SRAM dynamic stability estimation using MPFP and its applications

In this paper, an accurate approach for estimating the dynamic stability of static random access memory (SRAM) is proposed. The conventional methods of SRAM stability estimation suffer from two major drawbacks: (1) using static failure criteria, such as SNM, which does not capture the transient and dynamic behavior of SRAM operation, and (2) using quasi-Monte-Carlo simulation, which approximates the failure distribution, resulting in large errors at the tails where the desired failure probabilities exist. These drawbacks are eliminated by employing accurate simulation-based dynamic failure criteria along with a new distribution-independent, Most-probable-failure-point search technique for accurate probability calculation. Compared to previously published techniques, the proposed dynamic stability technique offers orders of magnitude improvement in accuracy. Furthermore, the proposed dynamic stability technique enables the correct evaluation of stability in real operation conditions and for different dynamic circuit techniques, such as dynamic write back, where the conventional methods are not applicable.     

非挥发性记忆体Read Disturb测试方法的研究

DDF是一种高容量的NAND Flash。以DDF产品为例,研究和讨论了它的Read Disturb测试方法。受测试时间的限制,只能选择局部的存储区间进行DDF的Read Disturb测试。这样局部区间的测试结果是否能够代表整个芯片的性能,设计了一套实验,对这个课题进行了研究和讨论。依据非挥发性记忆体产品的特性,主要以阈值电压的分布为参考来评价DDF芯片性能的一致性和性能恶化趋势的一致度。最后的实验结果证明了这种测试方法的正确性和合理性。这种分析方法也可以用于其他非挥发性记忆体产品的其他可靠性测试项目的评估。     

Design and analysis of noise margin,write ability and read stability of organic and hybrid 6-T SRAM cell

This paper analyzes SRAM cell designs based on organic and inorganic thin film transistors (TFTs). The performance in terms of static noise margin (SNM), read stability and write ability for all-p organic (Pentacene–Pentacene), organic complementary (Pentacene–C₆₀) and hybrid complementary (Pentacene–ZnO) configurations of SRAM cell is evaluated using benchmarked industry standard Atlas 2-D numerical device simulator. Moreover, the cell behaviour is analyzed at different cell and pull-up ratios. The electrical characteristics and performance parameters of individual TFT used in SRAM cell is verified with reported experimental results. Furthermore, the analytical result for SNM of all-p organic SRAM cell is validated with respect to the simulated result. Besides this, the cell and pull-up ratios of the hybrid and organic SRAM cells are optimized for achieving best performance of read and write operations and thereafter, the results are verified analytically also. The SNM of hybrid cell is almost two times higher than the all-p SRAM, whereas this improvement is just 18% in comparison to the organic memory cell. On the other hand, the organic complementary SRAM cell shows an improvement of 26% and 22% for the read stability in comparison to the all-p organic and hybrid SRAM cells, respectively. Contrastingly, this organic cell demonstrates a reduction of 16% in the SNM and an increment of 76% in write access time in comparison to the hybrid cell. To achieve an overall improved performance, the organic complementary SRAM cell is designed such that the access transistors are pentacene based p-type instead of often used n-type transistor. Favorably, this organic SRAM design shows reasonably lower write access time in comparison to the cell with n-type access OTFTs. Moreover, this cell shows adequate SNM and read stability that too at substantially lower width of p-type access OTFTs.     

On the entropy method and exponential convergence to equilibrium for a recombination–drift–diffusion system with self-consistent potential

We consider a Shockley–Read–Hall recombination–drift–diffusion model coupled to Poisson’s equation and subject to boundary conditions, which imply conservation of the total charge. As main result, we derive an explicit functional inequality between relative entropy and entropy production rate, which implies exponential convergence to equilibrium with explicit constant and rate. We report that the key entropy–entropy production inequality ought rather not to be formulated on the states space of the parabolic–elliptic system, but on the reduced states space of the associated nonlocal drift–diffusion problem, where the Poisson equation is replaced by the corresponding Green function.     

