• 전자공학회논문지A
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• 제31A권8호
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• pp.46-52
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• 1994

DC and AC current crowding effects for microwave and high speed bipolar transistors are investigated in detail using a new and accurate measurement technique based on Z-parameter equationa. Using the new measurement technique dc and ac current crowding effects have been explained clearly in bipolar junction transistors. To model ac crowding effects a capacitive element defined as base capacitance (C$_b$), called ac crowding capacitance is added to base resistance in parallel thereby treating the base resistance(R$_b$) as base impedance Z$_b$. It is shown that base resistance decreases with increasing collector current due to dc current crowding and approaches to a certain limited value at high collector current due to current crowding and approaches to a certain limited value at high collector currents regardless of the emitter size. It is also observed that due to ac current crowding base capacitance increases with increasing collector current. To quantigy the ac crowding effects for SPICE circuit simulation the base capacitance(C$_b$) including the base depletion and diffusion components has been modeled with an analytical expression form.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권5호
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• pp.588-593
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• 2014

Current crowding problem can worsen the internal quantum efficiency and the negative-voltage ESD of InGaN-based LEDs. In this paper, by using photon emission microscope and thermal emission microscope measurement, we confirmed that the electric field and the current of the InGaN-based LED sample are crowded in specific regions where the distance between p-type metal contact and n-type metal contact is shorter than other regions. To improve this crowding problem of electric field and current, modified metal contact geometry having uniform distance between the two contacts is proposed and verified by a numerical simulation. It is confirmed that the proposed structure shows better current spreading, resulting in higher internal quantum efficiency and reduced reverse leakage current.

• 한국광학회:학술대회논문집
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• 한국광학회 2008년도 동계학술발표회 논문집
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• pp.93-94
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• 2008

In order to suppress the current crowding in light emitting diodes (LEDs) grown on sapphire substrate, the effect of nonuniform contact resistivity between TME layer and p-GaN layer on the LED surface was theoretically investigated. The analysis results showed that current crowding occurring around p-electrode could be considerably improved, which in turn would be helpful to improve the electrostatic discharge (ESD) characteristic.

• 한국조경학회지
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• 제30권6호
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• pp.38-46
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• 2003

Perceived crowding is known as a necessary method to evaluate social carrying capacity in recreational settings. But according to the results of previous research, perceived crowding, use density, and satisfaction have shown weak and indirect correlations. The theory of visitors’ adjustment is one of several possible explanations for this poor relation. But the validity of the visitors’ adjustment theory has not been not inspected clearly. Therefore, the purposes of this study are to understand visitors’ adjustment theory and to examine visitors’ adjustment to the overuse of recreational settings. Study hypotheses were formulated through literature review and related to visitors’ adjustment in recreation density. Pour hypotheses were established and inspected with the case study, i.e., Rationalization : Visitors’ satisfaction isn't related to use density in recreation setting, 2) Product-shift : Preference norm is related to current use density, 3) Self-selection : Visitors’ satisfaction for the use level is generally high, and 4) Displacement : Norm interference is related to willingness to revisit. The case study was conducted during May and June,2001. According to the results of this survey, visitors adjust to overuse of recreation setting through rationalization and product shift (hypotheses l/2 acceptance). Current use density isn't related to visitors’ satisfaction and willingness to revisit (see table 3). And visitors’ preference norm is modified by situation (see table 4). Visitors’ satisfaction and willingness to revisit don't show a high correlation but moderately high (see table 5, hypothesis 3 acceptance). Differences between visitors’ preference norm and current use density is norm interference. Norm interference isn't related to willingness to revisit (see table 7). Therefore, the norm interference concept is not a useful method to explain visitors’ adjustment to the degree of overuse in a recreational setting (hypothesis 4 rejection). As for future directions, the following are proposed: 1) correctly understanding and reestablishing the visitor norm and norm interference concept, 2) introducing a composite research method to monitor visitors’ behavior and survey visitors’ attitudes and coping responses. These efforts would be helpful in the Planning and management of recreational settings to improve the quality of visitors’ experiences.

• Journal of Microbiology
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• 제40권4호
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• pp.319-326
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• 2002

Cellular DNA in prokaryotes is organized in nucleic acid-protein self-assemblies referred to as the nucleoid. The physical forces responsible for its stability inside the poor solvent properties of the cytoplasm and their functional implications are not understood. Studies on the organisation and functioning of the cytosol of cells largely rely on experimental protocols performed in highly dilute solutions using biochemically purified molecules, which is not a reliable substitute for the situation existing in vivo. Our current research interest is focused on the characterization of biological and physical forces determining the compaction and phase separation of DNA in Escherichia coli cytoplasm. We have emphasized the effect of excluded volume in solutions with high macromolecular concentrations (macromolecular crowding) upon self-association patterns of reactions. The prokaryotic cytosol was simulated by addition of inert polymer polyethylene glycol (PEG) (average molecular weight 20000), as an agent which afterwards facilitates the self-association of macromolecules. Fluorescence microscopy was used for direct visualization of nucleoids in intact cells, after staining with DAPI (4',6-diamidino-2-phenylindole dihydrochloride). Addition of the crowding agent PEG 20,000, in increasing concentrations generated progressively enhanced nucleoid compaction, the effect being stronger in the presence of 0.2 M NaCl and 5 mM MgCl$\_$2/. Under these conditions, the nucleoids were compacted to volumes of around 2 ㎛$\^$3/ or comparable sizes with that of living cells.

