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Large‐Area Dual‐Scale Metal Transfer by Adhesive Force
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Abstract
We report a large-area, dual-scale metal transfer method by using a difference in adhesive force. Rigiflex polyurethane acrylate (PUA) molds with engraved nanoscale patterns were used to transfer metal layers (Au or Al) to flexible polyethylene terephthalate (PET) substrate. Transfer process was performed sequentially for the metal layers on ridge and valley regions of the mold, resulting in a dual-scale metal transfer from a single master. A simple metal wire grid polarizer was fabricated and analyzed using this method.
... If the spreading coefficient S is negative, the liquid will undergo dewetting between the mold and the film. 17 The interfacial energy between two surfaces, for instance, γ SM in the case of the substrate−mold interface, can be obtained from the geometric mean equation given as 18 ...
... Putting these values to eq 5 and solving the simultaneous equations, we can obtain γ i d , γ i p , and γ i for the micropatterned PDMS mold and PPF substrate as summarized in Table 2 along with the known values reported elsewhere. 11,18,19 Putting these to eq 4 and calculating eq 3, we finally get the spreading coefficient of −58.5 mJ/m 2 , confirming that our material system generates adequate dewetting for perforating the PUA resin layer between the PDMS mold and the PPF substrate. ...
... This can also be analytically verified by comparing the work of adhesion between the PDMS mold and the cured PUA and that of the cured PUA and PPF. A work of adhesion can be calculated as the harmonic mean equation given as 18 ...
We present the physics of sequential dewetting phenomenon and continuous fabrication of a polymeric microstencil using dewetting phenomenon with roll-to-roll imprinting equipment. To realize dewetting-assisted residual-free imprinting, mold material, polymer resin, and substrate were selected via interfacial surface energy analysis. In addition, optimal parameters of the continuous process were also studied by experimentally comparing the resultant shape of the microstencil depending on the process speed, aspect ratio of the mold, and applied pressure. As a result, the polymeric microstencil was produced continuously in very high yields, and its maximum resolution reached 20 μm in diameter. For an easy, continuous demolding during the roll-to-roll process, the material chosen for the substrate film was paraffin-coated film, which has the surface energy low enough for dewetting while having a higher adhesion value than polydimethylsiloxane mold. This versatile, high-throughput microstencil fabrication process can be used in many applications requiring flexibility, scalability, and specific material, and high productivity.
... Recently, some investigations have provided high-quality pattern transfer results by adhering a gold pattern onto an adhesion layer [1][2][3][4][5][6][7][8][9][10][11][12]. Typically, thin gold or copper film is deposited on polymeric elastic or rigiflex mold, formed by polydimethyl siloxane (PDMS) or poly(urethane acrylate) (PUA). ...
... The adhesion work of the metal-mold interface is minimized by choosing a mold having relatively low surface energy and carefully depositing the gold on the pattern surfaces, avoiding excessive deposition on lateral walls. Typically, the adhesion work of the metal-substrate interface is promoted by plasma or UV/ozone activation on both surfaces [7], or by adding a thin layer of self-assembled monolayer [8], a softening polymer [9,10], or a photo-adhesive [11]. For instance, nanotransfer printing (NTP) developed by Rogers et al was employed to transfer a deposited metal pattern from the protrusion of a mold to a substrate by the chemical bonding between Au and thiolated surface. ...
... Suh's group found that a commercialized optical adhesive NOA71 could also successfully transfer gold from a relatively rigid PUA mold. NOA71 was formulated to provide a strong bond to glass surfaces [11]. In order to use the pattern transfer method in the application of flexible electronics, the large-scaled fidelity of gold electrodes on a polymer substrate was required. ...
This study was aimed at developing a metal-transfer technique to fabricate micro/nano metal patterns by using the adhesion force between metal layers and polymer surfaces. The force was generated by partial curing on a UV-curable polymer surface. This polymer contained glycido methacrylate, polyurethane diacrylate (PU-2) and O2-sensitive initiators, and was polymerized by covering it with an O2-permeable film under UV irradiation. Another UV-curable polymer, containing isobonyl acrylate, hexa-acrylated PU (PU-6) and O2-insensitive initiators, was utilized as the master mold. A layer of gold, pre-coated on the mold, was adhered to the partially cured intermediate layer, transferring gold patterns onto the intermediate layer. A scanning electron microscope, an optical microscope and atomic force microscopy were used to inspect the transferred yield and morphology of the gold patterns. A force–distance evaluation was also carried out to explore the adhesion force of the surfaces. The results show that the partially cured polymer can maintain the morphology of the pattern after a short period of irradiation and still displays its adhesive property on its surfaces. Instead of using the traditional photolithography and the lift-off process, the technique was performed to fabricate some complex patterns having micro and nano features, and interdigital electrodes, giving the potential for direct printing of microelectrodes and flexible circuits.
... The work of adhesion (W a ) between two interfaces can be calculated by harmonic-mean equation [37,38], given by: ...
... where the subscript s is for the interface of solid and the superscripts d and p are for the dispersive and polar components of the surface tension γ, respectively. At this point, surface tension is determined by the geometric-mean equation [37,38], given by: ...
