Integrating vertically aligned carbon nanotubes on micromechanical structures

The integration of high yield, uniform and preferential growth of vertically aligned carbon nanotubes (VACNT) on low stress micromechanical structures was analyzed. A combination of electron-beam crosslinked surface micromachining and direct current plasma enhanced chemical vapor deposition of electric field aligned carbon nanotubes was used for the analysis. The selective placement of high yield and uniform VACNTs on a partially suspended Ni/SiO2/Ti microstructure was also demonstrated.

3D thermo-electro-mechanical simulations of gas sensors based on SOI membranes

3D thermo-electro-mechanical device simulations are presented of a novel fully CMOS-compatible MOSFET gas sensor operating in a SOI membrane. A comprehensive stress analysis of a Si-SiO2-based multilayer membrane has been performed to ensure a high degree of mechanical reliability at a high operating temperature (e.g. up to 400°C). Moreover, optimisation of the layout dimensions of the SOI membrane, in particular the aspect ratio between the membrane length and membrane thickness, has been carried out to find the best trade-off between minimal device power consumption and acceptable mechanical stress.

Design and coupled-effect simulations of CMOS micro gas-sensors built on SOI thin membranes

This paper describes coupled-effect simulations of smart micro gas-sensors based on standard BiCMOS technology. The smart sensor features very low power consumption, high sensitivity and potential low fabrication cost achieved through full CMOS integration. For the first time the micro heaters are made of active CMOS elements (i.e. MOSFET transistors) and embedded in a thin SOI membrane consisting of Si and SiO2 thin layers. Micro gas-sensors such as chemoresistive, microcalorimeteric and Pd/polymer gate FET sensors can be made using this technology. Full numerical analyses including 3D electro-thermo-mechanical simulations, in particular stress and deflection studies on the SOI membranes are presented. The transducer circuit design and the post-CMOS fabrication process, which includes single sided back-etching, are also reported.

High tuning range AlSi RF MEMS capacitors fabricated with sacrificial amorphous silicon surface micromachining

This paper reports the fabrication and electrical characterization of high tuning range AlSi RF MEMS capacitors. We present experimental results obtained by a surface micromachining process that uses dry etching of sacrificial amorphous silicon to release Al-1%Si membranes and has a low thermal budget (<450 °C) being compatible with CMOS post-processing. The proposed silicon sacrificial layer dry etching (SSLDE) process is able to provide very high Si etch rates (3-15 μm/min, depending on process parameters) with high Si: SiO2 selectivity (>10,000:1). Single- and double-air-gap MEMS capacitors, as well as some dedicated test structures needed to calibrate the electro-mechanical parameters and explore the reliability of the proposed technology, have been fabricated with the new process. S-parameter measurements from 100 MHz up to 2 GHz have shown a capacitance tuning range higher than 100% with the double-air-gap architecture. The tuning range can be enlarged with a proper DC electrical bias of the capacitor electrodes. Finally, the reported results make the proposed MEMS tuneable capacitor a good candidate for above-IC integration in communications applications. © 2004 Elsevier B.V. All rights reserved.

Refractive index and thickness analysis of natural silicon dioxide film growing on silicon with variable-angle spectroscopic ellipsometry

The refractive index and thickness of SiO2 thin films naturally grown on Si substrates were determined simultaneously within the wavelength range of 220-1100 nm with variable-angle spectroscopic ellipsometry. Different angles of incidence and wavelength ranges were chosen to enhance the analysis sensitivity for more accurate results. Several optical models describing the practical SiO2-Si system were investigated, and best results were obtained with the optical model, including an interface layer between SiO2 and Si, which proved the existence of the interface layer in this work as described in other publications.

