• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.530-538
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• 2016

There is a close relationship between the performance and the heat generation of the electronic device. Heat generation causes a significant degradation of the durability and/or efficiency of the device. It is necessary to have an effective method to release the generated heat. Based on demands of the printed circuit board (PCB) manufacturing, it is necessary to develop a robust and reliable plating technique for substrates with high thermal conductivity, such as alumina ($Al_2O_3$), aluminium nitride (AlN), and silicon nitride ($Si_3N_4$). In this study, the plating of metal layers on an insulating silicon nitride ($Si_3N_4$) ceramic substrate was developed. We formed a Pd-$TiO_2$ adhesion layer and used APTES(3-Aminopropyltriethoxysilane) to form OH groups on the surface and adhere the metal layer on the insulating $Si_3N_4$ substrate. We used an electroless Ni plating without sensitization/activation process, as Pd particles were nucleated on the $TiO_2$ layer. The electrical resistivity of Ni and Cu layers is $7.27{\times}10^{-5}$ and $1.32{\times}10^{-6}ohm-cm$ by 4 point prober, respectively. The adhesion strength is 2.506 N by scratch test.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.699-704
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• 2017

Recently, the use of an aluminum nitride(AlN) buffer layer has been actively studied for fabricating a high quality gallium nitride(GaN) template for high efficiency Light Emitting Diode(LED) production. We confirmed that AlN deposition after $N_2$ plasma treatment of the substrate has a positive influence on GaN epitaxial growth. In this study, $N_2$ plasma treatment was performed on a commercial patterned sapphire substrate by RF magnetron sputtering equipment. GaN was grown by metal organic chemical vapor deposition(MOCVD). The surface treated with $N_2$ plasma was analyzed by x-ray photoelectron spectroscopy(XPS) to determine the binding energy. The XPS results indicated the surface was changed from $Al_2O_3$ to AlN and AlON, and we confirmed that the thickness of the pretreated layer was about 1 nm using high resolution transmission electron microscopy(HR-TEM). The AlN buffer layer deposited on the grown pretreated layer had lower crystallinity than the as-treated PSS. Therefore, the surface $N_2$ plasma treatment on PSS resulted in a reduction in the crystallinity of the AlN buffer layer, which can improve the epitaxial growth quality of the GaN template.

• Korean Journal of Metals and Materials
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• v.48 no.10
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• pp.901-906
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• 2010

The first stage blade of a gas turbine was operated under a severe environment which included both $1300^{\circ}C$ hot gas and thermal stress. To obtain high efficiency, a thermal barrier coating (TBC) and an internal cooling system were used to increase the firing temperature. The TBC consists of multi-layer coatings of a ceramic outer layer (top coating) and a metallic inner layer (bond coat) between the ceramic and the substrate. The top and bond coating layer respectively act as a thermal barrier against hot gas and a buffer against the thermal stress caused by the difference in the thermal expansion coefficient between the ceramic and the substrate. Particularly, the bondcoating layer improves the resistance against oxidation and corrosion. An inter-diffusion layer is generated between the bond coat and the substrate due to the exposure at a high temperature and the diffusion phenomenon. A thickness measurement result showed that the bond coat of the suction side was thicker than that of the pressure side. The thickest inter-diffusion zone was noted at SS1 (Suction Side point 1). A chemical composition analysis of the bond coat showed aluminum depletion around the inter-diffusion layer. In this study, we evaluated the properties of the bond coat and the degradation of the coating layer used on a $1300^{\circ}C$-class gas turbine blade. Moreover, the operation temperature of the blade was estimated using the Arrhenius equation and this was compared with the result of a thermal analysis.

• Korean Journal of Metals and Materials
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• v.50 no.2
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• pp.159-163
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• 2012

A TCO-less ruthenium (Ru) catalytic layer on glass substrate instead of conventional Ru/TCO/ glass substrate was assessed as counter electrode (CE) material in dye sensitized solar cells (DSSCs) by examining the effect of the Ru thickness on the DSSC performance. Ru films with different thicknesses (34, 46, 69, and 90 nm) were deposited by atomic layer deposition (ALD) on glass substrates to replace both existing catalyst and electrode layer. In order to make our comparison, we also prepared an Ru catalytic layer by a similar method on FTO/glass substrate. Finally, we prepared the $0.45cm^2$ DSSC device the properties of the DSSCs were examined by cyclic voltammetry (CV), impedance spectroscopy (EIS), and current-voltage (I-V) method. CV measurements revealed an increase in catalytic activity with increasing film thickness. The charge transfer resistance at the interface between the electrolyte and Rudecreased with increasing Ru thickness. I-V results showed that the energy conversion efficiency increased up to 1.96%. Our results imply that TCO-less Ru/glass might perform as both catalyst and electrode layer when it is used in counter electrodes in DSSCs.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.4
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• pp.1845-1865
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• 2019

