• Title/Summary/Keyword: Field Effect Mobility

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Channel and Gate Workfunction-Engineered CNTFETs for Low-Power and High-Speed Logic and Memory Applications

  • Wang, Wei;Xu, Hongsong;Huang, Zhicheng;Zhang, Lu;Wang, Huan;Jiang, Sitao;Xu, Min;Gao, Jian
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.16 no.1
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    • pp.91-105
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    • 2016
  • Carbon Nanotube Field-Effect Transistors (CNTFETs) have been studied as candidates for post Si CMOS owing to the better electrostatic control and high mobility. To enhance the immunity against short - channel effects (SCEs), the novel channel and gate engineered architectures have been proposed to improve CNTFETs performance. This work presents a comprehensive study of the influence of channel and gate engineering on the CNTFET switching, high frequency and circuit level performance of carbon nanotube field-effect transistors (CNTFETs). At device level, the effects of channel and gate engineering on the switching and high frequency characteristics for CNTFET have been theoretically investigated by using a quantum kinetic model. This model is based on two-dimensional non-equilibrium Green's functions (NEGF) solved self - consistently with Poisson's equations. It is revealed that hetero - material - gate and lightly doped drain and source CNTFET (HMG - LDDS - CNTFET) structure can significantly reduce leakage current, enhance control ability of the gate on channel, improve the switching speed, and is more suitable for use in low power, high frequency circuits. At circuit level, using the HSPICE with look - up table(LUT) based Verilog - A models, the impact of the channel and gate engineering on basic digital circuits (inverter, static random access memory cell) have been investigated systematically. The performance parameters of circuits have been calculated and the optimum metal gate workfunction combinations of ${\Phi}_{M1}/{\Phi}_{M2}$ have been concluded in terms of power consumption, average delay, stability, energy consumption and power - delay product (PDP). In addition, we discuss and compare the CNTFET-based circuit designs of various logic gates, including ternary and binary logic. Simulation results indicate that LDDS - HMG - CNTFET circuits with ternary logic gate design have significantly better performance in comparison with other structures.

Improved Electrical Properties by In Situ Nitrogen Incorporation during Atomic Layer Deposition of HfO2 on Ge Substrate (Ge 기판 위에 HfO2 게이트 산화물의 원자층 증착 중 In Situ 질소 혼입에 의한 전기적 특성 변화)

  • Kim, Woo-Hee;Kim, Bum-Soo;Kim, Hyung-Jun
    • Journal of the Korean Vacuum Society
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    • v.19 no.1
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    • pp.14-21
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    • 2010
  • Ge is one of the attractive channel materials for the next generation high speed metal oxide semiconductor field effect transistors (MOSFETs) due to its higher carrier mobility than Si. But the absence of a chemically stable thermal oxide has been the main obstacle hindering the use of Ge channels in MOS devices. Especially, the fabrication of gate oxide on Ge with high quality interface is essential requirement. In this study, $HfO_xN_y$ thin films were prepared by plasma-enhanced atomic layer deposition on Ge substrate. The nitrogen was incorporated in situ during PE-ALD by using the mixture of nitrogen and oxygen plasma as a reactant. The effects of nitrogen to oxygen gas ratio were studied focusing on the improvements on the electrical and interface properties. When the nitrogen to oxygen gas flow ratio was 1, we obtained good quality with 10% EOT reduction. Additional analysis techniques including X-ray photoemission spectroscopy and high resolution transmission electron microscopy were used for chemical and microstructural analysis.