Advantages of top-gate, high-k dielectric carbon nanotube field-effect transistors

The subthreshold slope, transconductance, threshold voltage, and hysteresis of a carbon nanotube field-effect transistor (CNT FET) were examined as its configuration was changed from bottom-gate exposed channel, bottom-gate covered channel to top-gate FET. An individual single wall CNT was grown by chemical vapor deposition and its gate configuration was changed while determining its transistor characteristics to ensure that the measurements were not a function of different chirality or diameter CNTs. The bottom-gate exposed CNT FET utilized 900 nm SiO2 as the gate insulator. This CNT FET was then covered with TiO2 to form the bottom-gate covered channel CNT FET. Finally, the top-gate CNT FET was fabricated and the device utilized TiO 2 (K ∼ 80, equivalent oxide thickness=0.25 nm) as the gate insulator. Of the three configurations investigated, the top-gate device exhibited best subthreshold slope (67-70 mV/dec), highest transconductance (1.3 μS), and negligible hysteresis in terms of threshold voltage shift. © 2006 American Institute of Physics.

Optimization Of Off-Null Ellipsometry For Air/Solid Interfaces

The optimization of off-null ellipsometry is described with emphasis on the improvement of sample thickness sensitivity. Optimal conditions are dependent on azimuth angle settings of the polarizer, compensator, and analyzer in a polarizer-compensator-sample-analyzer ellipsometer arrangement. Numerical simulation utilized offers an approach to present the dependence of the sensitivity on the azimuth angle settings, from which optimal settings corresponding to the best sensitivity are derived. For a series of samples of SiO2 layer (thickness in the range of 1.8-6.5 nm) on silicon substrate, the theory analysis proves that sensitivity at the optimal settings is increased 20 times compared to that at null settings used in most works, and the relationship between intensity and thickness is simplified as a linear type instead of the original nonlinear type, with the relative error reduced to similar to 1/100 at the optimal settings. Furthermore the discussion has been extended toward other factors affecting the sensitivity of the practical system, such as the linear dynamic range of the detector, the signal-to-noise ratio and the intensity from the light source, etc. Experimental results from the investigation Of SiO2 layer on silicon substrate are chosen to verify the optimization. (c) 2007 Optical Society of America.

Anisotropic Deformation Of Polystyrene Particles By Mev Au Ion Irradiation

MeV An irradiation leads to a shape change of polystyrene (PS) and SiO2 particles from spherical to ellipsoidal, with an aspect ratio that can be precisely controlled by the ion fluence. Sub-micrometer PS and SiO2 particles were deposited on copper substrates and irradiated with Au ions at 230 K, using an ion energy and fluence ranging from 2 to 10 MeV and 1 x 10(14) ions/cm(2) to 1 x 10(15) ions/cm(2). The mechanisms of anisotropic deformation of PS and SiO2 particles are different because of their distinct physical and chemical properties. At the start of irradiation, the volume of PS particles decrease, then the aspect ratio increases with fluence, whereas for SiO2 particles the volume remains constant. (C) 2008 Elsevier B.V. All rights reserved.

纳米压痕和划痕法测定氧化硅薄膜材料的力学特性

为了研究不同制备工艺对材料力学性能的影响 ,选择了热氧化、LPCVD和PECVD三种典型工艺 ,在硅片上制备 1μm氧化硅薄膜。通过纳米压痕和划痕检测可知 ,热氧化工艺制备的SiO2薄膜的硬度和模量最大 ,LPCVD制备的样品界面结合强度高于PECVD。纳米压痕和划痕技术为此提供了丰富的近表面弹塑性变形和断裂等的信息 ,是评价微米薄膜力学性能的有效手段

An automatic imaging spectroscopic ellipsometer for characterization of nano-film pattern on solid substrate

In order to characterize the physical and spatial properties of nano-film pattern on solid substrates, an automatic imaging spectroscopic ellipsometer (ISE) based on a polarizer - compensator - specimen - analyzer configuration in the visible region is presented. It can provide the spectroscopic ellipsometric parameters psi (x, y, lambda) and Delta (x, y, lambda) of a large area specimen with a lateral resolution in the order of some microns. A SiO2 stepped layers pattern is used to demonstrate the function of the ISE which shows potential application in thin film devices' such as high-throughput bio-chips.

