avoiding scattering caused by the presence of NPs.

[0057] Organic (meth)acrylate monomers and oligomers typically have a refractive index of approximately 1.5 at a wavelength of 532 nm. Sulfur atoms and aromatic groups, both of which are highly polarizable, can be incorporated into these acrylate components to increase the refractive index of the formulation. This effect can be limited due to the fluid viscosity limit of less than 20-25 cP for inkjet processing, and by the upper refractive index limit of sulfur-containing molecules. This approach results in jettable and imprintable resists with refractive indices as low as 1.72 at wavelengths of light at 532 nm.

[0058] Incorporating inorganic nanoparticles (NPs) such as ZrO2 and TiO2 can significantly further increase the refractive index. Pure ZrO2 and TiO2 crystals can reach refractive indices of 2.2 and 2.4-2.6, respectively, at 532 nm. In the preparation of optical nanocomposites of acrylate monomers and inorganic nanoparticles, the particle size is less than 10 nm to avoid excessive Rayleigh scattering. Due to their high specific surface area, high polarity, and incompatibility with cross-linked polymer matrices, ZrO2 NPs have a tendency to aggregate in the polymer matrix. To overcome this problem, surface modification of the NPs can be used. In this technique, the hydrophilic surface of ZrO2 is modified to be compatible with organics, thus allowing the NPs to be homogeneously mixed with the polymer. Such modification can be performed with silane and carboxylic acid-containing capping agents. One end of the capping agent is bonded to the ZrO2 surface, and the other end of the capping agent contains either a functional group or a non-functional organic moiety that can participate in acrylate cross-linking. Examples of surface-modified sub-10 nm ZrO2 particles are those supplied by Pixelligent Technologies™ and Cerion Advanced Materials™. These functionalized nanoparticles are typically sold as homogeneous formulations, uniformly suspended in a solvent, and can be combined with other substrates to obtain resist formulations with jettable viscosity and increased refractive index.

[0059] The higher surface tension of some high refractive index components can pose implementation challenges for inkjet-based nanoimprint lithography (NIL) processes. High surface tension tends to encourage the formation of air bubbles in the fluid. The formation of air bubbles and subsequent air blockage of nozzles and fluid channels is a common reliability issue for inkjet processes. As channel and nozzle sizes shrink to encourage the formation of smaller drops as used in the techniques described herein, this problem becomes more severe. Thus, the implementations described herein provide systems and methods that include continuous circulation of resist fluid. The continuous flow of fluid through the channels in the system 100 flushes air bubbles out of the narrow channels and maintains a steady supply of fluid.

[0060] This approach is also compatible with the incorporation into the resist formulation of resist solutions containing higher vapor pressure solvents, such as high refractive index inorganic nanoparticles dispersed in the solvent. Without recirculation, solvent evaporation at the faceplate of the fluid dispenser 106 can cause viscosity buildup and nozzle failure. This, in turn, can adversely affect the quality of the imprint, RLtu, and nanofeature fidelity, severely impacting the image quality of the fabricated eyepiece waveguide in terms of image sharpness, contrast, uniformity, and efficiency.

[0061] The formation and accurate placement of small droplets is particularly important for dispensing high viscosity and high surface tension fluids. High viscosity and high surface tension adversely affect the NIL process by slowing down feature filling and droplet pre-spreading, respectively. Low refractive index materials typically spread and fill more easily and are less likely to generate RLT variations. Furthermore, high refractive index imprint layers (e.g., n>1.6) are more optically sensitive to RLT variations compared to imprints of lower refractive index resists (e.g., n=1.53). For resist formulations containing nanoparticles, a long delay before the droplets merge can allow material phase separation and undesirable variations in refractive index throughout the applied resist. Smaller droplets with smaller droplet gap spacing provide greater benefits when using high refractive index materials because smaller droplets can be more accurately and more densely placed on the substrate, thus mitigating the problems of slow droplet pre-spreading and slow feature filling that may otherwise be present when using high refractive index fluids that exhibit high viscosity and high surface tension. Thus, by modifying the conventional J-FIL process through the use of high refractive index materials, smaller drop sizes, and reliable operation with fluid recirculation, implementations enable the production of high performance optical components. Advantages provided by the implementations described herein are further described with reference to FIG.

[0062] FIG. 2 is a flow chart illustrating an exemplary process 200 for fabrication of an optical device according to implementations described herein. At 202, a fluid dispenser is used to dispense droplets of resist onto a substrate. As discussed herein, the fluid dispenser (also referred to as a print head) may be configured to dispense droplets using the volume control dispensing mechanism of FIG. 1. At 204, a meniscus pump is used to move resist from a reservoir through a first channel to the fluid dispenser. At 206, the fluid pump is operated to return resist (e.g., excess resist that was not dispensed) from the fluid dispenser through a second channel to the reservoir. At 208, an imprint mechanism is operated to apply an imprint template to the resist on the substrate to generate an optical device (e.g., an imprint substrate to be used as a waveguide). The process may also include steps for curing the resist using UV light and / or heat, as described herein.

