高电子迁移率晶体管放大器高功率微波损伤机理

在TCAD半导体仿真环境中,建立了0.25 m栅长的AlGaAs/InGaAs高电子迁移率晶体管(HEMT)低噪声放大器与微波脉冲作用的仿真模型,基于器件内部的电场强度、电流密度和温度分布的变化,研究了1 GHz的微波从栅极和漏极注入的损伤机理。研究结果表明,从栅极注入约40.1 dBm的微波时,HEMT内部峰值温度随着时间的变化振荡上升,最终使得器件失效,栅下靠源侧电流通道和强电场的同时存在使得该位置最容易损伤;从漏极注入微波时,注入功率的高低会使器件内部出现不同的响应过程,注入功率存在一个临界值,高于该值,器件有可能在第一个周期内损伤,损伤位置均在漏极附近。在1 GHz的微波作用下,漏极注入比栅极注入更难损伤。     

非晶InGaZnO薄膜成分配比对透明性和迁移率的影响

利用固相反应法制备了富铟含量在不同成分配比下的高质量InGaZnO陶瓷靶材,采用脉冲激光沉积法,在基片温度为20 ℃、氧压为1 Pa条件下,在石英玻璃衬底上生长了非晶InGaZnO薄膜,并对薄膜进行X射线衍射、透射吸收光谱、拉曼光谱与霍尔效应测试。通过对InGaZnO薄膜的测试表征,在较低温度条件下,铟含量较高的薄膜样品保持了非晶结构、可见光的高透明性和高电子迁移率,InGaZnO薄膜有望应用于电子器件。     

高电子迁移率晶体管微波损伤仿真与实验研究

针对AlGaAs/InGaAs型高电子迁移率晶体管,利用TCAD半导体仿真工具,从器件内部空间电荷密度、电场强度、电流密度和温度分布变化分析出发,研究了从栅极注入1 GHz微波信号时器件内部的损伤过程与机理。研究表明,器件的损伤过程发生在微波信号的正半周,负半周器件处于截止状态;器件内部损伤过程与机理在不同幅值的注入微波信号下是不同的。当注入微波信号幅值较低时,器件内部峰值温度出现在栅极下方靠源极侧栅极与InGaAs沟道间,由于升温时间占整个周期的比例太小,峰值温度很难达到GaAs的熔点;但器件内部雪崩击穿产生的栅极电流比小信号下栅极泄漏电流高4个量级,栅极条在如此大的电流下很容易烧毁熔断。当注入微波信号幅值较高时,在信号正半周的下降阶段,在栅极中间偏漏极下方发生二次击穿,栅极电流出现双峰现象,器件内部峰值温度转移到栅极中间偏漏极下方,峰值温度超过GaAs熔点。利用扫描电子显微镜对微波损伤的高电子迁移率晶体管器件进行表面形貌失效分析,仿真和实验结果符合较好。     

聚(3-己基)噻吩薄膜中电荷传导的研究

对两种具有相同化学结构的聚(3-己基)噻吩膜进行了电荷传导研究以检验膜的结构对载流子迁移率的影响. 一种膜是由3-己基噻吩单体经电化学合成直接制备的膜(原位生长膜); 另一种膜是将原位生长膜溶于三氯甲烷后重新滴涂而成的(滴涂膜). 研究表明, 虽然两种膜的制备方法不一样, 但在最低(0.02%)和较高(20%～30%)掺杂率下两膜中的载流子迁移率相一致; 然而在中等掺杂率区域, 两膜中的载流子迁移率明显不同. 对于原位生长膜, 载流子迁移率在低掺杂区域几乎保持不变, 当掺杂率大于1%后开始上升; 而在滴涂膜中, 随着掺杂率的增加, 迁移率先下降然后迅速升高. 上述两种迁移率变化特征分别与以前研究中观察到的电化学合成高分子膜和化学合成高分子旋涂或滴涂膜中迁移率的变化特征相一致, 表明了迁移率随掺杂率变化特征的改变是由膜的结构变化而引起的     

Monitoring of Airborne Organic Vapors Using Ion Mobility Spectrometry

Abstract

Automated, continuous monitoring of organic vapors in air under three field designs for plume drift was demonstrated using a hand-held ion mobility spectrometer (IMS) in characterizing IMS behavior as a point sensor. In one field study, the IMS was placed 50cm from a 9m² grass plot contaminated with methylsalicylate and response to airborne vapors was recorded during a 13hr period of atmospheric turbulence to illustrate susceptibility of point sensors to wind direction. A similar study under near-quiescent atmospheric conditions was made using dimethylsulfoxide. In a third study, the plume from a point source of dipropyleneglycolmonomethylether was interrogated over a 25m × 12m grid downwind with windspeeds of 6–18km h^?. Laboratory studies were used to measure instrumental response times and influences from potentially interfering atmospheric organic pollutants.     