电子封装中的不流动芯下材料力学性能和封装可靠性的研究

可控坍塌芯片互连（C4）技术可以实现高速、高密度、小外形的封装，因此日渐得到关注和发展。本文针对发展新一代c4技术所面临的不流动芯下材料的机械性能问题，采用具有不同填充颗粒含量的不流动芯下材料，通过对材料的机械性能的测试和分析以及有限元模拟，初步揭示了不流动芯下材料变形行为的特点，填充颗粒含量对芯下材料机械性能的影响，以及芯下材料机械性能和芯下材料工艺导致的颗粒沉积对封装可靠性的影响。首先在差示扫描量热仪（DSC）、热一力学分析仪（TMA）上对材料的固条件、热膨胀系数、玻璃化转变温度进行了测试，接着又在六轴微型试验机上对材料在不同温度和应变率下的应力一应变行为进行了测试。测试结果表明，所用材料的固化条件和玻璃化转变温度可以满足不流动芯下材料的性能要求，材料的热膨胀系数高于芯下材料理想的热膨胀系数值，材料中填充颗粒含量、温度、应变率等对材料的应力一应变行为有重要的影响。为了解芯下材料中填充颗粒含量对机械性能的影响，对不同颗粒含量材料在各测试温度和应变率下的杨氏模量、屈服强度和流动应力进行了对比和分析。结果表明，在各测试条件下，芯下材料的杨氏模量基本随着颗粒含量的增加而升高；温度较低时，材料的屈服强度随颗粒含量的增加而升高，但是，较高温度时，材料的屈服强度和流动应力随着颗粒含量的增加呈现先升高后降低再升高的变化趋势。为理解芯下材料的屈服强度和流动应力随着颗粒含量非单调变化的行为，采用广义Eshelby等效夹杂法对含颗粒试样在单轴拉伸时试样内的应力分布进行了分析，并用纳米硬度计对材料纳米尺度的性能进行了测量。应力分析的结果表明，不流动芯下材料的SiO2填充颗粒的加入会在基体里引起应力集中，应力集中系数随着颗粒含量的增加先升高后降低，试样内的应力集中有使材料屈服强度降低的趋势。纳米硬度计的测试结果表明，芯～卜材料内形成了性能介于颗粒Z基体之间的界面相，界面相的形成有使芯下材料屈服强度提高的趋势。芯下材料屈服强度随着填充颗粒含量的非单调的变化是应力集中和界面效应藕合作用的结果。温度和应变率是影响芯下材料机械性能的重要因素。为刻画温度和应变率的效应，采用Pe化yna模型描述材料的应力一应变行为。结果表明，Per叮na模型可以拟合材料应变率相关的应力一应变行为，描述不流动芯下材料应力一应变曲线的基本趋势，对材料在测试范围外的行为给出较合理的预测，并且Perzyna模型可以很方便地用于ABAQUS中，这将易于工业应用。最后，采用商用有限元程序AB AQus分析了芯下材料机械性能和芯下材料工艺导致的填充颗粒沉积对C4封装可靠性的影响。结果表明，在芯片／基板的缝隙中填入芯下材料可以显著延长可控坍塌倒装封装焊点的热疲劳寿命，提高封装可靠性，可控坍塌倒装封装焊点的热疲劳寿命随着芯下材料中填充颗粒含量的增加而增长；芯下材料中填充颗粒在C4封装基板侧的沉积将导致封装焊点的热疲劳寿命缩短，而颗粒在芯片侧的沉积则可使焊点的热疲劳寿命稍稍延长。

MeV金离子辐照聚苯乙烯微球的各向异性形变

在低温条件下用Au离子辐照法实现了聚苯乙烯(PS)微球的各向异性形变.PS微球在离子辐照下呈现出不同于SiO2微球的形变特点.照后PS微球整体收缩,在平行于离子入射方向上收缩尤甚,使照后PS微球呈长轴垂直与离子入射方向的椭球.采用加掩膜辐照法,在同一晶体上特定区域实现微球的形变.此工作为重离子辐照在光子晶体中引入可控缺陷奠定了基础.

