• Title/Summary/Keyword: pinch off

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A MODEL FOR THE PENETRATION RATE OF A BOUSSINESQ STARTING FORCED PLUME

  • LAW ADRIAN WING-KEUNG;AI JIAO JIAN;YU S.C.M
    • Proceedings of the Korea Water Resources Association Conference
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    • 2005.09b
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    • pp.951-951
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    • 2005
  • The characteristics of Boussinesq starting forced plumes were investigated in this study. Two distinct periods in the transient plume penetration were identified, namely the Period of Flow Development (PFD) and Period of Developed Flow (PDF). PFD refers to the time period whereby the penetration rate is governed by the complex vortex dynamics initiated by the exit conditions that can include vortex coalescence, vortex leapfrogging, pinching off of the head vortex from the trailing stem and the eventual reconnection. The pinch-off and reconnection leads to an overshoot of the plume front which is a common observation reported in previous studies. The penetration rate in PDF is more predictable and depends on the continuous feeding of buoyancy and momentum into the head vortex by the trailing buoyant-jet stem. Similarity solutions are developed for PDF to describe the temporal variation of the penetration rate, by incorporating the behavior of an isolated buoyant vortex ring and recent laboratory results on the trailing buoyant jet. In particular, the variations of velocity ratios between the head vortex and trailing buoyant jet are analytically computed. To verify the similarity solutions, experiments were conducted on vertical starting forced plumes using planar laser induced fluorescence (PLIF).

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Simulation of 4H-SiC MESFET for High Power and High Frequency Response

  • Chattopadhyay, S.N.;Pandey, P.;Overton, C.B.;Krishnamoorthy, S.;Leong, S.K.
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.8 no.3
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    • pp.251-263
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    • 2008
  • In this paper, we report an analytical modeling and 2-D Synopsys Sentaurus TCAD simulation of ion implanted silicon carbide MESFETs. The model has been developed to obtain the threshold voltage, drain-source current, intrinsic parameters such as, gate capacitance, drain-source resistance and transconductance considering different fabrication parameters such as ion dose, ion energy, ion range and annealing effect parameters. The model is useful in determining the ion implantation fabrication parameters from the optimization of the active implanted channel thickness for different ion doses resulting in the desired pinch off voltage needed for high drain current and high breakdown voltage. The drain current of approximately 10 A obtained from the analytical model agrees well with that of the Synopsys Sentaurus TCAD simulation and the breakdown voltage approximately 85 V obtained from the TCAD simulation agrees well with published experimental results. The gate-to-source capacitance and gate-to-drain capacitance, drain-source resistance and trans-conductance were studied to understand the device frequency response. Cut off and maximum frequencies of approximately 10 GHz and 29 GHz respectively were obtained from Sentaurus TCAD and verified by the Smith's chart.

A Study on Fabrications of GaAs Power MESFETs with an Undoped Surface Layer (Undoped 표면층을 갖는 전력용 GaAs ,ESFET의 제작에 관한 연구)

  • 김상명;이일형;신석현;서진호;서광석;이진구
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.31A no.1
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    • pp.65-70
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    • 1994
  • GaAs power MESFETs with 0.8$\mu$m gate lengths are fabricated using image reversal (IR) methods on the wafer with an undoped surface layer grown by MOCVD. The fabricated GaAs power MESFETs with an undoped surface layer show that an ideality factor 1.17, a built-in potential 0.83 V, a pinch-off voltage -2.7 V, a specfic contact resistance 1.21$\times$10$^{5}$ ~3.42$\times$10$^{2}$$\Omega$-cm$^{2}$ and an extrinsic g$_{m}$ = 103.5 mS/mm. The maximum RF output power densities of the 0.8$\mu$m devices are 360 mW/mm and 499 mW/mm, and power added efficiencies 29.67% and 29.05%, for the unit gate width 150$\mu$m and 200$\mu$m at 12 GHz.

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Deformation of the AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistor characteristics by UV irradiation

  • Lim, Jin Hong;Kim, Jeong Jin;Yang, Jeon Wook
    • Journal of IKEEE
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    • v.17 no.4
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    • pp.531-536
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    • 2013
  • The impact of UV irradiation process on the AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistor was investigated. Due to the high intensity UV irradiation before the gate dielectric deposition, the conductivity of AlGaN/GaN structure and the drain saturation current of the transistor increased by about 10 %. However, the pinch off characteristics of transistor was severely deformed by the process. By comparing the electrical characteristics of the transistors, it was proposed that the high intensity UV irradiation formed a sub-channel under the two dimensional electron gas of AlGaN/GaN structure even without additional impurity injection.