[0063] In some implementations, one or more additional steps may be performed at 210 to further reduce the RLT to create an optical device (e.g., a waveguide) with an ultra-thin RLT. For example, a suitable etching process may be performed to further reduce the RLT. For example, after dispensing resist and applying a template (and, in some implementations, curing), an etch may reduce the RLT from an initial level of 50 nm or less to an RLT in the range of approximately 0-10 nm. Such a reduction in RLT can be performed across the entire surface of the substrate or in specific areas, such as at least a portion of the pupil expander (EPE) region of the waveguide. In some examples, the etch may use a stencil or other type of mask to control which areas are etched to reduce the RLT.

[0064] In some implementations, the RLT can be reduced in one or more regions of the substrate by heating. For example, heat in the range of 120-200 degrees Celsius (C) can be applied to the substrate and / or the imprinted pattern to reduce the RLT. Such heating can also reduce the size of the imprinted nanofeatures. The applied heat can reduce the RLT and / or the nanofeatures by causing thermal contraction of crosslinked polymer chains. For example, if the desired nanogeometry includes features that are 20 nm tall (e.g., relative to the RLT), the dispense and imprint can be configured to create taller features, and then the features are reduced to the desired height by heating. Similarly, if the desired final RLT is below 10 nm, an initial RLT of 20 nm can be reduced to the desired RLT by heating. Similarly, one can start with a 30 nm imprint and end with a post-heat treatment imprint of less than 10 nm, and in some cases close to about 0 nm.

[0065] In some implementations, atmospheric pressure plasma etching (e.g., using a plasma that is a mixture of argon and O2) can reduce the RLT down to 0 nm as needed to provide substantially free-standing nanostructures on the substrate. Such a solution can be used where the template can have a pre-defined biased imprint geometry that accounts for isotropic etch loss of feature width when removing the RLT. Nanogeometry features can also be smoothly reduced using atmospheric pressure plasma at relatively low temperatures, such as below 60°C. Ar in the plasma afterglow +The presence of ions and O radicals can isotropically physically and / or chemically remove organic materials. In some implementations, UV O3 treatment at atmospheric pressure and temperatures below 50°C can also reduce the nanogeometry and RLT of imprints on such substrates. In this example, the generation of oxygen radicals from O3 in the presence of UV light tends to react isotropically to remove organic materials. In some implementations, reactive ion etching at pressures below atmospheric pressure can also be used to achieve a more anisotropic etch in the presence of a mixture of one or more of Ar, O2, N2, He, and CF4.

[0066] In some cases, one or more of the operations in process 200 are replaced or combined with another operation, the order of one or more of the operations is swapped, two or more operations are performed simultaneously or sequentially, or any combination thereof. In certain cases, process 200 may include one or more additional operations as described herein.

[0067] FIG. 3 provides a diagram 300 showing an example result of three different imprint processes. As described above, after resist is dispensed onto the substrate 102, an imprint template 124 is applied to the resist (e.g., fluid 120) to imprint a pattern onto the substrate 102. In this particular example, the template 124 includes three zones 302(1), 302(2), and 302(3) that include features of different heights of 90 nm, 60 nm, and 30 nm, respectively. It should be noted that the specific dimensions and other values ​​shown in FIG. 3 are examples, and the implementation is not limited to these examples. The goal of the imprint process is to use the template 124 to imprint a pattern onto the substrate 102 that most accurately reflects the template 124. In this example, the goal is to create a pattern on the substrate 102 that includes three corresponding zones 304(1), 304(2), and 304(3) that have corresponding height differences and have minimal RLT variation. The particular template 124 shown in FIG. 3 is an example and implementations are not so limited.

[0068] Implementations may use any suitable template to imprint any suitable pattern onto the substrate 102. Additionally, although this example illustrates the substrate 102 being 350 μm glass having a refractive index of 2.0, implementations may use substrates of any suitable dimensions and materials. For example, the substrate 102 may be comprised of a polymeric material instead of glass.

[0069] FIG. 3 shows three exemplary results 306, 308, and 310 obtained from three different imprinting techniques. In the first example 306, a spin-coating method is used. In this example, a uniform 100 nm spin-coated resist is paired with an exemplary template with three different feature height zones, which can be found in a diffractive optical element. Due to the shortcomings of the spin-coating technique as described above, this process results in a 15 nm step in the RLT height between the feature zones 304. The second example 308 shows the results using a conventional J-FIL technique. Using this process, the amount of fluid can be locally varied to match the feature requirements, thus reducing but not eliminating the RLT step between the zones. As described above, the large drop size used in conventional J-FIL can still lead to local thickness inconsistencies and thus RLT variations between the zones.