We describe a rapid and simple method to create Ag nanostructures by using direct mechanical patterning of ionic Ag ink coating under gentle pressure, then thermal annealing to reduce the ionic Ag ink to a metallic Ag layer. The ionic liquid-phase Ag coating is easily obtained by spin-coating ionic Ag ink that has appropriate Ag concentration and can be either printed or imprinted on the desired substrate by using a soft elastomer patterning mold, then reduced to the Ag nanostructure by subsequent thermal annealing. More specifically, we present two methods: transfer printing and soft nanoimprinting. In transfer printing, the ionic Ag ink is first inked onto the elastomer mold which then contacts the target substrate to transfer the Ag nanopattern. In soft nanoimprinting, the elastomer mold conducts soft imprinting to engineer the ionic Ag ink coating to the Ag nanostructure. We systematically investigate the optimal patterning conditions by controlling the initial Ag ink concentration and the coating, printing, imprinting, and annealing conditions, to derive Ag architecture that has tunable photonic functionality. As an example, we demonstrate polarization-sensitive reflective color filters that exploit shape-tunable Ag nanostructures fabricated by soft nanoimprinting using a controllably-stretched elastomer mold.
... There is a growing demand for methods that can be implemented across large areas, as the need for micro-or nanoscale surface features increases [1][2][3][4][5][6][7][8][9][10]. One example is the fabrication of wire grid polarizers (WGPs) for use in display devices, such as liquid crystal displays (LCDs). ...
The fabrication of nanoscale patterns over a large area has been considered important but difficult, because there are few ways to satisfy both conditions. Previously, visually tolerable tiling (VTT) for fabricating nanopatterns for optical applications has been reported as a candidate for large area fabrication. The essence of VTT is the inevitable stitching of the nanoscale optical component, which is not seen by the naked eye if the boundary is very narrow while the tiles are overlapped. However, it had been difficult to control the shape of the spread of liquid prepolymers in the previous work, and there was room for the development of tiling. Here, we propose a method for transferring various shapes of tiles, which can be defined with a shadow mask. The method of using a transparent shadow mask can provide a wide process window, because it allows the spreading of a liquid prepolymer to be more easily controlled. We optimize the coating condition of a liquid prepolymer and the ultraviolet (UV) exposure time. Using this method, we can attach tiles of various shapes without a significant visible trace in the overlapped region.
... Another method to achieve aligned nanopatterns over a large area is to transfer the desired pattern to the target substrate [32][33][34][35][36][37][38][39][40]. This technique, known as NTP, was introduced by Rogers et al. [32][33][34]. ...
In nanoscience and nanotechnology, nanofabrication is critical. Among the required processes for nanofabrication, lithography is one of core issues. Although conventional photolithography with recent remarkable improvement has contributed to the industry during the past few decades, fabrication of 3-dimensional (3D) nanostructure is still challenging. In this review, we summarize recent advances for the construction of 3D nanostructures by unconventional lithography and the combination of two
top-down
approaches or
top-down
and
bottom-up
approaches. We believe that the 3D hierarchical nanostructures described here will have a broad range of applications having adaptable levels of functional integration of precisely controlled nanoarchitectures that are required by not only academia, but also industry.
... 29 A bare PUA(non-pattern) surface has a water-contact angle of approximately 85 o ; while a much lower contact angle was measured for hierarchical patterns because Area between water and surface is larger than bare PUA. 30 The hydrophilic surface, which has micro-/nanopatterns, temporarily maintained the Cassie- Baxter state. However, the water-wetting state altered slightly from the Cassie-Baxter state to the Wenzel state owing to external vibrations or capillary forces. ...
We present a continuous fabrication method to make bio-inspired water collecting surface by using roll type photolithography for potential applications to real time air monitoring system. In this study, the carapace of the stenocara beetle was mimicked to achieve water collection from air, using a molding process involving micro-/nanofabrication techniques and roll type photolithography. We fabricated a super-hydrophilic surface on top of a super-hydrophobic surface and used two different setups to demonstrate water collection, a thermoelectric module and a humidifier. Also, the optimized geometric design for water collection was found from 16 different test samples. Detection of mercury is shown as a feasible practical application of such surfaces.
... In our experiment, the hydrophilic PUA 34,35 was mostly used as upper and lower moulds in order to replicate the hydrophobic PFPE resins [38][39][40] ; the materials can be swapped to obtain the exposed PFPE pillars with the background of the dewetted PUA domain (Fig. 1b). Although not shown, the PFPE mould could even dewet a highly viscous (140 cps) Norland Optical Adhesive (NOA73) 41 and other UV-curable resins in the same one-step moulding process. ...
Membranes with nano-apertures are versatile templates that possess a wide range of electronic, optical and biomedical applications. However, such membranes have been limited to silicon-based inorganic materials to utilize standard semiconductor processes. Here we report a new type of flexible and free-standing polymeric membrane with nano-apertures by exploiting high-wettability difference and geometrical reinforcement via multiscale, multilevel architecture. In the method, polymeric membranes with various pore sizes (50-800 nm) and shapes (dots, lines) are fabricated by a hierarchical mould-based dewetting of ultraviolet-curable resins. In particular, the nano-pores are monolithically integrated on a two-level hierarchical supporting layer, allowing for the rapid (<5 min) and robust formation of multiscale and multilevel nano-apertures over large areas (2 × 2 cm(2)).
... A low-cost and high-throughput method for patterning of metal features has become a main goal in a variety of fields such as displays, printed circuit boards, electronic circuits, transistors, plasmonics, optoelectronic devices, biological and chemical sensors [1][2][3][4][5][6][7][8]. In conventional metal patterning processes, the metal tracks are formed by etching the deposited metal layer using a photolithography technique. ...
