Papers by Author: Jung Yup Kim

Abstract: In this study, we propose a simplification scheme for modeling a complex bellows structure. Using 3-dimensional finite element analysis, vibration modes and natural frequencies are analyzed. The analysis results are compared with those measured by telemetry system of acceleration. It is found that bending mode of vibration can be activated even a low operation frequency and this leads to uneven distribution of stress. The uneven distribution of stress can be a possible cause for the early failure of a bellows with a large diameter.

Abstract: In this study, an analytical model is developed to analyze non-uniform deformation of a pantograph. The analytical model is verified by comparing predicted deformations with experimentally measured deformations of a pantograph. The effects of total displacement and gaps on non-uniformity are numerically simulated to provide the physical insight into the deformation mechanism of a pantograph. Design guidelines are suggested to minimize non-uniform deformation of a pantograph, and hence also of an associated bellows.

Abstract: We have developed a novel atomic force microscope (AFM) probe as a highly sensitive sensor and an application of the probe into various mechanical tests for characterizing micro/nanostructures. Using MEMS fabrication technique, we have designed and fabricated rhombus-shaped symmetric AFM probe. Adhesion forces between silicon tip and artificial nano-hair structures of cyclic olefin copolymer (COC) and polypropylene (PP) were measured using the probe with a flat tip. The results exhibited the usual characteristics of force-displacement curves of COC and PP nano-hair structures, in which a pull-off force was detected at the point of unloading. The average adhesion forces of the COC and PP hair structures are about 9.48 μN and 10.67 μN, respectively.

Abstract: NIL(Nano Imprint Lithography) is one of the most promising lithography techniques. There are many variants of NIL, and two major techniques of them are thermal NIL and UV NIL. Here, we focus ourselves on the thermal NIL. During the thermal NIL, the polymeric patterns experience large mechanical strain and high temperature, and this often leads to malformation of polymeric patterns. So it is needed to improve the pattern fidelity and contrast, and these are believed to be closely related to the process condition and mechanical properties. In thermal NIL, PMMA is widely used and chosen as target polymer. Generally, mechanical properties in nano scale are really hard to acquire. In this study, we estimate the mechanical properties of PMMA by molecular dynamic simulation. These properties will be used as input of continuum simulation. We will estimate stress-strain relationship of PMMA. This stress-strain relationship depends on strain rate and temperature. So we will study about strain rate and temperature effect.

Abstract: In the semiconductor inspection, number of pads at unit area is increasing and pad array have become irregular 2-dimensional. So we develop a bellows type micro contact probe. Our micro contact probe is a vertical-type micro contact probe for area arrays and narrow pitch electrode pads. We choose bellows type micro contact probe to prevent stress concentration. Our design targets are 120 um pad pitch, 20-50 um OD(over drive) and over 5 mN reaction force. In this research, micro contact probe is made by electroplating(Ni-Co). structural analysis is accomplished by FEM. And characterization of micro contact probe is done by our own mechanical tester. So material property is measured for structural analysis and structural analysis result will be compared with experimental result.

Abstract: Nanoimprint lithography is a promising technology to produce sub-100 nm scale features on silicon chips. One of key issues in the nanoimprint lithography is how to make uniform contact between the stamp and the substrate on a large area. In this study a rubber membrane unit under substrate is introduced to resolve this problem. Two layers of membrane were designed to consider air flow in the middle of resist on a silicon wafer. The geometry design for accomplishing uniform contact was carried out using finite element analysis. The material modeling of hyperelastic properties of rubber is characterized by the Mooney-Rivlin strain energy functions. Material constants in the strain energy functions are able to be determined via the curve fitting of experimental stress-strain data. Simple tension and equi-biaxial tests were performed to determine the material constants. To evaluate the effects of a rubber membrane unit, nanoimprint lithography process with it was executed. We could confirm that a distinct improvement of uniform contact was shown and air flow problem was solved during the process.