Seok-min Kim

Continuous ultraviolet roll nanoimprinting process for replicating large-scale nano- and micropatterns

With the increasing demand for large-scale nano- and micropatterns in the field of digital displays, nano- and micropattern replication technology has become a research priority. In this study, a continuous ultraviolet (UV) roll nanoimprinting process using a pattern roll stamper for the replication of large-scale nano- and micropatterns was designed and constructed. Several flexible nano- and micropatterns with large areas were fabricated and analyzed as tests of this continuous UV imprinting process.

Replication qualities and optical properties of UV-moulded microlens arrays

UV-moulded microlens arrays with high replication quality were fabricated using a parametric design method. It is important to maximize replication quality because one can obtain replicated micro-optical components with desired properties by accurate control of the shape. In this study, nickel mould inserts for microlens arrays with lenses having diameters between 3 and 230??m were fabricated by an electroforming process. The reflow method was used to make the master for the metallic mould insert. A UV-moulding system was designed and constructed, and the effects of compression pressure and UV-curing dose on the replication quality of UV-moulded microlens arrays with a diameter of 14??m were examined experimentally. Finally, geometrical and optical properties of the replicated microlens arrays were measured and analysed.

Development of an ultraviolet imprinting process for integrating a microlens array onto an image sensor.

We analyzed the feasibility of using a UV imprinting process to integrate a microlens array onto an image sensor. A simulated wafer-scale image sensor chip array was fabricated for the implementation. A microlens array with a side length of 4.63 microm, a sag height of 1.416 microm, and a residual-layer thickness of 1.15 microm was integrated onto the simulated image sensor. The standard deviations of the sag height and the residual-layer thickness were less than 0.038 microm and less than 0.164 microm, respectively, in whole-wafer-scale samples. The measured beam spot size (FWHM) at the imaging plane was 1.19 microm, with a uniform intensity distribution and pitch in the array.

Replication of micro-optical components by ultraviolet-molding process

An experimental method is presented to maximize the replication quality of UV-molded micro-optical components. It is important to maximize the replication quality to obtain the replicated micro-optical components with the desired properties by accurate control of the shape. We suggest a simple technique to avoid micro air bubbles. The effects of the UV-curing dose and the compression pressure on the replication quality of UV-molded structures are examined experimentally. Finally, as a practical application of the process design method, microlens arrays with diameters between 30 and 230 μm were fabricated by the presented method, and the replication quality and the optical properties of the replicated microlens are measured and analyzed.

Nanoimprinting of conductive tracks using metal nanopowders

A method for metal nanopowder imprinting is proposed as a patterning process for conductive tracks, which is inexpensive and scalable down to submicrometers. To examine the feasibility of the proposed method, conductive tracks with widths of submicrometers to a few tens of micrometers were formed using a thermal nanoimprinting system, and the effects of processing conditions on the degree of replication and the degree of sintering and the electric conductivity of imprinted conductive tracks were analyzed.

Design Optimization of Structural Parameters for Highly Sensitive Photonic Crystal Label-Free Biosensors

The effects of structural design parameters on the performance of nano-replicated photonic crystal (PC) label-free biosensors were examined by the analysis of simulated reflection spectra of PC structures. The grating pitch, duty, scaled grating height and scaled TiO2 layer thickness were selected as the design factors to optimize the PC structure. The peak wavelength value (PWV), full width at half maximum of the peak, figure of merit for the bulk and surface sensitivities, and surface/bulk sensitivity ratio were also selected as the responses to optimize the PC label-free biosensor performance. A parametric study showed that the grating pitch was the dominant factor for PWV, and that it had low interaction effects with other scaled design factors. Therefore, we can isolate the effect of grating pitch using scaled design factors. For the design of PC-label free biosensor, one should consider that: (1) the PWV can be measured by the reflection peak measurement instruments, (2) the grating pitch and duty can be manufactured using conventional lithography systems, and (3) the optimum design is less sensitive to the grating height and TiO2 layer thickness variations in the fabrication process. In this paper, we suggested a design guide for highly sensitive PC biosensor in which one select the grating pitch and duty based on the limitations of the lithography and measurement system, and conduct a multi objective optimization of the grating height and TiO2 layer thickness for maximizing performance and minimizing the influence of parameter variation. Through multi-objective optimization of a PC structure with a fixed grating height of 550 nm and a duty of 50%, we obtained a surface FOM of 66.18 RIU−1 and an S/B ratio of 34.8%, with a grating height of 117 nm and TiO2 height of 210 nm.

