• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.2
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• pp.321-324
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• 2020

In this work, we developed a selective etching process for GaN that is a key process in p-GaN/AlGaN/GaN enhancement-mode (E-mode) power switching field-effect transistor (FET) fabrication. In order to achieve a high current density of p-GaN/AlGaN/GaN E-mode FET, the p-GaN layer beside the gate region must be selectively etched whereas the underneath AlGaN layer should be maintained. A selective etching process was implemented by oxidizing the surface of the AlGaN layer and the GaN layer by adding O2 gas to Cl2/N2 gas which is generally used for GaN etching. A selective etching process was optimized using Cl2/N2/O2 gas mixture and a high selectivity of 53:1 (= GaN/AlGaN) was achieved.

• Journal of the Korean Society of Food Science and Nutrition
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• v.33 no.2
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• pp.271-277
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• 2004

This study was designed to evaluate the effect of Bu -Zhong-Yi-Qi-Tang extracts, a prescription of traditional oriental medicine, on development of the B cells. In the bone marrow cell cultures, progenitors viability, expressions of particular cell- surface proteins and production of immunoglobulins were investigated in the presence of Bu-Zhong-Yi-Qi-Tang extracts. The administration of Bu-Zhong -Yi-Qi-Tang polysaccharide fraction increased the viable cell numbers of the precursor B cells, and elevated expression levels of CD19/CD40 specific for pre-B cells after 10 days culture were demonstrated by flow cytometry analysis. The production of immunoglobulin M in the presence of polysaccharide fraction increased progressively in the culture supernatant, and preferentially induced class switching to IgG1, IgG2a and IgG3. These results indicated that Bu -Zhong -Yi-Qi -Tang strong1y correlated with the development of precursor B cells in the bone marrow cell culture. Therefore the polysaccharide fraction of Bu-Zhong-Yi -Qi-Tang might be a useful radioprotector, especially since it is a relatively non-toxic natural product. Further studies are needed to better characterize the protective nature of Bu-Zhong-Yi -Qi -Tang extract.

• Transactions on Electrical and Electronic Materials
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• v.8 no.3
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• pp.135-138
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• 2007

In this study, we investigated the electro-optical (EO) characteristic of fringe-field switching (FFS) mode cell by the two kinds of ultraviolet (UV) alignment method on the organic thin film (polyimide: PI). The suitable organic layers for FFS cell and the aligning capabilities of nematic liquid crystal (NLC) using the in-situ photoalignment method were studied; Disclination is observed after conventional photoalignment method for 1h, and in-situ photoalignment method for 1h. Monodomain alignment of the NLC can be observed via insitu photo alignment method for 2 h and 3 h. It is considered that NLC alignment is due to photo-depolymerization of the polymer with oblique non-polarized UV irradiation on PI surface. An unstable V-T curve of UV-aligned FFS-LCD with conventional photoalignment method can be achieved. However, a stable V-T curve of UV-aligned FFS-LCD with in-situ photoalignment method (1 h), and V-T curve of UV-aligned FFS-LCD with in-situ photo alignment method was much stable comparing with that of other UV-aligned FFSLCD's. As a result, more stable EO performance of UV-aligned FFS-LCD with in-situ photoalignment method for 3h is obtained than that of the other UV-aligned FFS-LCD's.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.5
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• pp.69-76
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• 2016

Current driving capability of MCT (MOS Controlled Thyristor) is determined by turn-off capability of conducting current, that is off-FET performance of MCT. On the other hand, having a good turn-on characteristics, including high peak anode current ($I_{peak}$) and rate of change of current (di/dt), is essential for pulsed power system which is one of major application field of MCTs. To satisfy above two requirements, careful control of on/off-FET performance is required. However, triple diffusion and several oxidation processes change surface doping profile and make it hard to control threshold voltage ($V_{th}$) of on/off-FET. In this paper, we have demonstrated the effect of $V_{th}$ adjustment ion implantation on the performance of MCT. The fabricated MCTs (active area = $0.465mm^2$) show forward voltage drop ($V_F$) of 1.25 V at $100A/cm^2$ and Ipeak of 290 A and di/dt of $5.8kA/{\mu}s$ at $V_A=800V$. While these characteristics are unaltered by $V_{th}$ adjustment ion implantation, the turn-off gate voltage is reduced from -3.5 V to -1.6 V for conducting current of $100A/cm^2$ when the $V_{th}$ adjustment ion implantation is carried out. This demonstrates that the current driving capability is enhanced without degradation of forward conduction and turn-on switching characteristics.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.183-184
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• 2013