In this work, we have developed novel methods to fabricate conductive silver tracks and dots directly from silver nitrate solution by transfer-printing and nanoimprinting lithography techniques, which are inexpensive and can be scaled down to the nanometer scale. The silver nitrate precursor can be reduced in ethylene glycol vapor to form silver at low temperatures. Energy dispersive spectrometric analysis results indicate that the silver nitrate has been converted to silver completely. In order to obtain smooth and continuous conductive patterned silver features with high resolution, the silver lines with widths of a few tens of micrometers to nanometers were patterned by using a spin-coating approach. Using a 14 M silver nitrate solution, continuous silver conductive lines with a resistivity of 8.45 × 10⁻⁵ Ω cm has been produced.
Metasurface holography, the reconstruction of holographic images by modulating the spatial amplitude and phase of light using metasurfaces, has emerged as a next‐generation display technology. However, conventional fabrication techniques used to realize metaholograms are limited by their small patterning areas, high manufacturing costs, and low throughput, which hinder their practical use. Herein, a high efficiency hologram using a one‐step nanomanufacturing method with a titanium dioxide nanoparticle‐embedded‐resin, allowing for high‐throughput and low‐cost fabrication is demonstrated. At a single wavelength, a record high theoretical efficiency of 96.9% is demonstrated with an experimentally measured conversion efficiency of 90.6% and zero‐order diffraction of 7.3% producing an ultrahigh‐efficiency, twin‐image free hologram that can even be directly observed under ambient light conditions. Moreover, a broadband meta‐atom with an average efficiency of 76.0% is designed, and a metahologram with an average efficiency of 62.4% at visible wavelengths from 450 to 650 nm is experimentally demonstrated. An ultrahigh‐efficiency hologram using a one‐step printing of a TiO2 nanoparticle‐embedded‐resin (nano‐PER) is designed and experimentally demonstrated. Record efficiencies of 96.9% and 90.6% are theoretically and experimentally realized. The extremely high efficiency allows the holographic images to be clearly observed even under ambient lighting conditions, while the one‐step nano‐PER nanoimprinting fabrication method allows the realization of high‐throughput and low‐cost metaholograms.
Herein, we develop an adhesive-free double-faced nanotransfer lithography (ADNT) technique based on the surface deformation of flexible substrates under the conditions of temperature and pressure control and thus address the challenge of realizing the mass production of large-area nanodevices for the fields of optics, meta-surfaces, and holograms. During ADNT, which is conducted on a flexible polymer substrate above its glass transition temperature in the absence of adhesive materials and chemical bonding agents, nanostructures from the polymer stamp are attached to the deformed polymer substrate. Various silicon masters are employed to prove our method applicable to arbitrary nanopatterns, and diverse Ag and Au nanostructures are deposited on polymer molds to demonstrate the wide scope of usable metals. Finally, ADNT is used to (i) produce a flexible large-area hologram on defect-free PMMA film and (ii) fabricate a meta-surface hologram and a color filter on the front and back surfaces of PMMA film, respectively, to realize dual functionality. Thus, it is concluded that the use of ADNT can decrease the fabrication time and cost of high-density nanodevices and facilitate their commercialization.
One of the main challenges in the widespread utilization of localized plasmon resonance-based biosensors is the fabrication of large-area and low-cost plasmonic nanostructures. In this work, we fabricated large-area and low-cost complementary plasmonic biosensors such as nanohole and nanodisk arrays using dual nanotransfer printing (NTP) with a single metal deposition and a single reusable mold. The suspended nanohole arrays (SNHA) and the suspended nanodisk arrays (SNDA) were fabricated using the subsequent dry etching process. We confirmed a maximum enhancement in bulk sensitivity in experiments and simulations by controlling the vertical and lateral etching depths of the dielectric layer underneath the gold (Au) nanohole and nanodisk arrays. Furthermore, we show that the surface sensitivity evaluated by atomic layer deposition of aluminum oxide increased because appropriate vertical and lateral etching depths allow the target analyte to access the additional near-field formed at the bottom of the Au nanostructure. The dual NTP method provides a practical solution for the realization of large-area and low-cost label-free plasmonic biosensing systems, with a reduction in complexity and cost of the fabrication process of complementary plasmonic structures and metasurfaces.
We report directional switchable adhesion behavior inspired by the locomotion mechanism of gecko lizard. The robust mushroom-like polydimethylsiloxane microline arrays are fabricated by using silicon based over-etching process and replica molding. The line gecko patterns attached to the glass substrate exhibit strong shear adhesion forces in parallel and perpendicular directions with respect to the line direction and high adhesion hysteresis property only in the parallel direction. We have explained the directional adhesion behavior of the line gecko pattern by comparing peeling propagation and normal adhesion phenomenon. Then, we have successfully demonstrated silicon wafer transportation with the line gecko pattern by using directional adhesion behavior of the pattern, which is high shear adhesion force and low peeling force in the parallel direction with respect to the line direction.
Many research groups have developed unique micro/nano-structured dry adhesives by mimicking the foot of the gecko with the use of molding methods. From these results, polydimethylsiloxane (PDMS) has been developed and become the most commonly used material for making artificial dry adhesives. The material properties of PDMS are well suited for making dry adhesives, such as conformal contact with almost zero preload, low elastic modulus for stickiness, and easy cleaning with low surface energy. From a performance point of view, dry adhesives made with PDMS can be highly evaluated but are limited by low productivity, as production takes an average of approximately two hours. Given the low productivity of PDMS, some research groups have developed dry adhesives using UV-curable materials, which are capable of continuous roll-to-roll production processes. However, UV-curable materials were too rigid to produce good adhesion. Thus, we established a PDMS continuous-production system to achieve good productivity and adhesion performance. We designed a thermal roll-imprinting lithography (TRL) system for the continuous production of PDMS microstructures through shortening curing time by controlling the curing temperature (production speed is up to 150 mm min-1). Dry adhesives composed of PDMS were fabricated continuously via the TRL system.
