Generation of Minimum Leakage Input Vectors with Constrained NBTI Degradation

Technology scaling has caused Negative Bias Temperature Instability (NBTI) to emerge as a major circuit reliability concern. Simultaneously leakage power is becoming a greater fraction of the total power dissipated by logic circuits. As both NBTI and leakage power are highly dependent on vectors applied at the circuit’s inputs, they can be minimized by applying carefully chosen input vectors during periods when the circuit is in standby or idle mode. Unfortunately input vectors that minimize leakage power are not the ones that minimize NBTI degradation, so there is a need for a methodology to generate input vectors that minimize both of these variables.This paper proposes such a systematic methodology for the generation of input vectors which minimize leakage power under the constraint that NBTI degradation does not exceed a specified limit. These input vectors can be applied at the primary inputs of a circuit when it is in standby/idle mode and are such that the gates dissipate only a small amount of leakage power and also allow a large majority of the transistors on critical paths to be in the “recovery” phase of NBTI degradation. The advantage of this methodology is that allowing circuit designers to constrain NBTI degradation to below a specified limit enables tighter guardbanding, increasing performance. Our methodology guarantees that the generated input vector dissipates the least leakage power among all the input vectors that satisfy the degradation constraint. We formulate the problem as a zero-one integer linear program and show that this formulation produces input vectors whose leakage power is within 1% of a minimum leakage vector selected by a search algorithm and simultaneously reduces NBTI by about 5.75% of maximum circuit delay as compared to the worst case NBTI degradation. Our paper also proposes two new algorithms for the identification of circuit paths that are affected the most by NBTI degradation. The number of such paths identified by our algorithms are an order of magnitude fewer than previously proposed heuristics.

Effect of microalloying with rare-earth elements on the texture of extruded magnesium-based alloys

A series of alloys have been produced with microalloying additions of rare-earth (RE) elements in the range of 0.1–0.4 wt.%. The alloys have been extruded to produce grain sizes of 23 ± 5 μm. The texture of the extruded alloys was measured, and it was found that the extrusion texture was weakened by the addition of RE elements. The samples with weakened extrusion textures exhibited an increase in the tensile elongation.

Grain refinement of an extruded Mg alloy via na microalloying

The effect of 0.3 wt pct Na on the microstructure of extruded alloy Mg-2Sn-1Zn is examined. We report that Na stabilizes the Mg2Sn phase, resulting in its precipitation during extrusion under conditions where a solid solution is otherwise expected. This effect appears to be thermodynamic in nature and is different from the kinetic enhancement of low- temperature aging reported by Mendis et al. [Phil. Mag. Letters, 86 (2006), 443]. The precipitates of the current study enable useful refinement of the grain size.

Morphological study of nitrides of NbTi (50:50, by weight) alloy

Plates of NbTi (50:50, by weight) were nitrided in a nitrogen atmosphere in the temperature range 800-1000 °C for 15, 30, 60, 120 and 180 min. X-Ray diffraction and optical and electronic microscopy were used to characterize the samples. Two nitride layers were identified on the substrate: an external and continuous phase of TiN, named δ, and a deeper and discontinuous phase of Ti 2N, named ε{lunate}. The electron micrographs reveal the presence of paths rich in Nb which may be responsible for the diffusion of nitrogen into the matrix. © 1993.

Vanadium microalloying for ultra-high strength steel sheet treated by hot-dip metallising

Ultra-high strength steel sheets have been subjected to heat treatments that simulate the thermal cycles in hot-dip galvanising and galvannealing processes and evaluated with respect to their resulting mechanical properties and microstructures. The steels contained suitable contents of carbon (∼0.2%), manganese (1.2%) and chromium (0.4%) to ensure that they could be fully transformed to martensite after austenitisation followed by rapid cooling in a continuous annealing line, prior to galvanising. Different contents of vanadium (0–0.1%) and nitrogen (0.002–0.012%) were used to investigate the possible role of these microalloying elements on the strength of the tempered martensite. Vanadium, especially when in combination with a raised nitrogen content, helps to resist the effect of tempering so that a larger proportion of the initial strengthening is preserved after the galvanising cycle, giving tensile strength levels exceeding 1000 MPa. Different deoxidation practices using aluminium or silicon have also been included. These showed similar strength levels at corresponding carbon contents but the bendability of the Si-killed steel sheet was considerably superior. Microstructural examinations have been made on the annealed steels but the reason for the beneficial effect of vanadium is still not fully explained. It is concluded that microalloying with vanadium is a very promising approach in the development of corrosion-resistant ultra-high strength steel sheet products.