[0070] A third example 310 shows the results of using a modified J-FIL technique according to implementations described herein. Because the implementations allow for the use of smaller drops with tighter pitch, local fluid density and boundaries can be controlled even more effectively, thus significantly mitigating or eliminating the RLT variation between zones, and also allowing for an overall smaller RLT, as shown. The tighter pitch corresponds to a reduced size of the gap between the drops. The use of smaller drop sizes provides the advantage that the packing density of the drops can be increased while still maintaining the desired total volume of dispensed resist. The smaller, more densely packed drops provide better RLT uniformity in both nanofeature zones and featureless blank areas.

[0071] The techniques described herein enable dispensing and imprinting of high index resist on a substrate, providing very low RLT compared to previously available solutions. For example, implementations described herein can provide RLTs of less than 30 nm, or even less than 15 nm. This can be achieved because the dispensing mechanism allows droplets of resist to be dispensed at locations on the substrate where resist is needed according to the template being used to perform the imprint. In other words, the mechanism allows for more precise spatial and volumetric control of the placement of resist on the substrate, such that more resist is placed where the template is creating larger structures that may require a larger volume of resist to more optimally fill the template during imprinting. The techniques described herein also enable imprinting of more complex or intricate structures compared to those that can be created using previously available methods, because the dispensing mechanism can precisely place droplets at locations that correspond to structures to be created by the template, compared to conventional (e.g., spin-coating) techniques that apply a substantially uniform layer of fluid over the entire area of ​​the substrate. This dispensing mechanism offers the flexibility to imprint more complex features to achieve desired optical effects in the waveguide, as well as more control over the specific RLT that can be imparted to different regions of the substrate.

[0072] In some examples, the diffractive surface relief imprint is fabricated on a substrate made of a high refractive index resist polymer with an ultra-thin RLT in the range of 0 nm to 50 nm. In some implementations where the imprint is performed to fabricate a waveguide for use in an optical device such as an AR / MR device, an RLT of 10-20 nm may be used in various parts of the waveguide such as the input coupling zone, combined pupil expander, exit pupil, orthogonal pupil expander, recycler, anti-reflection features, etc. The high refractive index ultra-thin RLT imprint on the waveguide substrate can provide nanofeatures of the desired gray scale in duty cycle and / or feature height in any gray scale zone within the waveguide eyepiece.

[0073] High refractive index ultrathin imprints can be performed on substrates to create nanogeometry of various configurations. For example, the nanogeometry can include features that are binary (e.g., rectangular), tilted, blazed, sawtooth, stepped, and / or more complex metafeatures. The features can include one-dimensional lines and spaces, two-dimensional features (e.g., asymmetric pillars and holes), alternating lattices of the same or two-dimensional features with different pitches, and / or three-dimensional features (e.g., asymmetric pillars and holes).

[0074] 4A-4C show exemplary imprint nanostructures according to implementations of the present disclosure, such as triangular or sawtooth structures 410, trapezoidal structures 420, and diamond shaped structures 430, respectively. Other suitable types of nanostructures may also be fabricated. 5A-5N show captured images of various shapes fabricated using the techniques described herein. In 5A-5F, the scale bar is 100 nm. 5A-5E show rectangular gratings of various sizes and spacing. 5F shows a sawtooth grating. 5G shows a multi-step grating. 5H shows a sawtooth grating. 5I shows a tilted grating. 5J shows a multi-level buried feature. 5K shows a two-dimensional structure. 5L shows a three-dimensional structure with two stacks of gratings. 5M shows a three-dimensional structure with lines and holes. 5N shows a three-dimensional blazed grating array.

[0075] In some examples, a refractive index resist has a refractive index of approximately 1.5-2.1 and is imprinted onto a substrate having a refractive index of approximately 1.5-2.7 to create a surface relief diffractive waveguide. Drop-on-demand dispensing of high refractive index resist is used to imprint with controlled RLT (e.g., in the range of 5 nm to 1000 nm) in different zones and / or provide RLT adjustment on the waveguide surface to change how light propagates through the eyepiece. In one example, different zones with different RLTs can be created, such as a first RLT zone (e.g., RLT<30 nm) below a first grating height in the CPE light path, a second RLT zone (e.g., RLT>40 nm) below a second grating height, and a third RLT zone (e.g., RLT<30 nm) above the remainder of the CPE grating height zones, such that the second zone is between the first and third zones. The imprints may be on one or both sides of the substrate and may be on any suitable substrate format such as a wafer, film, sheet, etc.

[0076] As discussed herein, the imprinting techniques described herein can be used to manufacture waveguides used in eyepieces for AR / MR devices or other suitable optical devices. Figures 6A and 6B illustrate an example eyepiece design with example dimensions according to implementations of the present disclosure. Figure 6A is a schematic diagram 600 of the world side (e.g., outward facing side) of the example eyepiece design. Figure 6B is a schematic diagram 650 of the eye side (e.g., inward facing side) of the example eyepiece design. The scales on the horizontal and vertical axes are in millimeters (mm).