In this communication, we present a simple and robust switchable dry adhesion system by using PDMS wrinkled-gecko surface. The PDMS substrate with gecko-inspired wide-tip arrays is a wrinkled area generated by UVO exposure using a shadow mask. The fabricated PDMS wrinkled-gecko device shows high dry adhesion hysteresis on a targeted surface. In the experiments, the difference of adhesion force of wrinkled PDMS surface between adhesion on and off modes increases with longer UVO treatment time. Also, it has durability with mechanical robustness without any defect or decrease in adhesion force even after 100 repeating cycles of the adhesion test. These remarkable properties can be used for precise, green-environmental transporting system with various applications in commercial and research areas.
Advances in flexible optoelectronic devices have led to increasing need for developing high performance, low cost, and flexible transparent conducting electrodes. Copper-based electrodes have been unattainable due to the relatively thermal instability and poor oxidation resistance. Herein, we present oxidation-resistive CuNi nanomesh electrodes that exhibit a low sheet resistance of ∼7.5 Ω/□ and a high optical transmittance of ∼81% at 550 nm. Further, high long-term stability against the effects of oxidation, heat, and chemicals is exhibited by the CuNi nanomesh, in comparison with the behavior of a pure Cu nanomesh sample.
This study describes polyurethane–acrylates (PUAs) as polymeric stamp materials that can be used in a number of contact printing applications. We demonstrate that the surface energy of PUA polymers can be controlled chemically, producing stamps with tunable polarity and eliminating the need to apply release coatings or to adjust stamping kinetics to facilitate material transfer. To demonstrate the general nature of the proposed materials, PUA polymers were used in the contact printing of organic molecules and organic thin films. The results suggest that PUA-based contact printing can be used as a simple alternative to a kinetically modulated PDMS stamping of thin films, and that thin film features with sub-micrometer lateral dimensions and sub-100 nm thicknesses can be accurately reproduced using a universal set of printing conditions.
A multiscale metallic pattern having in nanoscience exhibits unique and unusual optical properties in plasmonics. Conventional fabrication methods for multiscale metallic pattern involved many steps and restricted in shapes. Here we present a simple yet robust method for fabricating multiscale metal patterns through a transfer printing techniques by simply employing a polymeric hierarchical mold having low surface energy as a stamp. Multiscale metal patterns are easily transferred on a Norland Optical Adhesive (NOA) surface having relatively higher surface energy than that of PFPE hierarchical stamp without surface treatment.
The fabrication of large area mold is the one of most difficult challenges in roll to roll nanoimprint field and eliminating the visible seams on large area mold is even more difficult. We present a visually tolerable tiling (VTT) method to make large area micro/nano pattern without visible seams and its applications. In this study, with small area micro/nano pattern molds, VTT method could produce scaled up mold with same features as original mold without any visible seam lines. Also, fabricated large size mold was used in roll to roll imprinting process as flexible mold. By using VTT method, large size metal wire grid polarizers and micro prism sheet were fabricated and their potentials were confirmed as feasible applications.
We report the development of an optical micro-nanolithography method by using a roll-type mask. It includes phase-shift lithography and photolithography for realizing various target dimensions. For sub-wavelength resolution, a structure is achieved using the near-field exposure of a photoresist through a cylindrical phase-mask, allowing high-throughput continuous patterning. By using a film-type metal mask, continuous photolithography was achieved, and this method could be used to control the period of resultant patterns in real time by changing the rotating speed of the cylinder mask. As an application, we present the fabrication of a transparent electrode in the form of a metallic mesh by using the developed roll-type photolithography process. As a result, a transparent conductor with good properties was achieved by using a recently built cylindrical phase-shift lithography prototype, which was designed for patterning on 100-mm2 substrates.
Uniform metal nanomesh structures are promising candidates that may replace of indium-tin oxide (ITO) in transparent conducting electrodes (TCEs). However, the durability of the uniform metal mesh has not yet been studied. For this reason, a comparative analysis of the durability of TCEs based on pure Ag and AgNi nanomesh, which are fabricated by using simple transfer printing, is performed. The AgNi nanomesh shows high long-term stability to oxidation, heat, and chemicals compared with that of pure Ag nanomesh. This is because of nickel in the AgNi nanomesh. Furthermore, the AgNi nanomesh shows strong adhesion to a transparent substrate and good stability after repeated bending.
A simple method for the formation of multiscale metal patterns is presented using hierarchical polymeric stamps with perfluoropolyether (PFPE). A dual-scale PFPE structure is made via two-step moulding process under partial photocrosslinking conditions. The hierarchical PFPE stamp enables multiscale transfer printing (MTP) of metal pattern in one step within microwells as well as on curved surfaces.
In this work, we demonstrate the fabrication of bilayer metal wire-grid polarizers and the characterization of their performance. The polarizers with 200 nm period were fabricated on flexible plastic substrates by nanoimprint lithography (NIL), followed by aluminum deposition. Transmission efficiency over 0.51 and extinction ratio higher than 950 can be achieved in the visible range when the aluminum thickness of the polarizer is 100 nm. The fabrication process only involves direct imprinting on flexible plastic substrates and aluminum deposition, without any resist spin-coating, lift-off, and etching processes, which is much simpler, less costly, and applicable to large volume production. (C) 2011 Elsevier B.V. All rights reserved.