Influence of Equilibration Time in Solution on the Inclusion/Exclusion Topology Ratio of Host–Guest Complexes Probed by Ion Mobility and Collision‐Induced Dissociation

Host–guest complexes are formed by the creation of multiple noncovalent bonds between a large molecule (the host) and smaller molecule(s) or ion(s) (the guest(s)). Ion‐mobility separation coupled with mass spectrometry nowadays represents an ideal tool to assess whether the host–guest complexes, when transferred to the gas phase upon electrospray ionization, possess an exclusion or inclusion nature. Nevertheless, the influence of the solution conditions on the nature of the observed gas‐phase ions is often not considered. In the specific case of inclusion complexes, kinetic considerations must be taken into account beside thermodynamics; the guest ingression within the host cavity can be characterized by slow kinetics, which makes the complexation reaction kinetically driven on the timescale of the experiment. This is particularly the case for the cucurbituril family of macrocyclic host molecules. Herein, we selected para‐phenylenediamine and cucurbit[6]uril as a model system to demonstrate, by means of ion mobility and collision‐induced dissociation measurements, that the inclusion/exclusion topology ratio varies as a function of the equilibration time in solution prior to the electrospray process.     

Synthesis of novel side‐chain triphenylamine polymers with azobenzene moieties via RAFT polymerization and investigation on their photoelectric properties

Two novel and well‐defined polymers, poly[6‐(5‐(diphenylamino)‐2‐((4‐methoxyphenyl)diazenyl)phenoxy)hexyl methacrylate] (PDMMA) and poly[6‐(4‐((3‐ethynylphenyl)diazenyl) phenoxy)hexyl methacrylate] (PDPMMA), which bear triphenylamine (TPA) incorporated to azobenzene either directly (PDMMA) or with an interval (PDPMMA) as pendant groups were successfully prepared via reversible addition‐fragmentation chain transfer polymerization technique. The electrochemical behaviors of PDPMMA and PDMMA were investigated by cyclic voltammograms (CV) measurement. The hole mobilities of the polymer films were determined by fitting the J‐V (current‐voltage) curve into the space‐charge‐limited current method. The influence of photoisomerization of the azobenzene moiety on the behaviors of fluorescence emission, CV and hole mobilities of these two polymers were studied. The fluorescent emission intensities of these two polymers in CH₂Cl₂ were increased by about 100 times after UV irradiation. The oxidation peak currents (I_OX) of the PDMMA and PDPMMA in CH₂Cl₂ were increased after UV irradiation. The photoisomerization of the azobenzene moiety in PDMMA had significant effect on the electrochemical behavior, compared with that in PDPMMA. The changes of the hole mobility before and after UV irradiation were very small for both polymers. The HOMO energies (E_HOMO, HOMO: the highest occupied molecular orbital) of side chain moieties of TPA incorporated with cis‐isomer and trans‐isomer of azobenzene in PDMMA and PDPMMA were obtained by theoretical calculation, which are basically consistent with the experimental results. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Influence of the mode of deformation on recrystallisation kinetics in Nickel through experiments,theory and phase field model

Abstract

In this paper, we report the influence of the mode of deformation on recrystallisation kinetics through experiments, theory and a phase field model. Ni samples of 99.6% purity are subjected to torsion and rolling at two equivalent plastic strains and the recrystallisation kinetics and microstructure are compared experimentally. Due to significant differences in the distributions of the nuclei and stored energy for the same equivalent strain, large differences are observed in the recrystallisation kinetics of rolled and torsion-tested samples. Next, a multi-phase field model is developed in order to understand and predict the kinetics and microstructural evolution. The coarse-grained free energy parameters of the phase field model are taken to be a function of the stored energy. In order to account for the observed differences in recrystallisation kinetics, the phase field mobility parameter is a required constitutive input. The mobility is calculated by developing a mean field model of the recrystallisation process assuming that the strain free nuclei grow in a uniform stored energy field. The activation energy calculated from the mobilities obtained from the mean field calculation compares very well with the activation energy obtained from the kinetics of recrystallisation. The recrystallisation kinetics and microstructure as characterised by grain size distribution obtained from the phase field simulations match the experimental results to good accord. The novel combination of experiments, phase field simulations and mean field model facilitates a quantitative prediction of the microstructural evolution and kinetics.     

Transformation of the gas‐phase favored O‐protomer of p‐aminobenzoic acid to its unfavored N‐protomer by ion activation in the presence of water vapor: An ion‐mobility mass spectrometry study

An ion‐mobility mass spectrometry study showed that the preferred O‐protonated form of p‐aminobenzoic in the gas phase can be converted to the thermodynamically less favored N‐protomer by in‐source collision‐induced ion activation during the ion transfer process from the atmospheric region to the first vacuum region if the humidity is high in the ion source. Upon the addition of water vapor to the nitrogen gas used to promote the solid analyte to the gas phase under helium‐plasma ionization conditions, the intensity of the ion‐mobility arrival‐time peak for the N‐protomer increased dramatically. Evidently, the ion‐activation process in the first vacuum region is able to provide the energy required to surmount the barrier to isomerize the O‐protomer to the more energetic N‐protomer. The transfer of the proton attached to the carbonyl oxygen atom of the O‐protomer to the amino group takes place by a water‐bridge mechanism. Apparently, the postionization transformations that take place during the transmission of ions from the atmospheric‐pressure ion source to the detector, via different physical compartments of low to high vacuum, play an eminent role in determining the population ratios eventually manifested at the detector.