Design and Simulation of Short Channel Si:HfO2 Ferroelectric Field Effect Transistor (FeFET)

Non-volatile memories using ferroelectric capacitors, known as Ferroelectric Random Access Memory (FRAM) have been studied for many years, but they suffer from loss of data during read out process. Ferroelectric Field Effect Transistors (FeFETs), which are based on ferroelectric gate oxide, have been of recent interest for non-volatile memory applications. The FeFETs utilize the polarization of the ferroelectric layer incorporated into the transistor gate stack to control the channel conductivity. Therefore, in FeFET devices, the read out process is non-destructive because it is only processed by measuring the resistivity in the channel region. The drain current-gate voltage (ID-VG) characteristics of FeFETs exhibit a voltage shift due to polarization hysteresis known as the memory window , an important figure of merit of a FeFET that provides a window for the read voltage. A dielectric layer between semiconductor layer and the ferroelectric is required to reduce charge injection effect, and to compensate lattice mismatch between the ferroelectric and the semiconductor. In addition, a non-ferroelectric interfacial layer may form between the semiconductor and the ferroelectric layer. However, this dielectric layer causes a voltage drop since the system becomes equivalent to two serial capacitors. It also causes an electric field that opposes the polarization. Using a high permittivity material such as HfO2 reduces the voltage drop and the effect of depolarization. To date, the majority of the work involving FeFETs has been based on conventional ferroelectric materials such as Lead Zirconate Titanate (PZT) and Strontium Bismuth Tantalate (SBT). These materials are not compatible with standard IC processing and furthermore scaling thicknesses in PZT and SBT result in loss of polarization characteristics. Recently, ferroelectricity has been reported in doped hafnium oxide thin films with dopants such as Si, Al, and Gd. Particularly, silicon doped hafnium oxide (Si:HfO2) has shown promise. In this material, the remnant polarization considerably increases by decreasing the layer thickness. The lower permittivity of Si:HfO2 compared to that of PZT and SBT, allows to employ thinner films that reduce fringing effects. This study focuses on employing Si:HfO2 in short channel FeFETs. The study has two major objectives. First, to show that short channel FeFETs can be accomplished with large memory window. Second, to demonstrate the role of bulk layer thickness and permittivity on FeFET performance. N-channel metal oxide semiconductor FET (N-MOSFET) with printed channel length of 26 nm has been designed with Si:HfO2 as the ferroelectric layer, and TiN as the gate electrode. The effects of buffer layer thickness and permittivity and ferroelectric layer thickness on the memory window have been explored using Silvaco Atlas software that employs ferroelectric FET device physics developed by Miller et al. Polarization characteristics reported for Si:HfO2 have been incorporated in this model. The simulations performed in this study have shown that using Si:HfO2 as a ferroelectric material makes it possible to accomplish short channel FeFETs with good performance even without using buffer layers. This means it is possible to minimize depolarization effects. Using Si:HfO2 as a ferroelectric layer makes it possible to accomplish highly scaled and ultra-low-power FeFETs

Annual Report Readability And Corporate Bankruptcy

This study investigates the relationship between a firm’s annual report readability and its probability of bankruptcy. Findings show that firms with a larger 10-K file size have a higher probability of bankruptcy. More specifically, we suggest that there is a curvilinear relationship between annual report readability and bankruptcy probability. However, this relation is not significant for small firms. We further suggest that annual report readability has incremental power in predicting corporate bankruptcy. While prior accounting and finance research mainly used financial and accounting ratios as predictive variables of firm bankruptcy, we add a new non-financial predictive variable to these models

Tool-Based Design and Evaluation of Resilient Flight Control Systems

Communications engineering / telecommunication

Resistivity during cycle loading of fine grain heat affected zone (HAZ) of 17CrNiMo7 steel prepared into laboratory furnace

Structural components which are loaded in cyclic load mostly fail due to fatigue. The fatigue strength of metals as well as weld joint regions in metals depends on mechanical properties especially hardness, the size of defect and the size of grains. Resistivity of the fine grain HAZ prepared against fatigue crack initiation will be explained in this article. Samples of material with martensitic fine grain microstructure were prepared by laboratory furnace by proper thermal treatment. Mechanical properties of fine grain heat affected zone and its microstructure were investigated. Special attention was given to behavior of fine grain during the cycle loading under stress concentration. Stress concentration was similar to the one in real welds. The S-N curve and the fatigue limit were determined. The Paris curve and the threshold for crack propagating were also determined

Chapter Tool-Based Design and Evaluation of Resilient Flight Control Systems

Communications engineering / telecommunication

La publication d'une information financière non conforme à la loi et aux normes : déterminants et conséquences

Dans la mesure où il existe une certaine ambiguïté dans la définition de plusieurs concepts relevant de ce que nous appelons l’information non conforme à la loi et aux normes, cet article propose une synthèse générale, fondée sur la théorie de l’agence et établie à partir des littératures française et nord-américaine, sur les déterminants et les conséquences de cette information financière non conforme. Les auteurs étudient également l’efficacité des mécanismes de gouvernance utilisés pour prévenir ou détecter ces pratiques qui vont au-delà d’une gestion « stratégique » des données comptables.Fraude; gestion des données comptables; retraitement; gouvernance