We report a simple technique of selective gold nano-patterning on non-planar polycarbonate substrate by combining nanoimprinting and gold nanotransfer printing techniques in a single concurrent nano-patterning process: thermal nanoimprinting directly patterns a MPTMS (3-mercaptopropyl trimethoxysilane)-coated polycarbonate sheet to form the non-planar nanostructures using a gold-film deposited mold. Simultaneously, the gold-film from the mold is selectively transfer-printed either onto the protrusion or the base of the imprinted non-planar structures. This high nano-patterning selectivity is achieved due to a combined effect of a thiol-terminated MPTMS–gold surface chemistry, more importantly, aided by a surface area dependent differential work of adhesion. We show the high delineation of the patterned gold on the non-planar polycarbonate substrate of various geometries such as pillars, dimples, and gratings, down to nano-scale resolution (130 nm) as well as over micro-scale resolution (10 μm), thus demonstrating that this can be a generic metal patterning technique. Using this technique, we fabricate a metal nanowire grid polarizer to demonstrate a potential device application. The main advantage of this technique lies in its inherent self-aligned process that simplifies selective Au nano-patterning on non-planar polymer surfaces, which is otherwise difficult to be obtained using conventional patterning techniques.
In this paper, we report on a cost-effective and simple, nondestructive pattern transfer method that allows the fabrication of metallic nanostructures on a polydimethylsiloxane (PDMS) substrate on a wafer scale. The key idea is to use holographic nanopatterns of a photoresist (PR) layer as template structures, where a metal film is directly deposited in order to replicate the nanopatterns of the PR template layer. Then, the PDMS elastomer is molded onto the metal film and the metal/PDMS composite layer is directly peeled off from the PR surface. Many metallic materials including Ti, Al, and Ag were successfully nanopatterned on PDMS substrates by the pattern transfer process with no use of any adhesion promoter layer or coating. In case of Au that has poor adhesion to PDMS material, a salinization of the metal surface with 3-(aminopropyl)-triethoxysilane (APTES) monolayer promoted the adhesion and led to successful pattern transfer. A series of adhesion tests confirmed the good adhesion of the transferred metal films onto the molded PDMS substrates, including scotch-tape and wet immersion tests. The inexpensive and robust pattern transfer approach of metallic nanostructures onto transparent and flexible PDMS substrates will open the new door for many scientific and engineering applications such as micro-/nanofluidics, optofluidics, nanophotonics, and nanoelectronics.
Transfer printing represents a set of techniques for deterministic assembly of micro-and nanomaterials into spatially organized, functional arrangements with two and three-dimensional layouts. Such processes provide versatile routes not only to test structures and vehicles for scientific studies but also to high-performance, heterogeneously integrated functional systems, including those in flexible electronics, three-dimensional and/or curvilinear optoelectronics, and bio-integrated sensing and therapeutic devices. This article summarizes recent advances in a variety of transfer printing techniques, ranging from the mechanics and materials aspects that govern their operation to engineering features of their use in systems with varying levels of complexity. A concluding section presents perspectives on opportunities for basic and applied research, and on emerging use of these methods in high throughput, industrial-scale manufacturing.
We report the development of a near-field optical nanolithography method using a roll-type phase-shift mask. Sub-wavelength resolution is achieved using near-field exposure of photoresist through a cylindrical phase mask, allowing dynamic and high throughput continuous patterning. As an application, we present the fabrication of a transparent electrode in the form of a metallic wire grid by using the roller-based optical lithography method. To fabricate a mesh-type metal pattern, a specific phase-shift mask was designed and critical experimental parameters were also studied. As a result, a transparent conductor with suitable properties was achieved with a recently built cylindrical phase-shift lithography prototype designed to pattern on 100 mm(2) of substrate area.
A simple method is presented to form an array of shape-controllable microlenses by partial photocuring of an UV-curable polymer and direct transfer. Using the transferred lens array, nanoscale metal patterns as small as 130-nm gaps are detected under an optical microscope with a distinguishable resolution.
We demonstrate anisotropic optical films based on liquid crystalline polymer (LCP) using a capillary force lithography (CFL). The fabricated optical films can be used as both an optical component and a self-aligning capability of liquid crystal molecules introduced on the film. Additionally, HA or PA LC can be induced on same material by controlling the water repellency of LCP surface. Moreover, surface anchoring transitions could be controlled by variation of pattern sizes and surface treatment. In this point of view, one thin optical film can act both retarder and alignment layer and then shows good retardation, LC alignment, and transmittance at the same time.
The lower part of polymeric nanopillars is made mechanically stiff by surrounding it with metal, while the top part of the pillars is soft. The metal-shell-free tops of the pillars could be used for fabricating hollow structures or decorated with functional materials. This mechanical reinforcement shows stability against capillary-force-induced clustering and enables applications in a water environment.
A selective metal transfer (SMT) process is applied to organic light-emitting diode (OLED) metal electrodes. Multicolored OLED device fabrication is demonstrated using a vacuum-free, selective metal transfer process where an Al thin film (<100 nm) is transferred onto only the top of a light emitting layer containing polyvinyl carbazole. With this one-step process, it is possible to make separate, differently colored electrodes and to drive each independently. Scale-up of this process is relatively easy and SMT has a high potential in the industrial fabrication of metal electrodes for various organic electronics.
