GaN基SBD功率器件研究进展

作为第三代宽禁带半导体器件,GaN基肖特基势垒二极管(SBD)功率器件具有耐高温、耐高压和导通电阻小等优良特性,在功率器件方面具有显著的优势。概述了基于功率应用的GaN SBD功率器件的研究进展。根据器件结构,介绍了基于材料特性的GaN SBD和基于AlGaN/GaN异质结界面特性的GaN异质结SBD。根据器件结构对开启电压的影响,对不同阳极结构器件进行了详细的介绍。阐述了不同的肖特基金属的电学特性和热稳定性。分析了表面处理,包括表面清洗、表面等离子体处理和表面钝化对器件漏电流的影响。介绍了终端保护技术,尤其是场板技术对击穿电压的影响。最后探讨了GaN基SBD功率器件未来的发展趋势。     

TiW/Si的接触势垒以及SBD面积缩小原理

本文叙述Ti_XW_(1-X)合金薄膜的制备方法以及不同的TiW组份对Ti_XW_(1-X)/Si势垒高度的影响.结果表明:当TiW组分不同时,TiW/Si接触的势垒高度会在一定的范围内(0.54eV～0.66eV)变化.由于TiW/Si的势垒高度较低,所以在电路中采用TiW/Si SBD则有利于SBD面积的缩小.     

AlGaN/GaN横向肖特基势垒二极管的仿真与制作

基于GaN横向肖特基势垒二极管(SBD)的频率特性和应用的需要,设计了一种基于AlGaN/GaN异质结的横向SBD.利用Silvaco Atlas软件研究了 AlGaN势垒层的厚度和Al摩尔组分对异质结AlχGaN1-χ/GaN SBD电学性能的影响.仿真结果表明,SBD器件截止频率随Al摩尔组分的增加先增大再减小,当AlχGaN,1-χ层中Al摩尔组分为0.2～0.25,其厚度为20～30nm时,AlGaN/GaN SBD器件的频率特性最好.在仿真的基础上,设计制作出了肖特基接触直径为2 μm的非凹槽和凹槽型AlGaN/GaN横向空气桥SBD.通过直流I-V[测试和射频S参数测试,提取了两种SBD器件的理想因子、串联电阻、结电容、截止频率和品质因子等关键参数,该平面 SBD可应用于片上集成和混合集成的太赫兹电路的设计与制造.     

GaN基肖特基势垒二极管的漏电流传输与退化机制

通过比较反向偏压下AlGaN/GaN异质结肖特基势垒二极管(SBD)和GaN SBD的电流特性、电场分布和光发射位置,研究了GaN基SBD的漏电流传输与退化机制。结果表明,AlGaN/GaN SBD退化前后漏电流均由Frenkel-Poole(FP)发射机制主导,而GaN SBD低场下为FP发射电流,高场下则为Fowler-Nordheim(FN)隧穿电流。电场模拟和光发射测试结果表明,引起退化的主要原因是高电场,由于结构不同,两种SBD的退化机制和退化位置并不相同。根据实验结果,提出了一种高场FN隧穿退化模型,该模型强调应力后三角势垒变薄导致FN隧穿增强是GaN SBD退化的内在机制。     

肖特基二极管在LSTTL电路中的应用

对于我国急待开发的LSTTL电路!本文分析了SBD使其获取高速低功耗优良性能的基本原理,着重讨论了SBD的正向压降和反向击穿及其与电路的关系,最后提出SBD的一些设计思想。     

势垒材料对GaN基异质结电学特性的影响研究

基于势垒材料分别为Al0.27Ga0.73N和In0.17Al0.83N的GaN基异质结肖特基二极管(SBD),研究了GaN基异质结的漏电流输运机制、二维电子气密度和反向击穿电压等重要电学特性。结果表明,AlGaN/GaN SBD的反向电流主要由Frenkel-Poole(FP)发射机制主导,而InAlN/GaN SBD的反向电流在低电场下表现为FP发射电流,在高电场下则表现为Fowler-Nordheim隧穿电流。InAlN/GaN SBD的异质界面二维电子气密度明显高于AlGaN/GaN SBD,但是InAlN层存在高密度的缺陷,导致InAlN/GaN SBD的反向漏电流较大,且反向击穿电压较低。     

