Tae-Jin Je

Development of Micro Pattern Cutting Simulation Software

The micro pattern machining on the surface of wide mold is not easy to be simulated by conventional software. In this paper, a software is developed for micro pattern cutting simulation. The 3d geometry of v-groove, rectangular groove, pyramid and pillar patterns are visualized by C++ and OpenGL library. The micro cutting force is also simulated for each pattern.

A Study of the Micro Pole Structure Fabrication and Application Technology by Micro End-Milling Process

In the fields of the mechanical micro machining, examples of fabrication and utilization of micro pole or shaft structures with high aspect ratio (AR) by using the micro end-milling process are extremely rare. The micro shaft with high aspect ratio is generally being produced by grinding, turning, wire electro discharge grinding (WEDG), electrical chemical machining (ECM), and so on. Micro pole structures, such as column, rectangular pole, and gear shaft, made by the micro end-milling process, can be utilized in industry. Examples include electrode for electrical discharge machining and micro mold for injection molding. In this research, machining factors and the process were analyzed. Machining experiments of various micro pole configurations were performed. Analysis of the change and effect of the cutting force under the machining conditions was carried out. An analytical study of the deformation of the micro pole caused by the cutting conditions and the cutting force, through the finite element method and ANSYS program, was carried out. Introduction A study of the method capable of effectively fabricating micro structures was carried out actively to fabricate micro machine parts such as micro motor and actuator, such micro optical element parts as grating and micro molds with micro shape.[1,2] The machining of micro shape structures through mechanical methods was applied to the machining and application of micro barrier rib or channel.[3] However, examples of the machining and utility of the applied structures of micro pole or shaft with high aspect ratio by using the end-milling process are very rare. At present, micro shaft with high aspect ratio is manufactured by the methods such as grinding, turning, WEDG and ECM. According to that, the fabrication of the applied structures for micro pole or shaft with high aspect ratio in micro end-milling process is expected to be used as electrode for electro discharge machining, mold for injection molding and so on. Therefore, the various studies related to them were carried out. Outline of the Applied Method and Deformation Analysis for Micro Pole There are two types in the fabrication methods for micro pole by using end-mill tool. The first method as shown in Fig.1 is that whenever a tool turns a circular pole or rectangular pole, the tool allows a regular cutting depth and makes a necessary pole through the method of step-by-step. If this method is used, because the cutting force is worked only in the region being cut at each step and is not worked in the pole previously fabricated, it is theoretically possible that the micro pole of infinite length is fabricated. However, the possible pole length in real fabrication is limited owing to various causes such as effective length, processing condition, processing circumstance and so on. Key Engineering Materials Online: 2004-02-15 ISSN: 1662-9795, Vols. 257-258, pp 453-458 doi:10.4028/www.scientific.net/KEM.257-258.453

Fabrication of refractive and diffractive plastic micro-optical components using microcompression molding

As the demand of the micro-optics in the field of optical data storage, optical communication, and digital display has been increased, it has become important to establish fabrication technology for plastic micro-optics, which have advantage mainly in manufacturing cost. Micromolding methods such as micro-injection molding and micro- compression molding are most suitable for mass production of plastic micro-optics with low cost. In the present study, plastic micro-optical components, such as refractive microlenses and diffractive optical elements (DOEs) with various grating patterns, were fabricated using micro- compression molding process. The mold inserts were made by ultra precision mechanical machining, and silicon etching. A micro compression molding system was designed and developed. Polymer films and powders were used as molded materials. Various defects found during molding were analyzed, and the process was optimized experimentally by controlling the governing process parameters such as histories of mold temperature and compression pressure. Micro lenses of hemispherical shape with 153micrometers radius of curvature were fabricated. The blazed and 4 stepped diffractive optical elements with 24micrometers pitch and 5micrometers depth were also fabricated. Optical and geometrical properties of plastic molded parts were measured by interferometric technique.

Size-Dependent Inertial Focusing Position Shift and Particle Separations in Triangular Microchannels

A recent study of inertial microfluidics within nonrectangular cross-section channels showed that the inertial focusing positions changes with cross-sectional shapes; therefore, the cross-sectional shape can be a useful control parameter for microfluidic particle manipulations. Here, we conducted detail investigation on unique focusing position shift phenomena, which occurs strongly in channels with the cross-sectional shape of the isosceles right triangle. The top focusing positions shift along the channel walls to the direction away from the apex with increasing Reynolds number and decreasing particle size. A larger particle with its center further away from the side walls experiences shear gradient lift toward the apex, which leads to an opposite result with changes of Reynolds and particle size. The focusing position shift and the subsequent stabilization of corner focusing lead to changes in the number of focusing positions, which enables a novel method for microparticle separations with high efficiency (>95%) and resolution (<2 μm). The separation method based on equilibrium focusing; therefore, the operation is simple and no complex separation optimization is needed. Moreover, the separation threshold can be easily modulated with flow rate adjustment. Rare cell separation from blood cell was successfully demonstrated with spiked MCF-7 cells in blood by achieving the yield of ∼95% and the throughput of ∼106 cells/min.

