蒸镀法制备全有机并五苯薄膜场效应晶体管

以全蒸镀方法在真空室内一次性制备了正装结构的全有机并五苯薄膜场效应晶体管。正装结构全蒸镀法有利于简化工艺制备程序,缩小器件尺寸,提高集成度。制备的绝缘层厚度仅为50nm的全有机薄膜场效应晶体管,器件的工作电压降至10V,相同电压下饱和输出电流有了明显提高。筛选适当的有机绝缘材料,改善全有机薄膜场效应晶体管有源层/绝缘层的界面性能,使阈值电压几乎降至0V,场效应迁移率提高了3倍多,输出饱和电流也有了明显的提高。     

Thickness dependence of surface morphology and charge carrier mobility in organic field-effect transistors

With the aim of understanding the relationships between organic small molecule field-effect transistors (FETs) and organic conjugated polymer FETs, we investigate the thickness dependence of surface morphology and charge carrier mobility in pentacene and regioregular poly (3-hexylthiophene) (RR-P3HT) field-effect transistors. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility is largely related to the morphology of the organic active layer. We observe that the change trends of the surface morphologies (average size and average roughness) of pentacene and RR-P3HT thin films are mutually opposite, as the thickness of the organic layer increases. Further, we demonstrate that the change trends of the field-effect mobilities of pentacene and RR-P3HT FETs are also opposite to each other, as the thickness of the organic layer increases within its limit.     

Conductance Oscillations in Spin Field-Effect Transistors

Ballistic spin transport in spin field-effect transistors is studied by taking into account the Rashba spinorbit coupling, interfacial scattering, and band mismatch. It is shown that the spin conductance oscillation with the semiconductor channel length is a superimposition of the Rashba spin precession and spin interference oscillations. They have different oscillation periods π/kR and π/k with kR the Rashba wavevector and k the Fermi wavevector of the semiconductor channel, and play different parts of slow and rapid oscillations, depending upon the relative magnitude of π/kR and π/k. Only at k = kR does the spin conductance exhibit oscillations of a single period. Two types of different behaviors of the tunnelling magnetoresistance are discussed.     

Conductance Oscillations in Spin Field-Effect Transistors

Ballistic spin transport in spin field-effect transistors is studied by taking into account the Rashba spinorbit coupling, interracial scattering, and band mismatch. It is shown that the spin conductance oscillation with the semiconductor channel length is a superimposition of the Rashba spin precession and spin interference oscillations. They have different oscillation periods π/κR and π/κ with κR the Rashba wavevector and κ the Fermi wavevector of the semiconductor channel, and play different parts of slow and rapid oscillations, depending upon the relative magnitude of π/κR and π/κ. Only at κ = κR does the spin conductance exhibit oscillations of a single period. Two types of different behaviors of the tunnelling magnetoresistance are discussed.     

基于栅绝缘层表面修饰的有机场效应晶体管迁移率的研究进展

栅绝缘层的表面性质对有机场效应晶体管（OFETs）的半导体薄膜的形貌、晶粒生长的有序性和载流子的传输有着重大的影响．研究表明,通过改进栅绝缘层的表面性质,可以有效提高有机场效应晶体管的迁移率．本文综述了OFETs绝缘层表面的粗糙度和表面能对OFETs迁移率的影响,重点探讨了栅绝缘层表面修饰常用的方法,即自组装单层（SAMs）修饰和聚合物修饰与迁移率改进之间的研究进展．最后,展望了该研究方向未来可能的发展趋势．     

Fabrication and characterization of the normally-off N-channel lateral 4H–SiC metal–oxide–semiconductor field-effect transistors

In this paper, the normally-off N-channel lateral 4H–Si C metal–oxide–semiconductor field-effect transistors(MOSFFETs) have been fabricated and characterized. A sandwich-(nitridation–oxidation–nitridation) type process was used to grow the gate dielectric film to obtain high channel mobility. The interface properties of 4H–Si C/SiO_2 were examined by the measurement of HF I–V, G–V, and C–V over a range of frequencies. The ideal C–V curve with little hysteresis and the frequency dispersion were observed. As a result, the interface state density near the conduction band edge of 4H–Si C was reduced to 2 × 10~(11) e V~(-1)·cm~(-2), the breakdown field of the grown oxides was about 9.8 MV/cm, the median peak fieldeffect mobility is about 32.5 cm~2·V~(-1)·s~(-1), and the maximum peak field-effect mobility of 38 cm~2·V~(-1)·s~(-1) was achieved in fabricated lateral 4H–Si C MOSFFETs.     

