• Journal of Electrochemical Science and Technology
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• v.11 no.4
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• pp.352-360
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• 2020

Lithium cobalt oxide (LiCoO₂, LCO) has been widely used as a cathode material for Li-ion batteries (LIBs) owing to its excellent electrochemical performance and highly reproducible synthesis even with mass production. To improve the energy density of the LIBs for their deployment in electro-mobility, the full capacity and voltage of the cathode materials need to exploited, especially by operating them at a higher voltage. Herein, we doped LCO with divalent calcium-ion (Ca²⁺) to stabilize its layered structure during the batteries' operation. The Ca-doped LCO was synthesized by two different routes, namely solid-state and co-precipitation methods, which led to different average particle sizes and levels of dopant's homogeneity. Of these two, the solid-state synthesis resulted in smaller particles with a better homogeneity of the dopant, which led to better electrochemical performance, specifically when operated at a high voltage of 4.5 V. Electrochemical simulations based on a single particle model provided theoretical corroboration for the positive effects of the reduced particle size on the higher rate capability.

• Solar Energy
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• v.17 no.1
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• pp.59-66
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• 1997

The solar cell electrical output parameters such as the open circuit voltage($V_{oc}$) and short circuit current density($V_{sc}$) are intrinsic characteristics depending on junction depth, doping concentration, metal contacts barriers and cell structure. As a role of thumb for solar cell design, the metal contact barriers for phosphorus doped emitter should have lower work function in order to provide lower series resistance. The fabrication of PESC(passivated emitter solar cell) structure usually involves the use of titanium as a metal contact barrier. Chromium, which work function is similar to titanium but conductance is higher than titanium is being investigated as the new metal contact barrier. Although titanium has lower work function difference than chromium, the electric performances of chromium as contact barrier are higher than titanium. This better performance is attributed to the lower resistivity from chromium. This paper, therefore, compares the attributes of metal barrier contacts using titanium and chromium.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.220-221
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• 2003

Equiatomic FePt and CoPt alloy thin films have received considerable attention as possible magnetic and magneto-optic recording because of their high magnetic anisotropy energy and high coercivity. The high coercivity in these thin films is due to the presence of finely dispersed ordered FePt phase mixed with disordered FePt phase. However, a high temperature treatment, either substrate heating during deposition or post annealing, is needed to obtain the ordered L1$\_$0/ phase with high value of magneto crystalline anisotropy. Recent microstructural studies on these films suggest that the average grain size ranges from 10-50 nm and the grains are magnetically coupled between each other. On the other hand, the ultrahigh-density magnetic recording media with low media noise imposes the need of a material, which consists of magnetically isolated grains with size below 10 nm. The magnetic grain isolation can be controlled by the amount of additional non-magnetic element in the system which determines the interparticle separation and therefore the interparticle interactions. Recently, much research work has been done on various non-magnetic matrices. Preliminary studies showed that the samples prepared in B$_2$O$_3$ and Carbon matrices have shown strong perpendicular anisotropy and fine grain size down to 4nm, which suggest these nanocomposite films are very promising and may lead to the realization of a magnetic medium capable of recording densities beyond 1 Tb/in$^2$. So, in this work, the effect of Carbon doping on the magnetic properties of FePt nanoparticles were investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.98-98
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• 1999

Highly transparent and conducting tin-doped indium oxide (ITO) films were deposited on polycarbonate substrate by ion-assited deposition. Low substrate temperature (<10$0^{\circ}C$) was maintained during deposition to prevent the polycarbonate substrate from be deformed. The influence of ion beam energy, ion current density, and tin doping, on the structural, electrical and optical properties of deposited films was investigated. Indium oxide and tin-doped indium oxide (9 wt% SnO2) sources were evaporated with assisting ionized oxygen in high vacuum chamber at a pressure of 2$\times$10-5 torr and deposition temperature was varied from room temperature to 10$0^{\circ}C$. Oxygen gas was ionized and accelerated by cold hallow-cathode type ion gun at oxygen flow rate of 1 sccm(ml/min). Ion bea potential and ion current of oxygen ions was changed from 0 to 700 V and from 0.54 to 1.62 $\mu$A. The change of microstructure of deposited films was examined by XRD and SEM. The electrical resistivity and optical transmittance were measured by four-point porbe and conventional spectrophotometer. From the results of spectrophotometer, both the refractive index and the extinction coefficient were derived.

• JSTS:Journal of Semiconductor Technology and Science
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• v.6 no.2
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• pp.61-67
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• 2006

We fabricate local damascene FinFET cell array in sub-60nm feature sized DRAM. The local damascene structure can remove passing-gate-effects in FinFET cell array. p+ boron in-situ doped polysilicon is chosen for the gate material, and we obtain a uniform distribution of threshold voltages at around 0.7V. Sub-threshold swing of 75mV/d and extrapolated off-state leakage current of 0.03fA are obtained, which are much suppressed values against those of recessed channel array transistors. We also obtain a few times higher on-state current. Based on the improved on- and off-state current characteristics, we expect that the FinFET cell array could be a new mainstream structure in sub-60nm DRAM devices, satisfying high density, low power, and high-speed device requirements.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.3
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• pp.1-6
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• 2010

