UV Nanoimprint Lithography Research Articles

Towards high-throughput large-area metalens fabrication using UV-nanoimprint lithography and Bosch deep reactive ion etching.

We demonstrate the fabrication of diffraction-limited dielectric metasurface lenses for NIR by the use of standard industrial high-throughput silicon processing techniques: UV nano imprint lithography (UV-NIL) combined with continuous reactive ion etching (RIE) and pulsed Bosch deep reactive ion etching (DRIE). As the research field of metasurfaces moves towards applications, these techniques are relevant as potential replacements of commonly used cost-intensive fabrication methods utilizing electron beam ithography. We show that washboard-type sidewall surface roughness arising from the Bosch DRIE process can be compensated for in the design of the metasurface, without deteriorating lens quality. Particular attention is given to fabrication challenges that must be overcome towards high-throughput production of relevance to commercial applications. Lens efficiencies are measured to be 25.5% and 29.2% at wavelengths λ = 1.55μm and λ = 1.31μm, respectively. A number of routes towards process optimization are proposed in relation to encountered challenges.

Fabrication of Fiber Bragg Grating Stretchable Optical Filter By UV Nanorimprint Lithography

In this study, we propose a color filter using the characteristics of fiber Bragg grating as a substitute for organic color filter. To make fiber Bragg grating structure, periodic TiO2 grating structure is formed by ultraviolet nanoimprint lithography with a TiO2 nanoparticle dispersion resin. The TiO2 embedded PDMS color filter is completed using transfer printing by sacrificial layer. The reflectance peak is confirmed by a UV-vis-NIR spectrophotometer under strain conditions. When strain is applied, a reflectance peak red shift of color filter occurs. And, the red shift in the FDTD simulation data and actual measured values occur at similar levels, which suggests that the stretchable color filter is feasible.

UV-Nanoimprinting Lithography Photoresists with No Photoinitiator and Low Polymerization Shrinkage

In this work, a photopolymerizable disulfide monomer containing C(acryl)-S, disulfanediyl bis(4,1-phenylene) diacrylate (ADSDA), was designed and synthesized. Then, the UV nanoimprinting lithograph...

Design and fabrication of blazed gratings for a waveguide-type head mounted display.

In a waveguide-type display for augmented reality, the image is injected in the waveguide and extracted in front of the eye appearing superimposed on the real-world scene. An elegant and compact way of coupling these images in and out is by using blazed gratings, which can achieve high diffraction efficiencies. We report the design of blazed gratings for green light (λ = 543 nm) and a diffraction angle of 43°. The blazed gratings with a pitch of 508 nm and a fill factor of 0.66 are fabricated using grayscale electron beam lithography. We outline the subsequent replication in a polymer waveguide material with ultraviolet nanoimprint lithography and confirm a throughput efficiency of 17.4%. We finally show the in- and outcoupling of an image through two blazed gratings appearing sharp and non-distorted in the environment.

Cryogenic etching for pattern transfer into silicon of Mix-and-Match structured resist layers

A Mix-and-Match lithography method for a high-resolution, high-precision and cost effective lithography tool using DLW and FE-SPL was developed and successfully realized. The pattern transfer from the photoresist to the silicon substrate is done by so-called “cryogenic etching”. It means that the substrate is cooled down to cryogenic temperatures. In contrast to etching processes at standard room temperature, the cryogenic temperatures (below −100 °C) enable a highly anisotropic etching process. The difference between etching at room temperature compared to cryogenic etching is carried out in this work. The advantages of the etching process are highlighted for the pattern transfer from Mix-and-Match-structured samples. Therefore, the used photoresist mr-P 1201LIL (microresist technologies GmbH) has been examined concerning its silicon-to-resist selectivity which could be determined to be 6:1 for the applied etching recipe. Using cryogenic etching, we are now able to transfer the Mix-and-Match-structured patterns into silicon with appreciable high selectivities. This opens a novel pathway for the manufacturing of quantum devices on large wafers.The paper discusses current research results based on the TU Ilmenau Nanopositioning and Nanomeasuring Machines (NPMM) including the novel application of nanofabrication. First, the basic setup and the resulting benefits of the NPMMs for measuring and fabrication in a working volume of up to 200 mm × 200 mm × 25 mm while abiding nanometer accuracy is described. This is in contradiction to state-of-the-art AFM scanners, which have a limited working range of appr. 100 μm × 100 μm. Next, the principle and the results of different nanofabrication technologies are shown. These include Scanning Probe Lithography (SPL), Direct Laser Writing (DLW) and UV-nanoimprint lithography (NIL). Last, efforts for further improving the feature placement accuracy of the NPMMs as well as attempts to combine several fabrication technologies to improve their throughput are touched on.