Effects of concentration and annealing on the performance of regioregular poly（3-hexylthiophene） field-effect transistors

This paper investigates the effects of concentration on the crystalline structure, the morphology, and the charge carrier mobility of regioregular poly(3-hexylthiophene) (RR-P3HT) field-effect transistors (FETs). The RR-P3HT FETs with RR-P3HT as an active layer with different concentrations of RR-P3HT solution from 0.5~wt% to 2~wt% are prepared. The results indicate that the performance of RR-P3HT FETs improves drastically with the increase of RR-P3HT weight percentages in chloroform solution due to the formation of more microcrystalline lamellae and bigger nanoscale islands. It finds that the field-effect mobility of RR-P3HT FET with 2~wt% can reach 5.78× 10^-3~cm²/Vs which is higher by a factor of 13 than that with 0.5~wt%. Further, an appropriate thermal annealing is adopted to improve the performance of RR-P3HT FETs. The field-effect mobility of RR-P3HT FETs increases drastically to 0.09~cm²/Vs by thermal annealing at 150~℃, and the value of on/off current ratio can reach 10^4.     

Improving organic field-effect transistors based on double active layers structure

Organic field-effect transistors (OFETs) were fabricated based on double active layers structure. Different substrate temperatures and thermal treatment were adopted to prepare double active layers and optimize film morphology. The grain size of organic films can be effectively controlled by the change in substrate temperature in the process of deposition. An improved device performance was obtained compared with conventional single layer devices. This result is attributed to the introduction of double active layers. We believe that this kind of optimization will simultaneously improve charge injection and transportation of OFETs.     

Vacuum relaxation and annealing-induced enhancement of mobility of regioregular poly（3-hexylthiophene） field-effect transistors

In order to enhance the performance of regioregular poly(3-hexylthiophene) (RR-P3HT) field-effect transistors (FETs), RR-P3HT FETs are prepared by the spin-coating method followed by vacuum placement and annealing. This paper reports that the crystal structure, the molecule interconnection, the surface morphology, and the charge carrier mobility of RR-P3HT films are affected by vacuum relaxation and annealing. The results reveal that the field-effect mobility of RR-P3HT FETs can reach 4.17×10^ - 2~m²/(V.s) by vacuum relaxation at room temperature due to an enhanced local self-organization. Furthermore, it reports that an appropriate annealing temperature can facilitate the crystal structure, the orientation and the interconnection of polymer molecules. These results show that the field-effect mobility of device annealed at 150~℃ for 10 minutes in vacuum at atmosphere and followed by placement for 20 hours in vacuum at room temperature is enhanced dramatically to 9.00×10^ - 2 ~cm²/(V.s).     

Improved performance of 4H-SiC metal-semiconductor field-effect transistors with step p-buffer layer

An improved 4H-SiC metal-semiconductor field-effect transistors (MESFETs) with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer has been applied not only to increase the channel current, but also to improve the transconductance. This is due to the fact that the variation in p-buffer layer depth leads to the decrease in parasitic series resistance resulting from the change in the active channel thickness and modulation in the electric field distribution inside the channel. Detailed numerical simulations demonstrate that the saturation drain current and the maximum theoretical output power density of the proposed structure are about 30% and 37% larger than those of the conventional structure. The cut-off frequency and the maximum oscillation frequency of the proposed MESFETs are 14.5 and 62 GHz, respectively, which are higher than that of the conventional structure. Therefore, the 4H-SiC MESFETs with step p-buffer layer have superior direct-current and radio-frequency performances compared to the similar devices based on the conventional structure.     

衬底温度对TiOPc光敏有机场效应管的影响

制备了基于酞菁氧钛(TiOPc)的有机光敏场效应管,对氧化铟锡(ITO)衬底器件进行温度优化。实验结果表明,随着衬底温度(T_(sub))的增加,器件载流子迁移率(μ)、光暗电流比(P)和光响应度(R)先增加后减小,在T_(sub)=140℃时达到最大。T_(sub)=140℃的ITO衬底器件,在波长808 nm、光功率密度190 m W·cm~(-2)的近红外光照下,最大载流子迁移率达到1.35×10~(-2)cm~2·V~(-1)·s~(-1),最大光暗电流比为250,栅压为-50 V时的最大光响应度为1.51 m A/W。     

二维半导体过渡金属硫化物的逻辑集成器件

微电子器件沿摩尔定律持续发展超过50年,正面临着高功耗等挑战.二维层状材料可以将载流子限制在界面1 nm的空间内,部分材料展现出高迁移率、能带可调、拓扑奇异性等特点,有望给"后摩尔时代"微电子器件带来新的技术变革.其中,以MoS_2为代表的过渡金属硫化物具有1-2 eV的带隙、良好的空气稳定性和工艺兼容性,在逻辑集成方面有巨大潜力.本文综述了二维过渡金属硫化物在逻辑器件领域的研究进展,重点讨论电子输运机理、迁移率、接触电阻等关键问题及集成技术的现状,并为今后的发展指出了方向.     

