• Korean Journal of Materials Research
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• v.10 no.1
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• pp.90-96
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• 2000

The effects of the type and thickness of underlayers on the crystallographic texture and the sheet resistance of aluminum thin films were studied. Sputtered Ti and Ti/TiN were examined as the underlayer of the aluminum films. The texture and the sheet resistance of the metal thin film stacks were investigated at various thicknesses of Ti or TiN, and the sheet resistance was measured after annealing at $400^{\circ}C$ in an nitrogen ambient. For the Ti underlayer, the minimum thickness to obtain excellent texture of aluminum <111> was 10nm, and the sheet resistance of the metal stack was greatly increased after annealing due to the interdiffusion and reaction of Al and Ti. TiN between Ti and Al could suppress the Al-Ti reaction, while it deteriorated the texture of the aluminum film. For the Ti/TiN underlayer, the minimum Ti thickness to obtain excellent texture of aluminum <111> was 20nm, and the minimum thickness of TiN to function as a diffusion barrier between Ti and Al was 20nm.

• ETRI Journal
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• v.24 no.4
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• pp.270-279
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• 2002

We present a self-consistent numerical method for calculating the conduction-band profile and subband structure of AlGaN/GaN single heterojunctions. The subband calculations take into account the piezoelectric and spontaneous polarization effect and the Hartree and exchange-correlation interaction. We calculate the dependence of electron sheet concentration and subband energies on various structural parameters, such as the width and Al mole fraction of AlGaN, the density of donor impurities in AlGaN, and the density of acceptor impurities in GaN, as well as the electron temperature. The electron sheet concentration was sensitively dependent on the Al mole fraction and width of the AlGaN layer and the doping density of donor impurities in the AlGaN. The calculated results of electron sheet concentration as a function of the Al mole fraction are in excellent agreement with some experimental data available in the literature.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.431-434
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• 2012

In this paper, heat-releasing sheets made of AlN powder and acryl binder as thermoset were prepared using tape casting method. The crystal structure and morphology, the thermal properties as nonvolatile solid content and thermal conductivity, and the surface resistance of heat-releasing sheet were measured by using X-ray diffractometer, field emission-scanning electron microscopy, thermo gravimetric analyzer and laser flash instrument, and surface resistance meter. It was proved that thermal conductivity is greatly affected by the content of binder in heat-releasing sheet. Superior thermal conductivity above 3.5 W/mK and suface resistance were obtained at heat-releasing sheet with above 90% of AlN powder.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.394-399
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• 2000

The effects of the type and thickness of underlayer on the crystallographic texture and the sheet resistance of aluminum thin film were studied. Ti and Ti/TiN were examined as the underlayer of aluminum. Ti and TiN were prepared by ionized physical vapor deposition (I-PVD) metalorganic chemical vapor deposition (MOCVD), respectively. The texture and the sheet resistance of metal thin film stacks were investigated at various thicknesses of Ti or TiN, and the sheet resistance was measured after annealing at $400^{\circ}C$ in an nitrogen ambient. For I-PVD Ti underlayer, the excellent texture of aluminum <111> was obtained even at top of 5 nm of Ti. However, the sheet resistance of the metal stack was greatly increased after annealing due to the interdiffusion and reaction of Al and Ti. MOCVD TiN between Ti and Al could suppress the Al-Ti reaction without severe degradation of aluminum <111> texture. Excellent texture of aluminum was obtained for the MOCVD TiN thinner than 4 nm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.462-466
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• 2012

In this paper, heat-releasing composite sheets made of AlN, graphite, Al powder and acryl binder as thermoset were prepared using tape casting method. The crystal structure, morphology, thermal conductivity of heat-releasing composite sheet were measured by using X-ray diffractometer, field emission-scanning electron microscopy and laser flash instrument. It was found thermal conductivity of sheet was decided by solid content, composition including AlN, graphite, Al in heat-releasing composite sheets. As a result, 4.56 W/mK of thermal conductivity could be obtained by using LFA 447.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.157-160
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• 1999

