Silica to Silicon: Key Carbothermic Reactions and Kinetics

The primary carbothermic reactions for the reduction of silica to produce silicon were defined and the reaction kinetics were determined. Most possible reactions between silicon oxide and carbon or carbon compounds were studied by a series of thermogravimetric analyses at temperatures up to 2000°C. Four key sequential reactions occur with SiC and SiO as intermediate reactants; two reactions involve SiO₂ and two involve SiO. Reaction rate versus temperature, activation energy, and preexponential factors were determined for each of six reactions involving SiO₂ or SiO. These kinetic studies show that SiO, when combined with either carbon or Sic, reacts in the gaseous state, and the sublimation of SiO is not the rate-limiting reaction for forming silicon.     

Artifact removal in magnetoencephalogram background activity with independent component analysis

The aim of this study was to assess whether independent component analysis (ICA) could be valuable to remove power line noise, cardiac, and ocular artifacts from magnetoencephalogram (MEG) background activity. The MEGs were recorded from 11 subjects with a 148-channel whole-head magnetometer. We used a statistical criterion to estimate the number of independent components. Then, a robust ICA algorithm decomposed the MEG epochs and several methods were applied to detect those artifacts. The whole process had been previously tested on synthetic data. We found that the line noise components could be easily detected by their frequency spectrum. In addition, the ocular artifacts could be identified by their frequency characteristics and scalp topography. Moreover, the cardiac artifact was better recognized by its skewness value than by its kurtosis one. Finally, the MEG signals were compared before and after artifact rejection to evaluate our method.     

Exciton-polaritons in nanostructured nitride superlattices

In this work we study the propagation of exciton-polaritons (bulk and surface modes) in a binary superlattice ABAB…, truncated at z=0, where z is defined as the growth axis. Here A is the spatially dispersive medium, which alternates with a common dielectric medium B (sapphire-Al₂O₃). The excitonic medium (A) is modelled by a semiconductor from the nitride's family (III-V semiconductor) that has, as a main characteristic, a wide-direct gap. The exciton-polariton spectrum is determined, in both s and p-polarization, by using standard electromagnetic boundary conditions, together with an additional boundary condition (ABC) for the Wannier-Mott excitons, employing a transfer-matrix formalism to simplify the algebra. The dispersion relation shows a bottleneck profile for the superlattice modes, whose behavior is similar to those found in the bulk crystal. Furthermore, interesting properties are revealed from the ABC as well as from different ratios of the thickness of the two superlattices alternating materials.     

An asynchronous finite-state-machine-based buck-boost converter for on-chip adaptive power supply

In this paper we present an asynchronous finite-state machine digital controller co-integrated with an on-chip non-inverting buck-boost power converter with dynamic signal-tracking capabilities. The mostly-digital controller functionally implements a non-PWM zone-wise control law through asynchronous circuitry, thus exhibiting self-timed minimum latency and ultra low power operation due to gate switching activity. Experimental results on a 0.35 μm CMOS technology demonstrate an efficiency up to 80 % with a switching frequency of 2.86 MHz.     

A distributed data storage protocol for heterogeneous wireless sensor networks with mobile sinks

This paper presents ProFlex, a distributed data storage protocol for large-scale Heterogeneous Wireless Sensor Networks (HWSNs) with mobile sinks. ProFlex guarantees robustness in data collection by intelligently managing data replication among selected storage nodes in the network. Contrarily to related protocols in the literature, ProFlex considers the resource constraints of sensor nodes and constructs multiple data replication structures, which are managed by more powerful nodes. Additionally, ProFlex takes advantage of the higher communication range of such powerful nodes and uses the long-range links to improve data distribution by storage nodes. When compared with related protocols, we show through simulation that Proflex has an acceptable performance under message loss scenarios, decreases the overhead of transmitted messages, and decreases the occurrence of the energy hole problem. Moreover, we propose an improvement that allows the protocol to leverage the inherent data correlation and redundancy of wireless sensor networks in order to decrease even further the protocol’s overhead without affecting the quality of the data distribution by storage nodes.     

Coupled drift-diffusion/quantum transmitting boundary methodsimulations of thin oxide devices with specific application to a siliconbased tunnel switch diode

We present a method of coupling drift-diffusion simulations with quantum transmitting boundary method (QTBM) tunnel current calculations. This allows self-consistent simulation of thin oxide devices in which large tunnel currents can flow. Simulated results are presented for a thin oxide Al/SiO₂/Si structure and an Al/SiO₂/n-Si/p-Si tunnel switching diode. We demonstrate the careful use of the recombination lifetime as an adjustable or relaxable parameter in order to obtain converging solutions     

Adhesion studies of CVD copper metallization

The adhesion of chemical vapor deposition (CVD) Cu thin films to various barriers was observed to improve with a post-deposition anneal or a physical vapor deposition (PVD) Cu flash layer on the barrier before depositing CVD Cu. The ambient exposure of the barrier before the deposition of CVD Cu has been observed to lead to degradation of adhesion in both CVD Cu seed and CVD/PVD Cu high vacuum integrated metallization schemes. The integrated CVD and PVD Cu deposition scheme exhibits better adhesion due to the inherent annealing provided during the PVD deposition which is carried out at temperatures between 300 and 400°C. We have evaluated both qualitative and quantitative tests — tape test, Stud pull test and 4-point bend test — in understanding adhesion and observed that each of these tests give different details of interface breakdown.     

Onde de frange pour une discontinuité de courbure

The fringe wave is defined, following the physical theory of diffraction, as the difference between the total field and the field radiated by the physical optics currents. This concept is generalised to the case of the discontinuity in the curvature. It is necessary, to get a finite result for normal incidence, to define the fringe wave as the difference between the total field and the field radiated by the two first terms of the current given by the Luneburg-Kline development. Explicit formulas are given, for the perfectly conducting and for the impedance boundary condition cases.     

Ion sensitive field effect transistor modelling for multidomain simulation purposes

The proper design and simulation of modern electronic microsystems oriented towards environment monitoring requires accurate models of various ambient sensors. In particular, this paper presents a comprehensive model of an ion sensitive field effect transistor (ISFET). The model can be employed straightforwardly for simulations at device, circuit or system level.First, the model was validated with electrical measurements and simulations of real structures performed for different ion concentration and temperature values. Then, the ISFET sensor model was employed for mixed-signal simulations in VHDL-AMS, when the analysis of a microsystem consisting of the ISFET sensor and a sigma-delta analogue-to-digital converter was carried out. Additionally, the presence of other ions than hydrogen in the measured solution was also taken into account in the simulations.