Methods of patterning magnetic fields using bulk superconductors

High Temperature superconductors are able to carry very high current densities, and thereby sustain very high magnetic fields. There are many projects which use the first property and these have concentrated on power generation, transmission and utilization, however there are relatively few which are currently exploiting the ability to sustain high magnetic fields. There are two main reasons for this: high field wound magnets can and have been made from both BSCCO and YBCO but currently their cost is much higher than the alternative provided by low Tc materials such as Nb3Sn and NbTi. An alternative form of the material is the bulk form which can be magnetized to high fields and using flux pumping this can be done in situ. This paper explores some of the applications of bulk superconductors and describes methods of producing field patterns using the highly uniform magnetic fields required for MRI and accelerator magnets as the frame of reference. The patterns are not limited to uniform fields and it is entirely possible to produce a field varying sinusoidally in space such as would be required for a motor or a generator. The scheme described in this paper describes a dipole magnet such as is found in an accelerator magnet. The tunnel is 30 × 50 × 1000 mm and we achieve a uniformity of better than 200 ppm over the 1000 mm length and better than 1 ppm over the central 500 mm region. The paper presents results for both the overall uniformity and the integrated uniformity which is 302 ppm over the 1000 mm length. © 2010 IEEE.

A finite element model of magnetization of superconducting bulks using a solid-state flux pump

Superconductors have a bright future; they are able to carry very high current densities, switch rapidly in electronic circuits, detect extremely small perturbations in magnetic fields, and sustain very high magnetic fields. Of most interest to large-scale electrical engineering applications are the ability to carry large currents and to provide large magnetic fields. There are many projects that use the first property, and these have concentrated on power generation, transmission, and utilization; however, there are relatively few, which are currently exploiting the ability to sustain high magnetic fields. The main reason for this is that high field wound magnets can and have been made from both BSCCO and YBCO, but currently, their cost is much higher than the alternative provided by low-Tc materials such as Nb3Sn and NbTi. An alternative form of the material is the bulk form, which can be magnetized to high fields. This paper explains the mechanism, which allows superconductors to be magnetized without the need for high field magnets to perform magnetization. A finite-element model is presented, which is based on the E-J current law. Results from this model show how magnetization of the superconductor builds up cycle upon cycle when a traveling magnetic wave is induced above the superconductor. © 2011 IEEE.

A 3 Tesla Superconducting Magnet for Hall Sensor Calibration

A 3 T superconducting magnet with a 70 mm diameter warm bore and energy storage of 47 kJ has been successfully fabricated and tested, which can be used to calibrate Hall sensors in high magnetic field as well as conduct superconducting experiments. The magnet consists of three solenoid coils and an iron yoke. The homogeneity of the magnetic field in the region of interest (ROI) is +/- 6.0 x 10(-5). The coils of the magnet were fabricated with NbTi-Cu superconducting wire and the stray magnetic field is shielded by an iron yoke. The coils and yoke are fully immersed in a helium vessel. The optimized structural design, stress and quench simulation, fabrication and test results are presented in this paper.

3T超导螺线管的研制

超导螺线管广泛应用于核磁共振仪、粒子探测器等设备。本文设计了中心场值为3T，中心附近Φ30mm区域内均匀度达到1×10-4的超导螺线管。磁体线圈采用多芯NbTi-Cu复合超导线绕制，并利用铁轭屏蔽漏场。磁体采用温孔冷铁轭、全浸泡冷却方式结构。同时，为了减少辐射漏热，采用液氮冷屏、真空多层绝热结构。 本文重点对带有冷铁轭的超导螺线管的磁场进行了优化设计。设计过程中结合了专业磁场计算软件OPERA和多种优化方法。线圈采用六次槽型结构，利用遗传算法和优选法优化线圈尺寸；铁轭采用正交试验设计优化尺寸。 利用有限元软件ANSYS对超导磁体进行电磁力分析，并且对降温后线圈、支撑筒和箍筒的热应力进行了模拟计算。估算了支撑系统的传导漏热、磁体的辐射漏热以及剩余气体漏热。详细介绍了超导磁体绕制工艺，超导磁体液氦杜瓦的加工工艺，并且对杜瓦的绝热工艺进行了介绍。最后介绍了超导螺线管的总体加工进展