Two main MBE growth techniques have been used: plasma-assisted MBE (PA-MBE), which utilizes a rf plasma to supply active nitrogen, and ammonia MBE, in which nitrogen is supplied by pyrolysis of NH3 on the sample surface during growth. PA-MBE is typically performed under metal-rich growth conditions, which results in the formation of gallium droplets on the sample surface and a narrow range of conditions for optimal growth. In contrast, high-quality GaN films can be grown by ammonia MBE under an excess nitrogen flux, which in principle should result in improved device uniformity due to the elimination of droplets and wider range of stable growth conditions. A drawback of ammonia MBE, on the other hand, is a serious memory effect of NH3 condensed on the cryo-panels and the vicinity of heaters, which ruins the control of critical growth stages, i.e. the native oxide desorption and the surface reconstruction, and the accurate control of V/III ratio, especially in the initial stage of seed layer growth. In this paper, we demonstrate that the reliable and reproducible growth of GaN on Si (110) substrates is successfully achieved by combining two MBE growth technologies using rf plasma and ammonia and setting a proper growth protocol. Samples were grown in a MBE system equipped with both a nitrogen rf plasma source (SVT) and an ammonia source. The ammonia gas purity was ＞99.9999% and further purified by using a getter filter. The custom-made injector designed to focus the ammonia flux onto the substrate was used for the gas delivery, while aluminum and gallium were provided via conventional effusion cells. The growth sequence to minimize the residual ammonia and subsequent memory effects is the following: (1) Native oxides are desorbed at $750^{\circ}C$ (Fig. (a) for [$1^-10$] and [001] azimuth) (2) 40 nm thick AlN is first grown using nitrogen rf plasma source at $900^{\circ}C$ nder the optimized condition to maintain the layer by layer growth of AlN buffer layer and slightly Al-rich condition. (Fig. (b)) (3) After switching to ammonia source, GaN growth is initiated with different V/III ratio and temperature conditions. A streaky RHEED pattern with an appearance of a weak ($2{\times}2$) reconstruction characteristic of Ga-polarity is observed all along the growth of subsequent GaN layer under optimized conditions. (Fig. (c)) The structural properties as well as dislocation densities as a function of growth conditions have been investigated using symmetrical and asymmetrical x-ray rocking curves. The electrical characteristics as a function of buffer and GaN layer growth conditions as well as the growth sequence will be also discussed. Figure: (a) RHEED pattern after oxide desorption (b) after 40 nm thick AlN growth using nitrogen rf plasma source and (c) after 600 nm thick GaN growth using ammonia source for (upper) [110] and (lower) [001] azimuth.

• Korean Journal of Acupuncture
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• v.38 no.4
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• pp.282-289
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• 2021

Objectives : The purpose of this study is to construct a model of the possible thermal runaway of electronic moxibustion and to implement an appropriate risk management method. Methods : To reproduce the system error situation of the electronic moxibustion circuit equipped with microcontroller unit, temperature sensor and heater, a code was set to disable the signal input to temperature sensor and maintain "high" heating signal to heater. The temperature change of electronic moxibustion was compared between 3 types of heater module; module 1 consisting of a combination of heater+0 ohm+0 ohm resistance, module 2 consisting of a combination of heater+Polymeric Positive Temperature Coefficient (PPTC)+0 ohm resistance, and module 3 consisting of a combination of heater+PPTC+10 ohm resistance. The temperature change was measured using a polydimethylsiloxane (PDMS) silicone phantom. After maintaining surface temperature of the phantom at 31~32℃ for 20 seconds, electronic moxibustion was applied. After operating electronic moxibustion, the temperature change was measured for 660 seconds on the surface and 900 seconds at 2 mm depth. Results : Regardless of the module type, the time-dependent change in temperature showed a rapid rise followed by a gentle curve, and a sharp drop in temperature after reaching the maximum temperature about 10 minutes after the switching the moxibustion on. Temperature measured at the depth of 2 mm below the surface increased slower and to a lesser extent. Module 1 reached highest peak temperature with largest change of temperature at both depths followed by module 2, and 3. Conclusions : Through the combination of PPTC+resistance with the heater of electronic moxibustion, it is possible to limit the rise in temperature even with the software error. Thus, this setting can be used as an independent safety measure for the electronic moxibustion control unit.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.139.2-139.2
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• 2015

