1,721,090 research outputs found
Modeling the uniform transport in thin film SOI MOSFETs with a Monte-Carlo simulator for the 2D electron gas
No full textIn this paper, we present simulations of some of the most relevant transport properties of the inversion layer of ultra-thin film
SOI devices with a self-consistent Monte-Carlo transport code for a confined electron gas. We show that size induced quantization
not only decreases the low-field mobility (as experimentally found in [Uchida K, Koga J, Ohba R, Numata T, Takagi S. Experimental
eidences of quantum-mechanical effects on low-field mobility, gate-channel capacitance and threshold voltage of ultrathin body
SOI MOSFETs, IEEE IEDM Tech Dig 2001;633–6; Esseni D, Mastrapasqua M, Celler GK, Fiegna C, Selmi L, Sangiorgi E. Low
field electron and hole mobility of SOI transistors fabricated on ultra-thin silicon films for deep sub-micron technology application.
IEEE Trans Electron Dev 2001;48(12):2842–50; Esseni D, Mastrapasqua M, Celler GK, Fiegna C, Selmi L, Sangiorgi E, An experimental
study of mobility enhancement in ultra-thin SOI transistors operated in double-gate mode, IEEE Trans Electron Dev
2003;50(3):802–8. [1–3]]), but also the electron saturation velocity and the carrier heating depend on the subband structure, and thus
on the silicon film thickness
Macroscopic and microscopic picture of negative capacitance operation in ferroelectric capacitors
No full textThe negative capacitance (NC) operation of ferroelectric materials has been originally proposed based on a homogeneous Landau theory, leading to a simple NC stabilization condition expressed in terms of macroscopic quantities. A multi-domain theory, however, has pointed out the importance of microscopic parameters, such as the domain wall energy coupling constant, and it helped explain the somewhat contradicting experiments for ferroelectric capacitors with or without a metal interlayer. In this work we use comprehensive numerical simulations and simplified equations to correlate the macroscopic features of the NC operation to the underlying microscopic picture. We show that, while the domain wall coupling constant plays a critical role in a quasi static operation, the transient NC operation is less sensitive to this parameter. In particular, ferroelectric capacitors with a very small coupling constant can still display a robust transient NC behavior, closely tracking the 'S'-shaped polarization versus field curve and with negligible hysteresis. Our results have been developed in the framework of a systematic comparison between simulations and experiments, and they provide both a better understanding of the NC operation and a sound basis for the design of future NC based devices. This journal i
Fullband quantization analysis reveals a third valley in (001) silicon inversion layers
No full textThis letter presents calculations of the silicon two-dimensional (2-D) band structure obtained by accounting for the fullband energy dispersion of the three-dimensional silicon crystal, as derived from the non-local-pseudopotential method. The most interesting result is the identification of a third valley for the 2-D electron gas in the [001] quantization direction, besides the two families of subbands (the unprimed and primed ones) universally considered according to the effective mass approximation
Operation and Design of Ferroelectric FETs for a BEOL Compatible Device Implementation
Full text linkWe present a study based on numerical simulations and comparative analysis of recent experimental data concerning the operation and design of FeFETs. Our results show that a proper consideration of charge trapping in the ferroelectric-dielectric stack is indispensable to reconcile simulations with experiments, and to attain the desired hysteretic behavior of the current-voltage characteristics. Then we analyze a few design options for polysilicon channel FeFETs and, in particular, we study the influence of the channel thickness and doping concentration on the memory window, and on the ratio between the polarization dependent, high and low resistance state
Full-Band Quantum Transport of Heterojunction Electron Devices with Empirical Pseudopotentials
No full textThis article presents the methodology, implementation, and application of a full-band quantum transport model based on the nonequilibrium Green's function formalism and the empirical pseudopotentials. In particular, this article reports the treatment of heterojunctions between lattice-matched semiconductors, comprising a gradual transition region described according to a virtual crystal approximation. Our approach entails several numerical techniques to make the full-band quantum transport method computationally affordable and thus enable robust and efficient self-consistent device simulations. Then, we employ our simulation scheme for the analysis of some exemplary devices based on quantum tunneling, such as an Esaki tunneling diode, as well as n- and p-type heterojunction tunnel FETs. In particular, we investigate the influence on the current-voltage characteristics of the width of the heterojunction transition region. We observe that a gradual transition region mainly affects the device characteristics by lengthening the tunneling path at the heterojunction, which has a different impact on device current depending on the external bias conditions
Multi-level Operation of FeFETs Memristors: The Crucial Role of Three Dimensional Effects
No full textThis paper investigates and compares through a comprehensive TCAD analysis 2D and 3D simulations for ferro-electric based FETs. We provide clear evidence that the multiple read conductance values experimentally observed in FeFETs stem from source to drain percolation current paths, which are governed by the polarization patterns in the ferroelectric domains. Such a physical picture makes 3D simulations indispensable to capture even the qualitative features of the device behaviour, not to mention the quantitative aspects
Multilevel Operation in Scaled Back-End-of-Line Ferroelectric FETs With a Metal Interlayer
Full text linkMulti-level operation, conventionally obtained in ferroelectric devices thanks to a domain-dependent inhomogeneous polarization, poses a big challenge for highly-scaled ferroelectric devices, where the number of ferroelectric domains is drastically reduced. In this work, we study a highly scaled back-end-of-line (BEOL) compatible, ferroelectric field-effect transistor (FeFET) that integrates a metal interlayer in the gate stack. Through analytical models and calibrated TCAD simulations, we show how this device can achieve a multi-level operation exploiting the interplay between the ferroelectric polarization and the charge in the metal interlayer. Such a working principle does not rely on a domain-dependent inhomogeneous polarization, and the device operation is thus ensured also for a homogeneous ferroelectric material. We also demonstrate that the charge in the interlayer can effectively stabilize the ferroelectric polarization even in the absence of a high concentration of trapped charges in the gate stack. The potentiation and depression curves for the readout conductance confirm that the proposed device can be operated as a memristor for neuromorphic computing applications. Moreover, we show how the choice of the dielectric in the metal-ferroelectric-dielectric-metal gate stack can be used as a design knob to reduce the device operation voltage
On the extraction of the channel current in permeable gate oxide MOSFETs
No full textIt is a common practice to extract the channel current in permeable gate MOSFETs as the average of the source and drain currents. This paper analyzes the extraction error associated to this procedure by means of theoretical calculations, measurements in a nMOS technology with 1.5 nm oxide thickness and a simple distributed model of the permeable gate MOSFET. The main dependencies of the extraction error on the bias conditions, the oxide thickness and the channel length are discussed in detail
Stability of self-consistent Monte Carlo Simulations: effects of the grid size and of the coupling scheme
No full textComprehensive Analysis of Graphene Geometric Diodes: Role of Geometrical Asymmetry and Electrostatic Effects
Full text linkA self-consistent Monte Carlo/3-D Poisson simulator has been developed to analyze the current asymmetry in graphene geometric diodes. The model couples ballistic transport in the graphene layer with 3-D electrostatics in the graphene and oxide substrate. Results are given in terms of transmission coefficients and currents at the two terminals of the diode. We prove that while the current asymmetry is mainly induced by ballistic transport in the asymmetric structure, the electrostatics plays a relevant role that tends to substantially counterbalance the geometrical effect
- …
