Fabrication of antireflection nanostructures by hybrid nano-patterning lithography

Antireflection (AR) nanostructures are fabricated on a glass substrate using hybrid nano-patterning lithography (H-NPL) consisting of nanosphere lithography (NSL) and UV-nanoimprint lithography (UV-NIL). The shape and diameter of the AR nanostructures were controlled by fabricating Si masters with different RIE conditions. The shapes of the AR nanostructures were a pillar-type and a corn-type. The diameters of the AR nanostructures were about 350 and 250 nm, respectively. AR nanostructures were successfully nanoimprinted on glass in accordance with Si master prepared by NSL. The pillar-type AR nanostructure with diameter of 350 nm exhibited the transmittance of over 98% in the wavelength range from 1100 to 2200 nm. From the results, the fabricated AR nanostructures demonstrate the possibility to improve the efficiency of optoelectronic devices such as a photo-detector and an IR-LED.     

Fabrication of carbon nanotube arrays for field emission and sensor devices by nanoimprint lithography

This work brings forth the idea of incorporating insulation in the resist used for ultraviolet (UV) curing nanoimprint lithography (NIL). Carbon nanotubes (CNTs) are grown in the space between two insulated resist patterns on the conductive substrate to make CNTs arrays. Two imprinting processes, soft UV curing NIL with DRPPR process and novel NIL without cured residual resist, are presented to achieve the insulation patterns. First the fabricating process is performed using a polydimethylsiloxane (PDMS) stamp. Subsequently, inductively coupled plasma (ICP) is essential to wipe off the residual resist film. To avoid the ICP process, a novel UV curing NIL is presented. Its special hard quartz stamp with chrome shelter can protect the residual resist film out of curing during the UV exposure process, and the uncured resist can be easily removed by ultrasonic vibration in organic solutions. The CNT arrays are prepared on the patterned substrates by the pyrolysis of iron phthalocyanine (FePc). Field emission experiments reveal that the turn-on field of those CNTs arrays is low to 1.3 V/um.     

Fabrication and characterization of Co-Pt nanodot arrays by nanoimprint lithography and electrodeposition

Co-Pt nanodot arrays of 50 nm in diameter and 100 nm pitch were fabricated by nanoimprint lithography and electrodeposition process. A polymer mold used was replicated from a Si master mold with nanopatterns which were fabricated by EBL and ICP-RIE, where hydrophobic surface of these was achieved by FOTS coating. UV-NIL was successfully performed under pressures of 5 MPa for 5 min with an UV exposure time of 30 s, where the substrate was Ru (30 nm)/NiFe (10 nm)/Ta (5 nm)/Si (1 0 0). The size of patterns was measured at 53 nm in diameter, 25 nm in height, 100 nm in pitch. Finally, Co-Pt nanodot arrays were galvanostatically electrodeposited and characterized. The size and the composition of these arrays were measured to be 50 nm in diameter and 100 nm in pitch and Co-23.6 at.% Pt, respectively. According to MFM analysis, these arrays for the remnant states represent a single domain structure of perpendicular direction with a magnetic field, where a field of 15 kOe was applied perpendicular to the sample plane. These results show that for the Co-Pt dot arrays of 50 nm diameter perpendicular magnetic signal can be recorded and switched.     

Fabrication of low-cost mold and nanoimprint lithography using polystyrene nanosphere

The periodic arrays of nanostructure were successfully patterned on Si wafers by ultraviolet nanoimprint lithography (UV-NIL) using nanosphere lithography (NSL). Two-dimensional (2D) well ordered self-assembled arrays were obtained on Si wafer by using nanosphere and the tilted-drain method. We tried to combine two techniques and hard mold of Si mold for NIL and polymer mold of acrylate-based polymer were fabricated by NSL. The Si master mold and polymer mold were formed by Cr lift-off and ICP-RIE process. The surface has a low surface energy at the interface with 1H, 1H, 2H, 2H-perfluorooctyl-trichlorosilane (FOTS) vapor-coating, which can eliminate the problem of the adherence to the surface of the mold during demolding. Finally, nanopatterns were formed by UV-NIL, where the residual layer was not observed.     