Comparison of Machinability Between PCD Tool and SCD Tool for Large Area Mirror Surface Machining Using Multi-tool by Planer

Mirror surface machining for large area flattening in the display field has a problem such as a tool wear and a increase in machining time due to large area machining. It should be studied to decrease machining time and tool wear. In this paper, multi-tool machining method using a PCD tool and a SCD tool was applied in order to decrease machining time and tool wear. Machining characteristics (cutting force, machined surface and surface roughness) of PCD tool and SCD tool were evaluated in order to apply PCD tool to flattening machining. Based on basic experiments, the PCD/SCD multi-tool method and the SCD single-tool method were compared through surface roughness and machining time for appllying large area mold machining.

Piezoelectric actuator based on stiffness control and stroke amplification for large lateral actuation

We present a piezoelectric actuator using stiffness control and stroke amplification mechanism in order to make large lateral displacement. In this work, we suggest stiffness control approach that generates lateral displacement by increasing the vertical stiffness and reducing the lateral stiffness using additional structure. In addition, an additional structure of a serpentine spring amplifies the lateral displacement like leverage structure. The suggested lateral PZT actuator (bellows actuator) consists of serpentine spring and PZT/electrode layer which is located at the edge of the serpentine spring. The edge of the serpentine spring prevents the vertical motion of PZT layer, while the other edge of the serpentine spring makes stroke amplification like leverage structure. The bellows actuator shows the maximum 3.93/spl plusmn/0.2/spl mu/m lateral displacement at 16V with 1Hz sinusoidal voltage input. In the frequency response test, the fabricated bellows actuator showed consistent displacement from 1 Hz to 1 kHz at 10V.

Off-centered Double-slit Metamaterial for Elastic Wave Polarization Anomaly

The polarization anomaly refers to the polarization transition from longitudinal to shear modes along an equi-frequency contour of the same branch, which occurs only in some anisotropic elastic media, but the lack of natural materials exhibiting desired anisotropy makes its utilization impossible for potential novel applications. In this paper, we present a unique, non-resonant type elastic metamaterial made of off-centered, double-slit unit cells. We show that its wave polarization characteristics that determine the desired anomalous polarization for a certain application are tailorable. As an application, a mode converting wedge that transforms pure longitudinal into pure shear modes is designed by the proposed metamaterial. The physics involved in the mode conversion is investigated by simulations and experiments.

A Study on Manufacturing Method of Nano-Micro Hybrid Pattern Using Indentation Machining Method and AAO Process

Micro/nano patterns for optical concentration and diffusion have been studied in the various fields such as displays, optics, and sensors. Conventional micro patterns were continuous and linear shapes due to using linear-type light sources, however, recently non-continuous patterns have been applied as point sources are used for dot-type light sources such as LEDs and OLEDs. In this study, a hybrid machining technology combining an indentation machining method and an AAO process was developed for manufacturing the non-continuous micro patterns having nano patterns. First, mirror-like surfaces (R a <20nm) of pure Aluminum substrates were obtained by optimizing cutting conditions. Then, The letter of ‘K’ consisting of the arrays of the micro patterns was manufactured by the indentation machining method which has a similar principle to indentation hardness testing. Finally, nano patterns were machined by AAO process on the micro patterns. Conclusively, a specific letter having nano-micro hybrid patterns was manufactured in this study.

Study on Machining High-Aspect Ratio Micro Barrier Rib Array Structures using Orthogonal Cutting Method

The micro barrier rip array structures have been applied in a variety of areas including as privacy films, micro heat sinks, touch panel and optical waveguide. The increased aspect ratio (AR) of barrier rip array structures is required in order to increase the efficiency and performance of these products. There are several problems such as burr, defect of surface roughness and deformation and breakage of barrier rip structure with machining high-aspect ratio micro barrier rip array structure using orthogonal cutting method. It is essential to develop technological methods to solve these problems. The optimum machining conditions for machining micro barrier rip array structures having high-aspect ratio were determined according to lengths ( and ) and shape angles ( and ) of diamond tool, overlapped cutting depths ( and ), feed rates (100 mm/s) and three machining processes. Based on the optimum machining conditions, micro barrier rib array structures having aspect ratio 30 was machined in this study.

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.