Time-dependent dielectric wearout technique with temperature effect for reliability test of ultrathin (<2.0 nm) single layer and dual layer gate oxides

Ultrathin gate oxide is essential for low supply voltage and high drive current for ULSI devices. The continuous scaling of oxide thickness has been a challenge on reliability characterization with conventional time-dependent dielectric breakdown (TDDB) technique. A new technique, the time-dependent dielectric wearout (TDDW), is proposed as a more practical and effective way to measure oxide reliability and breakdown compared to conventional TDDB methodology. The wearout of oxide is defined as the gate current reaches a critical current density with the circuit operating voltage level. It is shown that although a noisy soft breakdown always exists for ultrathin oxide, with constant-voltage stressing, a big runaway can also be observed for oxides down to 1.8 nm by monitoring the I–V characteristics at a reduced voltage. Devices are found still working after soft breakdowns, but no longer functional after the big runaway. However, by applying E-model to project dielectric lifetime, it shows that the dielectric lifetime is almost infinity for the thermal oxide at 1.8 nm range. It is also demonstrated that the dual voltage TDDW technique is also able to monitor the breakdown mechanism for nitride/oxide (N/O) dual layer dielectrics.     

Quantitative luminescence mapping of Cu(In,Ga)Se2 thin‐film solar cells

We investigate photoluminescence and electroluminescence (PL and EL) emission images from Cu(In,Ga)Se₂‐based solar cells by means of a Hyperspectral Imager. Using the generalized Planck's law, maps of the effective quasi‐Fermi level splitting Δμ_eff in absolute values are obtained. A good agreement is found between the spatially averaged splitting in PL and the global open‐circuit voltage. However, from a local carrier transport discussion, we conclude that the equality does not hold locally. The spatial variations are rather attributed to local depth variations of the quasi‐Fermi level splitting due to material properties spatial fluctuations. By comparing PL and EL emissions, we discuss qualitatively the local effective lifetimes and collection efficiencies. Copyright © 2014 John Wiley & Sons, Ltd.     

Fluid analysis of a TCP connection over ABR

This paper reports on an analytical study of the performances of the ATM‐ABR service category in transporting TCP/IP flows over an ATM network. We explore the behavior of a TCP connection over an ATM‐ABR VC, in presence of exogenous non‐controlled traffic. This fluid analysis of the system allows the study of the interaction between the window‐based end‐to‐end flow control TCP protocol and the rate‐based flow control ABR mechanism, which is restricted to the ATM part of the network. The main aim of this study is to give performance evaluation formulae to model the behavior of such a TCP over ABR connection. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mapping of generalized template matching onto reconfigurable computers

Image processing algorithms for template matching, two-dimensional (2-D) digital filtering, morphologic operations, and motion estimation share some common properties. They can all benefit from using reconfigurable computers that use coprocessor boards based on field-programmable gate array (FPGA) chips. This paper characterizes those applications as generalized template matching (GTM) operations and describes the mapping of the GTM operations onto reconfigurable computers. A three-step approach is described. The first two steps enumerate and prune the design space of basic GTM building blocks, which consist of FPGA buffers and GTM computation cores. The last step is to achieve a solution through an optimal combination of these building blocks where the cost function is the FPGA computation time and the constraints are FPGA coprocessor board resources. Various FPGA buffers are presented so as to introduce design options of basic GTM building blocks. Algorithms used for the mapping are described. Experimental results are summarized to reveal the relationship between the GTM mapping results and FPGA board resource parameters.     

Structural Stabilities and Elastic Thermodynamic Properties of SrTe Compound and SrTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Alloy Under High Pressure

The effect of pressure on the structural, elastic, and thermodynamic properties of SrTe in both B1 (rocksalt) and B2 (CsCl-type) phases and the SrTe_1?x Ca _x alloys with Ca dopant concentrations at x = 0.16667, 0.20, 0.33333, 0.42857, 0.44444 and 0.50 have been investigated using the two new gradient-corrected functional developed by Perdew, J.P.; Burke, K.; Ernzerhof named Density-Gradient Expansion for Exchange in Solids (PBEsol) and generalized Wu–Cohen (WC), in a significant range of pressure from 0 GPa to 30 GPa. The structure parameters, elastic stiffness constants c _ij , the bulk modulus (B), Kleinman parameter (\( \xi \)), shear anisotropies A _shear are also determined. Furthermore, as reported in this study, the aggregate elastic modulus (B, G, E), Poisson’s ratio (ν) and the Lame’s coefficients (λ) are estimated. On the other hand, the ductility, brittleness, longitudinal, transverse sound velocities and the Debye temperature Θ_D(T) are also obtained. Importantly, our results are in reasonable agreement with the available theoretical and experimental data. To the best of our knowledge, this is the first study of the effect of the composition on the properties of the SrTe_1?x Ca _x alloys which may encourage other works for the confirmation of the reported results.     