V2O5电极修饰对C60/Pentacene双层异质结场效应晶体管性能的影响

制备了用过渡金属氧化物V₂O₅修饰Al源、漏电极的C₆₀/Pentacene双层异质结有机场效应管.该构型器件与未修饰器件相比,呈现出典型的双极型晶体管传输特性.电子迁移率和空穴迁移率分别达到8.6×10^-2cm²/V·s^-1和6.4×10^-2cm²/V·s^-1,阈值电压分别为25 V和-25 V.器件性能改善的原因主要是由于插入V₂O₅修饰层后,可以明显降低Al电极与Pentacene之间的接触势垒,提高空穴的有效注入,从而使电子和空穴的注入接近平衡.研究表明,采用V₂O₅修饰电极方法,是制备低成本、高性能的双极型有机场效应管并实现其商业应用的有效途径.     

对称三材料双栅应变硅金属氧化物半导体场效应晶体管二维解析模型

提出了对称三材料双栅应变硅金属氧化物半导体场效应晶体管器件结构,为该器件结构建立了全耗尽条件下的表面势模型、表面场强和阈值电压解析模型,并分析了应变对表面势、表面场强和阈值电压的影响,讨论了三栅长度比率对阈值电压和漏致势垒降低效应的影响,对该结构器件与单材料双栅结构器件的性能进行了对比研究.结果表明,该结构能进一步提高载流子的输运速率,更好地抑制漏致势垒降低效应.适当优化三材料栅的栅长比率,可以增强器件对短沟道效应和漏致势垒降低效应的抑制能力.     

高质量单层二硫化钼薄膜的研究进展

作为一种新型的二维半导体材料,单层二硫化钼薄膜由于其优异的特性,在电子学与光电子学等众多领域具有潜在的应用价值.本文综述了我们课题组在过去几年中针对单层二硫化钼薄膜的研究所取得的进展,具体包括:在二硫化钼薄膜的制备方面,通过氧辅助化学气相沉积方法,实现了大尺寸单层二硫化钼单晶的可控生长和晶圆级单层二硫化钼薄膜的高定向外延生长;在二硫化钼薄膜的加工方面,发展了单层二硫化钼薄膜的无损转移、洁净图案化加工、可控结构相变与局域相调控的方法,为场效应晶体管等电子学器件的制备与性能优化提供了基础;在二硫化钼异质结方面,研究了二硫化钼薄膜与其他二维材料形成的异质结的电学以及光电性质,为二维材料异质结的构筑和器件特性研究提供了实验参考;在二硫化钼薄膜功能化器件与应用方面,构筑了全二维材料、亚5 nm超短沟道场效应晶体管器件,验证了单层二硫化钼对短沟道效应的有效抑制及其在5 nm工艺节点器件中的应用优势;此外,利用制备的高质量单层二硫化钼和发展的器件洁净加工技术,实现了高性能柔性薄膜晶体管的集成,获得了超高灵敏度与稳定性的非接触型湿度传感器.我们在二硫化钼薄膜的制备、加工以及器件特性研究方面所取得的进展对于二硫化钼及其他二维过渡金属硫属化合物的基础和应用研究均具有指导意义.     

The study on mechanism and model of negative bias temperature instability degradation in P-channel metal-oxide-semiconductor field-effect transistors

Negative Bias Temperature Instability (NBTI) has become one of the most serious reliability problems of metal- oxide-semiconductor field-effect transistors (MOSFETs). The degradation mechanism and model of NBTI are studied in this paper. From the experimental results, the exponential value 0.25-0.5 which represents the relation of NBTI degradation and stress time is obtained. Based on the experimental results and existing model, the reaction-diffusion model with H+ related species generated is deduced, and the exponent 0.5 is obtained. The results suggest that there should be H+ generated in the NBTI degradation. With the real time method, the degradation with an exponent 0.5 appears clearly in drain current shift during the first seconds of stress and then verifies that H+ generated during NBTI stress.     

Field-effect transistors based on two-dimensional materials for logic applications

Field-effect transistors （FETs） for logic applications, graphene and MoS2, are discussed. These materials have based on two representative two-dimensional （2D） materials, drastically different properties and require different consider- ations. The unique band structure of graphene necessitates engineering of the Dirac point, including the opening of the bandgap, the doping and the interface, before the graphene can be used in logic applications. On the other hand, MoS2 is a semiconductor, and its electron transport depends heavily on the surface properties, the number of layers, and the carrier density. Finally, we discuss the prospects for the future developments in 2D material transistors.