[0077] Referring to FIG. 6A, the bottom portion 602 of the exemplary eyepiece design is a CPE region that combines the functions of an optical pupil expander (OPE) and an EPE. The top portion 604 of the design is a recycler region that includes a grating that returns light to the eyepiece that would otherwise have leaked out of the eyepiece or been absorbed at the edge of the eyepiece. The diameter of the eyepiece is 36.3 mm in this example. On the left side 606 of the eyepiece, the grating depth is 90 nm. On the right side 608 of the eyepiece, the grating depth is 15 nm. The central region 610 includes multiple zones with grating depths that decrease from 90 nm on the left side to 15 nm on the right side. Each of the zones may include thousands of grating lines, each of which may be approximately 200 nm wide. Each zone may have a substantially uniform grating depth throughout the zone. In some examples, the grating depth corresponds to the height of the feature, measured from the top of the feature to the base of the feature, with a substantially uniform RLT throughout the various zones and / or regions. Alternatively, the RLT may be different in different zones or regions. The zones have a width of 1 mm and are tilted at an angle of -30 degrees to the vertical. The gratings in these zones are square ridge cross-sections tilted at -60 degrees to the vertical. Region 612 includes multiple pie slice shaped regions as shown. These regions are anti-reflective structures. One of these regions may include an ICG 614 approximately 33 mm from the center of the CPE as in the example shown.

[0078] For the side view of the eye shown in Figure 6B, the same dimensions as described with reference to Figure 6A may be applied: the grating groove direction is at +60 degrees and the depth gradation direction is at a +30 degree inclination to the vertical.

[0079] In some implementations, different grid patterns may be used in different regions. For example, the ICG region may include triangular shaped features in its grid pattern, and the CPE region may include binary (e.g., rectangular) shaped features in its grid pattern. The different patterns may be used to provide different optical effects as desired.

[0080] In this exemplary eyepiece configuration, the projector that inputs the graphics into the eyepiece may be on the right side of the figure, corresponding to the location of the ICG. Thus, light input by the projector may propagate leftward through the waveguide and be output to the user's eye at various points within the CPE region. The grating depth may increase as the distance from the projector increases to provide greater outcoupling power as the distance from the projector increases. Considering that the propagated light may attenuate somewhat as it travels through the waveguide, a greater grating depth at a greater distance from the projector may lead to a more uniform outcoupling of light across the surface of the eyepiece as a whole.

[0081] 7A-7E show images of simulated test results for waveguides fabricated using various techniques. The simulations performed show how well different types of waveguides propagate a uniform input image across the entire field of view displayed. The simulations model the same lattice pattern used for all five results, with the variable being the RLT. Image 710 of FIG. 7A shows simulated test results for a waveguide fabricated in accordance with the innovative techniques described herein to provide a constant and small RLT across the area of ​​the waveguide. As shown here, a constant and small (e.g., about 20 nm) RLT result is one in which the resulting image is best conveyed to the eye of a user of the optical system, e.g., given a uniform input image across the entire field of view, the results here will substantially replicate the uniform input test image. The simulations can generate an Eye Box Energy (EBE) score, which describes what percentage of the energy of the input image will be carried to the eye box (the area occupied by the eye). Image 710 has an EBE score of 7.91%. The simulation can also generate a Low Frequency 80 / 20 (LF8020) score, which is the 80th percentile luminance minus the 20th percentile luminance divided by the 50th percentile luminance. Ideally, this score would be 0. The 710 has an LF8020 score of 1.32.

[0082] 7B-7E show simulation results for previously available methods (e.g., spin-on dispense methods) that can only apply a constant volume of resist across the entire surface of the substrate and therefore require dispensing a larger volume of resist to ensure the template is completely filled. Thus, these conventional methods produce products that are thicker and / or have a less uniform RLT compared to the innovative techniques described herein. Image 720 in FIG. 7B shows the results of applying a constant volume of resist with a minimum RLT of 20 nm. The simulation has an EBE score of 7.39% and an LF8020 score of 1.70. Image 730 in FIG. 7C shows the results of applying a constant volume of resist with a minimum RLT of 30 nm. The simulation has an EBE score of 7.2% and an LF8020 score of 1.77. Image 740 in FIG. 7D shows the results of applying a constant volume of resist with a minimum RLT of 40 nm. The simulation has an EBE score of 6.87% and an LF8020 score of 1.956. Image 750 in Figure 7E shows the result of applying resist with an RLT of 200 nm. As shown in the output image, the result using the innovative techniques described herein is a much more uniform output compared to other, more conventional methods. It is also worth noting that the simulations here were done in comparison to conventional methods that assume RLTs of 20, 30, and 40 nm. This is much lower than is typical for industry standard techniques currently in use, which tend to produce RLTs of 100-200 nm.

[0083] In some embodiments, dispensing less than 2 pL can be achieved by gravity without the use of a pump. One embodiment includes dispensing a drop of resist onto a substrate, contacting the resist with an imprint template to obtain a pattern of one or more structures in the resist, the pattern corresponding to the imprint template, polymerizing the resist to obtain the imprint nanostructures, and separating the imprint template from the imprint nanostructures. The resist has a refractive index in the range of 1.5 to 2.1, a residual film thickness (RLT) of the resist on at least a portion of the substrate is in the range of 0 nm to 50 nm, and the substrate is comprised of an inorganic material.

