CnSi(n=49,50)的理论研究

用量子化学从头算方法研究了C     

Numerical simulation of filler metal droplets spreading in laser brazing

A finite element model was constructed using a commercial software Fidap to analyze the Cu-base filler metal droplet spreading process in laser brazing,in which the temperature distribution,droplet geometry, and fluid flow velocity were calculated.Marangoni and buoyancy convection and gravity force were considered,and the effects of laser power and spot size on the spreading process were evaluated.Special attention was focused on the free surface of the droplet,which determines the profile of the brazing spot. The simulated results indicate that surface tension is the dominant flow driving force and laser spot size determines the droplet spreading domain.     

聚氧乙烯功能基复合修饰聚氨酯的合成 及其血液相容性研究(Ⅰ)

通过十八烷基聚氧乙烯和环氧氯丙烷的封端反应制备了α-环氧基-ω-十八烷基聚氧乙烯大单体.并采用BF     

三维超音进气道内外流场的数值模拟

用区域分裂有限体积法求解了三维Ｅｕｌｅｒ方程和Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程。空间方向采用Ｒｏｅ平均算法，时间方向采用Ｒｕｎｇｅ－Ｋｕｔｔａ方法。对某飞航导弹的全弹身－进气道流场和某型号战斗机进气道内外流场进行了计算，得出了满意的结果。     

聚芳醚酮单体结构与反应活性的研究

利用从头算ＲＨＦ方法研究了聚芳醚酮单体４，４’－对苯二酚、４，４’－联苯二酚及４，４’－二氟苯酮。结果表明，它们的苯环皆存在一定的扭转，首次给出联苯二酚全优化结构，其苯环二面角为５１．８°，活性稍强于对苯二酚，但引入更多的链支化活特点，含联苯基聚芳醚醚酮的链支化比不含联苯基的ＰＥＥＫ严重，故前者结晶性差，反应机理及实验还表明：前者凝胶化的浓硫酸溶液中存在一种羰基被极化后的红色阴离子。     

守恒型双曲方程的中心差分TVD格式研究

研究了如何利用迎风格式的耗散性构造中心差分ＴＶＤ格式的方法，给 相应的定理，构造出新的耗散表达式。新格式既保留了二阶中心差分格式灵活方便的优点，又吸收了迎风格式耗散项比较精细的特点，同时具有ＴＶＤ性质，使得新格式具有较同的激波分辨率。     

基于热释电探测器的重频脉冲激光诊断(英文)

以热释电探测器的工作原理为基础,研究了热释电探测器对重频脉冲激光的瞬态响应特性,建立了热释电探测器对单脉冲激光辐照响应的工作模型,分析了影响探测器频率特性的主要因素。根据材料和结构参数模拟计算了实际应用中的响应模型。设计了信号检测电路并对其进行计算仿真。完成了探测器的频率响应、脉宽响应等实验测量,验证了热释电探测器用于高重频、窄脉冲激光能量测量的可行性。     

Impact of symmetric gate-recess length on the DC and RF characteristics of InP HEMTs

We fabricated a set of symmetric gate-recess devices with gate length of 70 nm.We kept the source-to-drain spacing(L_SD)unchanged,and obtained a group of devices with gate-recess length(L_recess)from 0.4μm to 0.8μm through process improvement.In order to suppress the influence of the kink effect,we have done SiN_X passivation treatment.The maximum saturation current density(ID_max)and maximum transconductance(g_m,max)increase as L_recess decreases to 0.4μm.At this time,the device shows ID_max=749.6 mA/mm at V_GS=0.2 V,V_DS=1.5 V,and g_m,max=1111 mS/mm at V_GS=?0.35 V,V_DS=1.5 V.Meanwhile,as L_recess increases,it causes parasitic capacitance C_gd and g_d to decrease,making f_max drastically increases.When L_recess=0.8μm,the device shows f_T=188 GHz and f_max=1112 GHz.     

Heterogeneous integration of InP HEMTs on quartz wafer using BCB bonding technology

Heterogeneous integrated InP high electron mobility transistors(HEMTs)on quartz wafers are fabricated successfully by using a reverse-grown InP epitaxial structure and benzocyclobutene(BCB)bonding technology.The channel of the new device is In_0.7Ga_0.3As,and the gate length is 100 nm.A maximum extrinsic transconductance gm,max of 855.5 mS/mm and a maximum drain current of 536.5 mA/mm are obtained.The current gain cutoff frequency is as high as 262 GHz and the maximum oscillation frequency reaches 288 GHz.In addition,a small signal equivalent circuit model of heterogeneous integration of InP HEMTs on quartz wafer is built to characterize device performance.     

Enhancement of fMAX of InP-based HEMTs by double-recessed offset gate process

A double-recessed offset gate process technology for InP-based high electron mobility transistors (HEMTs) has been developed in this paper. Single-recessed and double-recessed HEMTs with different gate offsets have been fabricated and characterized. Compared with single-recessed devices, the maximum drain-source current (I_D,max) and maximum extrinsic transconductance (g_m,max) of double-recessed devices decreased due to the increase in series resistances. However, in terms of RF performance, double-recessed HEMTs achieved higher maximum oscillation frequency (f_MAX) by reducing drain output conductance (g_ds) and drain to gate capacitance (C_gd). In addition, further improvement of f_MAX was observed by adjusting the gate offset of double-recessed devices. This can be explained by suppressing the ratio of C_gd to source to gate capacitance (C_gs) by extending drain-side recess length (L_rd). Compared with the single-recessed HEMTs, the f_MAX of double-recessed offset gate HEMTs was increased by about 20%.