一种碳纳米管场效应管半经典模型计算方法

基于弹道输运的碳纳米管场效应管半经典模型求解自洽电势通常采用牛顿-拉夫逊迭代法,每次迭代都需要对态密度方程积分计算,运算量巨大.我们用支持向量回归机近似表达自洽电势与载流子密度之间的关系,不需要反复迭代积分,并用梯度下降法求解自洽电势.仿真结果表明,与牛顿-拉夫逊迭代法比较,该方法精度较高,有效降低了运算量,为今后大规模集成电路中碳纳米管器件的设计和应用奠定理论基础.     

声子散射下碳纳米管场效应管建模方法研究

声子散射对碳纳米管场效应管(carbon nanotube field effect transistor, CNTFET)的特性有着不可忽略的影响. 传统研究方法基于弹道输运模型来分析发生声子散射时各参数对器件特性的影响, 进而建立CNTFET声子散射模型.为了降低模型复杂度, 提高仿真计算的速度, 本文深入研究了CNTFET的声子散射影响, 对手性、温度和能量三个参数的变化进行了仿真, 分析了参数对器件特性的影响. 采用线性近似拟合的方式建立了一种新的CNTFET声子散射模型.通过分析散射下电流的变化, 验证了该模型的正确性和有效性.与半经典散射模型相比, 该模型由于不需要进行积分计算, 计算过程较为简单, 降低了运算量. 关键词： 碳纳米管场效应管 声子散射模型 线性近似拟合     

欠叠异质栅纳米碳管场效应管的量子输运特性（英文）

采用量子力学模型,对欠叠栅对传统单质栅碳纳米管场效应管(简称C-CNTFET)和异质栅碳纳米管场效应管(简称HMG-CNTFET)电学特性的影响进行理论研究,该模型基于二维非平衡格林函数(NEGF)泊松方程自洽求解.仿真结果表明,C-CNTFET的截止频率可高达THz量级,另外,通过比较C-和HMG-CNTFET可以看出,CCNTFET增加欠叠栅后能够提高器件的开关速度,但不利于提高器件的开关电流比.在HMG-CNTFET中,欠叠栅的采用不仅能够同时改善亚阈值特性和开关电流比,还能降低输出电导.     

用于微显示的顶发射OLED的SPICE仿真模型研究

常用的EDA软件如HSPICE中没有顶发射有机发光器件的仿真模型,导致设计硅基有机发光器件微显示像素驱动电路时存在困难.为此,本文研究了用于微显示的顶发射有机发光器件的SPICE仿真模型,分别讨论了二极管连接的MOS管模型、单个二极管以及双二极管并联模型等方案,分析了其等效电路,同时根据顶发射有机发光器件的实验数据拟合了对应的电路参量,最后用HSPICE软件对三种模型的等效电路进行仿真和结果比较.比较发现采用二极管连接的MOS管模型得到的拟合误差最小,但仿真误差最大;采用单个二极管模型得到的拟合与仿真误差都较大;采用双二极管并联模型得到的拟合与仿真误差均较小且满足驱动电路设计的要求.结果表明双二极管并联模型可作为用于硅基有机发光器件微显示电路设计中的顶发射有机发光器件的SPICE仿真模型.     

彩色超声血流成像中基于回波频率跟踪的正交解调方法

为了消除由超声频率下移所引起的血流速度估计精度的下降,提出了一种基于回波频率跟踪的正交解调方法.首先建立了回波中心频率随深度下移的线性模型;然后使用传统I/Q(Inphase/Quadrature)解调方法得到有偏的基带信号,采用自相关方法沿深度方向分段估计中心频率的下移量,并利用估计出的这些值对所建立的线性模型进行拟合;最后利用拟合后的模型来实时跟踪回波的中心频率,并将其作为参考频率再进行I/Q解调.仿真和试验结果表明,基于回波频率跟踪的正交解调方法能够得到近似无偏的基带信号,提高血流速度估计的准确度和精度,改善彩色超声血流成像的质量.     

