Yeong-Eun Yoo

Machining characteristics of complex prism pattern on electroplated roll by copper

Abstract The BLU (back light unit) is the core component of the LCD for notebook, mobile-phone, navigation, as well as large sized TV, PID (public information display), etc. In order to enhance optical efficiency of LCD, optical films with the uniform prism patterns have been used for BLU by stacking two films up orthogonally. In this case, light interference-phenomenon occurred such as Morie, wet-out, u-turning, etc. It caused several problems such as low brightness, spots and stripes in LCD. Recently, the high-luminance micro complex prism patterns are actively studied to avoid the light interference-phenomenon and enhance the optical efficiency. In this study, the roll master to manufacture complex micro prism pattern film was machined by using the high precision lathe. The machined patterns on the roll master were 50, 45, 40, 35, 30, 25, 20, 15, 10 and 5 μm in the pitch with 25.0, 22.5, 20.0, 17.5, 15.0, 12.5, 10.0, 7.5, 5.0 and 2.5 μm in the peak height, respectively. The roll was 2u2008000 mm in length and 320 mm in diameter. The electroplated roll by copper and the natural single crystal diamond tool was used for machining the patterns. The cutting force was measured and analyzed for each cutting condition by using the dynamometer. The chips and the surfaces after being machined were analyzed by SEM and microscope.

Injection molding of micro patterned PMMA plate

A plastic plate with surface micro features was injection molded to investigate the effect of pressure rise of melt on the replication of the micro structures. Prism pattern, which is used in many optical applications, was selected as a model pattern. The prism pattern is 50 μm in pitch and 108° in the vertical angle. The overall size of the plate was 335 mm×213 mm and the thickness of the plate varied linearly from 2.6 mm to 0.7 mm. The prism pattern was firstly machined on the nickel plated core block using micro diamond tool and this machined pattern core was installed in a mold for injection molding of prism patterned plate. Polymethyl methacrylate (PMMA) was used as a molding material. The pressure and temperature of the melt in the cavity were measured at different positions in the cavity and the replication of the pattern was also measured at the same positions. The results show that the pressure or temperature profile through the process depends on the shape and the size of the plate. The replication is affected by the temperature and pressure profiles at the early stage of filling, which is right after the melt reaches the position to be measured.

Automated lipid membrane formation using a polydimethylsiloxane film for ion channel measurements.

A black lipid membrane (BLM) is a powerful platform for studying the electrophysiology of cell membranes as well as transmembrane proteins. However, BLMs have disadvantages in terms of stability, accessibility, and transportability, which preclude their industrial applications. To resolve these issues, frozen membrane precursor (MP) was devised to improve the transportability and storability of BLMs. As described previously, MP is a storable and transportable platform that can be delivered to the point-of-use, where BLMs are automatically formed upon thawing at room temperature. However, MP has an inconsistent thinning-out time, ranging from 30 min to 24 h, as well as a low success rate of BLM formation (~27%), which make it undesirable for practical use. In our study, polydimethylsiloxane (PDMS) was introduced as a replacement for conventionally used Teflon film to control thinning-out time. As such, we used a PDMS thin-film, a porous-structured hydrophobic polymer, and squalene, a high viscosity solvent, to facilitate membrane formation, whereas the absorption rates of solvents were controlled to achieve consistent BLM formation time. We successfully reduced thinning-out time down to <1 h as well as enhanced the success rate of BLM formation to greater than 80%. Moreover, we demonstrated the feasibility of our platform for use in drug screening using gramicidin A and guanidine.

Nano sand filter with functionalized nanoparticles embedded in anodic aluminum oxide templates

Since the ancient Egyptians had used sand as filter media for water purification, its principle has been inherited through generations and it is still being used now in industries. The sand filter consists of sand literally, and the voids within the sand bed are the pores for filtration. Here we present a filtration principle using nanoparticles, so that the voids between the nanoparticles can be considered as effective pores in nanoscale dimension. Anodic aluminum oxide (AAO) membrane has been used as the working template, and the nanoparticles have been injected and embedded within the pores of the AAO template. Nanoparticles with multiple sizes have been used in order to obtain smaller voids. Moreover, the nanoparticles have been functionalized, or electrically charged, with arginine/phenylalanine (RF) peptide group. In this way, filtration performance for charged particles or molecules, such as methylene blue, has been enhanced. Consequently, this study is expected to provide a new principle for fabrication of nano voids, or nano pores, and for filtration in nanoscale dimension.

Study on Molding of a Nanostructured Plastic Plate and Its Surface Properties

Plastic substrates with high-aspect-ratio surface nanostructures were fabricated by hot embossing using an anodic aluminum oxidation (AAO) membrane, and by injection molding using an AAO plate as a mold master with a very dense array of nanoholes on the surface. A new method of rapidly heating the AAO plate was used to injection-mold high-aspect-ratio nanostructures 120 nm in diameter and 1.5 µm high. The AAO plate was heated to over 150 °C to fill the nanoholes with melted polymer and then cooled to below 70 °C to release the molded nanostructures from the holes. Hot embossing was used to replicate surface nanostructures with an average diameter of 200 nm and a height of 60 µm. The contact angle and adhesive force of the hot-embossed textured surface were measured to estimate the effect of the surface nanostructures on the hydrophobicity and dry adhesiveness.