Use of signal processing imaging for the study of a 3D package in harsh environment

Assembly technologies follow the reduction in size of circuit board components and correlatively the number of active layers increases significantly. Therefore, during a conventional acoustic analysis, the obtained image becomes more and more complicated to analyze. In a previous paper, we focused our research on a method for a suitable visualization of the timescale of an acoustic signal (CWT). In this paper we present the use of the non-destructive control for the study of a 3D package submitted to accelerated ageing tests using harsh conditions.     

Electrically Activated Paper Actuators

This paper describes the design and fabrication of electrically controlled paper actuators that operate based on the dimensional changes that occur in paper when the moisture absorbed on the surface of the cellulose fibers changes. These actuators are called “Hygroexpansive Electrothermal Paper Actuators” (HEPAs). The actuators are made from paper, conducting polymer, and adhesive tape. They are lightweight, inexpensive, and can be fabricated using simple printing techniques. The central element of the HEPAs is a porous conducting path (used to provide electrothermal heating) that changes the moisture content of the paper and causes actuation. This conducting path is made by embedding a conducting polymer (PEDOT:PSS) within the paper, and thus making a paper/polymer composite that retains the porosity and hydrophilicity of paper. Different types of HEPAs (straight, precurved, and creased) achieved different types of motions (e.g., bending motion, accordion type motion). A theoretical model for their behavior is proposed. These actuators have been used for the manipulation of liquids and for the fabrication of an optical shutter.     

Cooperative localization techniques for wireless sensor networks: free,signal and angle based techniques

This paper addresses the problem of localization in sensor networks where, initially, a certain number of sensors are aware of their positions (either by using GPS or by being hand‐placed) and are referred to as anchors. Our goal is to localize all sensors with high accuracy, while using a limited number of anchors. Sensors can be equipped with different technologies for signal and angle measurements. These measures can be altered by some errors because of the network environment that induces position inaccuracies. In this paper, we propose a family (AT‐Family) of three new distributed localization techniques in wireless sensor networks: free‐measurement (AT‐Free) where sensors have no capability of measure, signal‐measurement (AT‐Dist) where sensors can calculate distances, and angle‐measurement (AT‐Angle) where sensors can calculate angles. These methods determine the position of each sensor while indicating the accuracy of its position. They have two important properties: first, a sensor node can deduce if its estimated position is close to its real position and contribute to the positioning of others nodes; second, a sensor can eliminate wrong information received about its position. This last property allows to manage measure errors that are the main drawback of measure‐based methods such as AT‐Dist and AT‐Angle techniques. By varying the density and the error rate, simulations show that the three proposed techniques achieve good performances in term of high accuracy of localized nodes and less energy consuming while assuming presence of measure errors and considering low number of anchors. Copyright © 2012 John Wiley & Sons, Ltd.     

Interfacial Strain Gradients Control Nanoscale Domain Morphology in Epitaxial BiFeO3 Multiferroic Films

Domain switching pathways fundamentally control performance in ferroelectric thin film devices. In epitaxial bismuth ferrite (BiFeO₃) films, the domain morphology is known to influence the multiferroic orders. While both striped and mosaic domains have been observed, the origins of the latter have remained unclear. Here, it is shown that domain morphology is defined by the strain profile across the film–substrate interface. In samples with mosaic domains, X‐ray diffraction analysis reveals strong strain gradients, while geometric phase analysis using scanning transmission electron microscopy finds that within 5 nm of the film–substrate interface, the out‐of‐plane strain shows an anomalous dip while the in‐plane strain is constant. Conversely, if uniform strain is maintained across the interface with zero strain gradient, striped domains are formed. Critically, an ex situ thermal treatment, which eliminates the interfacial strain gradient, converts the domains from mosaic to striped. The antiferromagnetic state of the BiFeO₃ is also influenced by the domain structure, whereby the mosaic domains disrupt the long‐range spin cycloid. This work demonstrates that atomic scale tuning of interfacial strain gradients is a powerful route to manipulate the global multiferroic orders in epitaxial films.