[0084] Implementations of this embodiment may have one or more of the following features.

[0085] In some implementations, the volume of each drop of resist is less than 6 picoliters, less than 5 picoliters, less than 4 picoliters, less than 3 picoliters, or less than 2 picoliters. In some implementations, the volume of each drop of resist is less than 1 picoliters.

[0086] In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, or 40-50 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0-40 nm, 0-30 nm, 0-20 nm, or 0-10 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 10-40 nm or 10-30 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 20-40 nm.

[0087] In some implementations, the substrate includes glass, LiTaO 3 , LiNbO 3 , SiC, or a combination thereof.

[0088] In some implementations, the resist does not include inorganic nanoparticles, in which case the resist typically has a refractive index in the range of 1.5 to 1.8.

[0089] In some implementations, the resist includes inorganic nanoparticles (e.g., TiO2, ZrO2, or both). The average diameter of the inorganic nanoparticles is typically in the range of 5 nm to 15 nm. The inorganic nanoparticles can comprise about 10 vol% to about 60 vol% of the resist. The resist typically has a refractive index in the range of 1.5 to 2.1.

[0090] In some implementations, the viscosity of the resist is in the range of 5 to 25 centipoise (cP) at 25°C.

[0091] In some implementations, the surface tension of the resist is in the range of 20 to 60 millinewtons (mN) per meter (m) at 25°C.

[0092] In some implementations, dispensing the droplets of resist includes pumping the resist from a reservoir through a first channel to a fluid dispenser. Some implementations include maintaining a continuous flow of resist between the reservoir and the fluid dispenser. In some implementations, maintaining a continuous flow of resist between the reservoir and the fluid dispenser includes pumping undispensed resist from the fluid dispenser through a second channel to the reservoir.

[0093] Embodiments of the present disclosure A first embodiment is a system for manufacturing an optical device, comprising: a reservoir configured to store a resist; a fluid dispenser including a dispensing mechanism configured to dispense droplets of resist onto a substrate; a meniscus pump configured to move the resist from the reservoir through the first channel to the fluid dispenser; a fluid pump configured to move undispensed resist from the fluid dispenser to the reservoir via the second channel; a fluid control device communicatively coupled to the fluid pump and the meniscus pump, the fluid control device configured to control operation of the fluid pump and the meniscus pump to maintain a continuous flow of resist between the reservoir and the fluid dispenser; an imprint mechanism operative to fabricate an optical device by applying an imprint template to resist dispensed on a substrate, wherein applying the imprint template creates a pattern of one or more structures in the resist, the pattern corresponding to the imprint template; The system comprises:

[0094] In embodiment 2, a control module communicatively coupled to the fluid control device, the fluid dispenser, and the imprint mechanism, the control module being programmed to send signals that control operation of the fluid control device, the fluid dispenser, and the imprint mechanism; The system of embodiment 1, further comprising:

[0095] Example 3 is the system of example 1 or 2, wherein the fluid dispenser is configured to dispense droplets of the resist having a volume of less than 6 picoliters.

[0096] Example 4 is the system of example 3, wherein the fluid dispenser is configured to dispense droplets of the resist having a volume of less than 4 picoliters.

[0097] Example 5 is the system of example 4, wherein the fluid dispenser is configured to dispense droplets of the resist having a volume of less than 2 picoliters.

[0098] Example 6 is the system of any one of Examples 1-5, wherein the resist has a refractive index greater than 1.6 for light having a wavelength of 532 nanometers.

[0099] Embodiment 7 is the system of any one of embodiments 1 to 6, wherein the substrate has a refractive index in the range of 1.5 to 2.7.

[0100] Example 8 is the system of any one of Examples 1-7, wherein the imprint template includes at least two zones having structures of different heights.

[0101]

[0023] Embodiment 9 is a method for manufacturing an optical device, comprising: operating a fluid dispenser including a dispensing mechanism to dispense droplets of resist onto the substrate; activating a meniscus pump to move resist from the reservoir through a first channel to a fluid dispenser; operating the fluid pump to move undispensed resist from the fluid dispenser to the reservoir through the second channel, the fluid pump and the meniscus pump operating to maintain a continuous flow of resist between the reservoir and the fluid dispenser; operating an imprint mechanism to fabricate an optical device by applying an imprint template to resist dispensed on a substrate, where applying the imprint template creates a pattern of one or more structures in the resist, the pattern corresponding to the imprint template; The method includes:

[0102] Embodiment 10 is Etching at least a portion of the optical device to reduce a residual thickness (RLT) of resist on the substrate, the etching including one or more of heating or atmospheric etching. 10. The method of embodiment 9, further comprising:

[0103] Example 11 is the method of example 10, wherein the etching further reduces a dimension of at least one structure of the pattern created by applying the imprint template.

