• Title/Summary/Keyword: subthreshold swing

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Analysis of Subthreshold Swing Mechanism by Device Parameter of Asymmetric Double Gate MOSFET (소자 파라미터에 따른 비대칭 DGMOSFET의 문턱전압이하 스윙 분석)

  • Jung, Hakkee
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.19 no.1
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    • pp.156-162
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    • 2015
  • This paper has analyzed how conduction path and electron concentration for the device parameters such as oxide thickness, channel doping, and top and bottom gate voltage influence on subthreshold swing of asymmetric double gate MOSFET. Compared with symmetric and asymmetric double gate MOSFET, asymmetric double gate MOSFET has the advantage that the factors to be able to control the short channel effects increase since top and bottom gate oxide thickness and voltages can be set differently. Therefore the conduction path and electron concentration for top and bottom gate oxide thickness and voltages are investigated, and it is found the optimum conditions that the degradation of subthreshold swing, severe short channel effects, can reduce. To obtain the analytical subthreshold swing, the analytical potential distribution is derived from Possion's equation. As a result, conduction path and electron concentration are greatly changed for device parameters, and subthreshold swing is influenced by conduction path and electron concentration of top and bottom.

Analysis of subthreshold region transport characteristics according to channel thickness for DGMOSFET (DGMOSFET의 채널두께에 따른 문턱전압이하영역에서의 전송특성분석)

  • Han, Ji-Hyung;Jung, Hak-Kee;Lee, Jong-In;Jeong, Dong-Soo;Kwon, Oh-Shin
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2010.10a
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    • pp.737-739
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    • 2010
  • In this paper, the subthreshold characteristics have been alanyzed using MicroTec4.0 for double gate MOSFET(DGMOSFET). The technology for characteristic analysis of device for high integration is changing rapidly. Therefore to understand characteristics of high-integrated device by computer simulation and fabricate the device having such characteristics became one of very important subjects. The oxide thickness and channel thickness in DG MOSFET determines threshold voltage and extensively influences on Ss(Subthreshold swing). We have investigated the threshold voltage and Ss(Subthreshold swing) characteristics according to variation of channel thickness from 1nm to 3nm in this study.

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The Shift of Threshold Voltage and Subthreshold Current Curve in LDD MOSFET Degraded Under Different DC Stress-Biases (DC 스트레스에 의해 노쇠화된 LDD MOSFET에서 문턱 전압과 Subthreshold 전류곡선의 변화)

  • Lee, Myung-Buk;Lee, Jung-Il;Kang, Kwang-Nham
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.26 no.5
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    • pp.46-51
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    • 1989
  • The degradation phenomena induced by hot-carrier injection was studied from the shift of threshold voltage and subthreshold current curve in LDD NMOSFET degraded under different DC stress-biases. Threshold voltage shift ${Delta}V_{tex}$ defined in saturation region was separated into contri butions due to trapped oxide charge $V_{ot}$ and interface traps ${Delta}V_{it}$ generated from midgap to threshold voltage. Under th positive stress electric field (TEX>$V_g>V_d$) condition, the shift of threshold voltage was attributed to the electrons traped ar gate oxide but subthreshold swing was not negative stress electric field ($V_g) condition, holes seems to be injected positive charges so threshold voltage and subthreshold swing were increased.

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Analysis of Subthreshold Characteristics for Device Parameter of DGMOSFET Using Gaussian Function

  • Jung, Hak-Kee
    • Journal of information and communication convergence engineering
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    • v.9 no.6
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    • pp.733-737
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    • 2011
  • This paper has studied subthreshold characteristics for double gate(DG) MOSFET using Gaussian function in solving Poisson's equation. Typical two dimensional analytical transport models have been presented for symmetrical Double Gate MOSFETs (DGMOSFETs). Subthreshold swing and threshold voltage are very important factors for digital devices because of determination of ON and OFF. In general, subthreshold swings have to be under 100mV/dec, and threshold voltage roll-off small in short channel devices. These models are used to obtain the change of subthreshold swings and threshold voltage for DGMOSFET according to channel doping profiles. Also subthreshold swings and threshold voltages have been analyzed for device parameters such as channel length, channel thickness and channel doping profiles.