We present a simple method of utilizing anodized aluminum oxide (AAO) as a reproducible template for fabricating high-aspect-ratio uniformly bent polymeric nanopillars that can be used as a physical adhesive. It is shown how to achieve straight high-aspect-ratio nanopillars with concepts of the work of adhesion and lateral collapse between polymer pillars without serious damage to the master template. With the support of manufacturing polymeric nanopillars from the reusable AAO, a simple route to asymmetric dry adhesive nanopillars bent by residual stresses was demonstrated.
Two-dimensional patterned microstructures of multicomponent polymers are fabricated by utilizing the reversible nature of buckling. The polymers were selectively deposited in the trenches of the buckled surfaces to form unconventional patterns that were transferred to other substrates.
(Figure Presented) The simple production of micro/nanoscale patterns with very high aspect ratios exceeding that of the mold used is demonstrated using unconventional top-surface lithography. The method combines inkless contact printing and subsequent dry pattern development by oxygen reactive ion etching, making it possible to form high-resolution, high-aspect-ratio patterns without the aid of expensive optical protocols.
We present a simple flexographic printing method mediated by edge dewetting for potential applications to roll-to-roll or plate-to-roll pattern transfer. By controlling dewetting of a thin, conductive ink material under conformal contact with a patterned elastomeric mold (e.g., polydimethylsiloxane, PDMS), the liquid ink layer is broken and then selectively wets the protruding part of the mold with high fidelity. Subsequently, a thin photoresist layer that is coated on 300 mm-diameter aluminum cylinder is brought in contact with the ink-coated PDMS mold, resulting in a plate-to-roll pattern transfer without collapse or merging of neighboring features. Using this method, conductive silver lines are fabricated on the cylindrical surface with the resolution of approximately 20 microm and the sheet resistance less than approximately 4.3 ohms after 10 repeated transfer cycles.
Wire-grid polarizers (WGPs) can be fabricated easily by reversal rigiflex printing. Metal films with gratings were fabricated on a transparent glass substrate by transfer printing with a metal coated rigiflex mold, and the transferred metal gratings were then etched slightly to eliminate the residual layer. As a result, aligned metal wires (70 nm line/space width, 120 nm height) occupying an area of 3.0 cm x 2.5 cm were obtained. The maximum and minimum transmittances of a WGP replicated from a commercial Moxtek polarizer at 800 nm were 85% and 27%, respectively.
A number of methods can be used to fabricate patterns with features having dimensions <100 nm. These techniques, however, can require specialized equipment and are often restricted to a cleanroom environment. Nanofabrication can be made accessible to multiple users by using elastomeric molds or stamps to transfer high-resolution patterns into other materials. These techniques are inexpensive and can transfer patterns into functional materials and onto a number of surfaces. This review describes recent advances in fabricating nanostructures using these techniques.
We describe a technique for fabricating micron and submicron-sized polydimethylsiloxane (PDMS) patterns on electronic material substrates using decal transfer lithography (DTL) in conjunction with reactive ion-beam etching (RIE). We validate the use of this unconventional polymeric system as a suitable resist material for fabricating Si-based microelectronic devices. In this process, an O2/CF4 gas mixture was used to etch a supporting PDMS thin film that resides atop a closed-form decal polymer to reveal conventional resist structures. These structures provide an effective latent image that, in turn, provides for an extension of soft lithography as a form of multilayer lithography—one yielding submicron structures similar to those obtained from the conventional photochemical methods used to prepare such resists. This combined DTL/RIE patterning procedure was found to be compatible with commercially available planarization layers and provides a direct means for preparing high aspect ratio resist features. We illustrate the applicability of soft lithography as a means for fabricating electronic devices by using it to prepare model silicon-based thin-film transistors exploiting silicon-on-insulator wafer technology.
An increasing number of technologies require large-scale integration of disparate classes of separately fabricated objects into spatially organized, functional systems1-9. Here we introduce an approach for heterogeneous integration based on kinetically controlled switching between adhesion and release of solid objects to and from an elastomeric stamp. We describe the physics of soft adhesion that govern this process and demonstrate the method by printing objects with a wide range of sizes and shapes, made of single-crystal silicon and GaN, mica, highly ordered pyrolytic graphite, silica and pollen, onto a variety of substrates without specially designed surface chemistries or separate adhesive layers. Printed p-n junctions and photodiodes fixed directly on highly curved surfaces illustrate some unique device-level capabilities of this approach.
Nanoimprint is an emerging lithographic technology that promises high-throughput patterning of nanostructures. Based on the mechanical embossing principle, nanoimprint technique can achieve pattern resolutions beyond the limitations set by the light diffractions or beam scatterings in other conventional techniques. This article reviews the basic principles of nanoimprint technology and some of the recent progress in this field. It also explores a few alternative approaches that are related to nanoimprint as well as additive approaches for patterning polymer structures. Nanoimprint technology can not only create resist patterns as in lithography but can also imprint functional device structures in polymers. This property is exploited in several non-traditional microelectronic applications in the areas of photonics and biotechnology.