Transfer durability of high aspect ratio moth-eye structure on glassy carbon mold using release agent

The moth-eye structure is an anti-reflection structure that is expected to effective over a wide range of wavelengths and angles of incident light. In addition, since the moth-eye structure is a single layer, it can be easily replicated using ultraviolet nanoimprint lithography (UV-NIL). However the moth-eye structure is fragile, because it has a lot of small sharp needles, and it has been reported that the durability decreases as the aspect ratio increases. The moth-eye structure exhibits anti-reflection function even with a low aspect ratio, but in this study, a fragile moth-eye structure with a high aspect ratio was used to facilitate evaluation of the releasability. In this experiment, a glassy carbon mold with high aspect ratio was release treated using a newly developed release agent. Furthermore, using the “partial-filling method” led to a dramatic improvement in the durability when compared to the conventional method using repeated cycles of the UV-NIL machine.

Controllable Subtractive Nanoimprint Lithography for Precisely Fabricating Paclitaxel-Loaded PLGA Nanocylinders to Enhance Anticancer Efficacy.

Nanoimprint lithography presents a new strategy for preparing uniform nanostructures with predefined sizes and shapes and has the potential for developing nanosized drug delivery systems. However, the current nanoimprint lithography is a type of an additive nanofabrication method that has limited potential due to its restricted template-dependent innate character. Herein, we have developed a novel subtractive UV-nanoimprint lithography (sUNL) for the scalable fabrication of PLGA nanostructures with variable sizes for the first time. sUNL can not only fabricate a variety of predefined nanostructures by simply utilizing different nanoimprint molds but also precisely prepare scalable nanocylinders with different length to diameter ratios. Particularly, sUNL can fabricate paclitaxel-loaded PLGA nanocylinders (PTX-PLGA NCs) with high drug-loading rate of 40% and long storage stability over a year. We demonstrate that PTX-PLGA NCs target clathrin- and caveolae-mediated cell transport pathways and display increased cellular uptake, in comparison to traditional PTX-loaded PLGA nanoparticles (PTX-PLGA NPs), leading to enhanced anticancer effects. Therefore, sUNL represents a promising nanofabrication method for efficiently developing predefined drug delivery systems.

Microchannel fabrication via ultraviolet-nanoimprint lithography and electron-beam lithography using an ultraviolet-curable positive-tone electron-beam resist

In this study, we propose a process to fabricate microchannels for in-situ cell cultivation and observation to facilitate a variety of biological experiments. The fabrication process involved a combination of ultraviolet nanoimprint lithography (UV-NIL) followed by electron-beam lithography (EBL) with a UV-curable EB resist polymer to form micropatterns directly on the imprinted microscale patterns. Here, we demonstrate the fabrication of microscale flow paths and reservoirs by UV-NIL and the subsequent formation of capillary flow paths and cell traps on the order of 2–4 μm by EBL. The UV-NIL/EBL hybrid technique can be used to fabricate complex microfluidic devices and is expected to be useful for lab-on-a-chip applications that require fine and complex flow paths.

Design of a disulfide bond-containing photoresist with extremely low volume shrinkage and excellent degradation ability for UV-nanoimprinting lithography

UV-nanoimprinting lithography has the merits of high throughput and resolution, low cost of manufacture and room temperature operation, and thus finds wide applications in various fields. Herein, a novel disulfide bond-containing photoresist for UV nanoimprint lithography was designed and prepared based on the disulfide compound, 2,2-dithiodiethanol diacrylate (DTDA), isobornyl acrylate (IBOA) and methyl methacrylate (MMA). The addition of DTDA could obviously enhance the double bond conversion (97%), polymerization rate (19% s−1) and thermal stability of the photoresist, but slightly reduce the Young’s modulus and indentation hardness. Remarkably, the as-prepared photoresist exhibited very low volume shrinkage that was as low as 0.93% owing to the reversible nature of the disulfide bond under UV light irradiation. Meanwhile, it had an excellent degradation ability in the presence of tributyl phosphine (TBP) and easily was removed from the mold. More importantly, the photoresist manifested an outstanding pattern transfer ability and could precisely duplicate the pattern with the line width of 206 nm and the height of 108 nm in the quartz mold without distortion.

