碳纳米管非对称接触结构制作及电学性能研究

实验研究了多根或单根单壁碳纳米管与非对称金属电极接触结构的制作方法。先用介电泳方法(DEP)将碳纳米管定向排列在Au电极对之间,再用电子束光刻(EBL)在碳纳米管的一端加工Al电极,获得多根碳纳米管与金铝电极的非对称接触结构。先用EBL在Au电极对一端覆盖Al电极,再用DEP排列碳纳米管,实现单根碳管与金铝电极的非对称接触结构。非对称结构器件的电学测试研究表明,器件的I-V曲线不再对称,呈现出整流特性。     

用于电机发电的氧化锌纳米结构制备及性能研究

选择了均匀沉淀法来制备氧化锌纳米颗粒,用PEG200进行表面改性,使制备的氧化锌纳米颗粒更加分散。利用X-射线衍射（XRD）、扫描电子显微镜（SEM）表征证明了制备样品是粒径约20nm的氧化锌纳米颗粒,结晶性良好、粒径均匀,单个颗粒呈米粒状,颗粒相连呈薄片状。最后通过半导体特性分析仪（Agilent 4156C）和精密阻抗特性分析仪（Agilent 4284A）分别测量了受不同力时的氧化锌纳米颗粒的特性粘度（I-V特性）和阻抗值,并进行分析,得出其力敏特性。     

裁剪层数对石墨烯纳米带电学输运性能的研究

基于密度泛函理论和非平衡格林函数结合的方法,研究了裁剪层数对扶手椅型石墨烯纳米带电子输运性质的影响。研究结果表明,裁剪不同层数对扶手椅型石墨烯纳米带的整流特性会产生不同的影响。当裁剪层数为1,2,3,5层时,器件的电流-电压曲线呈现为准对称结构,器件产生较弱的整流现象;当裁剪层数为4层时,正负偏压下电流的对称性消失。在正向偏压下,电流随电压的增加而增大;而负向偏压下,电流几乎不随电压的变化而变化,可以看出器件产生了明显的整流现象。也就是说,可以通过裁剪的方式对分子器件的整流特性进行调整和改进。该研究结果对未来石墨烯整流器件的设计具有指导意义。     

磁控溅射制备Co／Al2O3／FeNi磁隧道结

利用磁控溅射设备和光刻技术，采用金属等离子体氧化法，设计制作了10μm×15μm的Co／Al2O3／FeNi磁隧道结，并在77K下对其输运特性进行了研究。测得了11％的隧道磁电阻。随着外加电压增加，隧道结的磁电阻单调减小。测量了样品的I-V特性曲线，发现随着外加电压的增加，曲线逐渐偏离线性，电阻变小，这与理论相符合。电阻随温度变化曲线表明电阻随温度升高而减小，而且在210K处有一个拐点。表现出典型的隧穿过程的特征。     

S0l—Gel法制备BST铁电薄膜及其性能分析

用SoI—Gel法制备出表面致密，界面清晰的BST铁电薄膜。分析了BST薄膜的J-V特性，由于使用了不同的上下电极，导致J—V曲线的不对称，且在外延生长的Pt电极上制备的BST薄膜有较低的漏电流。分别在大气和干燥气氛下测量了BST薄膜的介电特性，分析结果表明：湿度对BST薄膜的介电特性有很大的影响,为了得到正确的介电特性，其测量必须在真空或干燥气氛下进行。     

沉积时间对Au/Si-NPA电学特性的影响

采用浸渍法在硅纳米孔柱阵列(Silicon Nanoporous Pillar Array,Si-NPA)衬底上制得了一系列金/硅纳米孔柱阵列(Au/Si-NPA),不同Au/Si-NPA所用沉积时间不同.通过测试分析所制Au/Si-NPA的,I-V特性曲线,研究了沉积时间对Au/Si-NPA电学特性的影响.结果表明:...     

