绝缘体上硅金属氧化物半导体场效应晶体管中辐射导致的寄生效应研究

基于⁶⁰Co γ射线源研究了总剂量辐射对绝缘体上硅（silicon on insulator,SOI）金属氧化物半导体场效应晶体管器件的影响.通过对比不同尺寸器件的辐射响应,分析了导致辐照后器件性能退化的不同机制.实验表明：器件的性能退化来源于辐射增强的寄生效应;浅沟槽隔离（shallow trench isolation,STI）寄生晶体管的开启导致了关态漏电流随总剂量呈指数增加,直到达到饱和;STI氧化层的陷阱电荷共享导致了窄沟道器件的阈值电压漂移,而短沟道器件的阈值电压漂移则来自于背栅阈值耦合;在同一工艺下,尺寸较小的器件对总剂量效应更敏感.探讨了背栅和体区加负偏压对总剂量效应的影响,SOI器件背栅或体区的负偏压可以在一定程度上抑制辐射增强的寄生效应,从而改善辐照后器件的电学特性.     

石墨烯场效应晶体管的X射线总剂量效应

本文针对不同结构、尺寸的石墨烯场效应晶体管(graphene field effect transistors, GFET)开展了基于10 keVX射线的总剂量效应研究.结果表明,随累积剂量的增大,不同结构GFET的狄拉克电压V_Dirac和载流子迁移率μ不断退化;相比于背栅型GFET,顶栅型GFET的辐射损伤更加严重;尺寸对GFET器件的总剂量效应决定于器件结构; 200μm×200μm尺寸的顶栅型GFET损伤最严重,而背栅型GFET是50μm×50μm尺寸的器件损伤最严重.研究表明:对于顶栅型GFET,辐照过程中在栅氧层中形成的氧化物陷阱电荷的积累是V_Dirac和μ降低的主要原因.背栅型GFET不仅受到辐射在栅氧化层中产生的陷阱电荷的影响,还受到石墨烯表面的氧吸附的影响.在此基础上,结合TCAD仿真工具实现了顶栅器件氧化层中辐射产生的氧化物陷阱电荷对器件辐射响应规律的仿真.相关研究结果对于石墨烯器件的抗辐照加固研究具有重大意义.     

改进型异质栅对深亚微米栅长碳化硅MESFET特性影响

基于器件物理分析方法,结合高场迁移率、肖特基栅势垒降低、势垒隧穿等物理模型, 分析了改进型异质栅结构对深亚微米栅长碳化硅肖特基栅场效应晶体管沟道电势、 夹断电压以及栅下电场分布的影响.通过与传统栅结构器件特性的对比表明, 异质栅结构在碳化硅肖特基栅场效应晶体管的沟道电势中引入了多阶梯分布,加强了近源端电场; 另一方面,相比于双栅器件,改进型异质栅器件沟道最大电势的位置远离源端, 因此载流子在沟道中加速更快,在一定程度上屏蔽了漏压引起的电势变化,更好抑制了短沟道效应. 此外,研究了不同结构参数的异质栅对短沟道器件特性的影响,获得了优化的设计方案, 减小了器件的亚阈值倾斜因子.为发挥碳化硅器件在大功率应用中的优势,设计了非对称异质栅结构, 改善了栅电极边缘的电场分布,提高了小栅长器件的耐压.     

品质因子可调的石墨烯纳米机械振子

纳米机械振子尺寸小,质量轻,可以用来制作探测力、质量等微小物理量的超灵敏探测器.石墨烯拥有质量轻、密度低和杨氏模量高等特性,被认为是制作纳米机械振子的理想材料.石墨烯纳米机械振子因其具有的谐振频率高、品质因子高和谐振频率可调性高等优势,近年来得到了人们的广泛关注.作为表征纳米机械振子性能的一个重要指标,品质因子越高,意味着纳米机械振子耗散越低,纳米机械振子的灵敏度越高.本文通过微纳加工的工艺制备出一种谐振频率随栅压可调(调节的范围为73MHz~90MHz)的石墨烯纳米机械振子样品,研究其在极低温高真空环境下的品质因子与栅极电压之间的关系.实验表明通过栅压调节振子的内部应力,能够使石墨烯纳米机械振子品质因子从220提高到1000.我们的结果为二维材料纳米机械振子的耗散研究提供了一种新的研究思路.     

