Fabrication and Characteristics of AIInN/A1N/GaN MOS-HEMTs with Ultra-Thin Atomic Layer Deposited Al2O3 Gate Dielectric

Al0.85In0.15N//AlN/GaN metal-oxide-semiconductor high electron mobility transistors （MOS-HEMTs） employing a 3-nm ultra-thin atomic-layer deposited （ALD） Al2O3 gate dielectric layer are reported. Devices with 0.6μm gate lengths exhibit an improved maximum drain current density of 1227mA/mm at a gate bias of 3 V, a peak transeonductance of 328mS/mm, a cutoff frequency fr of 16 GHz, a maximum frequency of oscillation fmax of 45 GHz, as well as significant gate leakage suppression in both reverse and forward directions, compared with the conventionM Al0.85In0.15N/AlN/GaN HEMT. Negligible C - V hysteresis, together with a smaller pinch-off voltage shift, is observed, demonstrating few bulk traps in the dielectric and high quality of the Al2O3/AIInN interface, it is most notable that not only the transconductance profile of the MOS-HEMT is almost the same as that of the conventional HEMT with a negative shift, but also the peak transconduetance of the MOS-HEMT is increased slightly. It is an exeitin~ inwrovement in the transconductance performance.     

60Co γ射线辐射对AlGaN/GaN HEMT器件的影响

采用⁶⁰Co γ射线辐射源对非钝化保护的AlGaN/GaN高电子迁移率晶体管(HEMT)器件进行了1 Mrad(Si)的总剂量辐射,实验发现辐射累积剂量越大,器件尺寸越小,器件饱和漏电流和跨导下降越明显,同时辐射后器件栅泄漏电流明显增大,而阈值电压变化很小. 对辐射前后器件的沟道串联电阻和阈值电压变化的分析表明,辐射感生表面态负电荷的产生是造成AlGaN/GaN HEMT器件电特性退化的主要原因之一. 关键词： AlGaN/GaN HEMT器件 γ射线辐射 表面态     

多声源的自由场有源声吸收

本文利用声源辐射阻抗讨论了三维空间有源声吸收问题.推导出适用于任意初级声场条件下的多次级源最优复强度的一般表达式,并通过分析声源辐射阻抗的变化规律阐明了声吸收的机理.在此基础上,以两个点源在平面波声场中的声吸收为例,详细讨论了次级源吸收功率与两源位置的变化关系,并给出消声区域分布规律.最后在半消声室中获得了良好的实验效果,验证了所得结论.     

甲胺水合离子团簇的结构模型及红外光谱研究

本文利用量子化学计算方法,研究了甲胺和水复合离子团簇[(CH₃NH₂)(H₂O)_n]⁺的几何结构、能量和红外光谱,揭示了结构生长模型、氢键作用机制和质子转移机理. 研究结果表明,在[(CH₃NH₂)(H₂O)_n]⁺团簇中,甲胺甲基上的一个氢原子转移到氨基上,形成分子内质子转移的CH₂NH₃⁺离子核心结构模型,水分子作为氢键受体,与质子化氨基NH₃⁺形成氢键. CH₃NH₂⁺离子核心结构模型没有CH₂NH₃⁺离子核心结构模型稳定. 在团簇的红外光谱中,CH振动、自由NH振动、氢键结合的NH振动和OH振动模式在CH₃NH₂⁺和CH₂NH₃⁺两种离子核心结构模型的理论计算红外光谱中明显不同,因此可用于鉴别甲胺水合离子团簇的结构模型,有助于理解甲胺和水复合团簇的氢键网络结构.     

Degradation mechanism of enhancement-mode AlGaN/GaN HEMTs using fluorine ion implantation under the on-state gate overdrive stress

The degradation mechanism of enhancement-mode Al Ga N/Ga N high electron mobility transistors(HEMTs)fabricated by fluorine plasma ion implantation technology is one major concern of HEMT’s reliability.It is observed that the threshold voltage shows a significant negative shift during the typical long-term on-state gate overdrive stress.The degradation does not originate from the presence of as-grown traps in the Al Ga N barrier layer or the generated traps during fluorine ion implantation process.By comparing the relationships between the shift of threshold voltage and the cumulative injected electrons under different stress conditions,a good agreement is observed.It provides direct experimental evidence to support the impact ionization physical model,in which the degradation of E-mode HEMTs under gate overdrive stress can be explained by the ionization of fluorine ions in the Al Ga N barrier layer by electrons injected from 2DEG channel.Furthermore,our results show that there are few new traps generated in the Al Ga N barrier layer during the gate overdrive stress,and the ionized fluorine ions cannot recapture the electrons.     