Optimal placement of droplets for UV nanoimprint lithography

Optimizing the locations and sizes of droplets are key to reduce defects and increase throughput of ultraviolet nanoimprint lithography (UVNIL). Previously, simulation models describing the flow and coalescence of multiple fluid drops were developed and used to predict the fluid flow during spreading and feature filling. However, the effect of small channels on the resulting capillary pressure is neglected even though the flow along small channels or grooves is encountered in UVNIL. In this study, an accurate method to estimate capillary pressure boundary conditions at the fluid-air interface is developed along with fluid simulation. A method to estimate and compute the anisotropic capillary pressure for templates with line and space patterns is presented. It is found that the droplets flow faster in the direction of the pattern not only because of anisotropic permeability but also the nanostructure of the template, which further propels anisotropic spreading of the droplets by exerting larger capillary pressure. Using the new capillary pressure boundary condition, the simulation of multidrop spreading in UVNIL is performed to study the effects of anisotropic capillary pressures caused by the template structure. A simulation approach to determine optimal droplet placement was developed. From the simulation, a general rule of thumb is developed: delaying droplet merging as much as possible and reducing the number of merging events.

Fabrication of a micropatterned composite electrode for solid oxide fuel cells via ultraviolet nanoimprint lithography

A micropatterned object composed of La0.75Sr0.25Co0.50Mn0.50O3/Gadolinium-doped Ceria (LSCM/GDC) nanocomposite was fabricated for anode of solid oxide fuel cells (SOFCs) via ultraviolet nanoimprint lithography (UV-NIL). The LSCM/GDC nanocomposite particles were mixed with UV-curable resin and then UV imprinted on a dense yttria-stabilized zirconia (YSZ) substrate. The UV-NIL derived micropillars kept their structure on the YSZ substrate after the UV-curable resin was removed in the sintering process. After fabrication of the patterned SOFC anode electrode, its impedance was experimentally investigated. The ability of the developed method to fabricate micropatterned composite SOFC materials was demonstrated.

Effect of ITO electrode patterning on the properties of organic heterostructures based on non-fullerene acceptor prepared by MAPLE

This paper presents some studies on the organic heterostructures realized by Matrix Assisted Pulsed Laser Evaporation in both bi-layer and mixed layer configurations on glass substrates covered by flat or nano-patterned ITO. The donor, a star-shaped arylenevinylene compound, 4,4′,4″-tris[(4′-diphenylamino) styryl] triphenylamine, and acceptor, a non-fullerene compound, N,N′-bis-(1-dodecyl)perylene-3,4,9,10 tetracarboxylic diimide, were blended in three weight ratios: 1:2, 1:3 and 1:4.A grating of cylindrical pillars with a periodicity of 1.1 μm has been developed by UV-Nanoimprint Lithography in a polymer layer. The shape of the nanostructures changed to cone trunk by the Pulsed Laser Deposition of ITO on this nanostructured surface.The effect of the nanostructures and composition on the optical and electrical properties of the heterostructures was analyzed.The nano-patterning affected both the UV–Vis transmission and photoluminescence through the multiple reflections inside the cavities and at interfaces and the particularities of the molecular arrangement. The patterning was preserved independently of composition, but the roughness increased with increasing acceptor amount.The I-V characteristics drawn at room temperature in dark revealed an ohmic contact behavior for all heterostructures. The nano-patterning had a similar effect on the current in the heterostructures with mixed layer (1:2) and stacked bi-layer.

High-throughput roll-to-roll production of polymer biochips for multiplexed DNA detection in point-of-care diagnostics.

Roll-to-roll UV nanoimprint lithography has superior advantages for high-throughput manufacturing of micro- or nano-structures on flexible polymer foils with various geometries and configurations. Our pilot line provides large-scale structure imprinting for cost-effective polymer biochips (4500 biochips/hour), enabling rapid and multiplexed detections. A complete high-volume process chain of the technology for producing structures like μ-sized, triangular optical out-couplers or capillary channels (width: from 1 μm to 2 mm, height: from 200 nm up to 100 μm) to obtain biochips (width: 25 mm, length: 75 mm, height: 100 μm to 1.5 mm) was described. The imprinting process was performed with custom-developed resins on polymer foils with resin thicknesses ranging between 125-190 μm. The produced chips were tested in a commercial point-of-care diagnostic system for multiplexed DNA analysis of methicillin resistant Staphylococcus aureus (e.g., mecA, mecC gene detections). Specific target DNA capturing was based on hybridisation between surface bound DNA probes and biotinylated targets from the sample. The immobilised biotinylated targets subsequently bind streptavidin-horseradish peroxidase conjugates, which in turn generate light upon incubation with a chemiluminescent substrate. To enhance the light out-coupling thus to improve the system performance, optical structures were integrated into the design. The limits-of-detection of mecA (25 bp) for chips with and without structures were calculated as 0.06 and 0.07 μM, respectively. Further, foil-based chips with fluidic channels were DNA functionalised in our roll-to-roll micro-array spotter following the imprinting. This straightforward approach of sequential imprinting and multiplexed DNA functionalisation on a single foil was also realised for the first time. The corresponding foil-based chips were able to detect mecA gene DNA sequences down to a 0.25 μM concentration.