A comparative analysis of quantum-mechanical and classical simulation regarding corner effect in a Saddle MOSFET has been carried out using a 3-D numerical simulator. The comparison has shown that quantum simulation gives correct description of device by providing accurate peak E-density position and magnitude at the Si-fin cross-section, hence accurate analysis of corner effect and its impact on device threshold voltage (Vth) characteristics is carried out. Moreover, rounding the Si-fin comers or lowering the body doping have been shown as two possible techniques to suppress the undesirable corner effect.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.773-776
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• 2002

Efficient organic white light-emitting diodes are fabricated by doping [bis(2-methyl-8-quinolinolato) (tripheny-siloxy)aluminium (III)] (SAlq), a blue-emitting layer, with a red fluorescent dye of 4-dicyanomethylene-2-methyl-6-{2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-8-yl)vinyl}-4H-pyran (DCM2). The incomplete energy transfer from blue-emitting SAlq to red-emitting DCM2 enables to obtain a balanced white light-emission. A device with the structure of ITO/TPD (50 nm)/SAlq:DCM2 (30 nm, 0.5 %)/$Alq_3$ (20 nm)/LiF (0.5 nm)/AI shows emission peaks at 456 nm and 482 nm from SAlq and at 570 nm from DCM2. The white light-emitting device shows an external quantum efficiency of about 2.3 %, a luminous efficiency of about 2.4 lm/W, and the CIE chromaticity coordinates of (0.32, 0.37) at 100 cd/m^2. A maximum luminance of about 23,800 cd/m^2. is obtained at 15 V and the current density of 782 mA/cm^2.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.196-196
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• 2012

Graphene, two-dimensional one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbled appreciable attention due to its extraordinary mechanical, thermal, electrical, and optical properties. Based on the graphene's high carrier mobility, high frequency graphene field effect transistors have been developed. Graphene is useful for photonic components as well as for the applications in electronic devices. Graphene's unique optical properties allowed us to develop ultra wide-bandwidth optical modulator, photo-detector, and broadband polarizer. Graphene can support SPP-like surface wave because it is considered as a two-dimensional metal-like systems. The SPPs are associated with the coupling between collective oscillation of free electrons in the metal and electromagnetic waves. The charged free carriers in the graphene contribute to support the surface waves at the graphene-dielectric interface by coupling to the electromagnetic wave. In addition, graphene can control the surface waves because its charge carrier density is tunable by means of a chemical doping method, varying the Fermi level by applying gate bias voltage, and/or applying magnetic field. As an extended application of graphene in photonics, we investigated the characteristics of the graphene-based plasmonic waveguide for optical signal transmission. The graphene strips embedded in a dielectric are served as a high-frequency optical signal guiding medium. The TM polarization wave is transmitted 6 mm-long graphene waveguide with the averaged extinction ratio of 19 dB at the telecom wavelength of $1.31{\mu}m$. 2.5 Gbps data transmission was successfully accomplished with the graphene waveguide. Based on these experimental results, we concluded that the graphene-based plasmonic waveguide can be exploited further for development of next-generation integrated photonic circuits on a chip.

• Transactions on Electrical and Electronic Materials
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• v.13 no.6
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• pp.283-286
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• 2012

(1-X)$(Na_{0.5}K_{0.5})NbO_3-XK_{5.4}Cu_{1.3}Ta_{10}O_{29}$ (NKN-KCT) lead-free piezoelectric ceramics have been synthesized by the conventional solid state sintering method, and their sinterability and piezoelectric properties were investigated. Typically, this material is sintered between 1,025 and $1,100^{\circ}C$ for 2 hours to achieve the required densification. Crystalline structures and Microstructures were analyzed by X-ray diffraction and scanning electron microscope. The density, dielectric constant (${\varepsilon}_r$), piezoelectric constant $d_{33}$, electromechanical coupling factor $k_p$ and mechanical quality factor $Q_m$ value of the NKN ceramics depended upon the KCT content and the sintering temperature. In particular, the KCT addition to NKN greatly improved the mechanical quality factor $Q_m$ value. The ceramic with X = 1.0 mol% sintered at $1,050^{\circ}C$ exhibited optimum properties (${\varepsilon}_r$=246, $d_{33}$=95, $k_p$=0.38 and $Q_m$=1,826). These results indicate that the ceramic is a promising candidate material for applications in lead free piezoelectric transformer and filter materials.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.227-233
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• 1992

The simulation code was developed for the development of the split-disk geometry glass amplifier, which could design the laser apparatus and analyze the properties of the laser system. The flashlamp emission energy at the short wavelength region must be reduced, while maintaining a current density between 2000 and 4000 A/$\textrm{cm}^{2}$, in order to reduce the thermal loading in the laser glass and to raise the coupling efficiency between the emission spectrum of the flashlamps and the absorption spectrum of the laser glass. By cutting the laser glass into three equal pieces, the temperature rise in the laser glass dropped by 70% due to the efficient removal of the heat in the laser glass. It was found that the $Nd^{3+}$ doping rate of each laser glass should be properly selected and the optimum value of the product of the absorption coefficient $\alpha$ and the thickness d of the laser glass is about 0.26 in the split-disk geometry.