Design of microlens illuminated aperture array fabricated by aligned ultraviolet imprinting process for optical read only memory card system

A microlens illuminated aperture array (MLIAA) was designed for the multiprobe optical read only memory card system. As a method to integrate the microlens array (MLA) with the aperture array containing 1000×1000 apertures, an aligned ultraviolet imprinting process was used to satisfy the system objectives of reduced focal length and reduced spot size. An analysis using diffraction theory was performed to obtain the design tolerances for both MLIAA and the imprinting process. The maximum intensity of the optical probes at the Talbot [Philos. Mag. 9, 401 (1836)] position from the fabricated MLIAA was 12 times higher than that from the aperture array without a MLA.

A programmable nanoreplica molding for the fabrication of nanophotonic devices

The ability to fabricate periodic structures with sub-wavelength features has a great potential for impact on integrated optics, optical sensors, and photovoltaic devices. Here, we report a programmable nanoreplica molding process to fabricate a variety of sub-micrometer periodic patterns using a single mold. The process utilizes a stretchable mold to produce the desired periodic structure in a photopolymer on glass or plastic substrates. During the replica molding process, a uniaxial force is applied to the mold and results in changes of the periodic structure, which resides on the surface of the mold. Direction and magnitude of the force determine the array geometry, including the lattice constant and arrangement. By stretching the mold, 2D arrays with square, rectangular, and triangular lattice structures can be fabricated. As one example, we present a plasmonic crystal device with surface plasmon resonances determined by the force applied during molding. In addition, photonic crystal slabs with different array patterns are fabricated and characterized. This unique process offers the capability of generating various periodic nanostructures rapidly and inexpensively.

β-catenin mediates the inflammatory cytokine expression induced by the Der p 1 house dust mite allergen

The modulations of β-catenin were analyzed during the inflammatory response induced by the Der p 1 house dust mite allergen. Der p 1 induced the dose-dependent expression of inflammatory cytokines, including interleukin (IL)-6, IL-8, monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-α (TNF-α) in THP-1 human monocytic cells. The mRNA expression levels of β-catenin were not altered, however protein levels increased following Der p 1 treatment, demonstrating that β-catenin was modulated by post-transcriptional processes. It was also revealed that nuclear β-catenin levels were significantly increased while cytoplasmic β-catenin levels were reduced, which demonstrated the nuclear translocation of β-catenin by the Der p 1 allergen. Glycogen synthase kinase 3β (GSK3β), a regulator of β-catenin stability, was demonstrated to be phosphorylated following Der p 1 treatment. When β-catenin was knocked down by the transfection of its small interfering RNA (siRNA), inflammatory cytokine expression as well as nuclear factor-κB (NF-κB) activity, which were induced by Der p 1 treatment, were all significantly reduced. The results demonstrated that Der p 1-induced inflammatory responses were mediated by β-catenin.

Design and fabrication of a diffractive optical element for the objective lens of a small form factor optical data storage device

The demand for small and high-capacity optical data storage devices has rapidly increased. The areal density of the optical disk is increased using a higher numerical aperture objective lens and a shorter wavelength source. We have designed and fabricated a wafer-scale stacked micro objective lens with a numerical aperture of 0.85 and a focal length of 0.467 mm for the 405 nm blue?violet laser. To compensate the chromatic aberration of the objective lens, a diffractive optical element (DOE) was used. Among the various fabrication methods for micro DOE, the UV-replication process is more suitable for mass-production. In this study, an eight-stepped DOE pattern as a master was fabricated by photolithography and reactive ion etching processes. A flexible mold was fabricated for improving the releasing properties and shape accuracy in the UV-molding process. In the replication process, the effects of exposing time and applied pressure on the replication quality were analyzed. Finally, the shapes of the master mold and the molded pattern were measured by an optical scanning profiler. The deviation between the master and the molded DOE was less than 0.1 ?m. The efficiency of the molded DOE was measured by a DOE efficiency measurement system which consists of a laser source, a sample holder, an aperture and an optical power meter, and the measured value was 84.5%.