Acceleration of heavy ions in a thruster

The acceleration of heavy ions in a Hall thruster is analyzed. The numerical solutions to the 1D hydrodynamic equations that describe the three-component system (neutral particles, electrons, and ions) are obtained. The conditions for the collisionless motion of ions, ion acceleration in the presence of the self-consistent electric field, and electron diffusion across the magnetic field are considered. The self-consistent field is calculated using the Poisson equation. The absence of singularity in the case when the ion velocity coincides with the velocity of ion sound is demonstrated. The critical magnetic field above which the propagation of ion beam is impossible is determined.     

用于LIA强流脉冲电子束能谱测量的磁分析器设计

为了测量一台直线感应加速器输出的强流脉冲电子束的能谱宽度,开展了磁分析器的设计研究工作。从磁分析器测试能谱的原理出发,根据被测对象以及测试的一些基本条件提出了磁分析器的基本参数,据此进行了磁铁的理论设计,利用Vector Fields公司的Opera3D／Tosca软件对磁铁进行了三维仿真计算,并对理论设计的结果进行了优化。设计得到的磁分析器为C型磁铁,偏转半径300mm,硬边近似后偏转角度60°,磁极间隙30mm,好场区宽度65．4mm。磁分析器的设计结果很好地满足了物理需求。     

A reliable fabrication technique for very low resistance ohmic contacts top-InGaAs using low energy Ar+ ion beam sputtering

A new fabrication technique for ohmic Au/Pt/Ti contacts top-InGaAs is presented employing anodic oxidization and sputter etching by low energy Ar⁺ ions prior to the metal deposition. This cleaning procedure was found to be superior to wet chemical pre-etching as it provides low resistivity contacts with excellent homogeneity and good uniformity after rapid thermal processing (RTP).     

Dynamic I-V characteristics of ion currents in SiO2 films at low concentrations of mobile charges: Measurements of low concentrations of mobile ions

Factors that affect the accuracy and sensitivity of the method of dynamic I-V characteristics for ion currents of metal/oxide/semiconductor structures with a low (N _S ～ 10⁹–10¹⁰ cm^?2) concentration of mobile ions in the oxide are analyzed comprehensively. Simultaneous measurements of the dynamic I-V and low-frequency C-V characteristics show that the measurement error is about 10% for concentrations of no less than 10⁹ cm^?2.     

Effects of incident energy and angle on carbon cluster ions implantation on silicon substrate:a molecular dynamics study

Carbon cluster ion implantation is an important technique in fabricating functional devices at micro/nanoscale. In this work, a numerical model is constructed for implantation and implemented with a cutting-edge molecular dynamics method. A series of simulations with varying incident energies and incident angles is performed for incidence on silicon substrate and correlated effects are compared in detail. Meanwhile, the behavior of the cluster during implantation is also examined under elevated temperatures. By mapping the nanoscopic morphology with variable parameters, numerical formalism is proposed to explain the different impacts on phrase transition and surface pattern formation. Particularly, implantation efficiency (IE) is computed and further used to evaluate the performance of the overall process. The calculated results could be properly adopted as the theoretical basis for designing nano-structures and adjusting devices'' properties.     

Thermally stimulated current measurements on silicon junctions produced by implantation of low energy boron ions

Thermally stimulated current (TSC) measurements have been performed directly on junctions realized by implantation of low energy (15 keV) boron ions into N-type silicon after annealing treatments at different temperatures between 180 and 500°C. The TSC curves have been analysed by a new method based on the measurement of the mean time before re-emission of the trapped carriers and compared with that of Grossweiner. Both methods indicate that the dominant level is a hole trap located at >Ev + 0·25 eV. This defect anneals at 260°C and is believed to be correlated with the vacancy-vacancy association.     

Kinetics of the growth of an amorphous layer at the surface of silicon bombarded with fast heavy ions at low temperatures

The accumulation of defects in the surface region of Si bombarded with 0.5-MeV Bi ions at a temperature of ?196°C is considered. It is shown that the buildup of disorder in the surface region as the ion dose increases manifests itself in the planar growth of an amorphous layer starting from the Si-SiO₂ interface, and this growth sets in after a threshold implantation dose is attained. The results obtained can be described adequately in the context of a model based on the migration of mobile point defects generated by fast ions to the surface, subsequent processes of segregation of these defects at the interphase boundary, and the presence of saturable sinks in the initial samples.     

Cluster ion implantation: a molecular dynamics study

The collisions of 5.7 keV silicon atom and clusters with a silicon surface are simulated by molecular dynamics. Using a parameter surveillance system for simultaneous execution of multiple simulations on parallel/distributed computers, we have studied the impact dependence of cluster ions on the surface. The channeling effect of the implanted atoms is inevitable in the single-atom case, but is suppressed by the macroscopic vibrations of the surface in the cluster-ion case.     

