• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.121-124
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• 2006

A novel quantum chemical molecular dynamics program, 'Colors' was developed to simulate the electronic structure of rare earth-doped phosphor materials as well as the destruction processes of MgO protecting layer in plasma display panel (PDP). We have also developed a quantitative prediction method based on Monte Carlo simulation technique to evaluate the electrical conductivity of insulators, semiconductors, and metals as well as the spatial distribution of electron density by Colors code. All these original simulators enable us to study theoretically a variety of materials related to PDP.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.231-232
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• 2008

The coupling between electric, magnetic, and structural order parameters results in the so-called multiferroics, which possess ferroelectricity, ferromagnetism, and/or ferroelasticity. The simultaneous ferroelectricity and ferromagnetism (magnetoelectricity) allow potential applications in information storage, spintronics, and in magnetic or electric field sensors. Perovskite compound $BiFeO_3$ (BFO) is antiferromagnetic below Neel temperature of 647K and ferroelectric with a high Curie temperature of 1043K. It exhibits weak magnetism at room temperature(RT) due to the residual moment from a canted spin structure. It is likely that non-stoichiometry and second-phase formation are the factors which cause leakage in BFO. It has been suggested that oxygen non-stoichiometry leads to valence fluctuations of Fe ions in BFO, resulting in high conductivity. To reduce the large leakage current of BFO, one attempt is fabricating donor doped BFO compounds and thin films. We report here the successful fabrication of the Nd, Ti co-doped $BiFeO_3$ ceramics and thin films by pulsed laser deposition technique.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.5
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• pp.106-112
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• 1994

We have developed a large area ion shower doping system with an RF plasma ion source. The ion current density (i.e., doping concentration) increases with RF power and acceleration voltage. Using this technique, we investigated the optimum condition for ion doping of phosphorus in a-Si:H and poly-Si films. The optimum acceleration voltage and doping time are 6KV and 90sec, respectively, in a-Si:H films. Under this condition the electrical conductivity of ion-doped a-Si:H film is obtained ~10$^{-3}$/cm at room temperature. The sheet resistance decreases witnh acceleration voltage in ion-doped poly-Si, and a heavily-doped layer with a sheet resistance of 920$\Omega$/ㅁ is obtained by using ion doping and subsequent activation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.257-262
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• 2008

In this paper, the key parameters of $CO_2$ laser(focus depth, air blow rate, total laser beam time, number of pulse) are experimented for thru-hole and scribing line on AIN(aluminum nitride) substrate with high thermal conductivity. And, microstrip line & spiral planar inductor are fabricated on AIN substrate using 5 um Cu-plating with self-masking technique. The microstrip line of AIN has 0.1 dB/mm attenuation at 10 GHz and 6 nH spiral planar inductor has 56 maximum quality factor at 1 GHz. Thus, the AIN substrate is promising for GHz applications of high power area.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.593-602
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• 2000

The shape optimization is performed to minimize the judder of ventilated disc brake rotor that is induced by the thermal deformation of the disc. A three-dimensional finite element is developed to analyze the coupled system of temperature and displacement field, and the thermal conductivity and mechanical stiffness matrices are simultaneously taken into account. To reduce computing time, an equivalent heat transfer rate is introduced approximating the heat transfer rate on the disc surface. A deformation factor is introduced to describe the thermal deformation causing the judder. The deformation factor is chosen as an objective function in the optimization process. Consequently an optimum design is then performed minimizing the deformation factor with the design variables of the shape of the disc. The optimum design procedure presented in this study is proven to be an effective method of minimizing the judder, and it reduces the thermal deformation by 23% of the initial geometry.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.9
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• pp.839-844
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• 2017

In the past few years, three-dimensional (3D) printing has been developed as a rapid prototyping (RP) technique. The fused deposition modeling (FDM)-type 3D printing is one of the most useful RP methods; however, it still has several disadvantages, such as low conductivity, heat degradation, and low surface quality. In this study, test specimens are fabricated using an FDM-type 3D printer with an ABS material. Then, the specimens undergo post-processing on submerging in acetone with various processing times. As the processing time increases, surface roughness is enhanced significantly within the first five seconds by chemical processing, following which the processing effects are reduced. Furthermore, post processing causes the ultimate strength and strain to increase slightly with increased processing time.

