Papers by Author: Eung Sug Lee

Abstract: The objective of this research was to apply the artificial neural network algorithm to predict the surface roughness in high speed milling operation. Tool length, feed rate, spindle speed, cutting path interval and run-out were used as five input neurons; and artificial neural networks model based on back-propagation algorithm was developed to predict the output neuron-surface roughness. A series of experiments was performed, and the results were estimated. The experimental results showed that the applied artificial neural network surface roughness prediction gave good accuracy in predicting the surface roughness under a variety of combinations of cutting conditions.

Abstract: Recently, the trends of industrial products move towards more miniaturization, variety and mass production. Micro drilling which take high precision in cutting work is required to perform more micro hole and high speed working. Especially, Micro deep hole drilling is becoming more important in a wide spectrum of precision production industries, ranging from the production of automotive fuel injection nozzle, watch and camera parts, medical needles, and thick multilayered Printed Circuit Boards(PCB) that are demanded for very high density electric circuitry. The industries of precision production require smaller holes, high aspect ratio and high speed working for micro deep hole drilling. However the undesirable characteristics of micro drilling is the small signal to noise ratios, wandering motion of drill, high aspect ratio and the increase of cutting force as cutting depth increases. In order to optimize cutting conditions, an experimental study on the characteristics of micro deep hole machining processes using a tool dynamometer was carried out. And additionally, microscope with built-in an inspection monitor showed the relationship between burr in workpieces and chip form of micro drill machining.

Abstract: The reliable reproducibility of nano patterns or other nano structures is one of many issues in the nano-imprint lithography process. An important prerequisite for reproducibility is suitable adhesion properties of adhesion promoters or anti-sticking layer. In this study, rhombus shaped symmetrical probe with a flat tip was developed and fabricated using MEMS fabrication technique. For the experimental setup of the adhesion test using a UV curable PAK01 resin coated AFM tip with several adhesion promoters, the flat tip is covered by PAK01 resist using micromanipulator. Anti-sticking layers of silane agents were prepared on the tip by vapor deposition method. Adhesion force between various adhesion promoters (GPTS, APMDS, APTS, DUV30J, O2 planairzation) and PAK01 resist and the force between anti-sticking layer (FOTS, DDMS) and PAK01 resist were evaluated using the force-distance mode of AFM. Adhesion force of GPTS and FOTS are about 7180 nN and 1660 nN, respectively.

Abstract: The gate, source, and drain electrodes of organic thin-film transistor(OTFT) to use as a switching device for a flexible display was fabricated in microcontact printing process with hard poly(dimethylsiloxane)(h-PDMS) stamp. The OTFT with thin-film dielectric layer of parylene-C(4300Å, 5000Å, 6500Å, 7500Å, and 9000Å) were formed using special coating system, and organic semiconductor layer was ink-jet printing process at room temperature. The microcontact printing process using self-assembled monolayer(SAM) and h-PDMS stamp made it possible to fabricate OTFT with channel length down to 600nm, fabricated thin film electrode of Au/Cr (100nm/5nm), and reduced the fabrication process by 20steps compared with photolithography process. Since the fabrication process was done in room temperature, there was no appeared such as pattern shrinkage, pattern transformation and bending problem.

Abstract: We investigated the non-uniformity of the residual layer thickness caused by wafer deformation in an experiment that examined different wafer thicknesses using UV-NIL with an element-wise patterned stamp (EPS). Experiments using the EPS were performed on an EVG®620-NIL. Severe deformation of the wafer served as an obstacle to the spread of resin drops, which caused non-uniformity of the residual layer thickness. We also simulated the imprint process using a simplified model and finite element method to analyze the non-uniformity.

Abstract: The flexible organic thin film transistor(OTFT) array to use as a switching device for an organic light emitting diode(OLED) was designed and fabricated in the nanocontact printing and low-temperature process. The gate, source, and drain electrode patterns of OTFT were fabricated by nanocontact printing process. And dielectric layer of parylene and organic active semiconductor layer of pentacene formed at room temperature or at a temperature lower than 40
. The nanocontact printing process using SAM and PDMS stamp made it possible to fabricate OTFT arrays with channel lengths down to even submicron size, and reduced the fabrication process by 10 steps compared with photolithography. Since the process was done in room temperature, there was no pattern shrinkage, transformation, and bending problem appeared. Also, it was possible to improve electric field mobility, to decrease contact resistance, to increase close packing of molecules by SAM, and to reduce threshold voltage by using a parylene.