Analysis of Subthreshold Swings Based on Scaling Theory for Double Gate MOSFET (이중게이트 MOSFET의 스켈링 이론에 대한 문턱전압이하 스윙분석)

  • Jung, Hakkee
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.16 no.10
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    • pp.2267-2272
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    • 2012
  • This study has presented the analysis of subthreshold swings based on scaling theory for double gate MOSFET. To solve the analytical potential distribution of Poisson's equation, we use Gaussian function to charge distribution. The scaling theory has been used to analyze short channel effect such as subthreshold swing degradation. These scaling factors for gate length, oxide thickness and channel thickness has been modified with the general scaling theory to include effects of double gates. We know subthreshold swing degradation is rapidly reduced when scaling factor of gate length is half of general scaling factor, and parameters such as projected range and standard projected deviation have greatly influenced on subthreshold swings.

Analysis of Dimension Dependent Subthreshold Swing for FinFET Under 20nm (20nm이하 FinFET의 크기변화에 따른 서브문턱스윙분석)

  • Jung, Hak-Kee
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.10 no.10
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    • pp.1815-1821
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    • 2006
  • In this paper, the subthreshold swing has been analyzed for FinFET under channel length of 20nm. The analytical current model has been developed , including thermionic current and tunneling current models. The potential distribution by Poisson equation and carrier distribution by Maxwell-Boltzman statistics are used to calculate thermionic emission current and WKB(Wentzel-Kramers-Brillouin) approximation to tunneling current. The cutoff current is obtained by simple adding two currents since two current is independent. The subthreshold swings by this model are compared with those by two dimensional simulation and two values agree well. Since the tunneling current increases especially under channel length of 10nm, the characteristics of subthreshold swing is degraded. The channel and gate oxide thickness have to be fabricated as am as possible to decrease this short channel effects, and this process has to be developed. The subthreshold swings as a function of channel doping concentrations are obtained. Note that subthreshold swings are resultly constant at low doping concentration.

Silicon-oxide-nitride-oxide-silicon구조를 가진 전하포획 플래시 메모리 소자의 Slicon-on-insulator 기판의 절연층 깊이에 따른 전기적 특성

  • Hwang, Jae-U;Kim, Gyeong-Won;Yu, Ju-Hyeong;Kim, Tae-Hwan
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.08a
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    • pp.229-229
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    • 2011
  • 부유 게이트 Floating gate (FG) 플래시 메모리 소자의 단점을 개선하기 위해 전하 포획 층에 전하를 저장하는 전하 포획 플래시 메모리 Charge trap flash (CTF)소자에 대한 연구가 활발히 진행되고 있다. CTF소자는 FG플래시 메모리 소자에 비해 비례축소가 용이하고 긴 retention time을 가지며, 낮은 구동 전압을 사용하는 장점을 가지고 있다. CTF 소자에서 비례축소에 따라 단채널 효과와 펀치-쓰루 현상이 증가하는 문제점이 있다.본 연구에서는 CTF 단채널 효과와 펀치-쓰루 현상을 감소시키기 위한 방법으로 silicon-on-insulator (SOI) 기판을 사용하였으며 SOI기판에서 절연층의 깊이에 따른 전기적 특성을 고찰하였다. silicon-oxide-nitride-oxide-silicon(SONOS) 구조를 가진 CTF 메모리 소자를 사용하여 절연층의 깊이 변화에 따른 subthreshold swing특성, 쓰기-지우기 동작 특성을 TCAD 시뮬레이션 툴인 Sentaurus를 사용하여 조사하였다. 소스와 드레인의 junction depth는 20 nm 사용하였고, 절연층의 깊이는 5 nm~25 nm까지 변화하면서 절연층의 깊이가 20 nm이하인 fully depletion 소자에 비해, 절연층의 깊이가 25 nm인 소자는 partially depletion으로 인해서 드레인 전류 레벨이 낮아지고 subthreshold swing값이 증가하는 현상이 나타났다. 절연층의 깊이가 너무 얕을 경우, 채널 형성의 어려움으로 인해 subthreshold swing과 드레인 전류 레벨의 전기적성질이 SOI기판을 사용하지 않았을 경우보다 떨어지는 경향을 보였다. 절연층의 깊이가 17.5 nm인 경우, CTF소자의 subthreshold swing과 드레인 전류 레벨이 가장 좋은 특성을 보였다.