[0104] Embodiment 12 is A substrate; a plurality of structures imprinted in a volume of resist dispensed on a substrate, the resist being comprised of a polymer, the resist having a refractive index in the range of 1.5 to 2.1, and a residual film thickness (RLT) of the resist in at least a portion of the substrate in the range of 0 nm to 50 nm; It is a waveguide comprising:

[0105] Embodiment 13 is the waveguide of embodiment 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 10-20 nm.

[0106] Embodiment 14 is the waveguide of embodiment 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 20-30 nm.

[0107] Embodiment 15 is the waveguide of embodiment 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 30-40 nm.

[0108] Embodiment 16 is the waveguide of embodiment 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 40-50 nm.

[0109] Embodiment 17 is the waveguide of any one of embodiments 12 to 16, wherein the plurality of structures provide one or more optically active zones including one or more of an input coupler, a combination pupil expander, an exit pupil expander, an orthogonal pupil expander, a recycler, or an anti-reflection feature.

[0110] Example 18 is the waveguide of any one of Examples 12 to 17, wherein the plurality of structures are imprinted with nanogeometry including one or more of binary features, tapered features, blazed features, sawtooth features, multi-step features, metafeature features, one-dimensional features, two-dimensional features, or three-dimensional features.

[0111] A nineteenth embodiment is the waveguide of any one of the twelfth to eighteenth embodiments, in which the substrate refractive index is in the range of 1.5 to 2.7.

[0112] A twentieth embodiment is the waveguide of any one of the twelfth to nineteenth embodiments, in which a plurality of structures are imprinted on one side of the substrate.

[0113] Embodiment 21 is the waveguide of any one of Embodiments 12 to 19, in which a plurality of structures are imprinted on both sides of the substrate.

[0114] Embodiment 22 is an imprint lithography method comprising the steps of: Dispensing a drop of resist onto a substrate; contacting the resist with an imprint template to obtain a pattern of one or more structures in the resist, the pattern corresponding to the imprint template; polymerizing the resist to obtain imprint nanostructures; Separating the imprint template from the imprint nanostructure. Including, The resist has a refractive index in the range of 1.5 to 2.1; the remaining resist thickness (RLT) on at least a portion of the substrate is in the range of 0 nm to 50 nm; An imprint lithography method in which the substrate is composed of an inorganic material.

[0115] Embodiment 23 is the imprint lithography method of embodiment 22, in which the volume of each drop of resist is less than 6 picoliters, less than 5 picoliters, less than 4 picoliters, less than 3 picoliters, or less than 2 picoliters.

[0116] Example 24 is the imprint lithography method of example 23, wherein the volume of each drop of resist is less than 1 picoliter.

[0117] Embodiment 25 is the imprint lithography method of any one of Embodiments 22-24, wherein the RLT of the resist in at least a portion of the substrate is in the range of 0-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, or 40-50 nm.

[0118] Embodiment 26 is the imprint lithography method of any one of Embodiments 22-24, wherein the RLT of the resist in at least a portion of the substrate is in the range of 0 to 40 nm, 0 to 30 nm, 0 to 20 nm, or 0 to 10 nm.

[0119] Embodiment 27 is the imprint lithography method of any one of embodiments 22-24, wherein the RLT of the resist in at least a portion of the substrate is in the range of 10 to 40 nm or 10 to 30 nm.

[0120] Embodiment 28 is the imprint lithography method of any one of embodiments 22-24, wherein the RLT of the resist in at least a portion of the substrate is in the range of 20-40 nm.

[0121] Example 29 is the imprint lithography method of any one of Examples 22 to 28, wherein the substrate comprises glass, LiTaO 3 , LiNbO 3 , SiC, or a combination thereof.

[0122] Embodiment 30 is the imprint lithography method of any one of embodiments 22-29, wherein the resist does not include inorganic nanoparticles.

[0123] Embodiment 31 is the imprint lithography method of embodiment 30, wherein the resist has a refractive index in the range of 1.5 to 1.8.

[0124] Embodiment 32 is the imprint lithography method of any one of embodiments 22 to 29, wherein the resist comprises inorganic nanoparticles.

[0125] Embodiment 33 is the imprint lithography method of embodiment 32, in which the inorganic nanoparticles comprise TiO 2 , ZrO 2 , or both.

[0126] Embodiment 34 is the imprint lithography method of embodiment 32 or 33, wherein the inorganic nanoparticles have an average diameter in the range of 5 nm to 15 nm.

[0127] Embodiment 35 is the imprint lithography method of any one of embodiments 32 to 34, wherein the inorganic nanoparticles constitute 10 vol % to 60 vol % of the resist.

[0128] Embodiment 36 is the imprint lithography method of any one of Embodiments 32 to 35, wherein the resist has a refractive index in the range of 1.5 to 2.1.

[0129] Example 37 is the imprint lithography method of any one of Examples 22 to 36, wherein the viscosity of the resist is in the range of 5 to 25 centipoise (cP) at 25° C.

[0130] Example 38 is the imprint lithography method of any one of Examples 22 to 37, wherein the surface tension of the resist is in the range of 20 to 60 millinewtons (mN) per meter (m) at 25° C.