100-nm-scale electroplated nickel stamper fabricated by e-beam lithography on chrome/quartz mask

We present a fabrication method of high aspect ratio 100nm-scale nickel stamper using e-beam writing on the chrome/quartz mask for the injection molding of optical grating patterns. Conventional nickel stamper is fabricated by nickel electroplating process which is followed by photoresist patterning. In the nickel electroplating process, seed layer deposition step is indispensable process. Seed layer of several tens or hundreds nanometer thickness may cause dimension error after fabrication of 100nm-scale nickel stamper. In this paper, we suggest new fabrication process of a 100nm-scale nickel stamper simplified the fabrication process using blank mask. By using chrome layer on blank mask as seed layer of electroplating process, we would like to simplify nickel stamper fabrication process and improve accuracy of the fabricated nickel stamper. Generally, blank mask used in lithography process consists of chrome layer and photoresist layer on quartz substrate. The chrome layer is composed of UV anti-reflection layer of CrON and UV shade layer of Cr(94%Cr-6%C). The UV anti-reflection layer of CrON plays a role of absorption of UV light in UV lithography process in order to prevent interference of incident light and reflection light. Conventional blank mask consists in order of PR, CrON, Cr and Quartz (PR/CrON/Cr/Qz). However, anti-reflection layer of CrON is electrically nonconducting material. Therefore, we have prepared blank mask without anti-reflection layer of CrON in order to use chrome layer as a seed layer of electroplating process. In the PR mold fabrication, we have changed the dosage of electron beam of 9μmC/cm2, 8.5μC/cm2, and 8μC/cm2 to find optimum e-beam dosage for the PR/Cr/Qz blank mask. At the optimum electron beam dosage condition of 8.5μC/cm2, PR molds on PR/Cr/Qz blank mask were fabricated within the maximum error of 24nm. The fabricated PR mold shows height of 300±10nm. The electric resistance of Cr layer in the fabricated PR mold of PR/Cr/Qz mask is measured as 100Ω. In the electroplating process, unfortunately, the 75nm-thick Cr layer underneath PR of PR/Cr/Qz mask was damaged due to the high resistance. In this work, we have deposited additional seed layer materials of Ni as thick as 100nm. Finally we got the resistance of 10Ω. Instead of 75nm-thick Cr layer, if we prepare 200nm-thick Cr layer PR/Cr/Qz blank mask, we can carry out electroplating process without additional deposition process of seed layer. After nickel electroplating process, the thickness of the fabricated nickel stamper was approximately 330±20μm. The minimum width of the fabricated nickel line was measured as 116±6nm. Using SPM (scanning probe microscope), we have measured the height of nickel line as 240±20nm. Finally we have fabricated 2.5-AR (Aspect Ratio) nickel stamper with the minimum width of 116±6nm. The fabricated 100nm-scale nickel stamper showed the maximum error of 20nm comparing the PR mold. Consequently, we have optimized electron-beam dosage for the PR/Cr/Qz blank mask and fabricated 100nm-scale nickel stamper of the optical grating patterns with 2.5-aspect ratio.

A study on arrangement characteristics of microparticles in sedimentation on flat and round substrates

Recent advances of microfabrication techniques have enabled diverse structures and devices on the microscale. This fabrication method using microparticles is one of the most promising technologies because it can provide a cost effective process for large areas. So, many researchers are studying modulation and manipulation of the microparticles in solution to obtain a proper arrangement. However, the microparticles are in sedimentation status during the process in many cases, which makes it difficult to control their arrangement. In this study, droplets containing microparticles were placed on a substrate with minimal force and we investigated the arrangement of these microparticles after evaporation of the liquid. Experiments have been performed with upward and downward substrates to change the direction of gravity. The geometry of substrates was also changed, which were flat or round. The results show that the arrangement depends on the size of particles and gravity and geometry of the substrate. The arr...

Wetting characteristics of the anodic aluminum oxide template and fabrication of cracks using ultraviolet curable resin solution

We have investigated the wetting characteristics of the anodic aluminum oxide (AAO) template with ultraviolet curable polymer resin. The wettability of the template depends on the pore size on the surface, where it is improved with smaller pores and vice versa. Plasma treatment on the surface of the template is used to improve the wettability and the adhesion of the cured polymer to the template. And we also introduce the cracks on the polymer layer for possible application as nano-sized cavities. The resin within the pore is cleaved during the curing process so that cavities or cracks could be made which are much smaller than the original pores of the AAO template.

Fabrication of Nanoscale Reusable Quartz Master for Nano Injection Molding Process

In this paper, we present reusable quartz master fabricated by electron-beam lithography and dry etching process of quartz, and results of injection molding based on the reusable quartz master for the manufacturing of nano-scale information media. Since patterned structures of photoresist can be easily damaged by separation (demolding) process of nickel stamper and master, a master with photoresist cannot be reused in stamper fabrication process. In this work, we have made it possible of the repeated use of master by directly patterning on quart in nickel stamper fabrication process. We have designed and fabricated four different specimens including 100nm, 140nm 200nm and 400nm pit patterns. In addition, both intaglio and embossed carving patterns are fabricated for each specimen. In the preliminary test of injection molding, we have fabricated polycarbonate patterns with varying mold temperature. We have experimentally verified the fabrication process of the reusable quart master and possibility of quartz master as direct stamper.

Development of Nano-Scale Reusable Quartz Master for the Fabrication of Nickel Stampers

In this paper, we present reusable quartz master fabricated by electron-beam lithography and dry etching process of quartz, and results of injection molding based on the reusable quartz master for the manufacturing of nano-scale information media. Since patterned structures of photoresist can be easily damaged by separation (demolding) process of nickel stamper and master, a master with photoresist cannot be reused in stamper fabrication process. In this work, we have made it possible of the repeated use of master by directly patterning on quartz in nickel stamper fabrication process. We have designed and fabricated four different specimens including 100nm, 140nm, 200nm and 400nm pit patterns. In addition, both intaglio and embossed carving patterns are fabricated for each specimen. In the preliminary test of injection molding, we have fabricated polycarbonate patterns with varying mold temperature. We have experimentally verified the fabrication process of the reusable quartz master and possibility of quartz master as direct stamper.Copyright