The direct nano-patterning of ZnO using nanoimprint lithography with ZnO-sol and thermal annealing

Nano-patterned ZnO layer was fabricated by ZnO-sol imprinting with a polymeric mold, followed by annealing. Instead of polymer based imprint resin, ZnO-sol was used as an imprint resin. During the imprinting process, the organic solvent in the ZnO-sol was absorbed into a polymeric mold and thus, ZnO-sol was converted to ZnO-gel. These patterns were subsequently annealed at 650 °C for 1 h in atmospheric ambient to form ZnO patterns. X-ray diffraction (XRD) and photoluminescence (PL) confirmed that ZnO-gel was completely converted into ZnO by annealing. Using this ZnO-sol imprinting method, ZnO nano-patterns, as small as 50 nm, were fabricated on Si and oxidized Si wafer substrates. The ZnO nano-patterns were characterized using scanning electron microscopy (SEM) and Transmission electron microscopy (TEM).     

Fabrication of multi-dimensional colloid crystals on raised surfaces via reversal nanoimprint lithography

Fabrication of multi-dimensional colloidal crystals on raised polymer substrate has been achieved by reversal nanoimprint technique. The combine effects of the feature size of the mold, particle diameter and imprinting steps control ordering of the colloidal particles. It is shown that using ‘Reversal nanoimprint lithography’, 3D colloidal particles can be selectively patterned on soft (polymer) substrates. Reversal nanoimprint lithography offers a relatively easy, fast and versatile method for patterning of colloidal particles.     

Influence of PEN thermal properties on flexible film patterned by nanoimprint lithography

Nanoimprint lithographies (NIL) are very promising for NIL applications on flexible plastic films. In this paper we present some studies and developments of the imprint of polyethylene naphthalate (PEN) films. Different NIL processes are developed successfully; they correspond to the imprint of different chemical phases of the material: semicrystalline, amorphous, and melt. The thermal properties of the film are analyzed, and related to imprint results, which demonstrate that high reproducibility and uniformity are obtained. Moreover, the imprint of such flexible films is much more promising since it avoids NIL limitations commonly observed on semiconductor substrates.     

The influence of stamp deformation on residual layer homogeneity in thermal nanoimprint lithography

This work studies the relation between the residual layer thickness and the patterned area size, fill factor and stamp thickness for identical stamps with opposite polarity (positive and negative) made in silicon and nickel. Important and different variations in the homogeneity of the residual layer are obtained in comparison with the values predicted by the theory. This will help to optimize stamp designs and choose appropriate process setups and parameters for nanoimprint with improved pattern transfer capability.     

Fabrication of sub-micron high aspect ratio diamond structures with nanoimprint lithography

Polycrystalline diamond with optical quality has been patterned using nanoimprint lithography. Nanoimprint lithography is a rather new method for fabrication of resist structures with features sizes down to at least 20 nm. The pattern used in this article is a grating with a period of 600 nm and a fill factor of 0.5. Using plasma etching the nanoimprinted grating is etched into a freestanding diamond substrate. We have accomplished the fabrication of 300 nm diamond features with a depth of about 2 μm, which corresponds to an aspect ratio of 7.     

UV nanoimprint lithography of sub-100 nm nanostructures using a novel UV curable epoxy siloxane polymer

We reported the replication of sub-100 nm nanostructures by an ultraviolet (UV) nanoimprint lithography (NIL) technique. We used a novel UV curable epoxy siloxane polymer as the NIL resist to achieve features as small as 50 nm. The polymeric soft molds for the NIL were fabricated by casting toluene diluted poly(dimethyl-siloxane) (PDMS) on the hydrogensilsesquioxane (HSQ) hard mold. The NIL results were characterized by using a scanning electron microscope and an atomic force microscope. Our results illustrate that, with the epoxy siloxane resist, the 50 nm HSQ features on the hard mold can be successfully replicated using PDMS soft molds.     