[0131] Example 39 is the imprint lithography method of any one of Examples 22 to 38, in which dispensing the droplets of resist includes pumping the resist from a reservoir through a first channel to a fluid dispenser.

[0132] Example 40 is the imprint lithography method of any one of Examples 22 to 39, further comprising maintaining a continuous flow of resist between the reservoir and the fluid dispenser.

[0133] Example 41 is the imprint lithography method of example 40, in which maintaining a continuous flow of resist between the reservoir and the fluid dispenser includes pumping undispensed resist from the fluid dispenser through a second channel to the reservoir.

[0134] Example 42 is the imprint lithography method of any one of Examples 22 to 38, in which dispensing the droplets is performed without pumping the resist.

[0135] Embodiment 43 is the imprint lithography method of embodiment 42, in which dispensing the droplets is performed without pumping the resist with a meniscus pump, a fluid pump, or both.

[0136] Although the present disclosure includes many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may be claimed, but rather as descriptions of features that may be specific to a particular embodiment. Certain features described in the present disclosure in the context of separate embodiments can also be implemented in a single embodiment in combination. Conversely, various features described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although the features described above may be described as working in a particular combination and may initially be claimed as such, one or more features from the claimed combination may, in some cases, be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination.

[0137] Specific embodiments of the subject matter have been described. Other embodiments, modifications, and permutations of the described embodiments are within the scope of the appended claims, as will be apparent to those skilled in the art. Although operations are shown in a particular order in the drawings or claims, this should not be understood as requiring such operations to be performed in the particular order illustrated, or sequentially, or that all illustrated operations be performed (some operations may be considered optional) to achieve desirable results.

[0138] Accordingly, the foregoing exemplary embodiments do not define or limit the disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of the disclosure.

Claims

1. 1. A system for manufacturing an optical device, the system comprising: a reservoir configured to store a resist; a fluid dispenser including a dispensing mechanism configured to dispense droplets of the resist onto a substrate; a meniscus pump configured to move the resist from the reservoir to the fluid dispenser through a first channel; a fluid pump configured to move resist not dispensed from the fluid dispenser to the reservoir via a second channel; a fluid control device communicatively coupled to the fluid pump and the meniscus pump, the fluid control device configured to control operation of the fluid pump and the meniscus pump to maintain a continuous flow of the resist between the reservoir and the fluid dispenser; an imprint mechanism operative to fabricate the optical device by applying an imprint template to the resist dispensed on the substrate, wherein applying the imprint template creates a pattern of one or more structures in the resist, the pattern corresponding to the imprint template; A system comprising:

2. a control module communicatively coupled to the fluid control device, the fluid dispenser, and the imprint mechanism, the control module being programmed to send signals that control operation of the fluid control device, the fluid dispenser, and the imprint mechanism. The system of claim 1 further comprising:

3. The system of claim 1 , wherein the fluid dispenser is configured to dispense droplets of the resist having a volume of less than 2 picoliters.

4. The system of claim 1 , wherein the fluid dispenser is configured to dispense droplets of the resist having a volume of less than 4 picoliters.

5. The system of claim 1 , wherein the fluid dispenser is configured to dispense droplets of the resist having a volume of less than 6 picoliters.

6. 10. The system of claim 1, wherein the resist has a refractive index greater than 1.6 for light having a wavelength of 532 nanometers.

7. The system of claim 1 , wherein the substrate has a refractive index in the range of 1.5 to 2.

7.

8. The system of claim 1 , wherein the imprint template includes at least two zones having structures of different heights.

9. 1. A method for manufacturing an optical device, the method comprising: operating a fluid dispenser including a dispensing mechanism to dispense droplets of resist onto the substrate; operating a meniscus pump to move the resist from a reservoir through a first channel to the fluid dispenser; operating a fluid pump to move any resist not dispensed from the fluid dispenser to the reservoir through a second channel, the fluid pump and the meniscus pump operating to maintain a continuous flow of the resist between the reservoir and the fluid dispenser; operating an imprint mechanism to fabricate the optical device by applying an imprint template to the resist dispensed on the substrate, wherein applying the imprint template creates a pattern of one or more structures in the resist, the pattern corresponding to the imprint template; A method comprising:

10. Etching at least a portion of the optical device to reduce a residual thickness (RLT) of the resist on the substrate, the etching including one or more of applying heat or atmospheric pressure etching. The method of claim 9 further comprising:

11. The method of claim 10 , wherein the etching further reduces a dimension of at least one structure of the pattern created by applying the imprint template.

12. A waveguide, the waveguide comprising: A substrate; a plurality of structures imprinted in a volume of resist dispensed onto the substrate, the resist being comprised of a polymer, the resist having a refractive index in the range of 1.5 to 2.1, and a residual thickness (RLT) of the resist in at least a portion of the substrate in the range of 0 nm to 50 nm; A waveguide comprising:

13. The waveguide of claim 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 0 nm to 10 nm, 10 nm to 20 nm, 20 nm to 30 nm, 30 nm to 40 nm, or 40 nm to 50 nm.