Amorphous Indium-Tin-Zinc-Oxide (ITZO) Thin Film Transistors

  • Jo, Gwang-Min;Lee, Gi-Chang;Seong, Sang-Yun;Kim, Se-Yun;Kim, Jeong-Ju;Lee, Jun-Hyeong;Heo, Yeong-U
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.08a
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    • pp.170-170
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    • 2010
  • Thin-film transistors (TFT) have become the key components of electronic and optoelectronic devices. Most conventional thin-film field-effect transistors in display applications use an amorphous or polycrystal Si:H layer as the channel. This silicon layers are opaque in the visible range and severely restrict the amount of light detected by the observer due to its bandgap energy smaller than the visible light. Therefore, Si:H TFT devices reduce the efficiency of light transmittance and brightness. One method to increase the efficiency is to use the transparent oxides for the channel, electrode, and gate insulator. The development of transparent oxides for the components of thin-film field-effect transistors and the room-temperature fabrication with low voltage operations of the devices can offer the flexibility in designing the devices and contribute to the progress of next generation display technologies based on transparent displays and flexible displays. In this thesis, I report on the dc performance of transparent thin-film transistors using amorphous indium tin zinc oxides for an active layer. $SiO_2$ was employed as the gate dielectric oxide. The amorphous indium tin zinc oxides were deposited by RF magnetron sputtering. The carrier concentration of amorphous indium tin zinc oxides was controlled by oxygen pressure in the sputtering ambient. Devices are realized that display a threshold voltage of 4.17V and an on/off ration of ${\sim}10^9$ operated as an n-type enhancement mode with saturation mobility with $15.8\;cm^2/Vs$. In conclusion, the fabrication and characterization of thin-film transistors using amorphous indium tin zinc oxides for an active layer were reported. The devices were fabricated at room temperature by RF magnetron sputtering. The operation of the devices was an n-type enhancement mode with good saturation characteristics.

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Electrical response of tungsten diselenide to the adsorption of trinitrotoluene molecules (폭발물 감지 시스템 개발을 위한 TNT 분자 흡착에 대한 WSe2 소자의 전기적 반응 특성 평가)

  • Chan Hwi Kim;Suyeon Cho;Hyeongtae Kim;Won Joo Lee;Jun Hong Park
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.33 no.6
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    • pp.255-260
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    • 2023
  • As demanding the detection of explosive molecules, it is required to develop rapidly and precisely responsive sensors with ultra-high sensitivity. Since two-dimensional semiconductors have an atomically thin body nature where mobile carriers accumulate, the abrupt modulation carrier in the thin body channel can be expected. To investigate the effectiveness of WSe2 semiconductor materials as a detection material for TNT (Trinitrotoluene) explosives, WSe2 was synthesized using thermal chemical vapor deposition, and afterward, WSe2 FETs (Field Effect Transistors) were fabricated using standard photo-lithograph processes. Raman Spectrum and FT-IR (Fourier-transform infrared) spectroscopy reveal that the adsorption of TNT molecules induces the structural transition of WSe2 crystalline. The electrical properties before and after adsorption of TNT molecules on the WSe2 surface were compared; as -50 V was applied as the back gate bias, 0.02 μA was recorded in the bare state, and the drain current increased to 0.41 μA with a dropping 0.6% (w/v) TNT while maintaining the p-type behavior. Afterward, the electrical characteristics were additionally evaluated by comparing the carrier mobility, hysteresis, and on/off ratio. Consequently, the present report provides the milestone for developing ultra-sensitive sensors with rapid response and high precision.

Growth and photocurrent study on the splitting of the valence band for $CuInSe_2$ single crystal thin film by hot wall epitaxy (Hot Wall Epitaxy(HWE)범에 의한 $CuInSe_2$ 단결정 박막 성장과 가전자대 갈라짐에 대한 광전류 연구)

  • Hong Myungseak;Hong Kwangjoon
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.14 no.6
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    • pp.244-252
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    • 2004
  • A stoichiometric mixture of evaporating materials for $CuInSe_2$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $_CuInSe2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $620^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuInSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.62\times10^{16}/\textrm{cm}^3$, 296 $\textrm{cm}^2$/Vㆍs at 293 K, respectively. The temperature dependence of the energy band gap of the $CuInSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T) = 1.1851 eV -($8.99\times10^{-4} eV/K)T^2$(T + 153 K). The crystal field and the spin-orbit splitting energies for the valence band of the CuInSe$_2$ have been estimated to be 0.0087 eV and 0.2329 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the $\Gamma$6 states of the valence band of the $CuInSe_2$. The three photocurrent peaks observed at 10 K are ascribed to the $A_1-, B_1$-와 $C_1$-exciton peaks for n = 1.