多层二硫化钼薄膜的制备及其接触电极研究

单分子层二硫化钼（MoS2）是一种具有直接带隙1.8eV的二维半导体,因其特殊的六方晶系层状结构,其晶体管比硅晶体管体积更小、更省电。通过采取化学气相沉积（CVD）法制备二硫化钼薄膜,利用电子束蒸发长约几纳米的金属钼薄膜,金属钼和硫粉在CVD系统发生化学反应生成均匀连续的二硫化钼薄膜,在这过程中硫蒸汽会腐蚀硅基底,所以要采用转移工艺把制备的MoS2薄膜转移到新硅基底上。通过光刻、长电极等工艺在MoS2薄膜沉积Ni、Ti、Al金属电极,采用探针法测试MoS2晶体管的I-V特性曲线,研究不同金属电极对接触电阻大小的影响,并找出接触电阻最小且最适合作接触电极的金属材料。     

Cu_2O氧气流量对ZnO-Cu_2O薄膜异质结特性的影响

利用磁控溅射法在BK-7玻璃基片上制备了ZnO-Cu_2O薄膜异质结。利用X射线衍射、分光光度计和范德堡方法分析了不同氧气流量对Cu_2O单层薄膜的结构、光学和电学性质的影响,并分析了不同氧气流量制备的Cu_2O对ZnO-Cu_2O异质结I-V特性的影响。研究结果表明:ZnO-Cu_2O薄膜异质结样品的I-V曲线具有二极管的整流特性,样品的正向阈值电压随着Cu_2O氧气流量的增加而增大。较大正向电流的样品(氧气流量为10.6 sccm)具有较小的串联电阻和泄露电阻,以及较大的载流子浓度。     

(p)nc-Si∶H/(n)c-Si异质结变容二极管

采用等离子体增强化学气相沉积技术和电子束蒸发技术制备了一种新型的线性缓变异质结变容二极管——Au/Cr合金（电极）/multi-layer(p)nc-Si∶H/(n)c-Si/（电极）Au/Ge合金结构．I-V，C-V，C-f以及DLTS的测试结果表明：其电容变化系数远大于单晶硅线性缓变异质结的电容变化系数，正向导电机制符合隧穿辅助辐射复合模型，这是nc-Si∶H层中nc-Si晶粒的量子效应所致；反向电流主要由异质结中空间电荷区的产生电流决定，且反向漏电流小，反向击穿电压高，表现出较好的整流特性．     

Sol-Gel法制备BST铁电薄膜及其性能分析

用Sol-Gel法制备出表面致密,界面清晰的BST铁电薄膜。分析了BST薄膜的J-V特性,由于使用了不同的上下电极,导致J-V曲线的不对称,且在外延生长的Pt电极上制备的BST薄膜有较低的漏电流。分别在大气和干燥气氛下测量了BST薄膜的介电特性,分析结果表明:湿度对BST薄膜的介电特性有很大的影响,为了得到正确的介电特性,其测量必须在真空或干燥气氛下进行。     

Ag/PEPC/NiPc/ZnO/Ag thin film capacitive and resistive humidity sensors

A thin film of blended poly-N-epoxypropylcarbazole (PEPC) (25 wt.%),nickel phthalocyanine (NiPc) (50 wt.%) and ZnO nano-powder (25 wt.%) in benzene (5 wt.%) was spin-coated on a glass substrate with silver electrodes to produce a surface-type Ag/PEPC/NiPc/ZnO/Ag capacitive and resistive sensor.Sensors with two different PEPC/NiPc/ZnO film thicknesses (330 and 400 nm) were fabricated and compared.The effects of humidity on capacitance and resistance of the Ag/PEPC/NiPc/ZnO/Ag sensors were investigated at two frequencies of the applied voltage:120 Hz and 1 kHz.It was observed that at 120 Hz under humidity of up to 95% RH the capacitance of the sensors increased by 540 times and resistance decreased by 450 times with respect to humidity conditions of 50% RH.It was found that the sensor with a thinner semiconducting film (330 nm) was more sensitive than the sensor with a thicker film (400 nm).The sensitivity was improved when the sensor was used at a lower frequency as compared with a high frequency.It is assumed that the humidity response of the sensors is associated with absorption of water vapors and doping of water molecules in the semiconductor blend layer.This had been proven by simulation of the capacitance-humidity relationship.     

