• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.6
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• pp.35-40
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• 2008

High performance light emitting diodes(LEDs) have been developed using GaN-based materials grown on sapphire substrates in recent years. Although these LEDs are already commercially available, we have to consider electrostatic discharge(ESD) damage related to both basic materials of diode and miniaturization of LEDs. ESD damage is one of the important parameters influencing reliability of the light emitting devices. We investigated mass production of GaN-based LEDs suffered from ESD during production process and present the solutions in order to improve the ESD problem. Most of EDS problems were controlled by using instruments properly and improvement of the process circumstances as well.

• Laser Solutions
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• v.17 no.2
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• pp.19-25
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• 2014

Optical embedded diffraction gratings with the bulk modification in BK-7 glass plates excited by tightly focused high-intensity femtosecond (130fs) Ti: sapphire laser (peak wavelength = 790nm) were demonstrated. The structural modifications with diameters ranging from 400nm to $4{\mu}m$ were photo-induced after plasma formation occurred upon irradiation with peak intensities of more than $1{\times}1013W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred. The maximum refractive index change was estimated to be $1.5{\times}10^{-2}$. The two optical embedded gratings in BK-7 glass plate were demonstrated with refractive index modification induced by the scanning of low-density plasma formation.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.3
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• pp.124-131
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• 2016

GaN and InN epilayers with nucleation layer (LT-buffer) were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). As-grown and annealed GaN and InN nucleation layers grown at various growth condition were observed by reflection high-energy electron diffraction (RHEED). When temperature of effusion cell for III source was very low, diffraction pattern with cubic symmetry was observed and zincblende nucleation layer was flattened easily by annealing. As cell temperature increased, LT-GaN and LT-InN showed typical diffraction pattern from wurtzite structure, and FWHM of (10-12) plane decreased remarkably which means much improved crystalline quality. Diffraction pattern was changed to be from streaky to spotty when plasma power was raised from 160 to 220 W because higher plasma power makes more nitrogen adatoms on the surface and suppressed surface mobility of III species. Therefore, though wurtzite nucleation layer was a little hard to be flattened compared to zincblende, higher cell temperature led to easier movement of III surface adatoms and resulted in better crystalline quality of GaN and InN epilayers.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.266.2-266.2
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• 2016

최근 디스플레이 산업의 확대에 따라 투명 전도 산화물(Transparent Conducting Oxides:TCOs)의 수요가 급증하고 있다. 이 중 ZnO는 wide bandgap (3.37eV)와 large exciton binding energy (60meV)의 값을 가져 차세대 투명 전도 산화물, LED와 LD 등의 소자 소재로 각광받고 있다. ZnO는 electron을 내어놓는 native defect 때문에 기본적으로 n-type 물성을 띈다. 그래서 dopant를 이용해 p-type ZnO를 제작할 때 native defect를 줄이는 것이 중요한 요점이 된다. 이 때 buffer layer를 사용하여 native defect를 줄이는 방법이 사용되고 있다. 본연구에서는 RF-magnetron sputtering법을 이용하여 c-plane sapphire 기판 위에 다양한 조건의 ZnO buffer layer를 증착하고, 그 위에 ZnO:(Al,P) co-doping한 APZO를 증착하였다. ZnO buffer layer 증착조건의 변수는 증착온도와 Ar:O2의 비율을 변수로 두었다. 이러한 박막을 FE-SEM, XRD, Hall effect measurement, AFM을 통하여 미세구조와 물성을 관찰하였다. 이 때 APZO보다 낮은 증착온도에서 ZnO buffer layer가 증착되면 APZO를 증착하는 동안 chamber 내부에서 열처리하는 효과를 얻게 되고, UHV(Ultra High Vaccum)에서 열처리 될 때 ZnO buffer layer의 mophology와 결정성이 변하게 되는 모습을 관찰아혔다. 또한 본 실험을 통해 ZnO buffer layer의 증착 온도가 APZO의 증착온도보다 높을 때 제어 가능한 실험이 됨을 확인 할 수 있었다.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.3
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• pp.111-119
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• 2018

We report the post-annealing effect of Sn doped ZnO (ZnO:Sn) thin film grown on sapphire (001) substrate using radio-frequency powder sputtering method. During thermal annealing in a vacuum atmosphere, the ZnO:Sn thin film is transformed into a porous thin film. Based on X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analyses, a possible mechanism for the production of pores is presented. Sn atoms segregate to form clusters that act as catalysts to dissociate Zn-O bonds. The Zn and O atoms subsequently vaporize, leading to the formation of pores in the ZnO:Sn thin film. We also found that Sn clusters were oxidized to form SnO or $SnO_2$ phases.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.135-137
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• 2002