SiC SBD基温度传感器灵敏度影响因素的研究

SiC基温度传感器由于可以实现比Si基温度传感器高得多的工作温度而备受重视。从理论和实验两方面研究影响SiC SBD基温度传感器灵敏度的因素。基于热电子发射理论的解析模型表明影响温度传感器灵敏度的因素主要是理想因子。采用Spice仿真不同偏置电流下SiC SBD的V-T关系,结果表明灵敏度随着正向电流的减小而增大并且线性度良好。采用10 mA的恒流源偏置电路测试了三个厂商的SiC SBD的V-T特性,结果发现三种SiC SBD测温上限均高于400℃,并且线性度较好,灵敏度均接近1.5 m V/℃。最后对提高SiC SBD基温度传感器的灵敏度提出了优化设计方案。     

Ni，Ti/4H-SiC肖特基势垒二极管

采用本实验室生长的4H-SiC外延片,分别用高真空电子束蒸Ni和Ti做肖特基接触金属,Ni合金作欧姆接触,SiO_2绝缘环隔离减小高压电场集边效应等技术,制作出4H-SiC肖特基势垒二极管(SBD)。该器件在室温下反向击穿电压大于600 V,对应的漏电流为2.00×10~(-6)A。对实验结果分析显示,采用Ni和Ti作肖特基势垒的器件的理想因子分别为1.18和1.52,肖特基势垒高度为1.54 eV和1.00 eV。实验表明,该器件具有较好的正向整流特性。     

AlGaN/GaN和AlGaN SBD的温度特性研究

研究了AlGaN/GaN异质结构上的肖特基接触的基本原理及载流子的高温输运特性.将AlGaN/GaN异质结SBD和AlGaN SBD,在27～250℃进行实验比较.发现随着温度上升,AlGaN SBD的势垒高度下降,理想因子增加,其影响因素包括热电子发射、场发射、隧穿效应及复合电流效应等机制.而AlGaN/GaN异质结SBD由于受到压电极化场和2DEG和的影响,其势垒高度和理想因子随温度的变化趋势与AlGaNSBD相反.实验结果还显示,AlGaN/GaN异质结SBD的反向电流随着温度的上升,呈现先增大后减小的趋势.     

4H-SiC SBD和JBS退火研究

在4H-SiC外延材料上制备了SBD和JBS器件,研究并分析了退火温度对这两种器件正反向特性的影响。结果表明,低于350℃退火可同时提高SBD和JBS的正反向特性。当退火温度高于350℃时,二者的正向特性都出现退化,SBD退化较JBS更为严重。JBS阻断电压随退火温度升高而增大,在退火温度高于450℃时增加趋势变缓。SBD阻断电压随退火温度升高先升后降,在500℃退火时达到一个最大值。可见一定程度的退火有助于提高4H-SiCSBD和JBS器件的正反向特性,但须考虑其对正反向特性的不同影响。综合而言,退火优化后JBS优于SBD器件性能。     