Current Internet is designed by lots of service providers with different objects and policies which make the direct deployment of radically new architecture and protocols on Internet nearly impossible without reaching a consensus among almost all of them. Network virtualization is proposed to fend off this ossification of Internet architecture and add diversity to the future Internet. As an important part of network virtualization, virtual network embedding (VNE) problem has received more and more attention. In order to solve the problems of large embedding cost, low acceptance ratio (AR) and environmental adaptability in VNE algorithms, cognitive method is introduced to improve the adaptability to the changing environment and a cognitive virtual network embedding algorithm based on weighted relative entropy (WRE-CVNE) is proposed in this paper. At first, the weighted relative entropy (WRE) method is proposed to select the suitable substrate nodes and paths in VNE. In WRE method, the ranking indicators and their weighting coefficients are selected to calculate the node importance and path importance. It is the basic of the WRE-CVNE. In virtual node embedding stage, the WRE method and breadth first search (BFS) algorithm are both used, and the node proximity is introduced into substrate node ranking to achieve the joint topology awareness. Finally, in virtual link embedding stage, the CPU resource balance degree, bandwidth resource balance degree and path hop counts are taken into account. The path importance is calculated based on the WRE method and the suitable substrate path is selected to reduce the resource fragmentation. Simulation results show that the proposed algorithm can significantly improve AR and the long-term average revenue to cost ratio (LTAR/CR) by adjusting the weighting coefficients in VNE stage according to the network environment. We also analyze the impact of weighting coefficient on the performance of the WRE-CVNE. In addition, the adaptability of the WRE-CVNE is researched in three different scenarios and the effectiveness and efficiency of the WRE-CVNE are demonstrated.

• Journal of the Semiconductor & Display Technology
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• v.21 no.2
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• pp.25-31
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• 2022

By an aid of needle coating, we have fabricated a spherical microlens array using poly(methyl methacrylate) for potential applications in light extraction of organic light-emitting diodes. With an attempt to achieve high-density and high-aspect-ratio microlens arrays, we have investigated the coating behaviors by varying the material parameters such as the solute concentration and wettability of the poly(methyl methacrylate) solution and process parameters such as the dwell time of needle near the substrate, retract distance of needle from the substrate, and coating gap between the needle and substrate. Under the optimized coating conditions, it is demonstrated that high-aspect-ratio microlens arrays can be obtained using a coating solution with high solute concentration and a small amount of a hydrophobic solvent. It is found that the diameter and height of microlens array are decreased with increasing poly(methyl methacrylate) concentration, yet the overall aspect ratio is rather enhanced. By the addition of 5 wt% hexylamine in 35 wt% poly(methyl methacrylate) solution, we have achieved a spherical microlens with the height of 7.7 ㎛ and the width of 94.24 ㎛ (the aspect ratio of 0.082). To estimate the capability of light extraction by the microlens array, we have performed ray tracing simulations and demonstrated that the light extraction efficiency of organic light-emitting diode is expected to be enhanced up to 24%.

• Journal of the Korean Institute of Gas
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• v.26 no.3
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• pp.21-26
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• 2022

Zinc is emerging as a environment-friendly plating material to replace cadmium, which is harmful to the human body, to prevent hydrogen gas penetration or release from metal materials. Electroplating of Zn and Zn alloys, which is usually performed in an aqueous acidic atmosphere, has disadvantages such as low coulombic efficiency, corrosion, and hydrogen release, resulting in industrial use difficult. In this study, a deep-eutectic solvent was synthesized using choline chloride and ethylene glycol. Using this as a solvent, an electrolyte for Zn plating was prepared, and then zinc was plated on the STS 304 substrate. The surface microstructure and roughness were observed using SEM and AFM. The crystal structure of the electro-plated film was analyzed using XRD. Finally, the preventing effects of hydrogen release through Zn-based deep-eutectic plating on the STS 304 substrate were compared with the uncoated substrate.