石墨烯射频器件研究进展

石墨烯因具有优良的电学特性,在半导体行业中受到广泛关注,特别因其具有超薄的结构和极高的载流子迁移率,为解决短沟道效应提供了可能,并且在高速电子领域具有应用前景.近年来,使用石墨烯作为沟道材料制备射频晶体管及射频电路是发挥石墨烯材料优势的一个重要研究方向.制造高性能的射频器件,首先要制备出高性能的石墨烯材料.在金属衬底上沉积均匀的单层石墨烯材料或者在绝缘衬底上外延生长单层、双层石墨烯材料都是获得高质量石墨烯材料的常用方法.器件结构及工艺流程的设计也是提升晶体管射频性能的重要因素,多指栅结构、T型栅结构、埋栅结构以及自对准工艺的发展能够有效改善石墨烯射频晶体管的截止频率及最大振荡频率.石墨烯晶体管独特的电学特性使得其除了可以构造与其他半导体材料电路相似的射频电路结构,还可以构造出功能完整并且结构更加简单的新型射频电路结构.     

部分耗尽结构绝缘体上硅器件的低频噪声特性

针对部分耗尽结构绝缘体上硅(silicon-on-insulator, SOI)器件低频噪声特性展开实验与理论研究. 实验结果表明, 器件低频噪声主要来源于SiO₂-Si界面附近缺陷态对载流子的俘获与释放过程; 基于此理论可提取前栅和背栅氧化层界面附近缺陷态密度分别为8×10¹⁷ eV^-1·cm^-3和2.76×10¹⁷ eV^-1·cm^-3. 基于电荷隧穿机理, 在考虑隧穿削弱因子、隧穿距离与时间常数之间关系的基础上, 提取了前、背栅氧化层内缺陷态密度随空间的分布情况. 此外, SOI器件沟道电流归一化噪声功率谱密度随沟道长度的增加而线性减小, 这表明器件低频噪声主要来源于沟道的闪烁噪声. 最后, 基于电荷耦合效应, 分析了背栅电压对前栅阈值电压、沟道电流以及沟道电流噪声功率谱密度的影响.     

10 nm金属氧化物半导体场效应晶体管中的热噪声特性分析

随着金属氧化物半导体场效应晶体管(MOSFET)器件等比例缩小至纳米级的较小尺寸,一方面导致的短沟道效应已严重影响热噪声;另一方面使栅、源、漏区及衬底区的热噪声占有比越来越高,而传统热噪声模型主要考虑较大尺寸器件的沟道热噪声,且其模型未考虑到沟道饱和区.本文针对小尺寸纳米级MOSFET器件,并根据器件结构特征和热噪声的基本特性,建立了10 nm器件的热噪声模型,该模型体现沟道区、衬底区及栅、源、漏区,同时考虑到沟道饱和区的热噪声.在模型的基础上,分析沟道热噪声、总热噪声随偏置参量及器件参数之间的关系,验证了沟道饱和区热噪声的存在,并与已有实验结果一致,所得结论有助于提高纳米级小尺寸MOSFET器件的工作效率、寿命及响应速度等.     

栅长对PDSOINMOS器件总剂量辐照效应影响的实验研究

本文对PDS01NMOS器件进行了60Coγ射线总剂量辐照的实验测试,分析了不同的栅长对器件辐射效应的影响及其物理机理．研究结果表明,短沟道器件辐照后感生的界面态密度更大,使器件跨导出现退化．PDSOI器件的局部浮体效应是造成不同栅长器件辐照后输出特性变化不一致的主要原因．短沟道器件输出特性的击穿电压更低．在关态偏置条件下,由于背栅晶体管更严重的辐射效应,短沟道SOI器件的电离辐射效应比同样偏置条件下长沟道器件严重．     

单层石墨烯场效应晶体管制备及低温导电特性北大核心CSCD

采用化学气相沉积法(CVD)制备单层石墨烯,将其转移到300nm厚的SiO_2/Si衬底上.通过真空蒸镀法在石墨烯表面沉积Au电极,获得SiO_2/Si背栅石墨烯场效应晶体管,对其进行低温导电特性的测试.结果表明,背栅石墨烯场效应晶体管呈双极导电性,并表现出P型导电特性.室温下器件的电子迁移率为3478cm^2/V.s,开关比(on/off)为1.88.在低温下器件的电子迁移率降至2913cm^2/V.s,开关比上升到2.53,狄拉克点左移,P型掺杂效应减弱,温度对器件起到调制作用.     