• 전기전자학회논문지
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• 제22권4호
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• pp.916-921
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• 2018

본 논문에서는 고전압, 고전류 동작을 위한 전력 MOSFET 소자에 대한 전기적 특성을 시뮬레이션을 통해 분석하였다. 소자의 정적 특성을 향상시키기 위해 기존의 Si대신 4H-SiC를 이용했다. 4H-SiC는 넓은 에너지 밴드 갭에 의한 높은 한계전계를 갖기 때문에 고전압, 고전류 동작에서 Si보다 유리한 특성을 갖는다. 4H-SiC를 사용한 기존 VDMOSFET 구조는 p-base 영역 모서리에 전계가 집중되는 현상으로 인해 항복 전압이 제한된다. 따라서 본 논문에서는 p-base 영역의 모서리에 곡률을 주어 전계의 집중을 완화시켜 항복 전압을 높이고, 정적 특성을 개선한 곡률 VDMOSFET 구조를 제안하였다. TCAD 시뮬레이션을 통해 기존 VDMOSFET과 곡률 VDMOSFET의 정적 특성을 비교, 분석 하였다. 곡률 VDMOSFET은 기존 구조에 비해 온저항의 증가 없이 68.6% 향상 된 항복 전압을 갖는다.

• 대한전자공학회논문지SD
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• 제41권7호
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• pp.7-12
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• 2004

본 논문에서는 교류전류 집중현상이 고려된 바이폴라 등가모델에서 내부 베이스-컬렉터 캐패시턴스(C/sub μ/)와 외부 베이스-컬렉터 캐패시턴스(C/sub μx/)를 분리해서 추출하는 개선된 방법을 연구하였다. 먼저, 기존 추출방법들의 문제점들을 파악하고, 교류전류 집중 캐패시턴스가 포함된 차단모드 등가회로로부터 개선된 추출방정식들을 유도하였다. 이렇게 추출된 C/sub μx/와 C/sub μx/를 사용하여 모델 된 전류 및 전력이득 주파수 응답곡선들은 기존 추출방법으로 얻어진 곡선보다 측정 데이터와 훨씬 잘 일치되었으며, 이는 개선된 추출방법의 정확도를 증명한다.

• Asia Marketing Journal
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• 제16권2호
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• pp.1-14
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• 2014

This study applies the job-demands resource (JD-R) model to investigate the interactive effect of job demands and job resources in predicting the development of service employee work engagement and customer-oriented attitude. This paper proposed a theoretical model that suggests that the service employee's work engagement is the consequence of the employee's perceived support from the organization and its customers (customer participation) and leads to a customer-oriented attitude. However, the effect of organizational support is somewhat hindered by job insecurity, demonstrating the inability of an organizationally provided job resource to overcome the job demand of job insecurity. As a type of job demand from customer's perspective, customer crowding is suggested as a negative moderator in the link between customer participation and work engagement. As such, this article proposes how different elements of a service employee's work environment interact to ultimately influence the service employee's customer-oriented attitude. Specifically, the current research focuses on how the negative contextual elements of job insecurity and job crowding (i.e., job demands) interact with the potentially positive elements of organizational support and customer participation (i.e., job resources), as well as with an employee's customer orientation, to ultimately develop a customer-oriented attitude. This study concludes with some propositions for potential causal relationships among key constructs that can be empirically tested in future research, as well as implications of the current study for both managers and researchers.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.349-353
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• 2012

Uniform spreading of injection current in light-emitting diodes (LEDs) is one of the crucial requirements for better device performances. It is reported that non-uniform current spreading leads to low output power, high current crowding, heating, and reliability degradation of the LED device. This paper reports on the effects of different surface and electrode geometries in the LEDs. To increase the output power of LEDs and reduce the series resistance, a rectangular-type LED (RT-LED) with a centered island cathode has been fabricated and investigated by comparison with a conventional LED (CV-LED). The performances of RT-LEDs were prominently enhanced via uniform current spreading and low current crowding. Performances in terms of increased output power and lower forward voltage of simulated RT-LEDs are much superior to those of CV-LEDs. Based on these results, we investigated the correlation between device geometries and optical characteristics through the fabricated CV and RT-LEDs. The measured output power and forward voltage of the RT-LEDs at 100 mA are 64.7% higher and 8% smaller compared with those of the CV-LEDs.

• Journal of Korean Vacuum Science & Technology
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• 제7권2호
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• pp.39-44
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• 2003

Recent ULSI and multilevel structure trends in microelectronic devices minimize the line width down to a quarter micron and below, which results in the high current densities in thin film interconnections. Under high current densities, an EM(electromigration) induced failure becomes one of the critical problems in a microelectronic device. This study is to improve thin film interconnection materials by investigating the EM characteristics in PSG(phosphosilicate glass)/SiO$_2$ passivated Al-l%Si thin film interconnections. Straight line patterns, wide and narrow link type patterns, and meander type patterns, etc. were fabricated by a standard photholithography process. The main results are as follows. The current crowding effects result in the decrease of the lifetime in thin film interconnections. The electric field effects accelerate the decrease of lifetime in the double-layered thin film interconnections. The lifetime of interconnections also depends upon the current conditions of P.D.C.(pulsed direct current) frequencies applied at the same duty factor.