基于非平衡Green函数理论的峰值掺杂-低掺杂漏结构碳纳米管场效应晶体管输运研究

为改善碳纳米管场效应晶体管的性能,将一种峰值掺杂-低掺杂漏(HALO-LDD)掺杂结构引入碳纳米管沟道.在量子力学非平衡Green函数理论框架内,通过自洽求解Poisson方程和Schrödinger方程,构建了适用于非均匀掺杂的碳纳米管场效应管的输运模型,该模型可实现场效应晶体管的输运性质与碳纳米管手性指数的对接. 利用该模型研究了单HALO双LDD 掺杂结构对碳纳米管场效应晶体管输运特性的影响.对比分析表明,这种非均匀掺杂结构的场效应管同本征碳纳米管沟道场效应晶体管相比,具有更低的泄漏电流、更大的电流开关比、更小的亚阈区栅电压摆幅,表明其具有更好的栅控能力; 具有更小的漏源电导,更适合应用于模拟集成电路中;具有更小的阈值电压漂移,表明更能抑制短沟道效应. 同本征沟道碳纳米管场效应晶体管相比,这种非均匀掺杂碳纳米管场效应晶体管在沟道区靠近源端位置,电场强度增大, 有利于增大电子的传输速率;在沟道区靠近漏端位置,电场强度减小,更有利于抑制热电子效应.     

自洽半经典方法与有限温度微观光学势 II虚部

以自洽半经典方法及定域密度近似为基础,计算并讨论了不同温度和能量下微观核子-核光学势的虚部.通过和以前工作的比较,强调了采用温度有关核密度的必要性.     

自洽半经典方法与有限温度微观光学势 Ⅱ.虚部

以自洽半经典方法及定域密度近似为基础,计算并讨论了不同温度和能量下微观核子-核光学势的虚部.通过和以前工作的比较,强调了采用温度有关核密度的必要性.     

用纠缠态表象推导广义Ehrenfest定理

利用两粒子相对坐标和总动量的共同本征态|η〉构成的连续变量纠缠态表象,推导了转动系统的Ehrenfest定理,从而说明了在满足某些近似的情况下,量子力学不但能够与经典物理完美自洽,而且利用量子力学的规律可以导出相应的经典物理规律.     

有限温度自洽半经典方程及其虚时迭代解

利用Skyrme力和半经典近似,推导了有限温度自洽半经典(FTSCSC)方程,即通常所说的Euler-Lagrange方程。利用虚时迭代方程对此方程作数值求解,以确定热核的核子密度,并研究其部分静态性质。 关键词：     

LDC-CNTFET: A carbon nanotube field effect transistor with linear doping profile channel

In this paper, a novel carbon nanotube field effect transistor with linear doping profile channel (LDC-CNTFET) is presented. The channel impurity concentration of the proposed structure is at maximum level at source side and linearly decreases toward zero at drain side. The simulation results show that the leakage current, on-off current ratio, subthreshold swing, drain induced barrier lowering, and voltage gain of the proposed structure improve in comparison with conventional CNTFET. Also, due to spreading the impurity throughout the channel region, the proposed structure has superior performance compared with a single halo CNTFET structure with equal saturation current. Design considerations show that the proposed structure enhances the device performance all over a wide range of channel lengths.     

Novel attributes in the performance and scaling effects of carbon nanotube field-effect transistors with halo doping

In this paper, we performed a comprehensive scaling study of a carbon nanotube field-effect transistor (CNTFET) with halo doping (HD) using self-consistent and atomistic scale simulations. Our simulation results demonstrate that drain induced barrier lowering (DIBL) diminishes in the HD-CNTFET due to a step in the potential of the CNT at the interface of p-doped and undoped regions in the channel. Also, the hot carrier effect minimizes with reduction of the peak of the electric field at the drain side of the HD-CNTFET. Moreover, the features of the HD-CNTFET can be controlled by the length and concentration engineering of the HD region. Leakage current, on–off current ratio and subthreshold swing improve with an increase of the length and concentration of the HD region, due to the increment of the threshold voltage and the barrier height of the p–n junction near the source. Therefore, this work can provide an incentive for further experimental exploration.     

