A simulation study of copper reflow characteristics in vias

The reliable and complete filling of vias and trenches with an appropriate metal is an important process in the fabrication of microelectronic components. Due to its favorable electronic properties and its reliability, copper is a common choice for replacing aluminum as a metallization material. One metallization procedure of interest is the sputter reflow of copper. The sputter reflow process begins with depositing copper via traditional sputter technologies. The films are subsequently made to fill micrometer and submicrometer trenches and vias through surface diffusion enhanced by annealing. This paper studies fundamental considerations such as deposition rates, underlayer material, and transport mechanisms through numerical simulation using the process simulators SIMSPUD and GROFILMS. The simulations are further used to study via filling using Cu reflow and alternative methods including in situ annealing, three-step deposition, and a four-stage deposition-chemical mechanical polishing procedure. Simulation results are presented as depictions of the film on the feature scale. A discussion of the algorithmic solutions to the three-dimensional problems associated with vias is also provided     

Structural characteristics of carbon nanostructures synthesized by ECR-CVD

In this study, carbon nanotubes (CNTs) and nanoparticles were synthesized by an electron cyclotron resonance-chemical vapor deposition (ECR-CVD) system. Results show that both high- and low-aspect-ratio CNTs and nanoparticles are found. The CNTs range in length from tens of nanometers to micrometers, and in outer diameter from about 5 to 50 nm. Transmission electron microscope (TEM) images show that the faceted nanoparticles exhibit polyhedral or onion or irregularly profiled fullerene structures, and the CNTs growth is from the interlayers lamination. The surface sheet resistance and average surface roughness of the CNT films are about 360 Ω per square and 7-17 nm, respectively. When the CNT sample has a higher amount of nanoparticles, the current density will be increased.     

Fabrication of magnetic micro- and nanostructures by scanning probe lithography

Planar magnetic structures based on cobalt nanofilms have been obtained by scanning probe lithography. It has been shown that ferromagnetic nanoparticles with different domain structures can be formed by local oxidation of a cobalt film on a graphite substrate with the use of a conductive probe of an atomic force microscope (AFM). Using AFM nanoengraving of polymethylmethacrylate, masks were formed to obtain microcontact pads connected by cobalt nanowires with a width of 250–1400 nm and a thickness of 10–30 nm on the silicon dioxide surface. The topography and magnetization structure of the obtained samples were controlled by atomic and magnetic force microscopy.     

引入探测器特性的空间目标红外灰度序列仿真研究

针对空间目标红外识别系统难以获取目标数据的问题,对目标红外灰度序列进行了仿真研究.通过计算目标和探测器的轨道运动参数,结合目标的微动特性得到探测器平面的投影面积观测模型;并构建目标表面温度分布模型,进而获得探测器接收的目标红外辐射强度序列.与以往方法不同的是,通过进一步考虑探测器自身成像效应,仿真得到了目标红外灰度序列...     

A spatio-temporal dipole simulation of gastrointestinal magnetic fields

We have developed a simulation of magnetic fields from gastrointestinal (GI) smooth muscle. Current sources are modeled as depolarization dipoles at the leading edge of the isopotential ring of electrical control activity (ECA) that is driven by coupled cells in the GI musculature. The dipole moment resulting from the known transmembrane potential distribution varies in frequency and phase depending on location in the GI tract. Magnetic fields in a homogeneous volume conductor are computed using the law of Biot-Savart and characterized by their spatial and temporal variation. The model predicts that the natural ECA frequency gradient may be detected by magnetic field detectors outside the abdomen. It also shows that propagation of the ECA in the gastric musculature results in propagating magnetic field patterns. Uncoupling of gastric smooth muscle cells disrupts the normal magnetic field propagation pattern. Intestinal ischemia, which has been experimentally characterized by lower-than-normal ECA frequencies, also produces external magnetic fields with lower ECA frequencies.     

Resistance network analog simulation of the magnetic field produced by a solenoid

A method is proposed for the analog simulation of the magnetic field produced by a solenoid with an arbitrary axially symmetric shape, having magnetic pole pieces also with arbitrary axially symmetric shapes. The ordinary resistance network analog for solving axially symmetric Poisson's problems is used in this method. The simulated magnetic field configurations for some specific cases are compared with theoretical ones. The results obtained by this method can be used directly as the input data for an automatic electron-trajectory tracing scheme in which a resistance network analog is used in conjunction with an electronic computer.     