Optimisation du traitement thermomécanique de pièces d’acier fabriquées par métallurgie des poudres

Le forgeage de préformes fabriquées par métallurgie des poudres nous permet d’atteindre une densification voisine de la densité théorique ce qui a comme incidence directe une amélioration substantielle des propriétés mécaniques finales des pièces, notamment la résistance en fatigue. La démarche préconisée pour améliorer cette performance critique de pièces forgées par métallurgie des poudres consiste à optimiser leurs caractéristiques métallurgiques et leur densité concomitante. À ce propos, une nouvelle formulation d’acier MP a été développée et caractérisée. La stratégie de développement portait sur l’utilisation d’éléments de microalliage préalliés, comme le vanadium et le niobium. Pour ce faire, on a optimisé le paramètre de mise en œuvre primordial, qui est la température de forgeage, afin d’obtenir une fine taille de grains à la fin du cycle du traitement réalisé accompagnée d’une densité élevée des pièces forgées. Une série de traitements d’austénisation sur une gamme étendue de température variant entre 900 °C à 1250 °C a été effectuée ce qui nous a permis par la suite de connaître, pour chaque mélange, l’évolution de la taille des grains en fonction de la température d’austénisation. La nouvelle formulation de composition chimique a démontré un impact marqué quant au contrôle de la taille de grains en fonction de la température d’austénitisation. Une étude comparative nous a permis d’identifier la température de forgeage la plus appropriée pour ce type de pièces et de dégager la méthodologie à suivre en fonction des propriétés mécaniques et microstructurales.

Hardenability reduction in VN microalloyed eutectoid steels

By dilatometry, it is shown that vanadium microalloying additions to eutectoid carbon steels, which also contain an increased level of nitrogen, cause a marked decrease in hardenability when transforming from fine grained austenite.

Ultrafine grained structure formation in steels using dynamic strain induced transformation processing

The refinement of ferrite grain size is the most generally accepted approach to simultaneously improve the strength and toughness in steels. Historically, the level of ferrite refinement is limited to 5-10 μm using conventional industrial approaches. Nowadays, though, several thermomechanical processes have been developed to produce ferrite grain sizes of 1-3 μm or less, ranging from extreme thermal and deformation cycles to more typical thermomechanical processes. The present paper reviews the status of the production of ultrafine grained steels through relatively simple thermomechanical processing. This requires deformation within the Ae3 to Ar3 temperature range for a given alloy. Here, the formation of ultrafine ferrite (UFF) involves the dynamic transformation of a significant volume fraction of the austenite to ferrite. This dynamic strain induced transformation (DSIT) arises from the introduction of extensive intragranular nucleation sites that are not present in conventional controlled rolling. The DSIT route has the potential to be adjusted to suit current industrial infrastructure. However, there are a number of significant issues that have been raised, both as gaps in our understanding and as obstacles to industrial implementation. One of the critical issues is that it appears that very large strains are required. Combined with this concern is the issue of whether a combination of dynamic and static transformation can be used to achieve an adequate level of refinement. Another issue that has also become apparent is that grain sizes of 1 μm can lead to low levels of ductility and hence many workers are attempting to obtain 2-3 μm grains, or to introduce a second phase to provide the required ductility. There are also a number of areas of disagreement between authors including the role of dynamic recrystallisation of ferrite in the production of UFF by DSIT, the reasons for the low coarsening rate of UFF grains, the role of microalloying elements and the effects of austenite grain size and strain rate. The present review discusses these areas of controversy and highlights cases where experimental results do not agree.

Modeling of the mechanical behavior of nanostructured HSLA steels

In the present paper the basic strengthening mechanisms operating in microstructures are discussed with respect to their application in submicron/nano materials. This analysis focuses on these strengthening mechanisms in bcc microstructures, where the effect of grain boundaries is very strong. An experimental study of the influence of the thermomechanical history on the microstructure and dislocation substructure was performed using two different grades of HSLA steels. As a result, a modified version of the Khan–Huang–Liang flow stress model (KHL) was developed and is discussed in the light of results from the present study. Comparison with experimental results showed significant diversity in the refinement and mechanical responses of each steel, due to different activity of strengthening mechanisms and microalloying elements in the microstructure evolution process. The effect of mechanical and microstructural inhomogeneity in severe plastic deformation (SPD) on the deformation induced grain refinement and mechanical properties was also considered.