Fabrication and characterization of bilayer metal wire-grid polarizer using nanoimprint lithography on flexible plastic substrate

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.     

Fabrication of sub-micron 3-D structure using duo-mold UV-RIL process

3-D polymeric micro- and nano-structures were fabricated by the reversal imprint lithography technique using nano-patterned molds. A surface-treated quartz mold and a water-soluble poly vinyl alcohol (PVA) mold were used to make dual-side patterned, 2-D polymeric, micro- and nano-structures. First, UV-curable, polymeric resin was dropped onto the quartz mold, which was then covered with the PVA mold. The two stacked molds were pressed and exposed to UV-light to cure the resin. The cured polymeric resin (the reversal layer) was easily released from the quartz mold, because the surface of the latter was treated with an anti-stiction layer. The reversal layer, bound to the PVA mold, was transferred to a Si substrate by applying a thin layer of a UV-curable bonding agent. After bonding the reversal layer, the PVA mold was selectively removed by dipping in water. As a result, the dual-side patterned, thin polymeric 2-D structure was formed on the silicon substrate and, by repeating this process, 2-D nano-structures were stacked to form a 3-D nano-structure. By making use of the anti-stiction-treated, quartz mold and the water-soluble characteristic of the PVA material, the reliable release of the reversal layer was achieved.     

The use of high glass temperature polymers in the production of transparent, structured surfaces using nanoimprint lithography

Polymers with high glass transition temperatures, fluorinated ethylene propylene copolymer (FEP) and poly(ethylene naphthalate) (PEN), have been used in imprint lithography as a protective support layer and as a secondary mould, to imprint superficial structures into a polymer with a lower glass transition temperature, namely poly(methyl methacrylate) (PMMA). As a support layer, FEP replaces fragile silicon based supports for the production of freestanding, structured sheets of PMMA, useful, for example, in biomedical applications where transmittance optical microscopy is required. Secondary PEN moulds, produced by imprinting using silicon-based primary moulds, have been used to transfer sub-micrometer tall structures to a freestanding PMMA sheet. Similarly, hole structures, with different dimensions, have been embossed in both sides of a PMMA sheet simultaneously.     

Fabrication of Ge2Sb2Te5 based PRAM device at 60 nm scale by using UV nanoimprint lithography

Phase change memory is one of the most promising non-volatile memory for the next generation memory media due to its simplicity, wide dynamic range, fast switching speed and possibly low power consumption. Low power consuming operation of phase change random access memory (PRAM) can be achieved by confining the switching volume of phase change media into nanometer scale. Nanoimprint lithography is an emerging lithographic technique in which surface protrusions of a mold such as sub-100 nm patterns are transferred into a resin layer easily. In this study, crossbar structures of phase change device array based on Ge₂Sb₂Te₅ were successfully fabricated at 60 nm scale by two consecutive UV nanoimprint lithography and metal lift-off process, which showed on/off resistance ratio up to 3000.     

A mathematical model for slip phenomenon in a cavity-filling process of nanoimprint lithography

Squeeze flow theory has been used as an effective tool to clarify how and which process conditions determine cavity-filling behavior in nanoimprint lithography (NIL). Conventional squeeze flow models used in NIL research fields have assumed no-slip conditions at the solid-to-liquid boundaries, that is, at the stamp-to-polymer or polymer-to-substrate boundaries. The no-slip assumptions are often violated, however, in micrometer- to nanometer-scale fluid flow. It is therefore necessary to adopt slip or partial slip boundary conditions. In this paper, an analytical mathematical model for the cavity-filling process of NIL that takes into account slip or partial slip boundary conditions is derived using squeeze flow theory. Velocity profiles, pressure distributions, imprinting forces, and evolutions of residual thickness can be predicted using this analytical model. This paper also aims to elucidate how far the slip phenomenon is able to promote the process rate.     