单层石墨烯场效应晶体管制备及低温导电特性

采用化学气相沉积法(CVD)制备单层石墨烯,将其转移到300nm厚的SiO_2/Si衬底上.通过真空蒸镀法在石墨烯表面沉积Au电极,获得SiO_2/Si背栅石墨烯场效应晶体管,对其进行低温导电特性的测试.结果表明,背栅石墨烯场效应晶体管呈双极导电性,并表现出P型导电特性.室温下器件的电子迁移率为3478cm~2/V.s,开关比(on/off)为1.88.在低温下器件的电子迁移率降至2913cm~2/V.s,开关比上升到2.53,狄拉克点左移,P型掺杂效应减弱,温度对器件起到调制作用.     

基于毫米级单晶石墨烯的倍频器性能研究

石墨烯作为一种拥有高电子迁移率和高饱和速度的二维材料,在射频电子学领域具有很大的应用潜力,引起了人们广泛的研究兴趣.近些年随着化学气相沉积制备石墨烯技术的发展,高质量大尺寸的单晶石墨烯生长技术也愈加成熟.本文基于化学气相沉积生长的毫米级单晶石墨烯,在高介电常数介质上制备出高性能的石墨烯倍频器,并且对其倍频特性做了系统的研究.研究结果表明:在输入信号频率为1 GHz时,倍频增益可以达到-23.4 dB,频谱纯度可以达到94%.研究了不同漏极偏压以及输入信号功率下倍频增益的变化特性,随着漏极偏压以及输入信号功率的增加,倍频增益增加.对具有不同跨导和电子空穴电导对称性的器件的倍频增益和频谱纯度随输入信号频率f_(in)的变化关系进行了研究.结果表明,跨导对于倍频增益影响显著,在f_(in)=1 GHz时器件的频谱纯度差别不大,均大于90%,但是随着f_(in)增加至4 GHz,电子空穴电导对称性较差的器件频谱纯度下降至42%,电子空穴电导对称性较好的器件仍能保持85%的频谱纯度.这是电子空穴电导对称性和电子空穴响应速度共同作用的结果.本文的研究结果对于高性能石墨烯倍频器设计具有一定的指导意义.     

Magnetotransport characterization of THz detectors based on plasma oscillations in submicron field-effect transistors

Magnetotransport characterization of field-effect transistors in view of their application as resonant detectors of THz radiation is presented. Three groups of different transistors based on GaAs/GaAlAs or GaInAs/AlGaAs heterostructures are investigated at liquid-helium temperatures and for magnetic fields of up to 14 T. The magnetic-field dependence of the transistor resistance is used for evaluation of the electron density and mobility in the transistor channel. The electron mobility and concentration determined from magnetotransport measurements are used for the interpretation of recently observed resonant detection of terahertz radiation in 0.15 μm gate length GaAs transistors and for the determination of the parameters of other field-effect transistors processed for resonant and voltage tunable detection of THz radiation. From Fizika Tverdogo Tela, Vol. 46, No. 1, 2004, pp. 138–145. Original English Text Copyright ? 2004 by Lusakowski, Knap, Dyakonova, Kaminska, Piotrowska, Golaszewska, Shur, Smirnov, Gavrilenko, Antonov, Morozov. This article was submitted by the authors in English.     

Electrical transport properties of graphene-covered-Cu wires grown by chemical vapor deposition

We investigated the field-effect transistor (FET) characteristics of 15-μm graphene-covered copper wires (G-wires). Unlike the previously reported graphene FET, carries initially showed p-type like FET characteristics in two-terminal transport measurements. Our results indicate that the electrical transport processes in a G-wire FET occur in both the heavily p-doped contact and the p-doped radial graphene channel, as a p-channel. The interfacial potential barrier between the contact electrode and the radial graphene channel is small, but there is a radial potential barrier that limits electrical transport through the copper core in chemical vapor deposition (CVD) grown samples. The p-type FET characteristics appeared clearly after the oxidation of the G-wires.     

