• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.199-202
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• 2005

We have studied the origin of coherent director rotation [CDR] as well as memory behavior in thiol-ene polymer stabilized ferroelectric liquid crystal [FLC]. The ene constituents are found to be always located at the inter-layer space and induce the coherent director rotation motion of liquid crystal molecule. On the other hand, the thiols are more intersticed between ferroelectric liquid crystal molecules at intra-layer as the thiol gets longer, and these intersticed thiols enhance the multistability and the resolution of memory state of FLCs.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.381-387
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• 2000

Si3N4/stainless steel 316 joints with Ni buffer layer were fabricated by direct active brazing method (DIB) using Ag-Cu-Ti brazing alloy only and double brazing method (DOB) using Ag-Cu brazing alloy with Si3N4 pretreated with Ag-Cu-Ti brazing alloy. For the joint brazed by DIB method, Ti was segregated at the Si3N4/brazing alloy interface, but was not enough to form a stable joint interface. In addition, large amounts of Ni-Ti inter-metallic compounds were formed in tehbrazing alloy near the joint interface, which could deplete the contents of Ti involved in the interfacial reaction. However, for the joint brazed by DOB method, segregation of Ti at the joint interface were enough to enhance the formation of stable interfacial reaction products such as TiN and Ti-Si-Ni-N-(Cu) multicompounds, which restricted the formation of Ni-Tio inter-metallic compounds in the brazing alloy during brazing with Ni buffer layer. Fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was much improved by using DOB method rather than DIB method. It could be deduced that the differences of fracture strength of the joint with Ni buffer layer depending on brazing process adapted were directly affected by the formation of stable joint interface and the change in microstructure of the brazing alloy near the joint interface. It was found that fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was gradually reduced as the thickness of interface. It was found that fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was gradually reduced as the thickness of Ni buffer layer in the joint was increased from 0.1 mm to 10 mm. It seems to due to the increased residual stress in the joint as the thickness of Ni buffer layer is increased. The maximum fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was 386 MPa, and the fracture of joint was originated at Si3N4/brazing alloy joint interface and propagated into Si3N4 matrix.

• Earthquakes and Structures
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• v.27 no.1
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• pp.17-29
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• 2024

The traditional double story isolated structure is a derivative of the base isolated and inter-story isolated structures, while the new double story isolated structure represents a novel variation derived from the traditional double story isolated structure. In order to investigate the seismic response of the new double story isolated structure, a comprehensive structural model was developed. Concurrently, models for the basic fixed, base isolated, inter-story isolated, and traditional double story isolated structures were also established for comparative analysis. The nonlinear dynamic time-history response of the new double story isolated structure under rare earthquake excitations was analyzed. The findings of the study reveal that, in comparison to the basic fixed structure, the new double story isolated structure exhibits superior performance across all evaluated aspects. Furthermore, when compared to the base isolated and inter-story isolated structures, the new double story isolated structure demonstrates significant reductions in inter-story shear force, top acceleration, and inter-frame displacement. The horizontal displacement of the new double story isolated structure is primarily localized within the two isolation layers, effectively dissipating the majority of input seismic energy. In contrast to the traditional double story isolated structure, the new design minimizes displacements within the inter-isolation layer situated in the central part of the frame, as well as mitigates the overturning forces acting on the lower frame column. Consequently, this design ensures the structural integrity of the core tube, thereby preventing potential collapse and structural damage.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1240_1241
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• 2009

In this paper, sol-gel-spin coated $Pb(ZrTi)O_3$ thin film with $ZrO_2$ buffer-layer and $PbTiO_3$ seed-layer was investigated for vibration MEMS energy harvester to scavenge power from ambient vibration via d33 piezoelectric mode. Piezoelectric thin film deposition techniques on insulating layer is the important key for $d_{33}$ mode of piezoelectric vibration energy harvester. $ZrO_2$ buff-layer was utilized as an insulating layer. $PbTIO_3$ seed-layer was applied as an inter-layer between PZT and $ZrO_2$ layer to improve the crystalline of PZT thin film. The fabricated PZT thin film had a remanent polarization of 5.3uC/$cm^2$ and the coercive field of 60kV/cm. The fabricated energy harvester using PZT thin film with PTO seed-layer generated 1.1uW of electrical power to $2.2M{\Omega}$ of load with $4.4V_{pvp}$ from vibration of 0.39g at 528Hz.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.4
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• pp.470-480
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• 2016

The reversal of a silicon chip to find out its security structure is common and possible at the present time. Thanks to reversing, it is possible to use a probing attack to obtain useful information such as personal information or a cryptographic key. For this reason, security-related blocks such as DES (Data Encryption Standard), AES (Advanced Encryption Standard), and RSA (Rivest Shamir Adleman) engines should be located in the lower layer of the chip to guard against a probing attack; in this regard, the addition of a silicon-surface-protection layer onto the chip surface is a crucial protective measure. But, for manufacturers, the implementation of an additional silicon layer is burdensome, because the addition of just one layer to a chip significantly increases the overall production cost; furthermore, the chip size is increased due to the bulk of the secure logic part and routing area of the silicon protection layer. To resolve this issue, this paper proposes a practical silicon-surface-protection method using a metal layer that increases the security level of the chip while minimizing its size and cost. The proposed method uses a shift register for the alternation and variation of the metal-layer data, and the inter-connection area is removed to minimize the size and cost of the chip in a more extensive manner than related methods.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.1
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• pp.114-121
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• 2015