• Journal of IKEEE
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• v.19 no.3
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• pp.407-414
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• 2015

Electrical impedance tomography is an imaging technique to reconstruct the internal conductivity distribution based on applied small currents and measured voltages through an array of electrodes attached on the boundary of a domain of interest. In this paper, an analytical solver with complete electrode model is derived and the analytical voltage data are calculated. Moreover, the voltage data are also computed with existing numerical solvers such as finite element method and boundary element method. The forward solutions using homogeneous and inhomogeneous conditions are compared with phantom experiments through the root mean square errors.

• International Journal of Aerospace System Engineering
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• v.7 no.1
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• pp.16-20
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• 2020

The recent trend is increasing towards the usage of polymer matrix composites since they have a wide variety of applications. They have applications in the field of aircraft and space industry, sporting goods, medical devices, marine and automotive applications and also in commercial usage. The most commonly used fibre-reinforced polymer matrix composite is Glass fibre reinforced epoxy (GFRE) composite which is used in aviation, sports and automotive industries. However, the strength of GFRE composites is not adequate for structural applications. Therefore, the current research focuses on increasing the strength of GFRE composites by reinforcing with micro Graphite (Gr) particulates. The Gr used is an ultra-fine powder with particle size 250 ㎛. Gr is known to have good wear resistance, thermal conductivity and can operate at high temperatures. Gr particulates are mixed with the epoxy matrix in various weight ratios. Hand-lay technique is used for fabricating the composites. Mechanical properties such as tensile strength, elongation, compressive strength and flexural strength are obtained experimentally to study the effect of change in Gr content (0-5 wt. %). The tests were done as per ASTM standards.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.200-204
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• 2011

Increase of surface area and decrease of band gap in $TiO_2$ semiconductors are significant to improve the efficiency of water splitting by photoelectrolysis. In this study $TiO_2$ nanotube arrays with ~7 um length and ~100 nm diameter were fabricated by an anodizing technique of titanium foils using DMSO (dimethyl sulfoxide)-based electrolytes. Then to control the band gap of the $TiO_2$ arrays, they were annealed at $550^{\circ}C$ for up to 180 min in $NH_3$ gas ambient. The samples annealed in $NH_3$ gas for 30 min and 60 min showed superior photo-conversion efficiency for water splitting under white and visible light. A $TiO_2$ nanotube annealed in $NH_3$ gas ambient for a period longer than 120 min showed 1 order higher leakage current. It is believed that the decrease of band gap and increase of conductivity in $TiO_2$ nanotube arrays due to $NH_3$ gas treatments result in the superior water-splitting performance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.3
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• pp.213-217
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• 2007

Copper has been used as an interconnect material in the fabrication of semiconductor devices, because of its higher electrical conductivity and superior electro-migration resistance. Chemical mechanical polishing(CMP) technique is required to planarize the overburden Cu film in an interconnect process. Various problems such as dishing, erosion, and delamination are caused by the high pressure and chemical effects in the Cu CMP process. But these problems have to be solved for the fabrication of the next generation semiconductor devices. Therefore, new process which is electro-chemical mechanical polishing(ECMP) or electro-chemical mechanical planarization was introduced to solve the technical difficulties and problems in CMP process. In the ECMP process, Cu ions are dissolved electrochemically by the applying an anodic potential energy on the Cu surface in an electrolyte. And then, Cu complex layer are mechanically removed by the mechanical effects between pad and abrasive. This paper focuses on the manufacturing of ECMP system and its process. ECMP equipment which has better performance and stability was manufactured for the planarization process.