固相萃取-超高效液相色谱串联质谱法同时检测禽畜粪便中多种抗生素残留

建立了固相萃取-超高效液相色谱串联质谱(SPE-UPLC/MS/MS)同时测定禽畜粪便中6种磺胺类(SAs)、4种四环素类(TCs)、3种氟喹诺酮类(FQs)、3种大环内酯类(MACs)以及1种硝基呋喃类(NFs)抗生素残留的方法。样品分别由McIlvaine-Na2EDTA缓冲液和有机混合提取液逐次超声提取,合并提取液,以正己烷去脂,过SAX-HLB固相萃取系统富集净化,经氮吹、定容后,以乙腈和0.1%甲酸-水溶液为流动相进行UPLC/MS分离检测,内标法定量。在0.1～1000μg/kg(Dry weight)浓度范围内,所有目标物标准曲线R2均大于0.99,样品加标回收率在42.3%～79.6%之间,相对标准偏差为1.4%～5.4%。方法检出限为0.1～2.0μg/kg,定量下限为0.3～6.6μg/kg。应用本方法检测华北地区多个禽畜养殖基地粪便样品32份,所有抗生素均有不同程度的检出,最高检出浓度为金霉素125μg/kg。     

Characteristics and threshold voltage model of GaN-based FinFET with recessed gate

In this work, AlGaN/GaN FinFETs with different fin widths have been successfully fabricated, and the recessed-gate FinFETs are fabricated for comparison. The recessed-gate FinFETs exhibit higher transconductance value and positive shift of threshold voltage. Moreover, with the fin width of the recessed-gate FinFETs increasing, the variations of both threshold voltage and the transconductance increase. Next, transfer characteristics of the recessed-gate FinFETs with different fin widths and recessed-gate depths are simulated by Silvaco software. The relationship between the threshold voltage and the AlGaN layer thickness has been investigated. The simulation results indicate that the slope of threshold voltage variation reduces with the fin width decreasing. Finally, a simplified threshold voltage model for recessed-gate FinFET is established,which agrees with both the experimental results and simulation results.     

具有语言评价信息的卓越组织绩效评价

针对企业卓越组织绩效评价时不容易定量的实际情况,提出了一种基于语言评价信息的系统评价方法.依据GB/T 19580-2004<卓越绩效评价准则>标准,提出了适合企业自我诊断的评价指标体系,结合2006年和2007年语言评价资料对某企业实施卓越组织绩效活动的效果进行了评价分析.     

AlGaN/GaN high-electron-mobility transistors with transparent gates by Al-doped ZnO

AlGaN/GaN high-electron-mobility transistors （HEMTs） with Al-doped ZnO （AZO） transparent gate electrodes are fabricated, and Ni/Au/Ni-gated HEMTs are produced in comparison. The AZO-gated HEMTs show good DC characteristics and Schottky rectifying characteristics, and the gate electrodes achieve excellent transparencies. Compared with Ni/Au/Ni-gated HEMTs, AZO-gated HEMTs show a low saturation current, high threshold voltage, high Schottky barrier height, and low gate reverse leakage current. Due to the higher gate resistivity, AZO-gated HEMTs exhibit a current-gain cutoff frequency （fT） of 10 GHz and a power gain cutoff frequency （fmax） of 5 GHz, and lower maximum oscillation frequency than Ni/Au/Ni-gated HEMTs. Moreover, the C-V characteristics are measured and the gate interface characteristics of the AZO-gated devices are investigated by a C-V dual sweep.     

AlGaN/GaN异质结Ni/Au肖特基表面处理及退火研究

采用O₂等离子体及HF溶液对AlGaN/GaN异质结材料进行表面处理后，Ni/Au肖特基接触特性比未处理有了明显改善，反向泄漏电流减小3个数量级.对制备的肖特基接触进行200—600℃ 5min的N₂气氛退火，发现退火冷却后肖特基反向泄漏电流随退火温度增大进一步减小.N₂气中600℃退火后肖特基二极管C-V特性曲线在不同频率下一致性变好，这表明退火中Ni向材料表面扩散减小了表面陷阱密度；C-V特性曲线随退火温度增大向右移动，从二维电子气耗尽电压绝对值减小反映了肖特基势垒的提高. 关键词： AlGaN/GaN 肖特基接触 表面处理 退火