In this study, We applied the magnetic field that has CW frequency and AM frequency to heating magnetic nano powder. For this experiment, We set up the devices flat-type magnetic field generator with CW frequency and AM frequency. We supplied the current to encircling coil by adjusting the power of generating of magnetic field device for AC voltage through Slidacs and using way of LC resonance circuit and SMPS(Switching Mode Power Supply). Above the encircling coil, We covered the circular flat insulator like glass. And we located the well plate containing the magnetic nano powder liquor above the circular flat insulator and exposed the magnetic field to this well plate. Using the flat-type magnetic field generator with CW and AM frequency and the magnetic field measurement sensor(Magnetic pick up coil or Hall sensor), We measured the strength of the magnetic field of circular flat insulator's surface in each position. The temperature of the magnetic nano powder in the well plate was quantitatively measured by the magnetic field strength through the Fluoroptic thermometer.

• Journal of the Korean Institute of Intelligent Systems
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• v.12 no.2
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• pp.164-170
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• 2002

Sliding mode control, as a typical method of variable structure control, has the robust characteristics for the uncertainty and the disturbance of the nonlinear system. Because, however, sliding mode control input includes a sign function that Is discontinuous on the predefined switching surface, its applications are primarily limited by the need of alleviation or reduction of chattering. In this paper, we propose a chattering alleviation strategy based on a special nonlinear function and a fuzzy system. By using the proposed control scheme, we can reduce the steady state error. Its tracking performance is as fast as that of conventional method using the fixed boundary layer. Especially, in the proposed method, we can adjust the trade-off between the steady state error and the degree of chattering by regulating the proper range of the output variable of the fuzzy system. To verify the validity of the proposed algorithm, the analysis of the control method using the fixed boundary layer and the computer simulations are shown to compare with them.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.752-758
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• 2004

This paper reports on the DC and RF characteristics of AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beau epitaxy(MBE) on sapphire substrates. The devices with a 0.5 ${\mu}$m gate-length exhibited relatively flat transconductance(g$\_$m/), which results from the enhanced carrier confinement of the InGaN channel. The maximum drain current was 880 mA/mm with a peak g$\_$m/ of 156 mS/mm, an f$\_$T/ of 17.3 GHz, and an f$\_$MAX/ or 28.7 GHz. In addition to promising DC and RF results, pulsed I-V and current-switching measurements showed little dispersion in the unpassivated AlGaN/InGaN HEMTs. These results suggest that the addition of In to the GaN channel improves the electron transport characteristics as well as suppressing current collapse that is related to the surface trap states.

• Korean Journal of Materials Research
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• v.11 no.11
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• pp.960-964
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• 2001

$Bi_{3.99}Ti_{2.97}V_{0.03}O_{12}$ (BTV) thin films with 3 mol% vanadium doping were Prepared on $Pt/Ti/SiO_2/Si$ substrate by sol-gel method. X-ray diffraction analysis indicated that single-phase layered perovskite were obtained and preferred orientation was not observed. Under the annealing temperature at $600^{\circ}C$, the surface morphology of the BTV thin films had fine-rounded particles and then changed plate-like at $650^{\circ}C$ and $700^{\circ}C$. The remanent polarization $(2P_r)$ and coercive field $(2E_c)$ of $700^{\circ}C$ annealed BTV thin film were 25 $\mu$C/cm$^2$ and 116 kV/cm, respectively. In addition, BTV thin film showed little polarization fatigue during $10_9$ switching cycles. These improved ferroelectric properties were attributed to the increased rattling space and reduced oxygen vacancies by substitution $Ti^{4+}$ ion (68 pm) with smaller $V^{5+}$ ion (59 pm). The dielectric constant and loss were measured 130 and 0.03 at 10 kHz, respectively.