基于石墨烯互补超表面的可调谐太赫兹吸波体

通过在石墨烯超表面设计周期性切条,实现了基于石墨烯互补超表面的可调谐太赫兹吸波体.通过改变外加电压来改变石墨烯的费米能级,吸波体实现频率可调谐特性.研究了石墨烯费米能级、结构尺寸对超材料吸波体吸收特性的影响,并利用多重反射理论研究了其物理机理并且证明了模拟方法的可行性.研究结果表明:当石墨烯费米能级取0.6 eV,基底厚度13μm,石墨烯上切条长宽分别为2.9μm,0.1μm时,吸波体在1.865 THz可以实现99.9%的完美吸收;石墨烯费米能级从0.4 eV增大到0.9 eV,吸波体共振频率从1.596 THz蓝移到2.168 THz,且伴随共振吸收率的改变,吸收率在0.6 eV时达到最大;通过改变费米能级实现的最大吸收率调制度达84.55%.     

等离激元增强的石墨烯光吸收

石墨烯中等离激元具有特殊的光电性质,其和入射光的强烈耦合可以引起光吸收的增强.本文基于时域有限差分法和多体自洽场理论研究了等离激元对处于光学谐振腔中的石墨烯光吸收的影响.由于石墨烯中等离激元与入射光动量和能量不匹配而不能直接相互作用,因此石墨烯上施加了金属光栅结构.研究发现光栅结构能够对入射光进行动量补偿并且能够引起其下石墨烯中的电场强度产生很大程度增强,从而导致在该石墨烯结构中太赫兹等离激元和入射光发生强烈耦合而产生太赫兹等离极化激元,同时引起石墨烯光吸收的增强.希望本文能够加深对石墨烯光电特性的理解以及可以为基于石墨烯的太赫兹光电装置提供一定的理论依据.     

Quantum dot resonant tunneling FET on graphene

At this paper a field effect transistor based on graphene nanoribbon (GNR) is modeled. Like in most GNR-FETs the GNR is chosen to be semiconductor with a gap, through which the current passes at on state of the device. The regions at the two ends of GNR are highly n-type doped and play the role of metallic reservoirs so called source and drain contacts. Two dielectric layers are placed on top and bottom of the GNR and a metallic gate is located on its top above the channel region. At this paper it is assumed that the gate length is less than the channel length so that the two ends of the channel region are un-gated. As a result of this geometry, the two un-gated regions of channel act as quantum barriers between channel and the contacts. By applying gate voltage, discrete energy levels are generated in channel and resonant tunneling transport occurs via these levels. By solving the NEGF and 3D Poisson equations self consistently, we have obtained electron density, potential profile and current. The current variations with the gate voltage give rise to negative transconductance.     

Frequency-comb-referenced molecular spectroscopy in the mid-infrared region

A simple method for absolute-frequency measurements of molecular transitions in the mid-IR region is reported. The method is based on a cw singly resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3.45?μm. The mid-IR frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute-frequency measurement of the P(7) transition of the ν3 band of CH4 are demonstrated.     

Tunable multichannel drop filters based on the two-dimensional photonic crystal with oval defects

Light propagation through the channel filter based on the two-dimensional photonic crystals with oval-rod defects is studied by the finite-difference time-domain method. In addition to the traditional size tuning, shape alteration of the defects from the usual circle to the ellipse offers a powerful approach to tune the resonant frequency of channel-drop filters based on two-dimensional photonic crystals. It is found that the resonant frequency can be flexibly adjusted only by changing the orientation angle of the oval defects. The sensitivity of the resonant frequency to the alteration of the oval rods’ rotation angle is systematically studied. Because the rotation angles of the ellipse can be continuously adjusted, so the channel drop filter based on this kind of defects with different rotation angles is more suitable to the occasion where a large number of output channel filters is need.     

Light propagation properties of two-dimensional photonic crystal channel filters with elliptical micro-cavities

Light propagation through a channel filter based on two-dimensional photonic crystals with elliptical-rod defects is studied by the finite-difference time-domain method. Shape alteration of the defects from the usual circle to an ellipse offers a powerful approach to engineer the resonant frequency of channel filters. It is found that the resonant frequency can be flexibly adjusted by just changing the orientation angle of the elliptical defects. The sensitivity of the resonant wavelength to the alteration of the oval rods' shape is also studied. This kind of multi-channel filter is very suitable for systems requiring a large number of output channel filters.