Aluminum 4343(filler thickness ; 10${\mu}{\textrm}{m}$/Al 3N03(core 80${\mu}{\textrm}{m}$)/Al 4343(filler 10${\mu}{\textrm}{m}$) clad sheet which is recently developed as brazing sheet materials for automotive condensers was fabricated by castinglongrightarrowhot rollinglongrightarrowcold rollinglongrightarrowintermediate annealing(IA)longrightarrowfinal cold rolling(CR). and the effect of IA/CR conditions on microstructure and sagging resistance were investigated the sheet which were fabricated by optimum conditions (IA'ed at 42$0^{\circ}C$ followed by CR'ed to 20~45%) showed good sagging resistance because the core obtained a coarsely recrystallized grain structure during brazing and consequently inhibited filled alloy penetration into the core.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.3
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• pp.81-85
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• 2000

The effects of $NH_3$ flow rate and reactor pressure on Al composition and the interface of AlGaN/GaN heterostructure were studied. Equilibrium partial pressure of Ga and Al over AiGaN alloy was calculated as a function of growth pressure, $NH_3$flow rate and temperature. It was found equilbrium vapor pressure of Al is significantly lower than that of Ga, thus, the alloy composition mainly controlled by Ga partial pressure. We believe that more decomposition of Ga occur at lower $NH_3$ flow rate and higher growth pressure leads to preferred Al incorporation into AlGaN. The alloy composition gradient became larger at AlGaN/GaN heterointerface at higher reactor pressures, higher Al composition and low $NH_3$ flow rate. This composition gradient lowered sheet carrier concentration and electron mobility as well. We obtained an AlGaN/GaN heterostructure with sheet carrier density of ${\sim}2{\times}10^{13}cm^{-2}$ and mobility of 1250 and 5000 $cm^2$/Vs at 300 K and 100 K, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.11
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• pp.862-866
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• 2012

Surface passivation of AlGaN/GaN heterojunction structure was examined through the thermal oxidation of evaporated Al. The Al-oxide passivation increased channel conductance of two dimensional electron gas (2DEG) on the AlGaN/GaN interface. The sheet resistance of 463 ohm/${\Box}$ for 2DEG channel before $Al_2O_3$ passivation was decreased to 417 ohm/${\Box}$ after passivation. The oxidation of Al induces tensile stress to the AlGaN/GaN structure and the stress seemed to enhance the sheet carrier density of the 2DEG channel. In addition, the $Al_2O_3$ films formed by thermal oxidation of Al suppressed thermal deterioration by the high temperature annealing.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.10
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• pp.23-28
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• 2010

In this paper, we investigated the polarization effects on the electrical and structural characteristics of AlGaN/GaN HEMT. Both the Al mole-fraction and the barrier thickness of AlGaN, which determine the profiles of a two-dimensional electron gas, were simulated to obtain the optimum HEMT structure affecting the polarization effect. As a results, we found that the amount of bound sheet charges was increased by 16% and the maximum drain current density ($I_D$,max) was increased by more than 37%, while AI mole fractions are changed from 0.3 to 0.4. We also observed a 37% improvement in maximum drain current density ($I_D$,max) by increasing AIGaN layer thickness from 17 to 38 nm. However when AlGaN layer thickness reached the critical thickness, DC characteristics were dramatically lowered due to 'bulk' relaxation in AlGaN layer.

• Transactions of Materials Processing
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• v.12 no.3
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• pp.202-207
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• 2003

In order to examine the springback amount and material properties of aluminum alloy sheets (AL1050 and AL5052) in the warm forming which forms the sheet above the room temperature, the stretch bending and draw bending tests and tensile test in various high temperatures are carried out. The warm forming temperature 15$0^{\circ}C$ is a transition in terms of the material properties: over the forming temperature 15$0^{\circ}C$, them $\sigma$$_{YS}$ , $\sigma$$_{TS}$ , E, K, n, etc. are bigger but $\varepsilon$ and plastic strain ratio are smaller. Below the forming temperature 15$0^{\circ}C$, there are no big differences in material properties as the forming temperature changes. AL5052 sheet has more springback effect than AL1050 sheet. While the springbacks of AL5052 and AL1050 sheets show a big reduction over the warm forming temperature 15$0^{\circ}C$ in the stretch bending test, the springback rapidly reduces in the warm forming temperature 15$0^{\circ}C$-20$0^{\circ}C$ for AL5052 sheet and 20$0^{\circ}C$-25$0^{\circ}C$ for AL1050 sheet in the draw bending test.