Voltage- and temperature-dependent gate capacitance and current model: application to ZrO/sub 2/ n-channel MOS capacitor

Based on the energy-dispersion relation in each region of the gate-dielectric-silicon system, a tunneling model is developed to understand the gate current as a function of voltage and temperature. The gate capacitance is self-consistently calculated from Schrodinger and Poisson equations subject to the Fermi-Dirac statistics, using the same band structure in the silicon as used for tunneling injection. Franz two-band dispersion is assumed in the dielectric bandgap. Using a Wentzel-Kramer-Brillouin (WKB)-based approach, direct and Fowler-Nordheim (FN) tunneling and thermionic emission are considered simultaneously. The model is implemented for both the silicon conduction and valence bands and both gate- and substrate-injected currents. ZrO/sub 2/ NMOSFETs were studied through temperature-dependent C/sub g/-V/sub g/ and I/sub g/-V, simulations. The extracted band gaps and band offsets of the ZrO/sub 2/- and interfacial-Zr-silicate-layer are found to be comparable with the reported values. The gate currents in ZrO/sub 2/-NMOSCAPs are found to be primarily contributed from the silicon conduction band and tunneling appears to be the most probable primary mechanism through the dielectric. Oscillations of gate currents and kinks of gate capacitance were observed near the flat-band in the experiments. These phenomena might be caused by the interface states.     

Bias-temperature instabilities of polysilicon gate HfO/sub 2/ MOSFETs

Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs.     

“电力电子技术”课程理论和实践同步教学法

为提高"电力电子技术"课程教学效果并培养学生主动学习能力,本文研究了理论和实践同步教学法,借助Matlab仿真和相应实验平台,让理论教学在实验室中完成。本文以三相桥式全控整流电路为例,建立了Matlab仿真模型,讨论了触发角和输出电压间的关系,给出了交流侧存在漏感、整流器故障的仿真分析。教学效果表明该教学方法对提高教学质量和加深学生对电力电子电路的理解有重要意义。     

响应面法优化超声辅助水酶法提取辣木籽油

以辣木籽为原料,通过超声辅助水酶法提取辣木籽油。以辣木籽油提取率为指标,利用单因素试验考察pH值、果胶酶添加量、提取时间、提取温度、超声功率对辣木籽油提取率的影响,在此基础上采用响应面法确定提取辣木籽油的最佳工艺条件。结果表明,最佳提取工艺为果胶酶添加量0.50%、pH3.5、提取温度54℃、提取时间12 h、超声功率84 W,此时辣木籽油提取率为30.56%。     

Serum levels of polybrominated diphenyl ethers (PBDEs) in foam recyclers and carpet installers working in the United States

Increased exposure to the flame retardants known as polybrominated diphenyl ethers (PBDEs) may be expected to occur during the recycling of polyurethane foam containing these chemicals. To date, no studies in the United States have investigated occupational exposure to these flame retardants during recycling processes. The objective of the present study was to determine if individuals working in foam recycling facilities, and/or carpet installers who may install carpet padding manufactured from recycled foam, possess significantly higher PBDE serum levels relative to that of the general U.S. population. As a control group, serum was collected from four spouses and one clerical worker. In addition, levels in workers were also compared to the recently published national health and nutrition examination survey (NHANES) data set on PBDEs in the general U.S. population. Serum samples were collected in duplicate and analyzed by two different laboratories as quality control. Total PBDE levels were found to be significantly higher (p < 0.05) in the individuals recycling foam and installing carpet (n = 15) relative to the control group (n = 5). Median sigmaPBDE levels in the foam recyclers, carpet layers, and control group were 160, 178, and 19 ng/g lipid, respectively. In contrast, concentrations of a polybrominated biphenyl (BB-153) and a polychlorinated biphenyl (CB-153) were equivalent among all groups tested. The PBDE congeners BDE-47, 99, 100, and 153 contributed 90% of the sigmaPBDE concentration in serum and no differences in congener patterns were apparent among the different groups. Relative to concentrations measured in the NHANES, foam recyclers and carpet layers have body burdens that are an order of magnitude higher. These data suggest individuals recycling foam-containing products, and/ or using products manufactured from recycled foam (i.e., carpet padding), have higher body burdens of PBDEs, and thus may be at higher risk from adverse health effects associated with brominated flame retardant exposure.     

Rapid pyrolysis of brown coal and oil shale

A brown coal, peat and oil shale were subjected to a rapid pyrolysis process and medium-heat-value gases together with tar were collected. The char residue was of high activity and suitable for gasification to create a two-stage gasification system. The coal-tar is used for manufacturing liquid fuels and chemicals.     

X80管线钢在力电化学耦合作用下CO2腐蚀行为的研究

以典型的管线钢材料X80钢为对象,采用动电位极化和电化学阻抗谱技术,研究了在弹性拉伸应力(60%σ_(ys))和塑性拉伸应力(108%σ_(ys))状态下,不同CO_2分压和Cl~-质量分数对材料腐蚀的影响规律。结果表明:受拉伸应力作用的X80钢腐蚀速率随CO_2分压的增大而增大,但并非单纯正相关关系;随Cl~-质量分数的增大,呈现先升高后降低的规律,当Cl~-质量分数为3.5%时,X80钢的腐蚀速率达到最大值。此外,塑性应力状态下X80钢的腐蚀速率明显高于弹性应力状态下的值,原因是塑性应力提高了金属表面的电化学反应活性。     

Deformation of metallic glasses with special emphasis in supercooled liquid region

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