基于异质双栅电极结构提高碳纳米管场效应晶体管电子输运效率

为改善碳纳米管场效应晶体管(CNTFET)器件性能, 提高电子输运效率, 提出了一种异质双金属栅(HDMG)电极结构CNTFET器件. 通过对单金属栅(SMG)-CNTFET器件输运模型的适当修改, 实现了对HDMG-CNTFET器件电子输运特性的研究.研究结果表明, 对于所提出的HDMG结构器件, 如果固定源端金属栅S-gate的功函数W_GS使其等于本征CNT 的功函数, 而选取漏端金属栅D-gate的功函数W_Gd, 使其在一定范围内小于W_GS, 可优化器件沟道中的电场分布, 提高器件沟道电子平均输运速率; 同时由于HDMG-CNTFET的D-gate对沟道电势具有调制作用, 使该器件阈值电压降低, 导致在相同的工作电压下, HDMG-CNTFET器件具有更大的通态电流; 而D-gate对漏电压的屏蔽作用又使HDMG-CNTFET与SMG-CNTFET相比具有更好的栅控能力 及减小 漏极感应势垒降低效应、热电子效应和双极导电性等优点. 本研究通过合理选取HDMG-CNTFET双栅电极的功函数, 有效克服了现有研究中存在的改善CNTFET性能需要以减小通态电流为代价的不足, 重要的是提高了器件的电子输运效率, 进而可提高特征频率、减小延迟时间, 有利于将CNTFET器件应用于高速/高频电路. 关键词： CNTFET 异质双栅 电子输运效率 双极导电性     

Monte Carlo study of coaxially gated CNTFETs: capacitive effects and dynamic performance

Carbon nanotubes (CNT) appear as a promising candidate to shrink field-effect transistors (FET) to the nanometer scale. Extensive experimental works have been performed recently to develop the appropriate technology and to explore DC characteristics of a carbon nanotube field effect transistor (CNTFET). In this work, we present results of a Monte Carlo simulation of a coaxially gated CNTFET, including electron–phonon scattering. Our purpose is to present the intrinsic transport properties of such material through the evaluation of the electron mean-free-path. To highlight the potential of the high performance level of CNTFET, we then perform a study of the DC characteristics and of the impact of capacitive effects. Finally, we compare the performance of CNTFET with that of a Si nanowire MOSFET. To cite this article: H. Cazin d'Honincthun et al., C. R. Physique 9 (2008).     

Nonlinear conductivity of single-walled zigzag carbon nanotubes

The conductivity of the single-walled zigzag carbon nanotube system was studied in an alternating electric field with the intensity vector along the axis of nanotubes. The electronic carbon nanotube system was macroscopically considered in terms of the Boltzmann kinetic equation in the constant relaxation time approximation while omitting the interaction with the phonon subsystem. The nonlinear responses to the applied harmonic field were calculated and analyzed.     

A Two-Dimensional Extremely Short Optical Pulse in a System of Carbon Nanotubes in a Direct Current Electric Field

The effect of an external dc electric field on the two-dimensional extremely short optical pulse propagating in a zigzag carbon nanotube array was investigated. The electromagnetic field evolution in the investigated nanotube system is described by the Maxwell equations. Using numerical simulation, the interaction between the pulse electromagnetic field and the external electric field applied to the carbon nanotube array is analyzed.     

Influence of constant electric field on generation of higher harmonics in semiconductor carbon nanotubes

The generation of higher harmonics by semiconductor carbon nanotubes in the presence of constant electric field polarized along the nanotube axis is considered. The analysis is performed in the semiclassical model of electron motion without taking into account interband transitions. The electron system of carbon nanotubes is described using the kinetic Boltzmann equation in the relaxation time approximation. The dependence of higher harmonic amplitude on the field characteristics is studied.