Title: Using Alignment and 2D Network Simulations to Study Charge Transport Through Doped ZnO Nanowire Thin Film Electrodes

Factors affecting charge transport through ZnO nanowire mat films were studied by aligning ZnO nanowires on substrates and coupling experimental measurements with 2D nanowire network simulations. Gallium doped ZnO nanowires were aligned on thermally oxidized silicon wafer by shearing a nanowire dispersion in ethanol. Sheet resistances of nanowire thin films that had current flowing parallel to nanowire alignment direction were compared to thin films that had current flowing perpendicular to nanowire alignment direction. Perpendicular devices showed ～5 fold greater sheet resistance than parallel devices supporting the hypothesis that aligning nanowires would increase conductivity of ZnO nanowire electrodes. 2‐D nanowire network simulations of thin films showed that the device sheet resistance was dominated by inter‐wire contact resistance. For a given resistivity of ZnO nanowires, the thin film electrodes would have the lowest possible sheet resistance if the inter‐wire contact resistance was one order of magnitude lower than the single nanowire resistance. Simulations suggest that the conductivity of such thin film devices could be further enhanced by using longer nanowires.     

一维WO3-ZnO异质结构的合成及生长机理研究

本文采用两步水热法成功合成出一维WO3-ZnO分级异质结构.TEM表征发现ZnO纳米棒在WO3纳米带表面均匀排列,ZnO纳米棒和WO3均各自沿着[0001]方向生长,且二者之间存在特定的取向关系,即生长方向成44°或者136°角.晶体学分析表明在ZnO和WO3之间存在失配度很小的取向关系,即(0001)WO3//(1(1)02)ZnO和(11(22))WO3//(0001)ZnO,以及经过翻转后出现的(0001)WO3//(1(1)02)ZnO和(11(2)2)WO3//(0001)ZnO.根据实验和晶体学分析结果,本文认为ZnO棒在WO3纳米带上的生长机理是符合Volmer-Weber模型的外延生长.     

Observation of a 2D Electron Gas and the Tuning of the Electrical Conductance of ZnO Nanowires by Controllable Surface Band‐Bending

Direct experimental evidence for the existence of a 2D electron gas in devices based on ZnO nanowires (NWs) is presented. A two‐channel core/shell model is proposed for the interpretation of the temperature‐dependent current–voltage (I–V) characteristics of the ZnO NW, where a mixed metallic–semiconducting behavior is observed. The experimental results are quantitatively analyzed using a weak‐localization theory, and suggest that the NW is composed of a “bulk” semiconducting core with a metallic surface accumulation layer, which is basically a 2D electron gas in which the electron–phonon inelastic scattering is much weaker than the electron–electron inelastic scattering. A series of I–V measurements on a single NW device are carried out by alternating the atmosphere (vacuum, H₂, vacuum, O₂), and a reversible change in the conductance from metallic to semiconducting is achieved, indicating the surface accumulation layer is likely hydroxide‐induced. Such results strongly support the two‐channel model and demonstrate the controllable tuning of the ZnO NW electrical behavior via surface band‐bending.     

Inkjet-printed polymer thin-film transistors: Enhancing performances by contact resistances engineering

In this paper, we demonstrate how to enhance polymer thin-film transistors (PTFTs) performances made by low-cost inkjet printing technique. Indeed, in PTFTs, contact resistances between semiconducting conjugated polymers (SCPs) and Source and Drain (S&D) contacts may dominate the transport properties of such electronic devices. Here, we report measurements of these parasitic resistances for several couples of (i) SCPs, as active material, and (ii) electrodes, as S&D contacts, in bottom-contact inkjetted PTFTs. The differences in PTFT performances are discussed upon these contact resistance. For this, we evaluate the performances of several inkjetted couples of SCP/S&D compared to devices with evaporated metal-based S&D. By this way, we show that inkjet printing is a suitable low-cost technique to dispense polymers and inorganic nanoparticles for direct-writing of PTFTs. A significant reduction in the contact resistance R_C was achieved when inkjetted Pedot:Pss-based S&D electrodes are used instead of evaporated metal-based S&D electrodes. The improved efficiency of charge carrier injection is assumed to be due to the formation of a p-doped interfacial layer at the interface between the SCP and the S&D electrodes. All these results pave the way towards flexible electronics applications by using inkjetted polymers both for electrodes and semiconducting active layer on flexible plastic substrate.     

