• Current Photovoltaic Research
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• 제7권1호
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• pp.9-14
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• 2019

Carrier selective solar cell structure has allured curiosity of photovoltaic researchers due to the use of wide band gap transition metal oxide (TMO). Distinctive p/n-type character, broad range of work functions (2 to 7 eV) and risk free fabrication of TMO has evolved new concept of heterojunction intrinsic thin layer (HIT) solar cell employing carrier selective layers such as $MoO_x$, $WO_x$, $V_2O_5$ and $TiO_2$ replacing the doped a-Si layers on either front side or back side. The p/n-doped hydrogenated amorphous silicon (a-Si:H) layers are deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD), which includes the flammable and toxic boron/phosphorous gas precursors. Due to this, carrier selective TMO is gaining popularity as analternative risk-free material in place of conventional a-Si:H. In this work hole selective materials such as $MoO_x$, $WO_x$ and $V_2O_5$has been investigated. Recently $MoO_x$, $WO_x$ & $V_2O_5$ hetero-structures showed conversion efficiency of 22.5%, 12.6% & 15.7% respectively at temperature below $200^{\circ}C$. In this work a concise review on few important aspects of the hole selective material solar cell such as historical developments, device structure, fabrication, factors effecting cell performance and dependency on temperature has been reported.

• 대한방사선기술학회지:방사선기술과학
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• 제43권6호
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• pp.481-487
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• 2020

Radiation measurement technology has steadily improved and its usage is expanding in various industries such as nuclear medicine, security search, satellite, nondestructive testing, environmental industries and the domain of nuclear power plants (NPPs). Especially, the simultaneous measurements of gamma rays and neutrons can be even more critical for nuclear safety management of spent nuclear fuel and monitoring of the nuclear material. A semiconductor detector comprising cadmium, zinc, and tellurium (CZT) enables to detect gamma-rays due to the significant atomic weight of the elements via immediate neutron and gamma-ray detection. Semiconductor sensors might be used for nuclear safety management by monitoring nuclear materials and spent nuclear fuel with high spatial resolution as well as providing real-time measurements. We aim to introduce a portable nuclide-analysis device that enables the simultaneous measurements of neutrons and gamma rays using a CZT sensor. The detector has a high density and wide energy band gap, and thus exhibits highly sensitive physical characteristics and characteristics are required for performing neutron and gamma-ray detection. Portable nuclide-analysis device is used on NPP-decommissioning sites or the purpose of nuclear nonproliferation, it will rapidly detect the nuclear material and provide radioactive-material information. Eventually, portable nuclide-analysis device can reduce measurement time and economic costs by providing a basis for rational decision making.

• 전기전자학회논문지
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• 제26권4호
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• pp.553-559
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• 2022

본 논문에서는 cascode GaN FET의 하프 브릿지 구성에서 오실레이션 억제를 위한 RC 스너버 회로 설계 기술을 분석한다. 대표적인 WBG 소자인 cascode GaN FET는 우수한 고속 스위칭 특성이 우수하다. 다만, 이러한 고속 스위칭 특성으로 인하여 false turn-off 문제가 야기되며, 이를 억제하기 위해 RC 스너버 회로가 필수적이다. 따라서, 일반적으로 많이 사용되는 실험 기반의 선정 기법과 근궤적법을 이용한 분석 기법을 비교한다. 일반적인 방법의 경우 실험적 경험을 바탕으로 오실레이션 억제 성능이 만족될 때까지 지속적인 회로 변경이 필요하다. 하지만, 근궤적 기법의 경우 비진동 R-C 맵을 기반으로 초기값을 설정 할 수 있다. 이러한 설계 기술에 따른 성능을 비교하기 위해 모의실험과 실제 더블 펄스 회로 구성을 통한 실험을 진행하였다.

• 한국치위생학회지
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• 제5권2호
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• pp.297-309
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• 2005

The purpose of this study was to develop a standardized preschool oral health education program as one of educational media and to apply it to preschool education. It's ultimately meant to help improve the oral health education policy of the nation toward young children and to provide multiple information on that. The subjects in this study were 250 young children who were at the age of 7 and attended kindergartens in the city of S. To evaluate an oral health education program prepared in the study, the selected young children were taught by using it, and a survey was conducted twice before offering education and three weeks after it to assess their knowledge. Besides, their patient hygiene performance was tested. For data handling, SPSS program was utilized, and in order to see if there would be any changes in their oral health behaviors, statistical data on percentage were obtained and crosstab was employed. To track any possible additional changes in their relevant knowledge and Simplified Oral Hygiene Index, t-test was implemented. The findings of the study were as follows: 1. As for changes in oral health behaviors, there were significant differences in tooth brushing time(p<0.05), tooth brushing method(p<0.01) and toothbrush keeping method(p<0.001) between before and after the education. 2. Regarding changes in oral health knowledge, there was a significant gap between before and after the education(p<0.001). In detail, their knowledge about the cause of dental caries(p<0.05), the right choice of toothbrush(p<0.001) and toothbrushing after meals(p<0.01) became significantly different. 3. There was no gap in patient hygiene performance index between before and after the education. 4. To boost the effect of oral health education on kindergarteners, it seems necessary to give a lecture on oral health, to demonstrate tooth brushing by using dntiform, and to offer instruction by utilizing disclosing solution. 5. Repeated education should be provided on a regular basis by preparing standardized teaching plans tailored to the characteristics of kindergarteners, and a wide variety of teaching materials that could be easy to understand, authentic and provide motivation to them should be developed.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.105-105
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• 2009

