In-situ SiN combined with etch-stop barrier structure for high-frequency AlGaN/GaN HEMT

The etch-stop structure including the in-situ SiN and AlGaN/GaN barrier is proposed for high frequency applications.The etch-stop process is realized by placing an in-situ SiN layer on the top of the thin AlGaN barrier.F-based etching can be self-terminated after removing SiN,leaving the AlGaN barrier in the gate region.With this in-situ SiN and thin barrier etch-stop structure,the short channel effect can be suppressed,meanwhile achieving highly precisely controlled and low damage etching process.The device shows a maximum drain current of 1022 mA/mm,a peak transconductance of 459 mS/mm,and a maximum oscillation frequency(fmax)of 248 GHz.     

High-frequency enhancement-mode millimeterwave AlGaN/GaN HEMT with an fT/fmax over 100 GHz/200 GHz

Ultra-thin barrier (UTB) 4-nm-AlGaN/GaN normally-off high electron mobility transistors (HEMTs) having a high current gain cut-off frequency (f_T) are demonstrated by the stress-engineered compressive SiN trench technology. The compressive in-situ SiN guarantees the UTB-AlGaN/GaN heterostructure can operate a high electron density of 1.27×10¹³cm^-2, a high uniform sheet resistance of 312.8 Ω /□, but a negative threshold for the short-gate devices fabricated on it. With the lateral stress-engineering by full removing in-situ SiN in the 600-nm SiN trench, the short-gated (70 nm) devices obtain a threshold of 0.2 V, achieving the devices operating at enhancement-mode (E-mode). Meanwhile, the novel device also can operate a large current of 610 mA/mm and a high transconductance of 394 mS/mm for the E-mode devices. Most of all, a high f_T/f_max of 128 GHz/255 GHz is obtained, which is the highest value among the reported E-mode AlGaN/GaN HEMTs. Besides, being together with the 211 GHz/346 GHz of f_T/f_max for the D-mode HEMTs fabricated on the same materials, this design of E/D-mode with the realization of f_max over 200 GHz in this work is the first one that can be used in Q-band mixed-signal application with further optimization. And the minimized processing difference between the E- and D-mode designs the addition of the SiN trench, will promise an enormous competitive advantage in the fabricating costs.     

冲击载荷形状对阻尼介质中结构最终塑性变形的影响

分析了在阻尼介质中当保持相关参量相同时，冲击载荷形状对简支刚塑性圆板和圆柱薄壳的最终塑性变形的影响。在结构物高载阶段的运动中，考虑了阻尼介质对塑性铰区移行的影响。结果表明:在阻尼介质中，文献［６］中相关参量的概念仍然可以沿用，但结构的最终塑性变形与相关参量的关系式Ｗ＿ｏｆ＝Ｉ￣２＿ｅＧ（Ｐ＿ｅ）应由更一般的表达式来代替。     

直杆动力屈曲问题研究进展

杆做为最基本的结构单元，其屈曲问题一直受到人们的极大关注，本文就这一研究领域的若干基本问题、处理方法、目前取得的成果以及人们共同关心的一些问题做一个简要的总结和评述     

结构静动力屈曲问题研究进展

近几十年来，结构的静动力屈曲问题一直是力学工作者极为关注的一个前沿课题．本文总结和综述了这一研究领域的几个基本问题：屈曲问题的分类、动态屈曲问题的特点及其特征量；介绍了屈曲问题的处理方法和目前已取得的成果；总结评述了人们关心的热点问题；屈曲问题的模型分析和实验技术、动态屈曲判别准则．     

爆炸破碎区域划分的模糊数学方法

本文以最大径向应力,最大剪应力和最大切向应力为主要的破碎准则,利用二元分配法分析了诸破碎准则间权的分配,采用正态函数、降正态函数和升正态函数为各个破碎准则的录属函数,由此提出了爆炸破碎的过粉碎区,初始裂缝区和纯粹拉断区划分的综合评价方法。实例证明,对于大药量或小药量爆炸,以上方法均可成立。     

砖砌烟囱爆破拆除倾倒过程的观测分析

本文通过对砖砌烟囱爆破拆除的实例分析得到,在砖砌烟囱的爆破拆除倾倒过程中,其倾倒支点是不断移动的,随着烟囱主体的不断下沉,相对于未垮部分的烟囱主体来说,该支点沿烟囱筒体不断向上移动。这表明,不能简单地按刚体模型描述砖砌烟囱的倾倒运动。     

Influence of Control Parameters on the Competition Between Spiral Waves and Target Waves

In this paper we systematically investigate the influence of control parameters on the competition results between spiral waves and target waves. Driving frequency f , amplitude A and injection area n of the input signals are three important parameters and the competition results between spiral waves and target waves are influenced by these three parameters remarkably. Based on these understandings we can control spiral waves effectively by suitable combination these parameters to generate faster target waves. And the effective controllable parameter regions are also studied.     

史丰收案件在中国科技史上的警示意义

中国珠算界人士于1973年发明、1974年归纳总结载入杭州小学课本的“29句口诀”和“本个加后进”的“乘法进位规律”,为传统珠算向珠心算新阶段的发展提供了“核心技术”之一。自中国珠算协会成立后的80年代初起。经珠算界不断的发展完善,珠心算从最初的用于珠算选手培养训练,继而用于幼少儿的启智教育。于今,珠心算已走向世界,为人类的启智造福。这是中国珠算界的贡献,也是全民族的骄傲。但是．上世纪末却有一位“速算名人”剽窃了珠算界的这一科研成果,之后竞反诬珠界人士“偷桃窃果”,随之提起诉讼。运作媒体,引发了一场惊动京城的舆论大哗。对于其人这种“偷桃毁树”的行径,中国珠算协会理所当然地派出专家组出庭维权．后来那位“速算名人”虽承认诬告失实,却一直回避核心技术的发明归属问题,一次次制造干扰。使应对真正“偷桃”行径的追究不了了之。之后,这位“速算名人”又一次次把水搅浑,混淆视听。制造了一场类似前苏联的“李森科现象”。为维护珠算界发明权,还正义于真面貌,本刊发表当年曾出庭维权的“珠界四老”的文章《史丰收案件在中国科技史上的警示意义》立此存照,以杜欺世盗名行为之继续。     

考虑交通出行惯例的双向行人流模型研究

推广了Baek等人最近提出的一个双向行人流模型,提出了两种改进策略,并从行人平均速度-密度关系、行人空间分布密度和位置分布等方面进行了数值分析. 研究发现,引入的两个新策略不仅可以提高行人流的平均速度,而且可以提高道路系统(尤其是道路中央区域)利用率,减轻拥堵状况,有效避免严重堵塞的发生. 改进的策略对行人的心理特点和行为特性等方面考虑更加全面,而且可以较好地模拟高密度的双向行人流. 关键词： 元胞自动机模型 双向行人流 交通惯例