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Subthreshold Swing Model Using Scale Length for Symmetric Junctionless Double Gate MOSFET (대칭형 무접합 이중게이트 MOSFET에서 스케일 길이를 이용한 문턱전압 이하 스윙 모델)

  • Jung, Hak Kee
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.34 no.2
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    • pp.142-147
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    • 2021
  • We present a subthreshold swing model for a symmetric junctionless double gate MOSFET. The scale length λ1 required to obtain the potential distribution using the Poisson's equation is a criterion for analyzing the short channel effect by an analytical model. In general, if the channel length Lg satisfies Lg > 1.5λ1, it is known that the analytical model can be sufficiently used to analyze short channel effects. The scale length varies depending on the channel and oxide thickness as well as the dielectric constant of the channel and the oxide film. In this paper, we obtain the scale length for a constant permittivity (silicon and silicon dioxide), and derive the relationship between the scale length and the channel length satisfying the error range within 5%, compared with a numerical method. As a result, when the thickness of the oxide film is reduced to 1 nm, even in the case of Lg < λ1, the analytical subthreshold swing model proposed in this paper is observed to satisfy the error range of 5%. However, if the oxide thickness is increased to 3 nm and the channel thickness decreased to 6 nm, the analytical model can be used only for the channel length of Lg > 1.8λ1.

Relation of Conduction Path and Subthreshold Swing for Doping Profile of Asymmetric Double Gate MOSFET (비대칭 DGMOSFET의 도핑분포함수에 따른 전도중심과 문턱전압이하 스윙의 관계)

  • Jung, Hakkee
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.18 no.8
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    • pp.1925-1930
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    • 2014
  • This paper has analyzed the relation of conduction path and subthreshold swing for doping profile in channel of asymmetric double gate(DG) MOSFET. Since the channel size of asymmetric DGMOSFET is greatly small and number of impurity is few, the high doping channel is analyzed. The analytical potential distribution is derived from Possion's equation, and Gaussian distribution function is used as doping profile. The conduction path and subthreshold swing are derived from this analytical potential distribution, and those are investigated for variables of doping profile, projected range and standard projected deviation, according to the change of channel length and thickness. As a result, subthreshold swing is reduced when conduction path is approaching to top gate, and that is increased with a decrease of channel length and a increase of channel thickness due to short channel effects.

SOI 기판 위에 SONOS 구조를 가진 플래쉬 메모리 소자의 subthreshold 전압 영역의 전기적 성질

  • Yu, Ju-Tae;Kim, Hyeon-U;Yu, Ju-Hyeong;Kim, Tae-Hwan
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.08a
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    • pp.216-216
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    • 2010
  • Floating gate를 이용한 플래시 메모리와 달리 질화막을 트랩 저장층으로 이용한 silicon-oxide-silicon nitride-oxide silicon (SONOS) 구조의 플래시 메모리 소자는 동작 전압이 낮고, 공정과정이 간단하며 비례 축소가 용이하여 고집적화하는데 유리하다. 그러나 SONOS 구조의 플래시 메모리소자는 비례 축소함에 따라 단 채널 효과와 펀치스루 현상이 커지는 문제점이 있다. 비례축소 할 때 발생하는 문제점을 해결하기 위해 플래시 메모리 소자를 FinFET과 같이 구조를 변화하는 연구는 활발히 진행되고 있으나, 플래시 메모리 소자를 제작하는 기판의 변화에 따른 메모리 소자의 전기적 특성 변화에 대한 연구는 많이 진행되지 않았다. 본 연구에서는 silicon-on insulator (SOI) 기판의 유무에 따른 멀티비트를 구현하기 위한 듀얼 게이트 가진 SONOS 구조를 가진 플래시 메모리 소자의 subthreshold 전압 영역에서의 전기적 특성 변화를 조사 하였다. 게이트 사이의 간격이 감소함에 따라 SOI 기판이 있을 때와 없을 때의 전류-전압 특성을 TCAD Simulation을 사용하여 계산하였다. 전류-전압 특성곡선에서 subthreshold swing을 계산하여 비교하므로 SONOS 구조의 플래시 메모리 소자에서 SOI 기판을 사용한 메모리 소자가 SOI 기판을 사용하지 않은 메모리 소자보다 단채널효과와 subthreshold swing이 감소하였다. 비례 축소에 따라 SOI 기판을 사용한 메모리 소자에서 단채널 효과와 subthreshold swing이 감소하는 비율이 증가하였다.

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