$ZrO_2$ is one of the most attractive high dielectric constant (high-k) materials. As integrated circuit device dimensions continue to be scaled down, high-k materials have been studied more to resolve the problems for replacing the EY31conventional $SiO_2$. $ZrO_2$ has many favorable properties as a high dielectric constant (k= 20~25), wide band gap (5~7 eV) as well as a close thermal expansion coefficient with Si that results in good thermal stability of the $ZrO_2/Si$ structure. In order to get fine-line patterns, plasma etching has been studied more in the fabrication of ultra large-scale integrated circuits. The relation between the etch characteristics of high-k dielectric materials and plasma properties is required to be studied more to match standard processing procedure with low damaged removal process. Due to the easy control of ion energy and flux, low ownership and simple structure of the inductively coupled plasma (ICP), we chose it for high-density plasma in our study. And the $BCl_3$ included in the gas due to the effective extraction of oxygen in the form of $BCl_xO_y$ compound In this study, the surface kinetic properties of $ZrO_2$ thin film was investigated in function of Ch addition to $BCl_3/Ar$ gas mixture ratio, RF power and DC-bias power based on substrate temperature. The figure 1 showed the etch rate of $ZrO_2$ thin film as function of gas mixing ratio of $Cl_2/BCl_3/Ar$ dependent on temperature. The chemical state of film was investigated using x-ray photoelectron spectroscopy (XPS). The characteristics of the plasma were estimated using optical emission spectroscopy (OES). Auger electron spectroscopy (AES) was used for elemental analysis of etched surface.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.399-399
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• 2008

Synthesis and characterization of ZnO structure such as nanowires, nanorods, nanotube, nanowall, etc. have been studied to multifunctional application such as optical, nanoscale electronic and chemical devices because it has a room-temperature wide band gap of 3.37eV, large exiton binding energy(60meV) and various properties. Various synthesis methods including chemical vapor deposition (CVD), physical vapor deposition, electrochemical deposition, micro-emulsion, and hydrothermal approach have been reported to fabricate various kinds of ZnO nanostructures. But some of these synthesis methods are expensive and difficult of mass production. Wet chemical method has several advantage such as simple process, mass production, low temperature process, and low cost. In the present work, ZnO nanorods are deposited on ITO/glass substrate by simple wet chemical method. The process is perfomed by two steps. One-step is deposition of ZnO seeds and two-step is growth of ZnO nanorods on substrates. In order to form ZnO seeds on substrates, mixture solution of Zn acetate and Methanol was prepared.(one-step) Seed layers were deposited for control of morpholgy of ZnO seed layers by spin coating process because ZnO seeds is deposited uniformly by centrifugal force of spin coating. The seed-deposited samples were pre-annealed for 30min at $180^{\circ}C$ to enhance adhesion and crystallinnity of ZnO seed layer on substrate. Vertically well-aligned ZnO nanorods were grown by the "dipping-and-holding" process of the substrates into the mixture solution consisting of the mixture solution of DI water, Zinc nitrate and hexamethylenetetramine for 4 hours at $90^{\circ}C$.(two-step) It was found that density and morphology of ZnO nanorods were controlled by manipulation of ZnO seeds through rpm of spin coating. The morphology, crystallinity, optical properties of the grown ZnO nanostructures were carried out by field-emission scanning electron microscopy, high-resolution electron microscopy, photoluminescence, respectively. We are convinced that this method is complementing problems of main techniques of existing reports.