酶蚀明胶法制作折射微透镜阵列

提出一种利用蛋白酶溶液刻蚀重铬酸铵明胶制作微光学元件的新方法。这种方法具有制作工艺简单、无需昂贵设备等优点,用此方法实际制作了具有良好连续面形的微透镜阵列,并给出了测量结果。     

Fabrication of high density nano-pillar type phase change memory devices using flexible AAO shaped template

In this study, the high density nano-pillar type phase change memory was fabricated using duplicating nano-patterns of the anodic alumina oxide (AAO) by nanoimprint process. The high density nano-hole array of AAO template was transferred to the flexible PVC polymer template using hot embossing method. To use the flexible AAO shaped template for UV-NIL, the high density nano-pillar type Ge₂Sb₂Te₅ patterns were fabricated, and the electrical properties of the device were evaluated by conducting atomic force microscopy, connected electrical measurement system. To use the flexible AAO shaped template for UV-NIL, high density GST pattern could be fabricated even on the flexible polyimide (PI) substrate.     

Fabrication of periodic square arrays by angle-resolved nanosphere lithography

We investigate the fabrication of periodic square arrays of solid gold islands by angle-resolved nanosphere lithography (ARNSL) in conjunction with thermal evaporation and etching. By varying θ (the tilt angle between the direction of gold deposition beam and the substrate surface normal) and ? (the substrate rotation angle about the beam axis), adjacent islands on a deposited hexagonal gold array will have a constant and periodic difference in height. Upon etching, this height bias will result in the shorter structures being removed to produce an array with a different symmetry from the original hexagonal symmetry of the parent mask. By depositing at three directions of ? = 0°, 120° and −120° with a constant θ = 20°, experimental results show that deposited two-dimensional gold periodic arrays will have a measurable difference in height between adjacent islands. Etching of the resulting patterns produced periodic near-square arrays with triangular nanostructures. Thus the combination of ARNSL and etching can allow selective periodic nanostructures to be removed, increasing the diversity of array symmetries available through nanosphere lithography.     

Advantages of nonuniform arrays using root-MUSIC

In this paper, we consider the Direction-Of-Arrival (DOA) estimation problem in the Nonuniform Linear Arrays (NLA) case, particularly the arrays with missing sensors. We show that the root-MUSIC algorithm can be directly applied to this case and that it can fully exploit the advantages of using an NLA instead of a Uniform Linear Array (ULA). Using theoretical analysis and simulations, we demonstrate that employing an NLA with the same number of sensors as the ULA, yields better performance. Moreover, reducing the number of sensors while keeping the same array aperture as the ULA slightly modifies the Mean Square Error (MSE). Therefore, thanks to the NLA, it is possible to maintain a good resolution while decreasing the number of sensors. We also show that root-MUSIC presents good performance and is one of the simplest high resolution methods for this type of arrays. Closed-form expressions of the estimator variance and the Cramer–Rao Bound (CRB) are derived in order to support our simulation results. In addition, the analytical expression of the CRB of the NLA to the CRB of the ULA ratio is calculated in order to show the advantages of the NLA.     

Low cost, rapid fabrication of durable molds of grating arrays for nanoimprint lithography

This study proposes a new fabrication method for the mold of a sub-micron grating array used in the nanoimprint lithography process. In general, the mold of a sub-micron grating array is fabricated by electron beam lithography (EBL) and reactive ion etching (RIE), and then, nanoimprint lithography (NIL) is used to achieve the required amount of replication. Such a method is expensive and has a low throughput, and the pattern is limited by the original mold. In this paper, we constructed a durable mold of a sub-micron grating array with good adaptability, using a commercial epoxy grating (EG) and a hybrid inorganic/organic sol-gel material combined with nanoimprint lithography and photolithography. Due to its low cost and ease of use, this method is suitable for both laboratory research and mass production without the need for expensive equipment like EBL or RIE.