Metadata Design for Reconfigurable Protocol Stacks in Systems Beyond 3G

Global consensus on the next generation of wireless mobile communications, broadly termed “beyond 3G”, sketches a heterogeneous infrastructure comprising different wireless systems in a complementary manner and vested with reconfiguration capabilities, which support a flexible and dynamic adaptation of the wireless network and its spectrum resources to meet the ever-changing service requirements. For ubiquitous reconfiguration to become a practical capability of mobile communication systems, it is necessary to establish a global architecture for modeling, expressing, and circulating essential metadata related to reconfiguration, including reconfigurable device capabilities and semantic properties of protocol stacks. We outline the relevant standardization initiatives in the mobile domain, summarize existing work in reconfiguration-supporting architectures, and identify key shortcomings that may hinder the advent of ubiquitously reconfigurable systems. Further on, we point out some major limitations of current metadata standards in the mobile domain for the representation of capability information pertaining to reconfigurable protocol stacks. Next, we identify essential metadata classes in support of reconfigurable communication systems, introducing an associated object-oriented UML model. We elaborate on the design rationale of the UML model, presenting and discussing the alternative metadata representation standards and suitable encoding formats. Finally, we demonstrate the suitability of our UML model by applying our reconfiguration-supporting vocabulary in the cases of a standardized protocol stack of 3G mobile devices and stationary 3G cellular network elements. Vangelis Gazis received his B.Sc. and M.Sc. (Communication Networking) degrees from the Department of Informatics & Telecommunications of the University of Athens, Greece, in 1995, and 1998, respectively. He also received an M.B.A. degree from the Athens University of Economics and Business in 2001. Since 1996 until, he has been with the research staff of the Communication Networks Laboratory (CNL) of the University of Athens. He has participated in national and European research projects (MOBIVAS, ANWIRE) of the IST framework programme. He specializes in reconfigurable mobile systems and networks for beyond 3G, metadata and ontology languages, reflective and component middleware, adaptable services and open API frameworks for telecommunications. He is currently a Ph.D. candidate in the Department of Informatics & Telecommunications of the University of Athens. Nancy Alonistioti holds a B.Sc. degree and a Ph.D. degree in informatics and telecommunications from the University of Athens. Presently, she is a senior researcher in the Department of Informatics and Telecommunications of the University of Athens. In the past, she has held a research position with the Institute of Informatics and Telecommunications of NCSR “Demokritos” in the areas of protocol and service design and testing, mobile systems (UMTS), open architectures, and software defined radio systems and networks. Her current research interests are in reconfigurable mobile systems and networks beyond 3G, and adaptable services, pervasive computing and context awareness. She has participated in several national and European R&D projects, and has been the technical manager of the IST-MOBIVAS and IST-ANWIRE projects, which have had a focus on reconfigurable mobile systems, networks an respective service provision. She is currently a member of the management team and workpackage leader in the FP6 IST-E2R project on reconfigurability; she also serves as technical manager for the University of Athens in the FP6 IST-LIAISON project, which focuses on location based services in working environments. Dr Alonistioti is co-editor and co-author of the book entitled “Software defined radio, Architectures, Systems and Functions”, published by John Wiley in May 2003. She has authored over 55 publications in the area of mobile communications and reconfigurable systems and networks. Lazaros Merakos received the Diploma in electrical and mechanical engineering from the National Technical University of Athens, Athens, Greece, in 1978, and the M.S. and Ph.D. degrees in electrical engineering from the State University of New York, Buffalo, in 1981 and 1984, respectively. From 1983 to 1986, he was on the faculty of the Electrical Engineering and Computer Science Department, University of Connecticut, Storrs. From 1986 to 1994, he was on the faculty of the Electrical and Computer Engineering Department, Northeastern University, Boston, MA. During the period 1993D1994, he served as Director of the Communications and Digital Processing Research Center, Northeastern University. During the summers of 1990 and 1991, he was a Visiting Scientist at the IBM T. J. Watson Research Center, Yorktown Heights, NY. In 1994, he joined the faculty of the University of Athens, Athens, Greece, where he is presently a Professor in the Department of Informatics and Telecommunications, and Director of the Communication Networks Laboratory (UoA-CNL) and the Networks Operations and Management Center. Since 1995, he is leading the research activities of UoA-CNL in the area of mobile communications, in the framework of the Advanced Communication Technologies and Services (ACTS) and Information Society Technologies (IST) programs funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS, ANWIRE, E2R, LIAISON). His research interests are in the design and performance analysis of communication networks, and wireless/mobile communication systems and services. He has authored more than 190 papers in the above areas. Dr. Merakos is Chairman of the Board of the Greek Universities Network, the Greek Schools Network, and Member of the Board of the Greek Research Network. In 1994, he received the Guanella Award for the Best Paper presented at the International Zurich Seminar on Mobile Communications.     