Optimization of scannable latches for low energy

This paper covers a range of issues in the design of latches and flip-flops for low-power applications. First it revisits, extends, and improves the energy-performance optimization methodology, attempting to make it more formal and comprehensive. The data-switching factor and the glitching activity are taken into consideration, using a formal analytical approach, then a notion of an energy-efficient family of configurations is introduced to make the comparison of different latch styles in the energy-performance space more fair. A recently proposed methodology for balancing hardware intensity in processor pipelines is applied to latch design to facilitate the selection of the objective function for tuning transistor sizes. The power dissipation of the clock distribution is taken into account, supported by simulations of extracted netlists for multibit datapath registers. Practical issues of building a low overhead scan mechanism are considered, and the power overhead of the scannable design is analyzed. A low-power level-sensitive scan mechanism is proposed, and results of a comparative study of scannable latches are shown. The applicability of the proposed scan mechanism to a wide variety of latches is demonstrated.     

Relaxation of a defect subsystem in silicon irradiated with high-energy heavy ions

The relaxation of a silicon defect subsystem modified by the implantation of high-energy heavy ions was studied by varying the electrical properties of irradiated Si crystal annealed at a temperature of 450°C. It is shown that quenched-in acceptors are introduced into Si crystals as a result of irradiation with comparatively low doses of Bi ions and subsequent relatively short annealing (no longer than 5 h); the distribution of these quenched-in acceptors has two peaks located at a depth of about 10 μm and at a depth corresponding approximately to the ions’ projected range (43.5 μm). The peaks in the distribution of quenched-in acceptors correspond to the regions enriched with vacancy-containing defects. As the heat-treatment duration increases, the acceptor centers are transformed into donor centers with the centers’ spatial distribution remaining intact. Simultaneously, an almost uniform introduction of quenched-in donors occurs in the entire crystal beyond the depth corresponding to the projected range of ions. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 5, 2003, pp. 565–569. Original Russian Text Copyright ? 2003 by Smagulova, Antonova, Neustroev, Skuratov.     

不同离子束参数诱导单晶硅纳米微结构与光学性能

使用微波回旋共振离子源,研究了低能Ar+离子束正入射时不同离子束能量和束流密度对单晶硅（100）表面的刻蚀效果及光学性能。结果表明,当离子束能量为1 000 eV,束流密度为88~310 A/cm2时,样品表面出现自组装纳米点状结构,且随着离子束流密度增加排列紧密而有序;粗糙度呈现先减小后迅速增大的趋势,在160 A/cm2附近达到极小值;刻蚀后,近红外波段内平均透过率由53%提高到57%以上,且随着纳米自组装结构有序性的提高而增大。当束流密度为270 A/cm2,能量为500~1 500 eV时,样品表面出现纳米点状结构,且随着离子束能量的增加趋于密集有序;粗糙度呈现先缓慢增加,在1 100 eV附近达到极大值,之后粗糙度迅速下降;刻蚀后样品透过率明显提高,且平均透过率随着点状结构有序性的提高而增大;刻蚀速率与离子束能量的平方成正比。自组织纳米结构的转变是溅射粗糙化和表面驰豫机制相互作用的结果。     

ALADIN: a multilevel testability analyzer for VLSI system design

In order to cope with tomorrow's challenges in the microelectronic market, the reliability of the first phases of the design process must be improved. The possibility of applying techniques for testability analysis at these abstract design levels can considerably help in achieving this goal, reducing at the same time system design costs. In this paper we introduce a novel approach for the application of functional testability at system design level and demonstrate the possibility of its application in an industrial environment. Testability conditions referring to both regular and irregular topologies have been defined, formalized and inserted into the knowledge base of the expert system, ALADIN. This tool operates as a testability analyzer able to identify critical areas for testability in designs whose functional modules and local interconnections are known and described in standard VHDL. The architecture of the tool has been defined in order to satisfy the users' requirements including the integrability into a standard CAD design flow through standard I/O interfaces. Then its application to both a regular and an irregular topology are presented in order to show on real examples which testability conditions apply, and how the tool operates in order to reach the testability assessment. From these industrial case studies, figures of merit are derived from which it is possible to evaluate the importance of the application of such a methodology to system level design     

HILT: a heavy ion large area proportional counter telescope forsolar and anomalous cosmic rays

The HILT sensor has been designed to measure heavy ion elemental abundances, energy spectra, and direction of incidence in the mass range from helium to iron and in the energy range 4-250 MeV/nucleon. With its large geometric factor of 60 cm² sr the sensor is optimized to provide compositional and spectral measurements for low-intensity cosmic rays, i.e., for small solar energetic particle events and for the anomalous component of cosmic rays. The instrument combines a large-area ion-drift-chamber-proportional-counter system with two arrays of 16 Li-drifted solid state detectors and 16 CsI crystals. The multi-dE /dx-E technique provides a low-background mass and energy determination. The sensor also measures particle direction. By combining these measurements with the information on the spacecraft position and attitude in the low-altitude polar orbit, it will be possible to infer the ionic charge of the ions from the local cutoff of the Earth's magnetic field. The ionic charge in this energy range is of particular interest because it provides unique clues to the origin of these particles and has not been investigated systematically so far     

