• Proceedings of the KSME Conference
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• 2004.11a
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• pp.297-301
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• 2004

The optimum design against contact crack initiation is investigated to find major parameters in designing desirable surface-coated asymmetric layered components. Hard ceramic coated soft materials with various elastic modulus mismatch are prepared for the analysis. Spherical indentation is conducted for producing contact cracks from the surface or interface between the coating and the substrate layer. A finite element analysis of the stress fields in the loaded layer components enables a direct correlation between the damage patterns and the stress distributions. Implications concerning the design of asymmetric layered components indicate that the coating thickness and the elastic modulus mismatch are important parameters for designing layered component to prevent the initiation of contact cracks.

• Journal of Power System Engineering
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• v.3 no.4
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• pp.57-62
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• 1999

The microaccelerometer using a tunnelling current effect concept has the potential of high performance, although it requires slightly complex signal-processing circuit for servo-system. The paddle of micro accelerometer is pulled to have the gap width of about 2nm which almost allows the flow tunnelling current. This paper demonstrates at capacitor of microaccelerometer the use of the coupled thermo-electric analysis for voltage, current, heat flux and Joule heating then tunnelling current flows. Two electrodes are applied to the microaccelerometer producing a unform difference of temperature gradient and electric potential between the paddle and the substrate.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.820-823
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• 2002

MEMS structures Generally have been fabricated using surface-machining, but the interface failure between silicon substrate and evaporated thin film frequently takes place due to difference of linear coefficient of thermal expansion. Therefore this paper studied the effect of the residual stress caused by variable external loads. This study did not analyzed accurate quantity of the residual stress but trend for the effect of residual stress. Several specimens were fabricated using other material(Al, Au and Cu) and thermal load was applied. The residual stress was measured by nano-indentation using AFM. The results showed the existence of the residual stress due to thermal load. The indentation area of the thermal loaded thin film reduced about 3.5% comparing with the virgin thin film caused by residual stress. The finite element analysis results are similar to indentation test.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.349-354
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• 2002

Significant improvements in bond strength between new and existing concrete can be achieved through the modification of the new concrete by latex modification. But, no test method has been adopted as a standard to measure the bond strength between the concrete used to repair and the substrate being repaired. The performance of old and the new concrete construction depends upon bond strength between old and the new concrete. Current adhesion strength measurement method ignores the effect of stress concentration by shape of specimens. Therefore, this research calculates stress concentration coefficient using finite element analysis and direction tensile strength test (pull-off test). The result shows that the required core depth is 2.5cm. Elastic modulus and overlay thickness do not influence in stress concentration.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.11
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• pp.108-115
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• 2007

We have designed a high transmission C-shaped aperture using finite differential time domain (FDTD) technique. The C-shaped aperture was fabricated in the aluminum thin film on a glass substrate using a focused ion beam (FIB) milling. Nano-size patterning was demonstrated with a vacuum contact device to keep tight contact between the Al mask and the photoresist. Using 405 nm laser, we recorded a 50 nm-size dot pattern on the photoresist with the aperture and analyzed the spot size dependent on the dose illuminated on the aperture.

• JSTS:Journal of Semiconductor Technology and Science
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• v.2 no.4
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• pp.288-294
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• 2002

This paper presents the design, fabrication and characterization of a 32 by 32 electroplated micromirror array on a glass, a low cost substrate. Approaches taken in this work for the fabrication of micromachined mirror arrays include a line addressing scheme, a seamless array design for high fill factor, planarization techniques of polymeric interlayers, a high yield methodology for the removal of sacrificial polymeric interlayers, and low temperature and chemically safe fabrication techniques. The micromirror is fabricated by aluminum and the size of a single micromirror is 200 $\mu\textrm{m}{\;}{\times}200{\;}\mu\textrm{m}$. Static deflection test of the micro-mirror has been carried out and pull-in voltage of 44V and releasing voltage of 30V was found.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.12
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• pp.1129-1132
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• 2005

The purpose of this reserch is to establish the new design technology for microwave Coplanar structure. The components in microwave circuit are classified to transmission devices, EM devices, and quasi-TEM devices. After design of these devices, we analyzed these CPWs electromagnetically using FDTD method, and suggested optimum CPW structure. In oder to realize a CPW module up to 30 GHz-100 GHz band, we research on a technology of 3-dimensional microwave CPW, and GaAs substrate with Si layer for ohmic loss. As a result this research, we suppressed the leakage, resonance, coupling, and radiation of CPW EMI, and improved resonance quality of CPW.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.11
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• pp.36-44
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• 1995

When sliding a hard cylinder along the surface of glass, periodic surface cracks appear on the flat surface due to tensile stresses induced by the slider. These cracks propagate into the substrate and will affect the fracture properties of a body. Crack spacings and the directions of crack propagation into glass were calculated numerically by applying the finite element method and linear elastic fracture mechanics. The calculated crack spacings were in the range of the experimental results. Stress intensity factors and crack extension angles depended on the radius of slider and the load, and from these two factors the possible directions of crack propagation were calculated. The calculated propagation directions were in good agreement with real crack propagation.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.9
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• pp.135-141
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• 2003

MEMS structures generally have been fabricated using surface-machining method, but the interface failure between silicon substrate and evaporated thin film frequently takes place due to the residual stress inducing by the applied the various loads. And the very important physical property in the heated environment is the linear coefficient of thermal expansion. Therefore this paper studied the residual stress caused the thermal loads in the thin film and introduced the simple method to measure the trend of the residual stress by the indentation. Specimens were made of materials such as Al, Au and Cu and thermal load was applied repeatedly. The residual stress was measured by nano-indentation using AFM and FEA. The existence of the residual stress due to thermal load was verified by the experimental results. The indentation length of the thermal loaded specimens increased minimum 11.8％ comparing with the virgin thin film caused by tensile residual stress. The finite element analysis results are similar to indentation test.

• Journal of the Korean Magnetics Society
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• v.11 no.2
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• pp.78-83
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• 2001

The thermal characteristics of TMR devices by using Fast Linear Annealing method has been studied. A computer program that employs the finite differential method has been developed to simulate the temperature distribution of a diameter of 4" silicon wafer, which is subjected to radiation heat from the halogen lamp. We adopted the temperature of 350$\^{C}$, which is the highest temperature usually used in annealing for magnetic thin films. We changed moving velocity of the lamp from 0.05 mm/sec to 1 mm/sec. The moving velocity of halogen lamp has less effect on the local peak temperature of the sample only about 40$\^{C}$. Therefore, we may be able to anneal TMR devices in such short time of 1 minute and 40 seconds per one wafer, using the Fast Linear Annealing method.