New developments, further details, and applications of imprint lithography are presented. Arrays of 10 nm diameter and 40 nm period holes were imprinted not only in polymethylmethacrylate (PMMA) on silicon, but also in PMMA on gold substrates. The smallest hole diameter imprinted in PMMA is 6 nm. All the PMMA patterns were transferred to a metal using a liftoff. In addition, PMMA mesa’s of a size from 45 nm to 50 μm were obtained in a single imprint. Moreover, imprint lithography was used to fabricate the silicon quantum dot, wire, and ring transistors, which showed the same behavior as those fabricated using electron (e)-beam lithography. Finally, imprint lithography was used to fabricate nanocompact disks with 10 nm features and 400 Gbits/in. 2 data density—near three orders of magnitude higher than current critical dimensions (CDs). A silicon scanning probe was used to read back the data successfully. The study of wear indicates that due to the ultrasmall force in tapping mode, both the nano-CD and the scanning probe will not show noticeable wear after a large number of scans. © 1997 American Vacuum Society.
Nanoimprint lithography, a high‐throughput, low‐cost, nonconventional lithographic method proposed and demonstrated recently, has been developed and investigated further. Nanoimprint lithography has demonstrated 25 nm feature size, 70 nm pitch, vertical and smooth sidewalls, and nearly 90° corners. Further experimental study indicates that the ultimate resolution of nanoimprint lithography could be sub‐10 nm, the imprint process is repeatable, and the mold is durable. In addition, uniformity over a 15 mm by 18 mm area was demonstrated and the uniformity area can be much larger if a better designed press is used. Nanoimprint lithography over a nonflat surface has also been achieved. Finally, nanoimprint lithography has been successfully used for fabricating nanoscale photodetectors, silicon quantum‐dot, quantum‐wire, and ring transistors. © 1996 American Vacuum Society
A simple yet robust method for large-area patterning of polymer films, capillary force lithography, is presented. The method, which combines the essential features of imprint lithography and microcontact printing, allows the replication of features down to 100 nm.
We have fabricated a nanowire polarizer for optical communications by using nanoimprint lithography (NIL). The nanowire polarizer has aluminum metal gratings with a period of 200 nm on a glass substrate. We used a SiO 2 stamp [1] for the patterning of the imprint resist mask on an aluminum film, Laser interference lithography (LIL) was introduced to achieve grating patterns with 200-nm period on the stamp. The polarization extinction ratio (PER) of the fabricated device was 38 decibel (dB) at a wavelength of 1550 nm. NIL is a promising and cost-effective way to fabricate subwavelength-period optical elements.
▪ Abstract Soft lithography represents a non-photolithographic strategy based on selfassembly and replica molding for carrying out micro- and nanofabrication. It provides a convenient, effective, and low-cost method for the formation and manufacturing of micro- and nanostructures. In soft lithography, an elastomeric stamp with patterned relief structures on its surface is used to generate patterns and structures with feature sizes ranging from 30 nm to 100 μm. Five techniques have been demonstrated: microcontact printing (μCP), replica molding (REM), microtransfer molding (μTM), micromolding in capillaries (MIMIC), and solvent-assisted micromolding (SAMIM). In this chapter we discuss the procedures for these techniques and their applications in micro- and nanofabrication, surface chemistry, materials science, optics, MEMS, and microelectronics.
We demonstrate a patterning method capable of producing features of submicron scale based on the transfer of a metal film from a stamp to a substrate assisted by cold welding. The patterned metal film can be used as an etch mask to replicate the pattern on the substrate, or the film itself can serve as contact electrodes for a wide range of electronic devices. We demonstrate the versatility of the technique by fabricating a polymer grating on SiO2 with lateral dimensions <80 nm and a pattern resolution approaching 10 nm, and by fabricating organic solar cells and pentacene channel organic thin-film transistors with channel lengths as short as 1 μm.
We introduce adhesive force lithography (AFL), a detachment-based method for patterning metal surface. In this method, all the polymer layer except for the desired pattern gets lifted up from the metal surface. The craze microstructure unique to thin polymer films on the order of 102 nm is utilized for this AFL along with a difference in adhesive force at two interfaces. Poly(urethaneacrylate) mold, which has a high enough work of adhesion with polymer, makes AFL effective. This technique is purely additive, fast ( ∼ 10 s contact time), and applicable to large area patterning (10 cm×10 cm).
Dry formation of polymer hole injection layer is introduced as an effective method for improving the performance of top emitting organic light emitting diodes (TOLEDs). This method involves transferring a metal/polymer bilayer to the surface of organic layers of the device by pressing. An added advantage of this method is the ability to pattern the anode in the transfer process. Fabrication of the inverted TOLED by this method results in a drastic reduction of the turn-on voltage, from 14.5 to 6.5 V, when compared with a reference.
Whole device printing is presented for realizing full colour displays with red (R), green (G) and blue (B) organic light emitting diodes (OLEDs). In this process, the whole OLED structure is transferred from a patterned mould to a glass substrate. Therefore, a simple step and repeat of the transfer of each of R, G and B OLED for RGB pixels completes the fabrication of the full colour display over a given area. A difference in the work of adhesion at two interfaces enables the transfer. A 'rigiflex' mould is used for the printing. It is rigid enough to allow sub-100 nm resolution and yet flexible enough for intimate contact with the glass substrate, which permits large area application.
The use of rigiflex lithography as an effective method of transferring the bilayer to a substrate was described. Rigiflex lithography allows to physically transfer nanostructures to a substrate at a pressure level that was reduced by almost an order of magnitude. It also allows to pattern nanostructures by a roller bilayer-transfer technique (BLT) with a cylindrical roller, suitable for high throughput. The temperature needed for the transfer is moderate enough to permit the step-and-repeat technique.
