• Title/Summary/Keyword: Thermionic emission

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Numerical Calculation Study on the Generalized Electron Emission Phenomenon

  • Kim, Hee-Tae;Yu, Soon-Jae
    • Journal of Information Display
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    • v.10 no.4
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    • pp.158-163
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    • 2009
  • There are two kinds of well-known electron emissions from metal: field and thermionic emission. For thermionic emission, electrons come out of a metal due to the thermal energy, whereas for field emission, electrons tunnel out of a metal through the strong electric field. In this study, the most general electron emission caused by the temperature and electric field with a free electron gas model was considered. The total current density of electron emission comes from the field emission effect, where the electron energy is lower than vacuum, and from the thermionic-emission effect, where the electron energy is higher than vacuum. The total current density of electron emission is shown as a function of the temperature for a constant electric field, and as a function of the electric field for a constant temperature.

Performance Analysis of A Variable-Spacing Cesium Thermionic Energy Converter (열전변환 장치의 특성 분석에 대한 연구)

  • Lee, Deuk-Yong
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.41 no.9
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    • pp.1085-1094
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    • 1992
  • A variable-spacing cesium thermionic energy conversion test station is designed and fabricated for the study of power generation. The diode is in the form of a guard-ringed plane-parallel geometry in which a polycrystalline rhenium emitter of 2 cmS02T area faces a radiation-cooled polycrystalline rhenium collector of 1.9 cmS02T area. The emission of plasma from heated refractory electrode metal is the driving reaction in the direct conversion of heat to electricity by thermionic energy conversion. The plasma is produced from electrons and positive ions formed simultaneously by thermionic emission and surface ionization of cesium atoms incident on the hot emitter from the cesium vapor in the diode. And high plasma density causes plasma multiplication within the gap due to volume ionization that results in high power output. The variation of the saturation current of a Knudsen converter is investigated at an emitter-collector gap of 0.1 mm and an emitter temperatures. A maximum power output of 13.47 watta/cmS02T is observed at a collector temperature of 963 K and a cesium reservoir temperature of 603 K.

Emission Profile Studies of Thermionic Cathodes and Field Emitters

  • Tawa, Yasuhiro;Kai, Junjiro;Tama, Masayoshi;Ijima, Kenji;Saito, Tsunenari
    • 한국정보디스플레이학회:학술대회논문집
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    • 2002.08a
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    • pp.371-375
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    • 2002
  • Emissions of thermionic cathodes and field emitters were studied using a cathode emission profiler which works based on the anode scanning method. Findings about impregnated cathodes in thermal activation and gas poisoning processes are shown. Effects of surface treatments for field emitters are studied from the viewpoint of emission profiles and characteristics of the emitters.

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Finite Element Analysis for Electron Optical System of a Thermionic SEM (열전자방사형 주사전자 현미경 전자광학계의 유한요소해석)

  • Park, Keun;Jung, Huen-U.;Kim, Dong-Hwan;Jang, Dong-Young
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.1288-1293
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    • 2007
  • The present study covers the design and analysis of a thermionic scanning electron microscope (SEM) column. The SEM column contains an electron optical system in which electrons are emitted and moved to form a focused beam, and this generates secondary electrons from the specimen surfaces, eventually making an image. The electron optical system mainly consists of a thermionic electron gun as the beam source, the lens system, the electron control unit, and the vacuum unit. In the design process, the dimension and capacity of the SEM components need to be optimally determined with the aid of finite element analyses. Considering the geometry of the filament, a three-dimensional (3D) finite element analysis is utilized. Through the analysis, the beam emission characteristics and relevant trajectories are predicted from which a systematic design of the electron optical system is enabled. The validity of the proposed 3D analysis is also discussed by comparing the directional beam spot radius. As a result, a prototype of a thermionic SEM is successfully developed with a relatively short time and low investment costs, which proves the adoptability of the proposed 3D analysis.

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Electron Emission Theory for LCD Backlight

  • Kim, Hee-Tae;Lee, Dong-Chin;Nam, Seok-Hyun;Jang, Tae-Seok
    • 한국정보디스플레이학회:학술대회논문집
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    • 2008.10a
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    • pp.1602-1605
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    • 2008
  • We considered most general electron emission caused by temperature as well as electric field with a free electron gas model. The total electron emission current density comes from field emission effect where electron energy is lower than vacuum and from thermionic emission effect where electron energy is higher than vacuum. The total electron emission current density is shown as a function of temperature for constant electric field, and as a function of electric field for constant temperature.

