• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.588-593
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• 2014

Current crowding problem can worsen the internal quantum efficiency and the negative-voltage ESD of InGaN-based LEDs. In this paper, by using photon emission microscope and thermal emission microscope measurement, we confirmed that the electric field and the current of the InGaN-based LED sample are crowded in specific regions where the distance between p-type metal contact and n-type metal contact is shorter than other regions. To improve this crowding problem of electric field and current, modified metal contact geometry having uniform distance between the two contacts is proposed and verified by a numerical simulation. It is confirmed that the proposed structure shows better current spreading, resulting in higher internal quantum efficiency and reduced reverse leakage current.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.371.2-371.2
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• 2016

Graphene electronics is one of the promising technologies for the next generation electronic devices due to the outstanding properties such as conductivity, high carrier mobility, mechanical, and optical properties along with extended applications using 2 dimensional heterostructures. However, large contact resistance between metal and graphene is one of the major obstacles for commercial application of graphene electronics. In order to achieve low contact resistance, numerous researches have been conducted such as gentle plasma treatment, ultraviolet ozone (UVO) treatment, annealing treatment, and one-dimensional graphene edge contact. In this report, we suggest a fabrication method of one-dimensional graphene metal edge contact without using graphene exfoliation. Graphene is grown on Cu foil by low pressure chemical vapor deposition. Then, the graphene is transferred on $SiO_2/Si$ wafer. The patterning of graphene channel and metal electrode is done by photolithography. $O_2$ plasma is applied to etch out the exposed graphene and then Ti/Au is deposited. As a result, the one-dimensional edge contact geometry is built between metal and graphene. The contact resistance of the fabricated one-dimensional metal-graphene edge contact is compared with the contact resistance of vertically stacked conventional metal-graphene contact.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.101-108
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• 2013

An aircraft fuel hose is a kind of high pressure hose, and generally consists of a nipple, a socket, an inner tube, and a reinforcement layer to increase the tensile strength. Especially the nipple supports the other components in manufacturing stages such as the swaging or crimping processes however, the nipple also serves to prevent leakage in cases of hose engagement with a hydraulic system. To ensure the seal of the hose assembly, a beam seal fitting with metal-to-metal contact is usually adopted at the end of a nipple. Therefore, the geometry of the beam is an important parameter to be determined to make sure there is sufficient contact force. This study aims to investigate the effects of beam seal geometry on the contact force by changing the inclined angle and the thickness of the beam. The results reveal that the proper thickness and inclined angle of the beam seal are 0.45 mm and $8.5^{\circ}$, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.4
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• pp.206-215
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• 1993

The finite element method is applied to analyze the mechanism of metal cutting, especially micro metal cutting. This paper introduces some effects, such as constitutive deformation laws of workpiece material, friction of tool-chip contact interfaces, tool rake angle and also simulate the cutting process, chip formation and geometry, tool-chip contact, reaction force of tool. Under the usual plane strain assumption, quasi-static analysis were performed with variation of tool-chip interface friction coefficients and tool rake angles. In this analysis, cutting speed, cutting depth set to 8m/sec, 0.02mm, respectively. Some cutting parameters are affected to cutting force, plastic deformation of chip, shear plane angle, chip thickness and tool-chip contact length and reaction forces on tool. Several aspects of the metal cutting process predicted by the finite element analysis provide information about tool shape design and optimal cutting conditions.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2357-2362
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• 2008

LHP is different from a conventional heat pipes in design and heat and fluid flow passages. The situations of the former is much complex than the latter. In LHPs, evaporation occurs at the contact interface between the heating plate and the porous wick, so some micro channels machined at the contact interface serve to let the vapor flow out of the evaporator. This complexity of contact geometry was known to cause a high resistance to heat flow. The present work was to study the problem of heat passage across the contact surface for LHPs and determine those values contact resistance. For two cases of contact structures, the thermal contact resistances were examined experimentally, one being obtained through mechanical contact under pressure and the other through sintered bonding. Nickel powder wick and copper plate were used for specimens. The result showed that a substantial reduction of contact resistance of an order of degree could be obtainable by sintered bonding.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1637-1639
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• 2001

Air arc interruption used in low rated voltage breaker, ACB and MCCB, have used the arc chamber composed of metal plates and insulating laminates which supposed these mechanically. and geometry and materials of arc chamber are very different by breaker manufacturer. These breakers have required to be smaller and to interrupt higher current by user. therefore the arc chamber geometry and material in breaker have been small, complex and various. The purpose of this study is to examine the effects of insulating laminates and contact materials on air arc interruption. Contacts were surrounded by a rectangle chamber of insulating laminates. Contact concoctions were composed of AgW, AgCdO that have used in low rated voltage breaker, and insulating laminates were polyester, epoxy. We found strong dependance of arc voltage on insulating material. The ablated vapor on polyester increased arc voltage that was useful in air arc interruption.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.608-611
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• 2002

In GMAW(Gas Metal Arc Welding) process, bead geometry (penetration, bead width and height) is a criterion to estimate welding quality. Bead geometry is affected by welding current, arc voltage and travel speed, shielding gas, CTWB (contact- tip to workpiece distance) and so on. In this paper, welding process variables were selected as welding current, arc voltage and travel speed. And bead geometry was reasoned from the chosen welding process variables using negro-fuzzy algorithm. Neural networks was applied to design FL(fuzzy logic). The parameters of input membership functions and those of consequence functions in FL were tuned through the method of learning by backpropagation algorithm. Bead geometry could be reasoned from welding current, arc voltage, travel speed on FL using the results learned by neural networks.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03a
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• pp.18-21
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• 1999

The wrinkling of thin sheet metal induced by compressive instability is one of major defects in sheet metal forming processes. compressive instability is influence by many factors such as mechanical properties of the sheet material geometry of the sheet contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show swide variations even for small deviations of the factors. in this work the bifurcation theory is introduced for the finite elemental analysis of the instability behavior of a thin sheet with initially sound geometry and property. All the above-mentioned factors are conveniently considered by the finite element method. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. Wrinkling initiation and growth in the deep drawing process are analyzed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.22-27
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• 1993

The finite element method is applied to analyze the mechanism of metal cutting. This paper introduces some effects, such constitutive deformation laws of workpiece material, friction of tool-chip contact interfaces, tool rake angles and also simulate the cutting process, chip formation and geometry, tool-chip contact, reaction force of tool, cutting temperature. Under the usual [lane strain assumption, quasi-static analysis were performed with variation of tool-chip interface friction coefficients and rake angles. In this analysis, various cutting speeds and depth of cut are adopted. Some cutting parameters are affected to cutting force, plastic deformation of chip, shear plane angle, chip thickness and tool-chip contact length and reaction forces on tool. Cutting temperature and Thermal behavior. Several aspects of the metal cutting process predicted by the finite element analysis provide information about tool shape design and optimal cutting conditions.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.478-482
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• 2014

Graphene have renewed considerable interest in inorganic, two-dimensional materials for future electronics. However, graphene does not have a bandgap, it is limited to apply directly to transistors and logic devices. Hence, other layered materials such as molybdenum disulphide ($MoS_2$) have been investigated to address this challenge. Here, we find that the nature of contacts plays a more important role than the semiconductor itself. In order to understand the nature of $MoS_2$/metal contacts, we perform density functional theory electronic structure calculations based on linear combination of atomic for the geometry, bonding, binding energy, PDOS, LDOS and electronic structure. We choose Au as a contact metal because it is the most common contact metal. In this paper, we demonstrate $MoS_2$/Au contacts have a more promising potential in flexible nanoelectronics than $MoS_2$ itself.