A new detachment patterning technique is applied to the fabrication of a green organic light-emitting diode (OLED). The method (applicable to organic and inorganic substrates) involves simply placing a patterned PDMS mold in conformal contact with the organic layer to be patterned, annealing at a temperature below the glass transition temperature for a period of time, and then removing the mold after cooling to room temperature. The parts of the organic layer in contact with the mold become detached from the substrate upon removing the mold.
A simple and economical method of patterning pentacene for organic thin-film transistors (OTFT) that involves a blanket deposition of pentacene on a mold and then transfer of the pentacene on the mold onto the active area of the OTFT, was investigated. This patterning technique did not required photolithography and it invoked no solvent, high temperature heating, or reactive ion etching. Pentacene was deposited to the desired thickness on a mold with a protruding feature that corresponds to a the active area. The hardness of the mold made it possible to fabricate sub-100 nm patterns, while the flexibility of the mold allowed for conformal contact and reduced processing pressure. The result showed that the electronic performance of an OTFT that was fabricated by transfer patterning was similar to that of an OTFT that was fabricated by the shadow-mask technique. This approach could be applicable to other organic semiconductors.
We have demonstrated subwavelength aluminum (Al) gratings with a period of 200 nm using nanoimprint lithography (NIL) and reactive ion etching (RIE). Al dry etching was attempted using the etch mask formed by NIL. The SiO2 stamp with a size of 5 × 5 cm2 was fabricated using laser interference lithography and RIE. The NIL process was optimized on Al/glass substrate and various imprint resists were tested for the Al etching. We could obtain a vertical etching profile and an etch selectivity of 2 with mrI-8020 imprint resist. The Al RIE combined with NIL will be useful for the realization of subwavelength Al gratings with a high aspect ratio.
A simple, one-step method is developed to fabricate various nanostructures such as
nanoholes and nanolines based on the detachment of an organic polymer film
in contact with a patterned polyurethane acrylate mould under a low physical
pressure (1–2 bar) at ambient conditions. Calculation of the work of adhesion
based on contact angle measurements indicates that the adhesion strength at
the organic/mould interface is greater than that at the organic/substrate
interface, resulting in a successful detachment without any surface modifications.
4,4'-bis[N-1-napthyl-N-phenyl-amino]biphenyl (NPB) is used as the organic film owing to its low cohesion energy
and stability in air. Nanoholes as small as 150 nm and nanolines as small as 50 nm have been
fabricated using this approach. These nanostructures are used as a template for selective
deposition of silver nanoparticles and a wet/dry etch resist for further pattern transfer.
A new soft-lithographic method for micropatterning polymeric resists, Decal Transfer Microlithography (DTM), is described. This technique is based on the transfer of elastomeric decal patterns via the engineered adhesion and release properties of a compliant poly(dimethylsiloxane) (PDMS) patterning tool. An important feature of the DTM method is the exceptionally broad spectrum of design rules that it embraces. This procedure is capable of transferring micron to submicron-sized features with high fidelity over large substrate areas and potentially simplifies to a significant degree the requirements for effecting multiple levels of registration. The DTM method offers some potential advantages over other soft-lithographic patterning methods in that it is amenable to transferring resist patterns with both open and closed forms, negative and positive image contrasts, and does so for a wide variety of aspect ratios and a significant range of pattern pitches that can be accommodated without degradation due to mechanical distortions of the pattern transfer tool. The most significant advance embodied in the DTM method, however, is that it offers useful new capabilities for the design and fabrication of advanced planar and 3D microfluidic assemblies and microreactors.
We describe two new procedures that appear to hold significant promise as means for patterning thin-film microstructures of the coinage metals (Cu, Ag, Au). A feature central to both is the modification of their surfaces to promote the adhesive transfer of PDMS thin-film microstructures, a material suitable for use as resist layers in large-area patterning, using Decal Transfer Lithography (DTL). The present work provides a significant extension of the capabilities of DTL patterning, providing general protocols that can be used to transfer decal resists to essentially any substrate surface. The first method involves the functionalization of a surface, specifically those of gold and silver films with a thiol-terminated silane coupling agent, (mercaptopropyl)trimethoxysilane. This self-assembled monolayer, when hydrolyzed to its silanol form, provides a robust adhesion-promoting layer suitable for use in DTL patterning. The second method exploits the surface chemistry provided by the deposition of a nanoscale silicon dioxide thin-film capping layer using e-beam evaporation. This procedure provides an exceptional method for patterning large-area, thin-film microstructures of Cu-one compatible with micrometer-scale design rules-that are essentially defect free. Both surface modification strategies enable high-quality poly(dimethylsiloxane) decal transfers, and as the current work shows, these structures are suitable for large-area micrometer-sized patterning of gold, silver, and copper thin films via both wet-etching and lift-off procedures.
We describe a novel soft-lithographic technique possessing broad utility for the fabrication of large area, nanoscale ( approximately 100 nm) multilayer resist structures on electronic material substrates. This additive patterning method transfers ultrathin poly(dimethylsiloxane) (PDMS) decals to an underlying SiO(2)-capped organic planarazation layer. The PDMS patterns serve as a latent image through which high-quality multilayer resist structures can be developed using reactive ion-beam etching.
We have discovered a micro/nanopatterning technique based on the patterning of a PDMS membrane/film, which involves bonding a PDMS structure/stamp (that has the desired patterns) to a PDMS film. The technique, which we call "bond-detach lithography", was demonstrated (in conjunction with other microfabrication techniques) by transferring several micro- and nanoscale patterns onto a variety of substrates. Bond-detach lithography is a parallel process technique in which a master mold can be used many times, and is particularly simple and inexpensive.
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