嵌入式存储器内建自测试时间的优化

存储器测试是集成电路测试的重要部分。随着集成电路存储器件向着高集成度发展,存储器测试成本在集成电路总测试成本中所占比例急剧增高。通过减少存储器测试时间来减小存储器测试成本,是一种高效的降低芯片测试成本的方法。本文以一款单周期同步存储器为例,选取读写时序为对象,详细分析了存储器内建自测试方法,给出了一种通过优化存储器内建自测试逻辑时序来减小存储器测试时间的设计实现方法。     

基于DSP和模糊逻辑技术的超声波干扰探测器US0012

US0012是一种基于数字信号处理器和模糊逻辑技术的高性能智能化超声波干扰探测器集成电路。它具有价格低、适用面广、便于安装等优点，可广泛用于车辆内部的安全系统。文中介绍了US0012的主要特点和功能原理，给出了US0012的典型应用电路及其连接方法。     

X波段硅里德型双漂移崩越二极管外延材料

采用全外延工艺，研制了Ｘ波段里德型双漂移崩越二极管所需πｐｎγＮ￣＋多层外延材料，分析了各过渡区的形成机理及减小其宽度的方法，实现了陡峭的杂质浓度分布。     

The mechanisms governing the activation of dislocation sources in aluminum at different strain rates

This article examines the time to activate Frank–Read sources in response to macroscopic strain rates ranging from 10¹ s⁻¹ to 10¹⁰ s⁻¹ in aluminium under athermal conditions. We develop analytical models of the bowing of a pinned dislocation segment as well as numerical simulations of three dimensional dislocation dynamics. We find that the strain rate has a direct influence on both the activation time and the source strength of Frank–Read sources at strain rates up to 10⁶ s⁻¹, and the source strength increases in almost direct proportion to the strain rate. This contributes to the increase in the yield stress of materials at these strain rates. Above 10⁶ s⁻¹, the speed of the bowing segments reaches values that exceed the domain of validity of the linear viscous drag law, and the drag law is modified to account for inertial effects on the motion of the dislocation. As a result the activation times of Frank–Read sources reach a finite limit at strain rates greater than 10⁸ s⁻¹, suggesting that Frank–Read sources are unable to operate before homogeneous nucleation relaxes elastic stresses at the higher strain rates of shock loading. Elastodynamic calculations are carried out to compare the contributions of Frank–Read sources and homogeneous nucleation of dislocations to plastic relaxation. We find that at strain rates of 5×10⁷ s⁻¹ homogeneous nucleation becomes the dominant generation mechanism.     

Improvement of magnetic intergranular isolation and evaluation of read/write characteristics on SmCo5 perpendicular magnetic thin films

SmCo₅ alloy is a promising candidate for ultra-high-density perpendicular magnetic recording (PMR) media because of its high uniaxial magnetocrystalline anisotropy K_u of more than 1.1×10⁸ erg/cm³. Previously, we successfully achieved high K_u in a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, in order to apply the SmCo₅ films to practical PMR media, it is necessary to decrease medium noise. A granulated magnetic film comprising of small and magnetically decoupled grains is effective in reducing the medium noise. In this paper, we have proposed a new granular film that is fabricated by partial thermodiffusion of Cu between the Sm-Co continuous layer and the Cu underlayer, which is granulated using compositional segregation caused by the addition of Ta₂O₅. We have analyzed the magnetic properties, magnetic domain size, and magnetization reversal process of the proposed SmCo₅ film. The magnetic domain size decreased and the magnetization reversal process changed from the magnetic-wall-motion mode to a coherent rotation mode to some extent on isolation of magnetic grains. The read/write characteristics of granulated SmCo₅ double-layered media were also evaluated. The medium noise decreased and the signal-to-noise ratio increased for the granulated double-layered (PMR) medium.     

Divergences without probability vectors and their applications

In general, divergences and measures of information are defined for probability vectors. However, in some cases, divergences are ‘informally’ used to measure the discrepancy between vectors, which are not necessarily probability vectors. In this paper we examine whether divergences with nonprobability vectors in their arguments share the properties of probabilistic or information theoretic divergences. The results indicate that divergences with nonprobability vectors share, under some conditions, some of the properties of probabilistic or information theoretic divergences and therefore can be considered and used as information measures. We then use these divergences in the problem of actuarial graduation of mortality rates. Copyright © 2009 John Wiley & Sons, Ltd.