Power MESFETs Fabricated using a Self-Aligned and Double Recessed Gate Process (자기정렬 이중 리쎄스 공정에 의한 전력 MESFET 소자의 제작)

  • 이종람;김도진;윤광준;이성재;강진영;이용탁
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.29A no.2
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    • pp.77-79
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    • 1992
  • We propose a self-aligned and double recessed technique for GaAs power MESFETs application. The gate length and the wide recess width are defined by a selective removal of the SiN layer using reactive ion etching(RIE) while the depth of the channel is defined by chemical etching of GaAs layers. The threshold voltages and the saturation drain voltage could be sucessfully controlled using this technique. The lateral-etched distance increases with the dry etching time and the source-drain breakdown voltage of MESFET increases up to about 30V at a pinch-off condition. The electrical characteristics of a MESFET with a gate length of 2 x10S0-6Tm and a source-gate spacing of 33 x10S0-6Tm show maximum transconductance of 120 mS/mm and saturation drain current density of 170-190mA/mm at a gate voltage of 0.8V.

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Analysis of the electrical characteristics for SiGe pMOSFET by the carrier transport models (캐리어 전송 모델에 따른 SiGe pMOSFET의 전기적 특성분석)

  • 김영동;고석웅;정학기;허창우
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2003.10a
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    • pp.773-776
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    • 2003
  • In this paper, we have designed the p-type SiGe MOSFET and analyzed the electrical characteristics. When the gate voltage is biased to -1.5V, the threshold voltage values are -0.97V and -1.15V at room temperature and 77K, respectively. We know that the operating characteristics of SiGe MOSFET is superior to the basic Si MOSFET which the threshold voltage is -1.36V.

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3-D Characterizing Analysis of Buried-Channel MOSFETs (매몰공핍형 MOS 트랜지스터의 3차원 특성 분석)

  • Kim, M. H.
    • Proceedings of the Optical Society of Korea Conference
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    • 2000.08a
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    • pp.162-163
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    • 2000
  • We have observed the short-channel effect, narrow-channel effect and small-geometry effect in terms of a variation of the threshold voltage. For a short-channel effect the threshold voltage was largely determined by the DIBL effect which stimulates more carrier injection in the channel by reducing the potential barrier between the source and channel. The effect becomes more significant for a shorter-channel device. However, the potential, field and current density distributions in the channel along the transverse direction showed a better uniformity for shorter-channel devices under the same voltage conditions. The uniformity of the current density distribution near the drain on the potential minimum point becomes worse with increasing the drain voltage due to the enhanced DIBL effect. This means that considerations for channel-width effect should be given due to the variation of the channel distributions for short-channel devices. For CCDs which are always operated at a pinch-off state the channel uniformity thus becomes significant since they often use a device structure with a channel length of > 4 ${\mu}{\textrm}{m}$ and a very high drain (or diffusion) voltage. (omitted)

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Optimized Design Technology of Closing Switch for High Voltage & Current (고전압/대전류 투입스위치의 최적설계기술)

  • Seo, Kil-Soo;Kim, Young-Bae;Cho, Kook-Hee;Lee, Hyeong-Ho
    • Proceedings of the KIEE Conference
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    • 1999.07e
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    • pp.2173-2175
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    • 1999
  • This paper presents the development of closing switch for high voltage and current in detail. Design concept of INPIStron triggered by the gas puffing, voltage hold-off, current capacity, insulating and electrode material, rise time etc, are described. Also for the dptimized design of the electrical triggering switch, pin, ring, wire brush, surface discharge and HCP(Hypo-Cycloidal Pinch) trigger are considered.

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A Study on Breakdown Voltage of GaAs Power MESFET's (GaAs Power MESFET의 항복전압에 관한 연구)

  • 김한수;김한구;박장우;기현철;박광민;손상희;곽계달
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.27 no.7
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    • pp.1033-1041
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    • 1990
  • In this paper, under pinch-off conditions, the gate-drain breakdown voltage characteristics of GaAs Power MESFET's as a function of device parameters such as channel thickness, doping concentration, gate length etc. are analyzed. Using the Green's function, the gate ionic charge induced by the depleted channel ionic charge is calculated. The impact ionization integral by avalanche multiplication between gate and drain is used to investigate breakdown phenomena. Especially, the localized excess surface charge effect as well as the uniform surface charge effect on breakdown voltage is considered.

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Design of Broadband 12GHz Active Frequency Multiplier (광대역 특성을 갖는 12GHz 능동 주파수 체배기 설계)

  • Jeon, Jong-Hwan;Kim, Tae-Yong;Choi, Won;Oh, Chung-Gyun;Koo, Kyung-Heon
    • Proceedings of the IEEK Conference
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    • 2003.11c
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    • pp.72-76
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    • 2003
  • In this paper, active frequency doubler with broadband characteristics and unconditional stability from 6GHz to 12GHz was designed and fabricated using PHEMT. The designed frequency multiplier has a bias point near pinch-off and a proposed RC circuit between bias line and input matching network for the improvement of stability. With 0dBm input power, second harmonic of 1.7dBm at 12GHz, - 27.5dBc suppression of 6GHz fundamental, -18dBc suppression of 18GHz 3rd harmonic and the output bandwidth of 1.8GHz have been measured.

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