水下拖缆动力学特性计算机仿真研究

作为水下拖缆实时控制策略设计的重要前提,对水下拖缆的动力学特性掌握至关重要。对于长达数千米的水下拖缆,采用计算机仿真技术对其研究,在成本上和效果上都有着比较理想的结果。在Ablow和Schechter[1]的经典模型基础之上建立三维拖缆动态模型,采用广义α算法对其求解。通过计算机仿真程序编译,实现对拖缆在拖船变速直线运动和升沉运动工况下的动力学特性仿真研究,为深入制定拖缆控制策略提供了良好的依据。     

Fast simulation of lossy transmission lines by the modified methodof characteristics

A set of recursive formulations based on the method of characteristics (MC) are derived to simulate lossy transmission lines in VLSI and multichip modules (MCMs) design     

多用户OFDM仿真研究

对多用户正交频分复用(OFDM)进行了研究,对自适应跳频技术(AFH)以及它的优点与不足进行了详细的论述,给出了自适应比特、功率、和子载波分配方法。使用MATIAB仿真了多用户OFDM系统,采用系统总的比特误码率(BER)作为性能评估参数,通过改变一些系统的参数,例如用户数量、每组子载波数量、超额功率等,然后比较对于理想系统的结果的影响,以此得出结论。     

钛酸和铌酸纳米结构的合成、表征和形成机制

自碳纳米管发现以来，纳米管、纳米线等纳米结构的研究受到广泛重视。钛酸和铌酸是半导体，有光催化和离子交换特性，可用于气体传感器，能量转换和环境净化等，由这些材料组成的纳米材料有可能成为很好的纳米器件。本文工作中，我们合成了这类层状化合物的多种纳米管、纳米线、纳米带和纳米片。     

Brillouin light scattering study of the spin dynamics in nanoscale permalloy stripes: Theory and experiment

The spin-wave modes in nanoscale permalloy stripes are studied using Brillouin light scattering for the case where an external magnetic field is applied transversely to the length of the stripes. By adjusting the magnitude of this external field, the overall magnetization may be varied between the approximately transverse and longitudinal orientations. The observed spin-wave frequencies are analysed using a recently developed microscopic dipole-exchange theory that is particularly appropriate when the magnetization displays strong spatial inhomogeneity. Comparison between theory and experiment for the two sizes of stripes studied gives fairly good agreement, allowing the magnetic parameters of permalloy to be deduced. A small magnetic anisotropy of the easy-plane type is shown to play an important role.     

线性啁啾脉冲频谱干涉特性的模拟研究

为了研究宽带脉冲因受外界瞬态扰动而引起的相移随频谱变化的规律,利用啁啾脉冲与扰动在频域上的卷积特性,采取将频谱干涉技术和线性啁啾脉冲相结合,当两束线性啁啾脉冲在频率域相遇时,相同的频谱成分产生干涉,从其干涉图中得到随脉冲频谱变化的相对相移。根据傅里叶变换的频谱干涉技术,对从两束线性啁啾脉冲的频谱干涉图中提取相移进行了数值模拟。结果表明,对假设具有不同类型的相移进行重构,还原出随频谱变化的相位扰动。这一结果对超快光学中的瞬态测量是有帮助的。     

A general simulation procedure for the electrical characteristics of metal-insulator-semiconductor tunnel structures

The algorithm is suggested for calculating the I–V characteristics of a voltage- or current-controlled metal-tunnel-thin insulator-semiconductor system. The basic underlying physical models are discussed. Applicability of the algorithm is confirmed by a comparison of the simulation results with the measurement data obtained by the authors and borrowed from the literature, for several different structures. The presented information is supposed to suffice for calculating the electrical characteristics of the investigated structures with the various combinations of materials: metal or polysilicon gate, single-layer or stacked insulator, and semiconductor with any doping type and level.     