Boundary slip measurement and mechanism analysis in ultraviolet nanoimprint lithography of subwavelength moth-eye nanostructure

Subwavelength moth-eye nanostructure has been commonly used to reduce the surface reflection of optoelectronic devices, such as liquid crystal display, solar cell, image sensor, etc. Among various fabrication processes, the ultraviolet nanoimprint lithography (UV-NIL) technique combined with anodic aluminum oxide (AAO) mold provides an effective way for high-precision and high-efficiency fabrication of moth-eye nanostructure. To obtain high-precision moth-eye nanostructure, accurate analysis of UV-curing resin filling process into nanoscale AAO mold is necessary. In this research, the boundary slip phenomenon in nanoscale flow was investigated using atomic force microscope (AFM) method and it was found that boundary slip could produce a significant effect on nanoscale flow. Besides, the slip law on rough surfaces was further investigated. It was found the slip length reduced from 23.7 nm to 12.7 nm as roughness Ra increased from 0.47 nm to 3.18 nm, indicating that the roughness suppressed the slip motion. Moreover, the physical mechanism of boundary slip was also revealed, that was, the fluid properties and wettability caused intrinsic slip motion while the roughness could suppress intrinsic slip motion due to enhancement of internal viscous dissipation loss. The research could provide guidance for a more accurate understanding of boundary slip in nanoscale flow and high-precision fabrication of subwavelength moth-eye nanostructure.

FABRICATION OF PhC STRUCTURES BY USING NANOIMPRINT LITHOGRAPHY AND THEIR OPTICAL PROPERTIES

The contribution deals with creating structure, which have unique properties for influencing the spectrum of light. Since these structures exhibit the period under the diffraction limit of visible light or UV radiation, they can’t be fabricated by standard photolithography. As a result, this nanoscale structure must be prepared with progressive nanostructure patterning technology known as nanoimprint lithography (NIL). Especially, in our work UV-nanoimprint lithography was used. Considering preservation of low production costs, which plays a crucial role in the industry, the UV-nanoimprint lithography will be best suit for this purpose. Using this technology result with respect to reproducibility and uniformity of created nanostructure has been achieved. Ability of influencing light spectrum for nanostructures with the period of 800 nm and 600 nm with various feature size were presented with observation and simulation also.

Low-cost, durable master molds for thermal-NIL, UV-NIL, and injection molding

Mold cost and mold lifetime are essential concerns for mass production of micro/nano-patterned surfaces by nanoimprint lithography or micro/nanoinjection molding. Master molds are typically produced by subtractive processing using wafer-based clean room techniques. For imprint lithography, polymer copies of such molds can often be employed, but the durability of such molds is quite limited. The conditions of high temperature and pressure for injection molding require use of the durable masters created in stainless steel, nickel or other robust materials, but such approaches are challenged by the high cost of patterning these substrates and limited lifetime. Here, we report the fabrication of durable crystalline zirconium dioxide (ZrO2) masters via a simple direct imprint technique. ZrO2 nanoparticles (NPs) were formulated into an ink and imprinted on a variety of substrates using a solvent-assisted patterning technique and subsequently annealed to increase the mechanical durability of the mold. The hardness and modulus values of the ZrO2 coatings reached 11 ± 2 GPa and 120 ± 10 GPa, respectively after annealing. The hard ZrO2 mold was then employed for precision patterning of polymer surfaces by thermal and UV nanoimprinting lithography (NIL) techniques, and by injection molding. High fidelity pattern transfer continued throughout 115 000 injection molding cycles, there was no evidence of delamination, breakage or wear in the ZrO2 mold. Our simple imprint patterning technique using ZrO2 NPs inks enable us to fabricate robust molds with excellent thermal and mechanical properties as easily as imprinting simple polymer replicas. This simple and low-cost approach to mold preparation can enable a large variety of high throughput or large area nano-replication technologies.