14. The waveguide of claim 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 0 nm to 40 nm, 0 nm to 30 nm, 0 nm to 20 nm, or 0 nm to 10 nm.

15. The waveguide of claim 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 10 nm to 40 nm or 10 nm to 30 nm.

16. The waveguide of claim 12, wherein the RLT of the resist in at least a portion of the substrate is in the range of 20 to 40 nm.

17. 13. The waveguide of claim 12, wherein the plurality of structures provide one or more optically active zones including one or more of an input coupler, a combination pupil expander, an exit pupil expander, an orthogonal pupil expander, a recycler, or an anti-reflection feature.

18. 13. The waveguide of claim 12, wherein the plurality of structures are imprinted with nanogeometry comprising one or more of binary features, tapered features, blazed features, sawtooth features, multi-step features, metafeature features, one-dimensional features, two-dimensional features, or three-dimensional features.

19. The waveguide of claim 12, wherein the substrate has a refractive index in the range of 1.5 to 2.

7.

20. The waveguide of claim 12 , wherein the plurality of structures are imprinted on one side of the substrate.

21. The waveguide of claim 12 , wherein the plurality of structures are imprinted on both sides of the substrate.

22. 1. An imprint lithography method comprising: Dispensing a drop of resist onto a substrate; contacting the resist with an imprint template to obtain a pattern of one or more structures in the resist, the pattern corresponding to the imprint template; polymerizing said resist to obtain imprint nanostructures; Separating the imprint template from the imprint nanostructure. Including, the resist has a refractive index in the range of 1.5 to 2.1; a residual thickness (RLT) of the resist on at least a portion of the substrate is in the range of 0 nm to 50 nm; The imprint lithography method, wherein the substrate is comprised of an inorganic material.

23. 23. The imprint lithography method of claim 22, wherein a volume of each drop of the resist is less than 6 picoliters, less than 5 picoliters, less than 4 picoliters, less than 3 picoliters, or less than 2 picoliters.

24. 24. The imprint lithography method of claim 23, wherein each drop of the resist has a volume of less than 1 picoliter.

25. The imprint lithography method of claim 22, wherein the RLT of the resist in at least a portion of the substrate is in the range of 0 to 10 nm, 10 to 20 nm, 20 to 30 nm, 30 to 40 nm, or 40 to 50 nm.

26. The imprint lithography method of claim 22, wherein the RLT of the resist in at least a portion of the substrate is in the range of 0 to 40 nm, 0 to 30 nm, 0 to 20 nm, or 0 to 10 nm.

27. The imprint lithography method of claim 22, wherein the RLT of the resist in at least a portion of the substrate is in the range of 10 to 40 nm or 10 to 30 nm.

28. The imprint lithography method of claim 22, wherein the RLT of the resist in at least a portion of the substrate is in the range of 20 to 40 nm.

29. The substrate is glass, LiTaO ３ , LiNbO ３ 23. The imprint lithography method of claim 22, comprising a silicon carbide (SiC), a silicon carbide (SiC), or a combination thereof.

30. The imprint lithography method of claim 22 , wherein the resist is free of inorganic nanoparticles.

31. The imprint lithography method of claim 30, wherein the resist has a refractive index in the range of 1.5 to 1.

8.

32. The imprint lithography method of claim 22 , wherein the resist comprises inorganic nanoparticles.

33. The inorganic nanoparticles are TiO ２ , ZrO ２ 33. The imprint lithography method of claim 32, comprising:

34. The imprint lithography method of claim 32, wherein the inorganic nanoparticles have an average diameter in the range of 5 nm to 15 nm.

35. The imprint lithography method of claim 32, wherein the inorganic nanoparticles constitute between 10 vol % and 60 vol % of the resist.

36. The imprint lithography method of claim 32, wherein the resist has a refractive index in the range of 1.5 to 2.

1.

37. The imprint lithography method of claim 22, wherein the viscosity of the resist is in the range of 5 to 25 centipoise (cP) at 25°C.

38. The imprint lithography method of claim 22, wherein the surface tension of the resist is in the range of 20 to 60 millinewtons (mN) per meter (m) at 25°C.

39. 23. The imprint lithography method of claim 22, wherein dispensing the droplet of the resist comprises pumping the resist from a reservoir through a first channel to a fluid dispenser.

40. 40. The imprint lithography method of claim 39, further comprising maintaining a continuous flow of the resist between the reservoir and the fluid dispenser.

41. 41. The imprint lithography method of claim 40, wherein maintaining the continuous flow of the resist between the reservoir and the fluid dispenser comprises pumping undispensed resist from the fluid dispenser through a second channel to the reservoir.

42. The imprint lithography method of claim 22 , wherein dispensing the droplet occurs without pumping the resist.

43. 44. The imprint lithography method of claim 43, wherein dispensing the droplet occurs without pumping the resist with a meniscus pump, a fluid pump, or both.

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