• Journal of Power Electronics
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• v.18 no.3
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• pp.702-713
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• 2018

Power loss reduction and total harmonic distortion(THD) minimization are two important goals of improving three-level inverters. In this paper, an optimized pulse width modulation (PWM) strategy that can reduce switching losses and balance the neutral point with an optional THD of three-level neutral-point-clamped inverters is proposed. An analysis of the two-level discontinuous PWM (DPWM) strategy indicates that the optimal goal of the proposed PWM strategy is to reduce switching losses to a minimum without increasing the THD compared to that of traditional SVPWMs. Thus, the analysis of the two-level DPWM strategy is introduced. Through the rational allocation of the zero vector, only two-phase switching devices are active in each sector, and their switching losses can be reduced by one-third compared with those of traditional PWM strategies. A detailed analysis of the impact of small vectors, which correspond to different zero vectors, on the neutral-point potential is conducted, and a hysteresis control method is proposed to balance the neutral point. This method is simple, does not judge the direction of midpoint currents, and can adjust the switching times of devices and the fluctuation of the neutral-point potential by changing the hysteresis loop width. Simulation and experimental results prove the effectiveness and feasibility of the proposed strategy.

• Journal of the Korean Vacuum Society
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• v.17 no.5
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• pp.461-465
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• 2008

The phase transformation in a film influences its surrounding. Effects of the precrystallization method, which removes influences on gate oxide caused by lateral crystallization, in metal-induced unilaterally crystallized polycrystalline silicon thin-film transistor devices and circuits were studied. Device by the method was shown to have a higher current drive, compared with conventional postcrystallized device. Moreover, we studied DC bias-induced changes in the performance of ring oscillator. PMOS inverters fabricated using precrystallized silicon films have very high dynamic and stable performance, compared with inverters fabricated using postcrystallized silicon films.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.1
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• pp.16-23
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• 2015

In this paper, a bent microstrip patch antenna, which is suitable for band-type wearable devices and RF configuration, to be used in the WCDMA2100 mobile network is proposed. The proposed antenna using RF configuration which is consisted of separated Tx and Rx frequency band is designed to operate or function in WCDMA2100 Tx frequency band only and it is not strongly affected by the human body because of the conductor at the bottom side. At both flat case and bent case, the proposed antenna's maximum gain satisfies at least 5.3 dBi, and its -6 dB return loss bandwidth is wider than 20 MHz. The simulated surface absorption rate($SAR_{1g}$) result is under 0.7 [W/kg]. The proposed antenna suits in band-type wearable devices which is worn on wrists or arms.

• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.566-574
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• 2015

We report for the first time highly efficient trans-reflective color filters capable of demonstrating coloration in both transmission and reflection modes by taking advantage of a multilayer stack consisting of MgF₂ and TiO₂ used respectively as the low and high index materials. In order to enable such trans-reflective performance, securing an optimal stop band assuming an appropriate bandwidth within the visible regime is pivotal, which was realized by tailoring the thicknesses and the numbers of TiO₂-MgF₂ bi-layers. Three devices were designed through rigorous simulations and developed via e-beam evaporation to demonstrate vivid blue, green, and red colors in the reflection mode, and yellow, magenta, and cyan colors in the transmission mode, featuring an enhanced efficiency exceeding 90% under normal incidence. The color performance of the filters was examined by referring to the chromaticity coordinates of the transmission and reflection spectra, alongside photographed color images. The dependence of the performance on the angle of incidence was explored with respect to incident polarization, indicating that a transmission surpassing 60% could be stably maintained up to an angle of 75°. Polarization independent transfer characteristics were especially achieved for the normal incidence. The proposed devices may be readily extended to other spectral regimes by adjusting the thicknesses of the films.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.4
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• pp.303-308
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• 2011

The Gallium-doped ZnO(GZO) film deposited at a temperature of $200^{\circ}C$ and a pressure of 10 mtorr has an optical transmittance of 89.0% and a resistivity of $2.0\;m{\Omega}{\cdot}cm$ because of its high crystallinity. Effect of $Al_2O_3$ oxide buffer layers on the optical and electrical properties of sputtered ZnO films were intensively investigated for developing the electrodes of opto-electronic devices which demanded high optical transmittance and low resistivity. The use of $Al_2O_3$ buffer layer could increase optical transmittance of GZO film to 90.7% at a wavelength of 550 nm by controlling optical spectrum. Resistivity of deposited GZO films were much dependent on the deposition condition of $O_2/(Ar+O_2)$ flow rate ratio during the buffer layer deposition. It is considered that the $Al_2O_3$ buffer layer could increase the carrier concentration of the GZO films by doping effect of diffused Al atoms through the rough interface.

