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.     

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.     

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。     

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.     

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。     

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     

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。     

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.     

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.     

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.     

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     

A novel self-aligned punchthrough implant: A simulation study

This paper presents a simulation study of a novel self-aligned punchthrough implant. The self-aligned dopant profile is achieved using a high-energy implant after polysilicon gate definition. The result is that in the channel region the implant peak is just below the surface and in the source-drain regions the implant peak is well below the junctions. Performance is increased through the reduction of parasitic junction capacitance. In this analysis an established 0.5 μm baseline technology shows a 100% reduction in the delay of a loaded inverter. Technologies with smaller or larger gate dimensions can benefit as well     

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.     

基于HLA的仿真程序设计研究

在分布式交互仿真中,高层体系结构HLA以其灵活性、开放性和突出的互操作和重用性成为当今的分布式交互仿真的标准IEEE1516。研究基于HLA的程序设计方法对于开发分布式交互仿真系统具有重要意义。本文从HLA的对象模型模板(OMT)和接口规范实现的运行支撑环境(RTI)所提供的6种服务入手,结合相应设计实例,给出了设计的步骤和一般方法。     

Numerical simulation of HgCdTe detector characteristics

We discuss analytic and numerical models for HgCdTe photodiodes and present examples of their application. Analytic models can account for the performance obtained by many device architectures. Numerical and analytic models agree in predicting several aspects of device performance, such as diffusion limited dark current, confirming the approximations used in deriving the analytic models. Areas are noted where improvement in the numerical models would allow application to a wider range of device simulations. Useful results are obtained from the numerical simulators that cannot be obtained from our analytic model. Flux dependent R₀A products are shown to be a direct result of bias dependent quantum efficiency, a mechanism that is much more evident in heterojunction device architectures. Material compositional grading is demonstrated to lead to lower signal to noise ratio in devices designed to detect a particular infrared wavelength. We also show, particularly for high temperature operation, that heterojunction detectors can at best equal the performance of well-designed homojunction detectors; so, for photodetector design, heterojunctions do not offer any inherent performance advantages over homojunctions. Nevertheless, heterostructures, though ideally not required, may be helpful in achieving high performance in practice.     

A simulation study on the evolution of hopping motions in animals

This work was designed to investigate biomechanical aspects of the evolution based on the hypothesis of dynamic cooperative interactions between the locomotion pattern and the body shape in the quadrupedal hopping and the bipedal hopping. The musculoskeletal sagittal-plane model used in the computer simulation consisted of several segments; foot, shank, thigh, trunk, forearm, upper arm, and tail. Two adjacent segments were connected by a hinge joint, and each joint angle was controlled by an extensor and a flexor muscle. The nervous system was represented by a rhythm pattern generator which consisted of 12 neuron models. The genetic algorithm was employed based on the natural selection theory to represent the evolutionary mechanism. The simulation results showed that although hopping could not be seen in the early evolution process, repeated manipulations of the selection and multiplication increased the step length and the locomotion speed and that the resulting hopping motion was close to that of living animals. It was suggested that the advantage of the quadrupedal hopping is high energy efficiency and that of the bipedal hopping is high stability due to the simple and easy motion control. The computational evolution method employed in this study can be a new powerful tool for investigation of the evolution process mostly due to its versatility.