1,721,090 research outputs found
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
On the accuracy of the formula used to extract trap density in MOSFETs from 1/f noise
No full textNoise spectroscopy is a powerful non-destructive technique to characterize the quality of gate dielectrics in MOSFETs. Trap densities are routinely extracted by fitting the 1/f part of the drain current noise spectrum with a widely known analytical expression containing several approximations within. This paper compares this 1/f noise analytical expression with microscopic simulations, evaluates its accuracy under different scenarios, and highlights when the main assumptions fall short. It is found that the expression agrees well with non-radiative multi-phonon (NMP) models at room temperature for devices featuring a thick dielectric. However, the formula fails to correctly predict the noise of nowadays aggressively scaled devices, because it neglects trapping/de-trapping with the gate electrode and the electrostatic charge scaling of the traps due to their distance from the channel
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
General model and equivalent circuit for the chemical noise spectrum associated to surface charge fluctuation in potentiometric sensors
Full text linkThis paper firstly reports a general and powerful approach to evaluate the power spectral density (PSD) of the surface charge fluctuations, so-called “chemical noise”, from a generic set of reactions at the sensing surface of potentiometric sensors such as, for instance, Ion-Sensitive Field Effect Transistors (ISFETs). Starting from the master equation, the spectral noise signature of a reaction set is derived as a function of the reaction kinetic parameters and of the interface concentration of the ionic species. Secondly, we derive an equivalent surface admittance, whose thermal noise PSD produces a noise PSD equal to that of the surface charge fluctuations. We also show how to expand this surface admittance into stair-case RC networks, with a number of elementary cells equal to the number of surface reactions involved. This admittance can be included in circuit simulations coupled with a SPICE compact model of the underlying FET, to enable the physically based modelling of frequency dispersion and noise of the sensing layer when simulating the sensor and the read-out. Validation with existing models and literature results as well as new application examples are provided. The proposed methodology to compute the PSD from rate equations is amenable to use in different contexts where fluctuations are generated by random transitions between discrete states with given exchange rates
Critical overview and comparison between models for adsorption-desorption noise in bio-chemical sensors
Full text linkWe critically review existing models for the adsorption-desorption noise in bio-chemical sensors, in particular the model based on simplified forward Kolmogorov equation and the models based on Langevin sources. For the latter models, we propose a generalized version to handle cases beyond the branched surface reactions (a binding site that can be alternatively occupied by different ions/molecules) and the chained reaction (a binding site that sequentially binds with ions/molecules). The models are benchmarked against kinetic Monte Carlo (kMC) simulations considering relevant case studies such as pH-sensitive ions, selective molecules binding on a functionalized surface and multi-layer adsorption on bare surfaces. It is found that although the mathematical formulation of the modeling approaches appears different, when dealing with independent binding sites, they are fully equivalent and perfectly match the kMC results. The case of competitive binding considering the correlation between the occupation of the binding sites has also been analyzed
General Approach to Model the Surface Charge Induced by Multiple Surface Chemical Reactions in Potentiometric FET Sensors
Full text linkWe propose a general methodology to calculate the individual sensitivity and the cross-sensitivities of potentiometric sensor devices (e.g., ion sensitive FETs (ISFETs), CHEMFETs) with an arbitrary number of non-interacting receptors binding to ionic species or analytes in the electrolyte. The surface charge generated at the (bare or functionalized) interface with the electrolyte is described by the Poisson equation coupled to a linear system of equations for each type of receptor, where the unknowns are the fractions of sites binding with a given ion/analyte. Our general model encompasses in a unique framework a few simple special cases so far separately reported in the literature and provides for them closed-form expressions of the average site occupation probability. Detailed procedural description of the usage and benefits of the model is shown for specific cases with concurring surface chemical reactions
Importance of Charge Trapping/Detrapping Involving the Gate Electrode on the Noise Currents of Scaled MOSFETs
No full textCarrier trapping/detrapping from/to the gate into dielectric traps is often neglected when modeling noise in MOSFETs and, to the best of our knowledge, no systematic study of its impacts on scaled devices is available. In this article, we show that this trapping mechanism cannot be neglected in nowadays aggressively scaled gate dielectric thicknesses without causing errors up to several orders of magnitude in the estimation of the drain current noise. The noise generation mechanism is modeled analytically and then analyzed through the use of 2-D and 3-D TCAD simulations of scaled MOSFETs with different architectures and channel/gate-stack materials. The results provide new insights for technology and device designers, highlight the relevance of the choice of the gate metal work function (WF) and the role of valence band electron trapping at high gate voltages
Stability of self-consistent Monte Carlo Simulations: effects of the grid size and of the coupling scheme
No full textBenchmarking of 3-D MOSFET Architectures: Focus on the Impact of Surface Roughness and Self-Heating
Full text linkTremendous improvements in the fabrication
technology have allowed to scale the physical dimensions
of the transistors and also to develop different promising
3-D architectures that may allow continuing Moore’s law.
In this paper, we perform a comparative delay analysis of different
3-D device architectures and study the impact of surface
roughness and self-heating on the on-current using a
comprehensive in-house simulation framework comprising
Schrödinger, Poisson, and Boltzmann transport equation
solvers and comprising relevant scattering mechanisms
and self-heating. Our results highlight that parasitic capacitance
can alter the relative ranking of the architectures from
delay point of view. We demonstrate that surface roughness
can cause architectureand material-dependentcurrent
degradation, and hence, it is necessary to account for it in
simulation-based benchmarking different architectures
Accurate Nonlocal Impact Ionization Models for Conventional and Staircase Avalanche Photodiodes derived by Full Band Monte Carlo Transport Simulations
Full text linkWe present a procedure to extract the nonlocal impact ionization coefficients in Avalanche Photodiodes (APDs) operating in the linear regime from Full Band Monte Carlo simulations. The Monte Carlo calculations have been calibrated on existing experimental data for GaAs p-i-n APDs with different thickness of the intrinsic region. Inspection of impact ionization generation rate in p-i-n and staircase GaAs APDs led us to identify the limitations of existing nonlocal-history dependent impact ionization models. The introduction of an energy dependent relaxation length for the computation of the effective fields significantly improves the model accuracy in predicting the gain and noise associated to conduction and valence band steps in staircase APDs without additional computational burden. This improved nonlocal-history dependent model is thus a powerful tool to design and optimize APDs with different architectures
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