• Journal of the Semiconductor & Display Technology
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• v.7 no.2
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• pp.49-53
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• 2008

The yellow base polymer light emitting diodes(PLEDs) with double emission and hole blocking layers were prepared to improve the light efficiency. ITO(indium tin oxide) and PEDOT : PSS[poly(3,4-ethylenedioxythiophene) : poly(styrene sulfolnate)] were used as cathode and hole transport materials. The PFO[poly(9,9-dioctylfluorene)] and MEH-PPV[poly(2-methoxy-5(2-ethylhe xoxy)-1,4-phenylenevinyle)] were used as the light emitting host and guest materials, respectively. TPBI[Tpbi1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene] was used as hole blocking layer. To investigate the optimization of device structure, we prepared four kinds of PLED devices with different structures such as single emission layer(PFO : MEH-PPV), two double emission layer(PFO/PFO : MEH-PPV, PFO : MEH-PPV/PFO) and double emission layer with hole blocking layer(PFO/PFO : MEH-PPV/TPBI). The electrical and optical properties of prepared devices were compared. The prepared PLED showed yellow emission color with CIE color coordinates of x = 0.48, y = 0.48 at the applied voltage of 14V. The maximum luminance and current density were found to be about 3920 cd/$m^2$ and 130 mA/$cm^2$ at 14V, respectively for the PLED device with the structure of ITO/PEDOT : PSS/PFO/PFO : MEH-PPV/TPBI/LiF/Al.

• Journal of Communications and Networks
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• v.18 no.4
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• pp.540-550
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• 2016

Since energy efficiency has become a significant concern for network infrastructure, next-generation network devices are expected to have embedded advanced power management capabilities. However, how to effectively exploit the green capabilities is still a big challenge, especially given the high heterogeneity of devices and their internal architectures. In this paper, we introduce a hierarchical power management architecture (HPMA) which represents physical components whose power can be monitored and controlled at various levels of a device as entities. We use energy aware state (EAS) as the power management setting mode of each device entity. The power policy controller is capable of getting information on how many EASes of the entity are manageable inside a device, and setting a certain EAS configuration for the entity. We propose the optimal local control policy which aims to minimize the router power consumption while meeting the performance constraints. A first-order Markov chain is used to model the statistical features of the network traffic load. The dynamic EAS configuration problem is formulated as a Markov decision process and solved using a dynamic programming algorithm. In addition, we demonstrate a reference implementation of the HPMA and EAS concept in a NetFPGA frequency scaled router which has the ability of toggling among five operating frequency options and/or turning off unused Ethernet ports.

• Transactions on Electrical and Electronic Materials
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• v.17 no.4
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• pp.196-200
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• 2016

We have developed new electrostatic discharge (ESD) protection devices with, bidirectional flip chip transient voltage suppression. The devices differ in their epitaxial (epi) layers, which were grown by reduced pressure chemical vapor deposition (RPCVD). Their ESD properties were characterized using current-voltage (I-V), capacitance-voltage (C-V) measurement, and ESD analysis, including IEC61000-4-2, surge, and transmission line pulse (TLP) methods. Two BD-FCTVS diodes consisting of either a thick (12 μm) or thin (6 μm), n-Si epi layer showed the same reverse voltage of 8 V, very small reverse current level, and symmetric I-V and C-V curves. The damage found near the corner of the metal pads indicates that the size and shape of the radius governs their failure modes. The BD-FCTVS device made with a thin n- epi layer showed better performance than that made with a thick one in terms of enhancement of the features of ESD robustness, reliability, and protection capability. Therefore, this works confirms that the optimization of device parameters in conjunction with the doping concentration and thickness of epi layers be used to achieve high performance ESD properties.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.2
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• pp.140-148
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• 2021

In this paper, we intend to improve the availability by integrating Sonobuoy, the most essential detection system used in anti-submarine operations, with LTE communication of smart devices. Anti-submarine capability to respond to the threat of North Korean submarine forces is becoming increasingly important, and continuous research and development is required. This paper aims to enhance the ability of acoustic tactics by using a military-only LTE communication system installed on a ship, smart devices that can be linked to it, and a multi-static sonobuoy controlled by them. The proposed system can increase the visual effect by not only displaying coordinate values by receiving accurate coordinate information of each sonobuoy to a smart device, but also displaying a marker on a map.

• Korean Journal of Metals and Materials
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• v.56 no.12
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• pp.910-914
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• 2018

Since catalyst technology is one of the promising technologies to improve the working performance of next generation energy and electronic devices, many efforts have been made to develop various catalysts with high efficiency at a low cost. However, there are remaining challenges to be resolved in order to use the suggested catalytic materials, such as platinum (Pt), gold (Au), and palladium (Pd), due to their poor cost-effectiveness for device applications. In this study, to overcome these challenges, we suggest a useful method to increase the surface area of a noble metal catalyst material, resulting in a reduction of the total amount of catalyst usage. By employing block copolymer (BCP) self-assembly and nano-transfer printing (n-TP) processes, we successfully fabricated sub-20 nm Pt line and cross-bar patterns. Furthermore, we obtained a highly ordered Pt cross-bar pattern on a Ni thin film and a Pt-embedded Ni thin film, which can be used as hetero hybrid alloy catalyst structure. For a detailed analysis of the hybrid catalytic material, we used scanning electron microscope (SEM), transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy (EDS), which revealed a well-defined nanoporous Pt nanostructure on the Ni thin film. Based on these results, we expect that the successful hybridization of various catalytic nanostructures can be extended to other material systems and devices in the near future.