In the favor of adjusting microwave signal, Hairpin type Filter, which delay microwave signal enough to several nanosecond, is a key component. One of the main advantage in using Hairpin type Filter is a conveniency for equipping with Delay Module, and because of having a wide bandwidth, Hairpin type Filter can be designed to satisfy the most applications. In this work, we attempted to estimate the delay time in a superconductive hairpin type filter A software to synthesize even and odd order equiripple hairpin type filter has been developed. This software arbitrarily locate its transfer zeros making symmetric of asymmetric amplitude response and equalizing group delay. Borland C++ compiler has been used. The program was designed to run under MS-DOS, Window 98, Window 2000. The program optimizes the position of the transfer function zeros in order to fulfill the group delay specification masks. We designed and fabricated a hairpin type HTS 2-pole microstrip bandpass filter to operate at 5.8Ghz. The fabrication method was pulsed laser deposition and YBCO films were deposited on sapphire substrates with a Ce$O_{2}$ thin layer as a buffer layer. We also developed a new style hairpin type filter by using interdigitide inner-pole. Compared to the same size regular hairpin type filters, our filters had a lower center frequency.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.9-9
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• 2009

1 wt % Ga-dope ZnO (ZnO:Ga) thin films with n-type semiconducting behavior were grown on c-sapphire substrates by radio frequency magnetron sputtering at various growth temperatures. The room temperature grown ZnO:Ga film showed the faint preferred orientation behavior along the c-axis with small domain size and high density of stacking faults, despite limited surface diffusion of the deposited atoms. The increase in the growth temperature in the range between $300\sim550^{\circ}C$ led to the granular shape of epitaxial ZnO:Ga films due to not enough thermal energy and large lattice mismatch. The growth temperature above $550^{\circ}C$ induced the quite flat surface and the simultaneous improvement of electrical carrier concentration and carrier mobility, $6.3\;\times\;10^{18}/cm^3$ and $27\;cm^2/Vs$, respectively. In addition, the increase in the grain size and the decrease in the dislocation density were observed in the high temperature grown films. The low-temperature photoluminescence of the ZnO:Ga films grown below $450^{\circ}C$ showed the redshift of deep-level emission, which was due to the transition from $Zn_j$ to $O_i$ level.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.253-254
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• 2009

본 연구는 다결정 알루미나 소결체와 사파이어웨이퍼(sapphire wafer)의 견고한 접합을 위해 활성금속 Ti가 함유된 Active Filler Metal을 사용하였고, 이를 브레이징한 후 접합 반응층과 Ti 거동 특성에 관한 것이다. 브레이징 (brazing)은 Ar 분위기 종에 $850^{\circ}C$에서 이행하였으며. 이때 다결정 알루미나, 사파이어와 Active Filler Metal 사이의 접합 반응층을 확인하였다. Active Filler Metal 내어| 존재하는 Ti가 접할 반응층의 양계면에 집중되는 것을 SEM을 이용하여 확인하였다. 또한 EDS Line Scanning을 실시하여 접합부에서 원소들의 분포를 관찰하였다.

• Laser Solutions
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• v.16 no.1
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• pp.5-9
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• 2013

We have successfully formed filament inside of a transparent soda-lime glass using a Ti:sapphire based femtosecond laser. To make filament form, keeping the laser intensity higher than critical intensity is essential. Also each of the machining parameters plays an important role for the formation of filament. In this paper, we study what parameter can possibly influence for formation of filament, and we introduce an application using filamentation by femtosecond laser for transparent material.

• Transactions of Materials Processing
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• v.29 no.1
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• pp.44-48
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• 2020

Aluminum nitride (AlN), as a substrate material in electronic packaging, has attracted considerable attention over the last few decades because of its excellent properties, which include high thermal conductivity, a coefficient of thermal expansion that matches well with that of silicon, and a moderately low dielectric constant. AlN films with c-axis orientation and thermal conductivity characteristics were deposited by using Pulsed Laser Deposition (PLD). The epitaxial AlN films were grown on sapphire (c-Al₂O₃) single crystals by PLD with AlN target and Y₂O₃ doped AlN target. A comparison of different targets associated with AlN films deposited by PLD was presented with particular emphasis on thermal conductivity properties. The quality of AlN films was found to strongly depend on the growth temperature that was exerted during deposition. AlN thin films deposited using Y₂O₃-AlN targets doped with sintering additives showed relatively higher thermal conductivity than while using pure AlN targets. AlN thin films deposited at 600℃ were confirmed to have highly c-axis orientation and thermal conductivity of 39.413 W/mK.