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An Analysis on the Leakage Current of Drain-offset Poly-Si TFT′s (드레인오프셋트 다결정실리콘 박막트랜지스터의 누설전력 해석)

  • 이인찬;김정규;마대영
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.14 no.2
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    • pp.111-116
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    • 2001
  • Poly-Si TFT's(Polysilicon thin filmtransistors) have been actively studied due to their applications in active matrix liquid crystal displays and active pull-up devices of CMOS SRAM's. For such applications, the leakage current has to be in the range of sub-picoampere. However, poly-Si TFT's suffer from anomalous high leakage currents, which is attributed to the emission of the traps present at gain boundaries in the drain junction. The leakage current has been analyzed by the field emission via grain-boundary traps and thermionic field emission over potential barrier located at the grain boundary. We found that the models proposed before are not consistent with the experimental results at far as drain-offset poly-Si TFT's we fabricated concern. In this paper, leakage current of drain-offset poly-Si TFT's with different offset lengths was studied. A conduction model based on the thermionic emission of the tunneling electrons is developed to identify the leakage mechanism. It was found that the effective grain size of the drain-offset region is important factor in the leakage current. A good agreement between experimental and simulated results of the leakage current is obtained.

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Numerical Analysis for the Image Evaluation of a Thermionic SEM (열전자형 주사전자현미경 결상특성의 수치해석)

  • Jung, H.U.;Park, M.J.;Kim, D.H.;Jang, D.Y.;Park, K.
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.16 no.6
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    • pp.153-158
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    • 2007
  • The present study covers numerical analysis of a thermionic scanning electron microscope(SEM) column. The SEM column contains an electron optical system in which electrons are emitted and moved to form a focused beam, and this generates secondary electrons from the specimen surfaces, eventually making an image. The electron optical system mainly consists of a thermionic electron gun as the beam source, the lens system, the electron control unit, and the vacuum unit. For a systematic design of the electron optical system, the beam trajectories are investigated through numerical analyses by tracing the ray path of the electron beams, and the quality of resulting image is evaluated from the analysis results.

Analysis of Schottky Barrier Height in Small Contacts Using a Thermionic-Field Emission Model

  • Jang, Moon-Gyu;Lee, Jung-Hwan
    • ETRI Journal
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    • v.24 no.6
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    • pp.455-461
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    • 2002
  • This paper reports on estimating the Schottky barrier height of small contacts using a thermionic-field emission model. Our results indicate that the logarithmic plot of the current as a function of bias voltage across the Schottky diode gives a linear relationship, while the plot as a function of the total applied voltage across a metal-silicon contact gives a parabolic relationship. The Schottky barrier height is extracted from the slope of the linear line resulting from the logarithmic plot of current versus bias voltage across the Schottky diode. The result reveals that the barrier height decreases from 0.6 eV to 0.49 eV when the thickness of the barrier metal is increased from 500 ${\AA}$ to 900 ${\AA}$. The extracted impurity concentration at the contact interface changes slightly with different Ti thicknesses with its maximum value at about $2.9{\times}10^{20}\;cm^{-3}$, which agrees well with the results from secondary ion mass spectroscopy (SIMS) measurements.

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Current Modeling for Accumulation Mode GaN Schottky Barrier MOSFET for Integrated UV Sensors

  • Park, Won-June;Hahm, Sung-Ho
    • Journal of Sensor Science and Technology
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    • v.26 no.2
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    • pp.79-84
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    • 2017
  • The drain current of the SB MOSFET was analytically modeled by an equation composed of thermionic emission and tunneling with consideration of the image force lowering. The depletion region electron concentration was used to model the channel electron concentration for the tunneling current. The Schottky barrier width is dependent on the channel electron concentration. The drain current is changed by the gate oxide thickness and Schottky barrier height, but it is hardly changed by the doping concentration. For a GaN SB MOSFET with ITO source and drain electrodes, the calculated threshold voltage was 3.5 V which was similar to the measured value of 3.75 V and the calculated drain current was 1.2 times higher than the measured.

Reverse-bias Leakage Current Mechanisms in Cu/n-type Schottky Junction Using Oxygen Plasma Treatment

  • Kim, Hogyoung
    • Transactions on Electrical and Electronic Materials
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    • v.17 no.2
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    • pp.113-117
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    • 2016
  • Temperature dependent reverse-bias current-voltage (I-V) characteristics in Cu Schottky contacts to oxygen plasma treated n-InP were investigated. For untreated sample, current transport mechanisms at low and high temperatures were explained by thermionic emission (TE) and TE combined with barrier lowering, respectively. For plasma treated sample, experimental I-V data were explained by TE or TE combined with barrier lowering models at low and high temperatures. However, the current transport was explained by a thermionic field emission (TFE) model at intermediate temperatures. From X-ray photoemission spectroscopy (XPS) measurements, phosphorus vacancies (VP) were suggested to be generated after oxygen plasma treatment. VP possibly involves defects contributing to the current transport at intermediate temperatures. Therefore, minimizing the generation of these defects after oxygen plasma treatment is required to reduce the reverse-bias leakage current.