• Current Photovoltaic Research
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• v.11 no.1
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• pp.8-12
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• 2023

In this work, we investigated the thickness of Ag precursor layer to improve the performance of flexible CIGSe solar cells grown on stainless steel (STS) substrates through three-stage co-evaporation with Ga grading followed by alkali treatments. The small amount of incorporated Ag in CIGSe films showed enhancement in the grain size and device efficiency. With an optimal 6 nm-thick Ag layer, the best cell on the STS substrate yielded more than 16%, which is comparable to the soda-lime glass (SLG) substrate. Thus, the addition of controlled Ag combined with alkali post-deposition treatment (PDT) led to increased open-circuit voltage (VOC), accompanied by the increased built-in potential as confirmed by capacitance-voltage (C-V) measurements. It is related to a reduction of charge recombination at the depletion region. The results suggest that Ag alloying and alkali PDT are essential for producing highly efficient flexible CIGSe solar cells.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.421-421
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• 2006

The light and energy-efficiency of classical liquid crystal displays is notoriously poor due to the use of absorption-based linear polarisers and colour filters. For instance, the light efficiency of PVAL polarisers is typically between 40 and 45 % and the colour filters have a typical efficiency below 35 % which results in a total light and energy-efficiency of the display below 10 %. In the past, a variety of polarizers were developed with an enhanced efficiency in generating linearly polarized light. Typically, these polarizers are based on the polarisationselective reflection, scattering or refraction of light i.e. one polarisation direction of light is directly transmitted to the LCD/viewer and the other polarization direction of light is depolarised and recycled which results in a typical efficiency for generating linearly polarized light of 70-85 %. Also, special colour filters have been proposed based on chiral-nematic reactive mesogens which increase the efficiency of generating colour. Despite the enormous progress in this field, a need persists for improved methods for generating polarized light and colour based on low cost optical components with a high efficiency. Here, the use of holographic phase gratings is reported for the generation of polarized light and colour. The phase grating are recorded in a photopolymer which is coated onto a backor frontlight for LCDs. Typically the recording is performed in the transmisson mode or in the waveguiding mode and slanted phase gratings are generated with their refractive index modulation at an angle between 20o and 45o with the normal of the substrate. It is shown that phase gratings with a high refractive index modulation and a high efficiency can be generated by a proper selection of the photopolymer and illumination conditions. These phase gratings coupleout linearly polarized light with a high contrast (> 100) and the light is directed directly to the LCD/viewer without the need for redirection foils. Dependent on the type of phase grating, the different colours are coupled-out at a slightly different angle which potentially increases the efficiency of classical colour filters. Moreover, the phase gratings are completely transparent in direct view which opens the possibility to use them in frontlights for LCDs. Holographic polarization gratings posses a periodic pattern in the polarization state of light (and not in the intensity of light). A periodic pattern in the polarization direction of linearly polarized light is obtained upon interference of two circularly polarized laser beams. In the second part of the lecture, it is shown that these periodic polarization patterns can be recorded in a linear photo-polymerizable polymer (LPP) and that such an alignment layer induces a period rotation in the director of (reactive and non-reactive) liquid crystals. By a proper design, optical components can be produced with only first order diffraction and with a very high efficiency (>0.98). It is shown that these diffraction gratings are potentially useful in projection displays with a high brightness and energy efficiency

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.12
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• pp.1069-1077
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• 2011

In this paper, a design and fabrication of a miniaturized 2.5 GHz 8 W power amplifier using selectively anodized aluminum oxide(SAAO) substrate are presented. The process of SAAO substrate is recently proposed and patented by Wavenics Inc. which uses aluminum as wafer. The selected active device is a commercially available GaN HEMT chip of TriQuint company, which is recently released. The optimum impedances for power amplifier design were extracted using the custom tuning jig composed of tunable passive components. The class-F power amplifier are designed based on EM co-simulation of impedance matching circuit. The matching circuit is realized in SAAO substrate. For integration and matching in the small package module, spiral inductors and single layer capacitors are used. The fabricated power amplifier with $4.4{\times}4.4\;mm^2$ shows the efficiency above 40 % and harmonic suppression above 30 dBc for the second(2nd) and the third(3rd) harmonic at the output power of 8 W.