Photocurrent study on the splitting of the valence band and growth of $CdGa_2Se_4$ single crystal thin film by hot wall epitaxy (Hot Wall epitaxy(HWE)법에 의한 $CdGa_2Se_4$ 단결정 박막의 성장과 가전자대 갈라짐에 대한 광전류 연구)

  • Park, Chang-Sun;Hong, Kwang-Joon
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.17 no.5
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    • pp.179-186
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    • 2007
  • Single crystal $CdGa_2Se_4$ layers were grown on a thoroughly etched semi-insulating GaAs(100) substrate at $420^{\circ}C$ with the hot wall epitaxy(HWE) system by evaporating the polycrystal source of $CdGa_2Se_4$ at $630^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction(DCXD). The carrier density and mobility of single crystal $CdGa_2Se_4$ thin films measured with Hall effect by van der Pauw method are $8.27{\times}10^{17}cm^{-3},\;345cm^2/V{\cdot}s$ at 293 K, respectively. The photocurrent and the absorption spectra of $CdGa_2Se_4/SI$(Semi-Insulated) GaAs(100) are measured ranging from 293 K to 10 K. The temperature dependence of the energy band gap of the $CdGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation $E_g(T)=2.6400eV-(7.721{\times}10^{-4}eV/K)T^2/(T+399K)$. Using the photocurrent spectra and the Hopfield quasicubic model, the crystal field energy(${\Delta}cr$) and the spin-orbit splitting energy(${\Delta}so$) far the valence band of the $CdGa_2Se_4$ have been estimated to be 106.5 meV and 418.9 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1^-},\;B_{1^-},\;and\;C_{11}-exciton$ peaks.

Highly Efficient Multi-Functional Material for Organic Light-Emitting Diodes; Hole Transporting Material, Blue and White Light Emitter

  • Kim, Myoung-Ki;Kwon, Jong-Chul;Hong, Jung-Pyo;Lee, Seong-Hoon;Hong, Jong-In
    • Bulletin of the Korean Chemical Society
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    • v.32 no.spc8
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    • pp.2899-2905
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    • 2011
  • We have demonstrated that TPyPA can be used as an efficient multi-functional material for OLEDs; hole transporting material (HTL), blue and white-light emitter. The device based on TPyPA as the HTL exhibited an external quantum efficiency of 1.7% and a luminance efficiency of 4.2 cd/A; these values are 40% higher than the external quantum efficiency and luminance efficiency of the NPD-based reference device. The device based on TPyPA as a blue-light emitter exhibited an external quantum efficiency of 4.2% and a luminance efficiency of 5.3 $cdA^{-1}$ with CIE coordinates at (0.16, 0.14), the device based on TPyPA as a white-light emitter exhibited an external quantum efficiency of 3.2% and a luminance efficiency of 7.7 $cdA^{-1}$ with CIE coordinates at (0.33, 0.39). Also, TPyPA-based organic solar cell (OSC) exhibited a maximum power conversion efficiency of 0.35%. TPyPA-based organic thin-film transistors (OTFTs) exhibited highly efficient field-effect mobility (${\mu}_{FET}$) of $1.7{\times}10^{-4}cm^2V^{-1}s^{-1}$, a threshold voltage ($V_{th}$) of -15.9 V, and an on/off current ratio of $8.6{\times}10^3$.

Effects of Mg Suppressor Layer on the InZnSnO Thin-Film Transistors

  • Song, Chang-Woo;Kim, Kyung-Hyun;Yang, Ji-Woong;Kim, Dae-Hwan;Choi, Yong-Jin;Hong, Chan-Hwa;Shin, Jae-Heon;Kwon, Hyuck-In;Song, Sang-Hun;Cheong, Woo-Seok
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.16 no.2
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    • pp.198-203
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    • 2016
  • We investigate the effects of magnesium (Mg) suppressor layer on the electrical performances and stabilities of amorphous indium-zinc-tin-oxide (a-ITZO) thin-film transistors (TFTs). Compared to the ITZO TFT without a Mg suppressor layer, the ITZO:Mg TFT exhibits slightly smaller field-effect mobility and much reduced subthreshold slope. The ITZO:Mg TFT shows improved electrical stabilities compared to the ITZO TFT under both positive-bias and negative-bias-illumination stresses. From the X-ray photoelectron spectroscopy O1s spectra with fitted curves for ITZO and ITZO:Mg films, we observe that Mg doping contributes to an enhancement of the oxygen bond without oxygen vacancy and a reduction of the oxygen bonds with oxygen vacancies. This result shows that the Mg can be an effective suppressor in a-ITZO TFTs.