Simulation based study of thermal effects on periodic nanostructures fabricated by laser interference

Laser interference based direct writing is a potential solution for wide range of fabrication of nanostructure. This paper deals with two dimensional heat conduction analysis and the simulation of the same on silicon and germanium surfaces. Simulation of direct writing of patterns with 193 nm, 27 nsec, single pulse laser source with power varied from 800 mJ/cm² to 1100 mJ/cm² are presented. The rise in the temperature on the surfaces as well as beneath the surface is analyzed on the basis of the results. We also report about the dependency of the thermal diffusion length on the homogeneity of the formed structures.     

Computer study of physical properties of silicon nanostructures

The method of molecular dynamics is applied to the study of variations in the physical properties of vitreous and amorphous silicon nanoparticles when heated from 300 to 1700 K. The nanoparticles consist of 300, 400, and 500 atoms. The energy and the average length of the Si-Si bond are calculated, and the average number of bonds per atom is determined. Thermally induced strains tend to change the distribution of the excess potential energy among the concentric layers in the nanoparticles. It is shown that, energetically, the most preferential layer is the middle spherical layer of the “warm” nanoparticle. The temperature behavior of the radial and tangential components of the atomic mobility coefficient in the concentric layers is considered. It is established that there is a liquid layer at the nanoparticle surface in the vicinity of the transition to melting. The vitrified Si_n nanoparticles are kinetically more stable than the similar-sized amorphous particles.     

A percolation study of RTS noise amplitudes in nano-MOSFETs by Monte Carlo simulation

A high efficiency 2D percolation model of RTS amplitudes in nanoscale MOSFETs based on the numerical results of potential and carriers density distributions in the channel obtained by solutions of coupled 2D Schrodinger and Poisson equations was presented. Using this model the dependences of relative RTS amplitudes ΔI_D/I_D on device geometry L_eff × W_eff, t_ox bias conditions I_D, V_G and trap locations along the channel were simulated and analyzed for a set of square n-MOSFETs. The results show reasonable agreement with published numerical or experimental data.     

Characterization of a new cobalt precursor for focused beam deposition of magnetic nanostructures

The electrical and magnetic properties of nanowires deposited from cobalt tricarbonyl nitrosyl (Co(CO)₃NO) precursor by focused electron beam- and focused ion beam-induced deposition (FEBID and FIBID) have been investigated. As-deposited nanowires have similar Co content, around 50-55 at.%, but different electrical behaviour: FEBID nanowire is highly resistive (6.3 mΩ cm at RT) and non-metallic at low T, while the FIBID one has much lower resistivity (189 μΩ cm at RT) and it is metallic. The magnetic properties, tested with magnetoresistance measurements, reveal a non-magnetic behaviour for both nanowires. After 400 °C annealing in vacuum FEBID wire is much less resistive (62 μΩ cm at RT) and recovers the metallic behaviour at low T, and both FEBID and FIBID wires display ferromagnetic behaviour. Structural analysis by low energy-scanning transmission electron microscopy (LE-STEM) suggests that coarsening and interconnection of the Co nanograins are responsible for the improvement in electrical and magnetic properties.     

超高温金属纳米结构增强吸收特性的仿真研究

利用表面等离子体改变材料吸收光谱特性越来越受到关注。为了增强超高温金属纳米结构的吸收特性,设计了超高温金属-金属以及膜层-金属-金属表面等离子体周期纳米结构,仿真分析其在波长200~4 000 nm光谱范围内,不同参数对材料吸收谱特性的影响。仿真分析表明,不同参数的吸收光谱中均会出现吸收峰,且吸收率达93%以上。而介电材料、金属纳米结构的周期、尺寸和深度是影响吸收率的主要因素。同时,介电材料和周期还会对吸收峰出现的位置产生影响。该仿真结果为超高温表面等离子体材料的吸收特性应用的研究提供了理论基础。     

A simulation study of high-speed silicon heteroemitter bipolartransistors

Using a two-dimensional numerical simulator, the upper limit of Si homotransistor cutoff frequency is estimated within the assumed conditions of punchthrough voltage. The potential speed advantages of silicon heteroemitter bipolar transistors (Si HBTs) (such as low emitter storage time, low emitter-base junction capacity, and possibility for large base width reduction) are shown by comparing Si HBTs with a Si homotransistor. It is confirmed that the cutoff frequency is enhanced from 48 to 127 GHz by the Si HBT structure. The optimum values of heteromaterial properties for high-speed HBT operation including energy gap, band discontinuity, and heterointerface recombination are discussed