rhegf-Loaded Plga-Alginate Microspheres Enhance The Healing Of Full-Thickness Excisional Wounds In Diabetised Wistar Rats

[EN] Diabetic foot ulcers (DFUs) represent a major clinical challenge in the ageing population. To address this problem, rhEGF-loaded Poly-Lactic-co-Glycolic-Acid (PLGA)-Alginate microspheres (MS) were prepared by a modified w/o/w-doubleemulsion/ solvent evaporation method. Different formulations were evaluated with the aim of optimising MSs properties by adding NaCl to the surfactant solution and/or the solvent removal phase and adding alginate as a second polymer. The characterization of the developed MS showed that alginate incorporation increased the encapsulation efficiency (EE) and NaCl besides increasing the EE also became the particle surface smooth and regular. Once the MS were optimised, the target loading of rhEGF was increased to 1% (PLGA-Alginate MS), and particles were sterilised by gamma radiation to provide the correct dosage for in vivo studies. In vitro cell culture assays demonstrated that neither the microencapsulation nor the sterilisation process affected rhEGF bioactivity or rhEGF wound contraction. Finally, the MS were evaluated in vivo for treatment of the full-thickness wound model in diabetised Wistar rats. rhEGF MS treated animals showed a statistically significant decrease of the wound area by days 7 and 11, a complete re-epithelisation by day 11 and an earlier resolution of the inflammatory process. Overall, these findings demonstrate the promising potential of rhEGF-loaded MS (PLGA-Alginate MS) to promote faster and more effective wound healing, and suggest its possible application in DFU treatment.

Plasma-Arc Technology For The Thermal Treatment Of Chemical Wastes

Plasma-arc technology was developed to dispose of chemical wastes from a chemical plant by the Institute of Mechanics, Chinese Academy of Sciences (CAS-IMECH). A pilot plant system with this technology was constructed to destroy two types of chemical wastes. The system included shredding, mixing, and feeding subsystems, a plasma-arc reactor of 150 kW, an off-gas burning subsystem, and a scrubbing subsystem. The additives (CaO, SiO2, and Fe) were added into the reactor to form vitrified slag and capture the hazardous elements. The molten slag was quickly quenched to form an amorphous glassy structure. A direct current (DC) experimental facility of 30kW with plasma-arc technology was also set up to study the pyrolysis process in the laboratory, and the experimental results showed the cooling speed is the most important factor for good vitrified structure of the slag. According to previous tests, the destruction and removal efficiency (DRE) for these chemical wastes was more than 99.999%, and the polychlorinated biphenyls (PCBs) concentration in the solid residues was in the range of 1.28 to 12.9mg/kg, which is far below the Chinese national emission limit for the hazardous wastes. A simplified electromagneto model for numerical simulation was developed to predict the temperature and velocity fields. This model can make satisfactory maximum temperature and velocity distributions in the arc region, as well as the results by the magneto hydrodynamic approach.

The formation mechanism of low leaching glassy slag during plasma arc vitrification treatment of fly ash

In this paper, the glass formation theory is applied to study the formation mechanism of the low leaching glassy slag during the process of plasma waste treatment. The research shows that SiO2 acts as network former to form a 3-dimensional Si-O tetrahedral network in which heavy metals are bonded or encapsulated, so the Si-O tetrahedron protect heavy metals against leaching from the vitrified slag or acid corrosion. For given chemical compositions of waste, the formation ability of the vitrified slag can be represented by the ratio of the whole oxygen ions to the whole network former ions in glass (O/Si) which is appropriate in the range of 2~3. A plasma arc reactor is used to conduct the vitrification experiments of two kinds of fly ashes with additives in which effects of various parameters including arc power, cooling speed, treatment temperature are studied. The chemical compositions of fly ashes are analyzed by X-ray fluorescence (XRF) spectrometry. The experimental results show that both cooling speed and O/Si have important influence on the formation of the vitrified slag, which is qualitatively in accordance with the predictions of the glass formation theory.