Investigating InSnZnO as an Active Layer for Non-volatile Memory Devices and Increasing Memory Window by Utilizing Silicon-rich SiOx for Charge Storage Layer

  • Park, Heejun;Nguyen, Cam Phu Thi;Raja, Jayapal;Jang, Kyungsoo;Jung, Junhee;Yi, Junsin
    • Proceedings of the Korean Vacuum Society Conference
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    • 2016.02a
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    • pp.324-326
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    • 2016
  • In this study, we have investigated indium tin zinc oxide (ITZO) as an active channel for non-volatile memory (NVM) devices. The electrical and memory characteristics of NVM devices using multi-stack gate insulator SiO2/SiOx/SiOxNy (OOxOy) with Si-rich SiOx for charge storage layer were also reported. The transmittance of ITZO films reached over 85%. Besides, ITZO-based NVM devices showed good electrical properties such as high field effect mobility of 25.8 cm2/V.s, low threshold voltage of 0.75 V, low subthreshold slope of 0.23 V/dec and high on-off current ratio of $1.25{\times}107$. The transmission Fourier Transform Infrared spectroscopy of SiOx charge storage layer with the richest silicon content showed an assignment at peaks around 2000-2300 cm-1. It indicates that many silicon phases and defect sources exist in the matrix of the SiOx films. In addition, the characteristics of NVM device showed a retention exceeding 97% of threshold voltage shift after 104 s and greater than 94% after 10 years with low operating voltage of +11 V at only 1 ms programming duration time. Therefore, the NVM fabricated by high transparent ITZO active layer and OOxOy memory stack has been applied for the flexible memory system.

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In-Ga-O 박막에서 Gallium 조성 변화에 의한 박막의 특성변화 연구 및 소자 응용

  • Jo, Gwang-Min;Lee, Jun-Hyeong;Kim, Jeong-Ju;Heo, Yeong-U
    • Proceedings of the Korean Vacuum Society Conference
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    • 2015.08a
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    • pp.169.1-169.1
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    • 2015
  • 최근 디스플레이 기술은 급속도로 발전해 가고 있다. 디스플레이 산업의 눈부신 성장에 발맞추어 초고화질, 초고선명, 고속 구동 및 대형화 등을 포함하는 최신 기술의 디스플레이 구동이 필요하다. 이러한 요구사항을 만족하기 위해서는 각 픽셀에 영상정보를 기입하는 충전시간을 급격히 감소시켜야 하고 따라서 픽셀 트랜지스터(TFT)의 이동도는 급격히 증가해야 한다. 따라서 차세대 디스플레이 실현을 위해서 고이동도 특성을 구현 할 수 있는 신물질의 개발이 매우 중요하다. 현재 산화물박막트랜지스터는 차세대 디스플레이 실현을 위해 가장 주목받고 있으며, 실제로 산화물박막 트랜지스터의 핵심소재인 In-Ga-Zn-O(a-IGZO) 산화물의 경우 국내외에서 디스플레이에 적용되어 생산이 시작되고있다. 그러나 a-IGZO 산화물의 경우 이동도가 $5-10cm^2V{\cdot}s$ 수준이어서 향후 개발 되어질 초고해상도/고속구동 디스플레이 실현(이동도 $50cm^2V{\cdot}s$)에는 한계가 있다. 따라서 본 연구에서는 이를 해결 할 수 있는 'post-IGZO' 개발을 위해 In2O3에 Ga2O3를 조성별로 고용시켜 박막의 구조적, 전기적, 광학적 특성 및 TFT를 제작하여 특성 연구를 진행하였다. 조성은 In2O3에 Ga2O3를 7.5%~15% 도핑 하였으며, Sputtering을 이용하여 indium gallium oxide(IGO) 박막을 제작하였다. 박막은 상온 및 $300^{\circ}C$에서 증착 하였으며 증착 된 IGO 박막은 Ga=12.5% 까지는 In2O3에 Ga이 모두 고용되어 cubic In2O3 poly crystalline을 나타내는 것을 확인하였으며 Ga=15%에서 Gallium 관련 2차상이 확인되었다. Ga양이 변화함에 따라 박막의 전기적 특성이 조절 가능하였으며 이를 이용하여 IGO 박막을 30 nm 두께로 증착 하여 IGO 박막을 channel layer로 사용하는 bottom gate structured TFTs를 제작 하였다. IGO TFTs는 Ga=10%에서 on/off ratio ${\sim}10^8$, 그리고 field-effect mobility $84.8cm^2/V{\cdot}S$를 나타내며 초고화질, 초고선명 차세대 디스플레이 적용 가능성을 보여 준다.

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