Bumpless Interconnect of 6- $mu$m-Pitch Cu Electrodes at Room Temperature

Bumpless interconnect of 6-$mu{rm m}$-pitch Cu electrodes was realized at room temperature with the surface activated bonding (SAB) method. In this study, we propose a novel bumpless structure, where the electrodes and a surrounding Cu frame are fabricated with the same height to increase bond strength and demonstrate the feasibility of a sealing interconnection between Cu surfaces. The damascene process, assisted by the reactive ion beam etching (RIE), was used to fabricate the Cu structures. 923$thinspace$521 electrodes placed inside the frame were arranged into a spiral chain to enable the detection of the positions with insufficient interconnection by electrical resistance measurements. Using the SAB conditions optimized with simple chemo-mechanical polishing (CMP)-Cu film samples, we found that 744$thinspace$769 electrodes were successfully interconnected, except some specific lines near the frame, which might be due to sample preparation error rather than a bond defect. The mean contact resistance was below 0.08 $Omega$; a sealing effect was achieved at the frame structure because there was little increase in the contact resistance in high temperature storage testing performed at 150 $^{circ}{rm C}$ for 1000 h, in ambient air.      

Photoconductivity and surface chemical analysis of ZnO thin films deposited by solution-processing techniques for nano and microstructure fabrication

The fabrication of zinc oxide(ZnO) from inexpensive solution-processing techniques,namely,electrochemical deposition and electrospinning were explored on various conducting and mesoporous semiconducting surfaces.Optimised conditions were derived for template- and self-assisted nano/micro structures and composites. ZnO thin films were annealed at a fixed temperature under ambient conditions and characterised using physical and optical techniques.The photocurrent response in the UV region shows a fast rise and double decay behaviour with a fast component followed by a slow oscillatory decay.Photocurrent results were correlated with surface chemical analysis from X-ray photoelectron spectroscopy.Various characterisation details reveal the importance of fabrication parameter optimisation for useful low-cost optoelectronic applications.     

Directly drawn ZnO semiconductors and MWCNT/PSS electrodes via electrohydrodynamic jet printing for use in thin-film transistors: The ideal combination for reliable device performances

Solution-processed deposition of conducting and semiconducting materials enables the fabrication of large-area and low-cost electronic devices without the use of high-vacuum equipment. To obtain the possibility of commercializing solution-processed devices such as thin-film transistors (TFTs), easy and simple patterning process of each component become an important issue. In this study, we prepare directly patterned semiconductors and electrodes with the electrohydrodynamic (EHD) printing technique and utilize them in reliable n-type TFTs. By utilizing EHD printing technique, straight lines of zinc oxide (ZnO) semiconductor are successfully drawn from the highly soluble precursor, zinc acrylate (ZnA), and used as the active layers of TFTs. The resulting devices exhibit good TFT characteristics, and doping with a small amount of indium can enhance their performances. Furthermore, we print three different conducting materials on pre-patterned ZnO substrates for the realization of ZnO TFT arrays consisting of directly-drawn semiconductors and source/drain (S/D) electrodes. Multiwall carbon nanotube/polystyrene sulfonate (MWCNT/PSS) electrodes are found to form stable lines and their solution-processed TFTs display reliable operation with negligible hysteresis.     

Changes in Electrical Characteristics of ZnO Thin Films Due to Environmental Factors

The impact of light and controlled gas ambient on the electrical characteristics of ZnO:P grown by pulsed laser deposition (PLD) is investigated with temperature-dependent Hall-effect and photo-Hall-effect using above-bandgap light. Exposure to blue/ultraviolet (UV) light results in long-lived persistent photoconductivity (PPC) effects dominated by electron conduction. However, these persistent effects can be largely reversed by exposing the sample to a controlled ambient of dry O₂ gas. These O₂-induced changes in the electronic properties persist in vacuum up to at least 400 K. Exposure to dry N₂ gas following blue/UV light has no effect on the observed PPC characteristics. The implications of these effects on the preparation of p-type ZnO will be discussed.     

BaTiO_3半导瓷在电功率作用下的PTC特性

ＢａＴｉＯ３半导瓷在电功率作用下的ＰＴＣ特性最好用电阻率－电场强度（ρ－Ｅ）特性曲线表示。ρ－Ｅ特性能很好地反映电功率作用下电阻突跃变化程度。不同散热条件的ρ－Ｅ特性也不同，ρ－Ｅ特性同时还能表示该元件的抗电场击穿能力。散热条件良好，可产生更大的电热功率，可承受更高的工作电压