In conventional LEDs, a mesa-structure is usually used and it causes the current to be overcrowded in a specific region. We propose a novel structure of GaN-based LED to overcome this problem. In order to distribute the current in an active region, a spreading pad is inserted at the p-type region in the GaN based LED device. The inserted spreading pad helps the current flow because it is more conductive than the p-type GaN layer. By performing electrical and optical simulations, the effects of the spreading pad insertion are confirmed. The results of electrical simulation show that the current spreads more uniformly and more radiative recombination is produced as well. Moreover, from the optical simulation, it is revealed that the ITO is less absorptive material than p-GaN if the condition of specific wavelength sources is satisfied. Considering all of the results, we can conclude that the luminescent power is enhanced by the spreading pad.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1291-1293
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• 2005

Hybrid insulator pentacene thin film transistors (TFTs) were fabricated with thermally grown oxide and cross-linked polyvinylalcohol (PVA) including surface treatment by dilute ploymethylmethacrylate (PMMA) layers on $n^+$ doped silicon wafer. Through the optimization of $SiO_2$ layer thickness in hybrid insulator structure, carrier mobility was increased to above 35 times than that of the TFT only with the gate insulator of $SiO_2$ at the same transverse electric field. The carrier mobility of 1.80 $cm^2$/V-s, subthreshold swing of 1.81 V/decade, and $I_{on}$/ $I_{off}$ current ratio > 1.10 × $10^5$ were obtained at low bias (less than -30 V) condition. The result is one of the best reported performances of pentacne TFTs with hybrid insulator including cross-linked PVA material at low voltage operation.

• Journal of Electrical Engineering and information Science
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• v.2 no.6
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• pp.212-216
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• 1997

A new metal tip fabrication process for low voltage operation is reported in this paper. The key element of the fabrication process is that isotropic silicon etching and oxidation process used in silicon tip fabrication is utilized for gate hole size reduction and gate oxide layer. A metal FEA with 625 tips was fabricated in order to demonstrate the validity of the new process and submicron gate apertures were successfully obtained from originally 1.7$\mu\textrm{m}$ diameter mask. The emission current above noise level was observed at the gate bias of 50V. The required gate voltage to obtain the anode current of 0.1${\mu}\textrm{A}$/tip was 74V and the emission current was stable above 2${\mu}\textrm{A}$/tip without any disruption. The local field conversion factor and the emitting area were calculated as 7.981${\times}$10\ulcornercm\ulcorner and 3.2${\times}$10\ulcorner$\textrm{cm}^2$/tip, respectively.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.291-295
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• 2007

The oxidation treatment of needle cokes with 70 wt% of nitric acid and sodium chlorate ($NaClO_3$) was attempted to achieve an electrochemically active material with a large capacitance. The structure of needle cokes was changed to graphite oxide after oxidation treatment of needle cokes with acidic solution having the composition ratio, $NaClO_3$/needle cokes, of 7.5, and the inter-layer distance of the oxidized needle cokes was extended to $6.9{\AA}$with increasing oxygen content. On the other hand, the electrochemical performance of oxidized needle cokes as a polarized electrode for an Electric Double Layer Capacitor (EDLC) was examined with an electrolyte of 1.2 M $TEABF_4$ (tetraethylammonium tetrafluoroborate) and $TEABF_4$ (triethylmethylammonium tetrafluoroborate) in acetonitrile. The capacitor cell using 1.2 M $TEABF_4$/acetonitrile has exhibited smaller electric resistance of $0.05{\Omega}$, and larger capacitance per weight and volume of 32.0 F/g and 25.5 F/mL at the two-electrode system in the potential range 0~2.5 V than that of the capacitor cell using $TEABF_4$. The observed electrochemical performance was discussed with the correlation between the inter-layer distance in graphite oxide structure and the anionic size of electrolyte.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.251-251
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• 2016

For several decades, industrial processes consume a huge amount of raw water for various objects that consequently results in the generation of large amounts of wastewater. Wastewaters are consisting of complex mixture of different inorganic and organic compounds and some of them can be toxic, hazardous and hard to degrade. These effluents are mainly treated by conventional technologies such are aerobic and anaerobic treatment and chemical coagulation. But, these processes are not suitable for eliminating all hazardous chemical compounds form wastewater and generate a large amount of toxic sludge. Therefore, other processes have been studied and applied together with these techniques to enhance purification results. These include photocatalysis, absorption, advanced oxidation processes, and ozonation, but also have their own drawbacks. In recent years, electrochemical techniques have received attention as wastewater treatment process that could be show higher purification results. Among them, boron doped diamond (BDD) attract attention as electrochemical electrode due to good chemical and electrochemical stability, long lifetime and wide potential window that necessary properties for anode electrode. So, there are many researches about high quality BDD on Nb, Ta, W and Si substrates, but, their application in effluents treatment is not suitable due to high cost of metal and low conductivity of Si. To solve these problems, Ti has been candidate as substrate in consideration of cost and property. But there are adhesion issues that must be overcome to apply Ti as BDD substrate. Al, Cu, Ti and Nb thin films were deposited on Ti substrate to improve adhesion between substrate and BDD thin film. In this paper, BDD films were deposited by hot filament chemical vapor deposition (HF-CVD) method. Prior to deposition, cleaning processes were conducted in acetone, ethanol, and isopropyl alcohol (IPA) using sonification machine for 7 min, respectively. And metal layer with the thickness of 200 nm were deposited by DC magnetron sputtering (DCMS). To analyze microstructure X-ray diffraction (XRD, Bruker gads) and field emission scanning electron microscopy (FE-SEM, Hitachi) were used. It is confirmed that metal layer was effective to adhesion property and improved electrode property. Electrochemical measurements were carried out in a three electrode electrochemical cell containing a 0.5 % H2SO4 in deionized water. As a result, it is confirmed that metal inter layer heavily effect on BDD property by improving adhesion property due to suppressing formation of titanium carbide.