Fluorinated low-viscosity copolymer with enhanced release property for roll-to-plate UV nanoimprint lithography

A new fluorinated low-viscosity copolymer resin with enhanced release properties has been developed to provide higher fidelity for roll-based ultraviolet (UV) nanoimprint lithography (NIL) and simplify the process. The properties are optimized by blending (2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononyl) oxirane (EP-F8) and 1,4-butanediol divinyl ether (BDDVE) with 3,4-epoxycyclohexylmethyl-3,4-epoxy cyclohexane carboxylate. The cured resin renders the hydrophobicity and allows demolding from the stamp mold without an anti-stick layer (ASL), as further verified by the contact angle and the work of adhesion measurements. Due to the addition of BDDVE, our resin also has much lower viscosity compared to commercially available low-viscosity resins. These properties enable the transfer of high-density dot patterns by roll-to-plate (R2P) UV NIL in the newly developed resin without adding solvent or coating it with an ASL. These results demonstrate that our resin is a good option for high-quality, low-cost R2P UV NIL, as its use eliminates several steps in the imprinting process, making it applicable to the scalable fabrication of flexible devices.

Design and Manufacture of a Novel Sunlight Guiding Panel

With technological advancement, energy consumption and lack of energy supply are inevitable. Approximately 20% of total energy consumption is used for artificial light in standard office buildings. To reduce energy consumption for illumination purposes, a sunlight guiding panel was used to increase the amount of sunlight available indoors. However, in most designs of a sunlight guiding panel, the panel has to be placed on the outdoor surface of a window glass. This type of design is inconvenient for assembling and cleaning. To enhance the practicality of a sunlight guiding panel, we attempted to place the sunlight guiding panel on the indoor surface of a window glass. The simulation results revealed that when the sunlight guiding panel was placed on the indoor surface of a window glass, the aspect ratio of the light-guiding structure of the sunlight guiding panel had to be increased for guiding the sunlight from outdoors so as to increase the amount of sunlight indoors. To fabricate the proposed sunlight guiding panel, UV nanoimprint lithography was applied to pattern the light-guiding structure of the sunlight guiding panel. Moreover, a mold with a high-precision light-guiding structure was used in UV nanoimprint lithography. The mold was fabricated using ultraprecision machining technology. Both analytical and experimental investigations were conducted to confirm the proposed design. The average light-guiding efficiency was 89.9% with a solar elevation angle range of 35° to 65°, and the experimental results agreed well with the simulation results. This study elucidates light-guiding efficiency when the sunlight guiding panel is placed on the indoor surface of a window glass, which can increase the usage convenience and application potential of sunlight guiding panels.

17.2: Invited Paper: Design of laboratory and production machinery for thermal and UV Nanoimprint for R2R and R2P applications

The application of nanoimprinted surfaces has led to highly improved properties, increased efficiencies of printed and traditional silicon electronical as well as optical devices. While providing a giant potential market for Nanoimprint Lithography (NIL) technologies in functional coatings of screens and touchscreens for mobile devices, fast imprinting of rigid materials has led to major challenges for mass production. For this range of applications with rigid and flexible materials, Coatema has developed a highly advanced set of UV NIL lab and production machinery for both roll‐to‐roll (R2R) and roll‐to‐plate (R2P) applications. Various methods have been applied to meet the recent requirements in accuracy and production speed at the same time. Therefore, Coatema’s latest developments in manufacturing technology for large area R2R and R2P, seamless UV‐ and thermal NIL provide polymer surfaces with light‐guiding, light‐trapping, light‐diffusing or micro lens effects as well as further advanced lithography techniques.

Electroless deposition of silver grids flexible transparent electrode integrated by ultra-violet nanoimprint lithography

Abstract Among recent explorations of flexible transparent electrodes (FTEs) applied in photoelectric devices, Ag nanowires (AgNWs) are widely used due to the advantages of high conductivity, large-scale manufacture and superior flexibility. However, relatively high roughness and contact resistance at junctions of Ag nanowire electrodes still affect the optoelectronic performance. Herein, adopting the ultraviolet nanoimprint lithography technology, the flexible Ag grids-based electrode without contact junctions has been prepared by electrolessly depositing metallic Ag on the exposed polydopamine (PDA) through coordination-bond interactions, which shows better flexibility and interfacial adhesion with comparison to the commercial PET/ITO. The light-emitting diode lamp bulb connected with PET/PDA@Ag grids electrode is still brilliantly lit after 200 continuous bending cycles with radius of 3 mm, suggesting robust mechanical stability. In addition, the PET/PDA@Ag grids-based polymer solar cells yield a power conversion efficiency of 11.6%.