Toward Robust Speech Recognition and Understanding

The principal cause of speech recognition errors is a mismatch between trained acoustic/language models and input speech due to the limited amount of training data in comparison with the vast variation of speech. It is crucial to establish methods that are robust against voice variation due to individuality, the physical and psychological condition of the speaker, telephone sets, microphones, network characteristics, additive background noise, speaking styles, and other aspects. This paper overviews robust architecture and modeling techniques for speech recognition and understanding. The topics include acoustic and language modeling for spontaneous speech recognition, unsupervised adaptation of acoustic and language models, robust architecture for spoken dialogue systems, multi-modal speech recognition, and speech summarization. This paper also discusses the most important research problems to be solved in order to achieve ultimate robust speech recognition and understanding systems. Dr. Sadaoki Furui is currently a Professor at Tokyo Institute of Technology, Department of Computer Science. He is engaged in a wide range of research on speech analysis, speech recognition, speaker recognition, speech synthesis, and multimodal human-computer interaction and has authored or coauthored over 450 published articles. From 1978 to 1979, he served on the staff of the Acoustics Research Department of Bell Laboratories, Murray Hill, New Jersey, as a visiting researcher working on speaker verification. He is a Fellow of the IEEE, the Acoustical Society of America and the Institute of Electronics, Information and Communication Engineers of Japan (IEICE). He was President of the Acoustical Society of Japan (ASJ) from 2001 to 2003 and the Permanent Council for International Conferences on Spoken Language Processing (PC-ICSLP) from 2000 to 2004. He is currently President of the International Speech Communication Association (ISCA). He was a Board of Governor of the IEEE Signal Processing Society from 2001 to 2003. He has served on the IEEE Technical Committees on Speech and MMSP and on numerous IEEE conference organizing committees. He has served as Editor-in-Chief of both Journal of Speech Communication and the Transaction of the IEICE. He is an Editorial Board member of Speech Communication, the Journal of Computer Speech and Language, and the Journal of Digital Signal Processing. He has received the Yonezawa Prize and the Paper Awards from the IEICE (1975, 88, 93, 2003), and the Sato Paper Award from the ASJ (1985, 87). He has received the Senior Award from the IEEE ASSP Society (1989) and the Achievement Award from the Minister of Science and Technology, Japan (1989). He has received the Technical Achievement Award and the Book Award from the IEICE (2003, 1990). He has also received the Mira Paul Memorial Award from the AFECT, India (2001). In 1993 he served as an IEEE SPS Distinguished Lecturer. He is the author of “Digital Speech Processing, Synthesis, and Recognition” (Marcel Dekker, 1989, revised, 2000) in English, “Digital Speech Processing” (Tokai University Press, 1985) in Japanese, “Acoustics and Speech Processing” (Kindai-Kagaku-Sha, 1992) in Japanese, and “Speech Information Processing” (Morikita, 1998) in Japanese. He edited “Advances in Speech Signal Processing” (Marcel Dekker, 1992) jointly with Dr. M.M. Sondhi. He has translated into Japanese “Fundamentals of Speech Recognition,” authored by Drs. L.R. Rabiner and B.-H. Juang (NTT Advanced Technology, 1995) and “Vector Quantization and Signal Compression,” authored by Drs. A. Gersho and R. M. Gray (Corona-sha, 1998).     

全光网的关键器件——光交叉连接器与光分插复用器

全光网（AON,all-optical network）以波长路由光交换技术和波分复用传输技术（WDM）为基础,它的网络节点由光分插复用器和光交叉连接器构成,能在光域上实现高速信息流的传输、交换、路由和故障恢复等功能。光交叉连接器（OXC）与光分插复用器（OADM）是全光网中最重要的网络器件,是真正实现全光网关键性功能的必要前提,也是目前国内外光通信器件厂商研究和开发的热点。本文结合全光网的发展,介绍了光交叉连接器（OXC）与光分插复用器（OADM）的基本原理、性能指标,对不同的节点结构进行了比较与讨论,并介绍与比较了目前国内外厂商的主要产品。     

基于物联网技术的矿井资产管理系统中的设计与实现

文中针对公司资产存在的形式多种多样,公司管理人员年底清查资产需要浪费大量宝贵的时间和人力物力,且容易遗漏或重复,实物很难与账面相符的管理情况,设计了一个基于物联网与FRID技术相结合的资产管理系统,在介绍了物联网技术与FRID技术后,详细介绍了该系统的整体架构设计,资产编码设计、RFID标签设计,资产管理系统设计。通过对该系统的实际应用表明,该系统实现了资产系统化、信息化、网络化的管理。对于合理配置和利用资产,降低投入成本,增加投入产出效益,提高管理水平和效率等方面上有着重大的意义。实现了资产管理的信息共享。     

云计算技术分析及其展望

云计算是在传统的数据存储、分布式计算和网络技术等计算机技术的基础之上发展而来的,它旨在分布式存储和处理海量数据,以方便人们按需及时获取相应服务。在当今这个数据信息"大爆炸"的时代,云计算的实现和发展日益显现出了它的强大存储计算能力和广泛应用前景。比较了现有的云计算的概念并给出新的理解,分析了云计算的服务模式和系统结构,总结了云计算的关键技术,阐述了云计算技术面临的问题,介绍并展望了云计算的国内外发展应用及其广阔前景。     

SDN/NFV发展中的关键:编排器的发展与挑战

网络功能虚拟化(NFV)和软件定义网络(SDN)已被业界普遍认定为下一代电信网络发展的主要方向,编排器作为未来网络的“大脑”,成为运营商灵活管理网络、最大化发挥新技术优势的关键.首先阐述了编排器在下一代网络中的核心地位,并对编排器的技术架构进行介绍.而后从标准化和开源的角度对编排器产业发展情况进行介绍和分析.最后阐述了编排器产业发展中标准与开源的关系,编排器与网管运营支撑系统(OSS)的融合、编排器对SDN的支持以及依托编排器实现网络自动化智能化运营的理念.     