Toward low LDPC-code floors: a case study

While LDPC codes have been widely acclaimed in recent years for their near-capacity performance, they have not found their way into many important applications. For some cases, this is due to their increased decoding complexity relative to the classical coding techniques. For other cases, this is due to their inability to reach very low bit error rates (e.g., 10?12) at low signal-to-noise ratios (SNRs), a consequence of the errorrate floor phenomenon associated with iterative LDPC decoders. In the present paper, we make strides in the low-floor problem by identifying the weaknesses of the code under study and applying compensatory counter-measures. These counter-measures include: modifying the code itself, modifying the decoder, or adding a properly designed outer algebraic code. Our results demonstrate that each of these techniques can successfully lower an LDPC code?s floor, and that, for the code under study, an outer BCH code appears to be particularly effective. All of our results are based on FPGA decoder simulations and so they are reliable and repeatable.     

PET: a proton/electron telescope for studies of magnetospheric,solar, and galactic particles

The proton/electron telescope (PET) on SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) is designed to provide measurements of energetic electrons and light nuclei from solar, Galactic, and magnetospheric sources. PET is an all solid-state system that will measure the differential energy spectra of electrons from ~1 to ~30 MeV and H and He nuclei from ~20 to ~300 MeV/nucleon, with isotope resolution of H and He extending from ~20 to ~80 MeV/nucleon. As SAMPEX scans all local times and geomagnetic cutoffs over the course of its near-polar orbit, PET will characterize precipitating relativistic electron events during periods of declining solar activity, and it will examine whether the production rate of odd nitrogen and hydrogen molecules in the middle atmosphere by precipitating electrons is sufficient to affect O₃ depletion. In addition, PET will complement studies of the elemental and isotopic composition of energetic heavy (Z>2) nuclei on SAMPEX by providing measurements of H, He, and electrons. Finally, PET has limited capability to identify energetic positrons from potential natural and man-made sources     

The effect of composition on the formation of light-emitting Si nanostructures in SiOx layers on irradiation with swift heavy ions

The SiO _x layers different in composition (0 < x < 2) are irradiated with Xe ions with the energy 167 MeV and the dose 10¹⁴ cm⁻² to stimulate the formation of light-emitting Si nanostructures. The irradiation gives rise to a photoluminescence band with the parameters dependent on x. As the Si content is increased, the photoluminescence is first enhanced, with the peak remaining arranged near the wavelength λ ≈ 600 nm, and then the peak shifts to λ ≈ 800 nm. It is concluded that the emission sources are quantum-confined nanoprecipitates formed by disproportionation of SiO _x in ion tracks due to profound ionization losses. Changes in the photoluminescence spectrum with increasing x are attributed firstly to the increase in the probability of formation of nanoprecipitates and then to the increase in their dimensions; the latter effect is accompanied with a shift of the emission band to longer wavelengths. The subsequent quenching of photoluminescence is interpreted as a result of the removal of quantum confinement in nanoprecipitates and their coagulation.     

Interrelation of equivalent values for linear energy transfer of heavy charged particles and the energy of focused laser radiation

The estimations of equivalent values for linear energy transfer of heavy charged particles based on the results of experimental investigations of sensitivity of LSICs to local radiation effects with the use of the procedure of local laser irradiation are presented. The possibility of recalculation of the energy of laser radiation into equivalent values of linear energy transfer with the use of the measurements of the ionization reaction in the supply circuit of LSIC is substantiated. Uncertainties caused by the characteristics of the interaction of optical radiation with semiconductor structures are eliminated in the suggested procedure.     

Comparison of the sensitivity to heavy ions of SRAM's in differentSIMOX technologies

We propose a simple model to evaluate the sensitivity to heavy ions of SRAM's in different CMOS/SIMOX technologies. The critical Linear Energy Transfer LETc and the asymptotic cross section σ characterize the sensitivity of a memory. Theoretical values of LETc and σ are calculated according to intrinsic characteristics of the technology (thickness of the silicon layer, lateral bipolar amplification) and design parameters of the memory, LETc and σ are then compared to experiments     

重离子诱导的电荷共享以及MBU敏感性的温度特性

The temperature dependence of charge sharing in a 130 nm CMOS technology has been investigated over a temperature range of 200 to 420 K.Device simulation results show that the charge sharing collection increases by 66%-325% when the temperature rises.The LETth of a MBU in two SRAM cells and one DICE cell is also quantified.Besides charge sharing, the circuit response＇s temperature dependence also has a significant influence on the LETth.     

Temperature dependence of charge sharing and MBU sensitivity induced by a heavy ion

e LETth of a MBU in two SRAM cells and one DICE cell is also quantified. Besides charge sharing, the circuit response's temperature dependence also has a significant influence on the LETth.