• 대한화학회지
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• 제59권5호
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• pp.397-406
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• 2015

II-VI 족 무기 화합물 반도체인 ZnO는 폭 넓은 응용분야 때문에 많은 관심을 받고 있다. ZnO는 넓은 밴드갭(3.37 eV)과 큰 excitation binding energy(60 meV)를 가지고 있고 광학특성, 반도체, 압전특성, 자성, 항균성, 광촉매 등 여러 분야에 응용 가능한 물질로 알려져 있다. 특히 광촉매 분야에 적용할 때 재수득의 문제를 위해 자성을 갖는 물질과 core-shell 구조를 이루는 연구가 활발히 진행 되고 있다. 본 연구에서, magnetic core-shell ZnFe₂O₄@ZnO@SiO₂ nanoparticles(NPs)는 3단계 과정을 통해 성공적으로 합성하였다. 합성된 물질들의 구조적 특성을 확인하기 위해 X-ray diffraction(XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy(FT-IR)을 사용하였다. ZnFe₂O₄ spinel 구조와 ZnO wurtzite 구조는 XRD를 사용하여 확인되었고, 전구체의 농도별 분석을 통해 ZnO 생성 비율을 확인 하였다. 합성된 물질들은SEM을 통하여 표면의 변화를 확인하였다. SiO₂층의 형성과 ZnFe₂O₄@ZnO@SiO₂ NPs의 합성은 FT-IR을 통해 Fe-O, Zn-O 및 Si-O-Si 결합을 확인하였다. 합성된 물질들의 자기적 성질은 Vibrating sample magnetometer(VSM)을 사용 하여 분석하였다. ZnO층과 SiO₂ 층의 형성의 결과는 자성의 증가와 감소로 확인하였다. 합성된 ZnFe₂O₄@ZnO@SiO₂ NPs의 광촉매 효과는 오염물질 대신 methylene blue(MB)를 사용하여 UV 조사 하에 암실에서 실험하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.115-116
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• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.

• 전기전자학회논문지
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• 제22권1호
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• pp.180-184
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• 2018

산화갈륨 ($Ga_2O_3$)과 탄화규소 (SiC)는 넓은 밴드 갭 ($Ga_2O_3-4.8{\sim}4.9eV$, SiC-3.3 eV)과 높은 임계전압을 갖는 물질로서 높은 항복 전압을 허용한다. 수직 DMOSFET 수평구조에 비해 높은 항복전압 특성을 갖기 때문에 고전압 전력소자에 많이 적용되는 구조이다. 본 연구에서는 2차원 소자 시뮬레이션 (2D-Simulation)을 사용하여 $Ga_2O_3$와 4H-SiC 수직 DMOSFET의 구조를 설계하였으며, 항복전압과 저항이 갖는 trade-off에 관한 파라미터를 분석하여 최적화 설계하였다. 그 결과, 제안된 4H-SiC와 $Ga_2O_3$ 수직 DMOSFET구조는 각각 ~1380 V 및 ~1420 V의 항복 전압을 가지며, 낮은 게이트 전압에서의 $Ga_2O_3-DMOSFET$이 보다 낮은 온-저항을 갖고 있지만, 게이트 전압이 높으면 4H-SiC-DMOSFET가 보다 낮은 온-저항을 갖을 수 있음을 확인하였다. 따라서 적절한 구조와 gate 전압 rating에 따라 소자 구조 및 gate dielectric등에 대한 심화 연구가 요구될 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.62-62
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• 1999

Carbon based materials have many attractive properties such as a wide band gap, a low electron affinity, and a high chemical and mechanical stability. Therefore, researches on the carbon-based materials as field emitters have been drawn extensively to enhance the field emission properties. Especially, diamond gives high current density, high current stability high thermal conductivity durable for high temperature operation, and low field emission behaviors, Among these properties understanding the origin of low field emission is a key factor for the application of diamond to a filed emitter and the verification of the emission site and its distribution of diamond is helpful to clarify the origin of low field emission from diamond There have been many investigations on the origin of low field emission behavior of diamond crystal or chemical vapor deposition (CVD) diamond films that is intentionally doped or not. However, the origin of the low field emission behavior and the consequent field emission mechanism is still not converged and those may be different between diamond crystal and CVD diamond films as well as the diamond that is doped or not. In addition, there have been no systematic studies on the dependence of nondiamond carbon on the spatial distribution of emission sites and its uniformity. Thus, clarifying a possible mechanism for the low field emission covering the diamond with various properties might be indeed a difficult work. On the other hand, it is believed that electron emission mechanisms of diamond are closely related to the emission sites and its distributions. In this context, it will be helpful to compare the spatial distribution of emission sites and field emission properties of the diamond films prepared by systematic variations of structural property. In this study, we have focused on an understanding of the field emission variations of structural property. In this study, we have focused on an understanding of the field emission mechanism for the CVD grown undoped polycrystalline diamond films with significantly different structural properties. The structural properties of the films were systematically modified by varying the CH4/H2 ratio and/or applying positive substrate bias examined. It was confirmed from the present study that the field emission characteristics are strongly dependent on the nondiamond carbon contents of the undoped polycrystalline diamond films, and a possible field emission mechanism for the undoped polycrystalline diamond films is suggested.