Alternative Schemes for Dynamic Secure VPN Deployment in UMTS

Three alternative schemes for secure Virtual Private Network (VPN) deployment over the Universal Mobile Telecommunication System (UMTS) are proposed and analyzed. The proposed schemes enable a mobile node to voluntarily establish an IPsec-based secure channel to a private network. The alternative schemes differ in the location where the IPsec functionality is placed within the UMTS network architecture (mobile node, access network, and UMTS network border), depending on the employed security model, and whether data in transit are ever in clear-text, or available to be tapped by outsiders. The provided levels of privacy in the deployed VPN schemes, as well as the employed authentication models are examined. An analysis in terms of cost, complexity, and performance overhead that each method imposes to the underlying network architecture, as well as to the mobile devices is presented. The level of system reliability and scalability in granting security services is presented. The VPN management, usability, and trusted relations, as well as their behavior when a mobile user moves are analyzed. The use of special applications that require access to encapsulated data traffic is explored. Finally, an overall comparison of the proposed schemes from the security and operation point of view summarizes their relative performance. Christos Xenakis received his B.Sc. degree in computer science in 1993 and his M.Sc. degree in telecommunication and computer networks in 1996, both from the Department of Informatics and Telecommunications, University of Athens, Greece. In 2004 he received his Ph.D. from the University of Athens (Department of Informatics and Telecommunications). From 1998–2000 was with the Greek telecoms system development firm Teletel S.A., where was involved in the design and development of advanced telecommunications subsystems for ISDN, ATM, GSM, and GPRS. Since 1996 he has been a member of the Communication Networks Laboratory of the University of Athens. He has participated in numerous projects realized in the context of EU Programs (ACTS, ESPRIT, IST). His research interests are in the field of mobile/wireless networks, security and distributed network management. He is the author of over 15 papers in the above areas. Lazaros Merakos received the Diploma in electrical and mechanical engineering from the National Technical University of Athens, Greece, in 1978, and the M.S. and Ph.D. degrees in electrical engineering from the State University of New York, Buffalo, in 1981 and 1984, respectively. From 1983 to 1986, he was on the faculty of Electrical Engineering and Computer Science at the University of Connecticut, Storrs. From 1986 to 1994 he was on the faculty of the Electrical and Computer Engineering Department at Northeastern University, Boston, MA. During the period 1993–1994 he served as Director of the Communications and Digital Processing Research Center at Northeastern University. During the summers of 1990 and 1991, he was a Visiting Scientist at the IBM T. J. Watson Research Center, Yorktown Heights, NY. In 1994, he joined the faculty of the University of Athens, Athens, Greece, where he is presently a Professor in the Department of Informatics and Telecommunications, and Director of the Communication Networks Laboratory (UoA-CNL) and the Networks Operations and Management Center. His research interests are in the design and performance analysis of broadband networks, and wireless/mobile communication systems and services. He has authored more than 150 papers in the above areas. Since 1995, he is leading the research activities of UoA-CNL in the area of mobile communications, in the framework of the Advanced Communication Technologies & Services (ACTS) and Information Society Technologies (IST) programmes funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS, ANWIRE). He is chairman of the board of the Greek Universities Network, the Greek Schools Network, and member of the board of the Greek Research Network. In 1994, he received the Guanella Award for the Best Paper presented at the International Zurich Seminar on Mobile Communications.     

游乐场设备机械设计问题分析

随着快节奏化都市的迅速发展,在城市工作、学习、生活的人们的精神压力越来越大,使得人们对于精神层面需求的满足越来越强烈.于是,多种多样的休闲娱乐项目应运而生.随着日益增长的生活水平,人们闲暇时间更多追求身心的放松,以缓解紧张的工作学习情绪,而游乐场成为人们短期假期休闲的不二去处.近年来,游乐场的发展十分迅速.然而,在游乐场建设发展过程中,安全问题一直是社会各界密切关注的问题.本文分析游乐场设备机械设计问题,希望提高游乐场机械设备质量的整体水平,实现良好的经济效益和社会效益.     

面向高速传输的连接器设计

随着社会对信息高速传输的需求日益增加,相应的通信系统连接故障也越来越多,这些故障背后往往都与连接器的接触不良有关。为了保障高速数据传输的安全,同时适应通信电子设备小型化、集成化的趋势,结合工厂设计制造的实际经验,针对连接器使用的各种不良现象分别从选材、电性能、电镀、结构形式等方面对连接器各个组成部件的设计做了一些总结,实现了从设计上控制连接器可靠性的目的。     

SDN协同控制器的智能内生技术研究与实现

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