A Physics-Based TCAD Simulator for Superconducting Electronics Based on Josephson Junctions

Topological phase transitions in free fermion systems can be characterized by closing of single-particle gap and change in topological invariants. However, in the presence of electronic interactions, topological phase transitions are more complicated. In paper I of this series (arXiv:1510.07816), we have developed an efficient scheme to evaluate the topological invariants based on Green's function formalism. Here, in paper II, we demonstrate four interaction-drive topological phase transitions (TPTs) in two-dimensional (2D) interacting topological insulators (TIs) via large-scale quantum Monte Carlo (QMC) simulations, based on the scheme of evaluating topological invariants presented in paper I. Across these transitions, the defining symmetries of the TIs have been neither explicitly nor spontaneously broken. In the first two models, the topological invariants calculated from Green's function formalism succeed in characterizing interaction-driven TPTs. However, in the second two models, we find single-particle gap does not close and the topological invariants constructed from single-particle Green's function acquire no change across the TPTs. Unexpected breakdown of the Green's function formalism in constructing topological invariants is thus discovered. We thence classify the TPTs in interacting TIs into two categories: those have noninteracting correspondence can be characterized successfully by the topological invariants constructed from Green's functions, while for the others that do not have noninteracting correspondence, the Green's function formalism experiences a breakdown but more interesting and exciting phenomena, such as emergent collective critical modes at the transition, arise. Discussion on the success and breakdown of topological invariants constructed from the Green's function formalism in the context of symmetry protected topological (SPT) states is presented.

Herein, a highly practical first‐principles approach for studying phonon transport across various materials, ranging from low‐dimensional systems to three‐dimensional bulk structures, as well as nanostructures, is presented. This method integrates the nonequilibrium Green's function (NEGF) formalism with ab initio calculations of dynamical matrices generated by Quantum Espresso. A detailed technical approach for extracting atomistic force constants and forming dynamical matrices that adhere to the tri‐diagonal technique within the NEGF framework is provided. Additionally, an efficient method for constructing dynamical matrices of conventional cells from those of primary cells is introduced, remarkably reducing the computational costs associated with density‐functional theory calculations. The robustness and applicability of this methodology are validated through several case studies.

We propose a physics-based analytical model that accurately captures the effects of buffer traps on dc characteristics of gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs). The model is then semi-analytically extended to additionally include the transient behavior. Analytical formulations for the shift in the threshold voltage <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${(}{V}_{\text {OFF}}{)}$ </tex-math></inline-formula> and two-dimensional electron gas (2-DEG) density due to the presence of buffer traps in the steady state are presented. In pulsed operation, technology computer-aided design (TCAD) simulations indicate that a time-dependent negative potential (NP) is developed under the gate, resulting in a modified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {OFF}}$ </tex-math></inline-formula> and current collapse (CC). An expression for the modified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {off}}$ </tex-math></inline-formula> helps capture the pulsed current–voltage characteristics. The model captures the dependence of bias, time, temperature, trap concentration, capture cross section area, and activation energy of traps on the steady-state and transient characteristics. The model is implemented in Verilog-A in an existing compact model framework using a diode and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> sub-circuit and validated using measured data and TCAD simulations. The modeling results are in excellent agreement with the experimental data and TCAD simulations. Since the model is physics-based, it requires fewer number of parameters compared to that in the existing models.

Study of parasitic oscillation of a multi-chip SiC MOSFET circuit based on a signal flow graph model by TCAD simulation

TFETs (Tunnel Field-Effects Transistors) are assumed to be ultra-low-power devices because they have steep subthreshold swing and a more favourable scaling characteristic. Their electrical characteristics, however, cannot be adequately simulated using extensive Technology Computer-Aided Design (TCAD) simulations, which are computationally intensive and time-consuming to analyze. In an attempt to overcome this bottleneck, a proposal for a machine learning (ML)-based surrogate modeling framework is provided where the prediction of the critical TFET properties of transfer curves, Ion, Ioff, threshold voltage (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text{th}}$</tex>), and subthreshold swing (SS) is endeavored with the help of the Random Forest Regression (RFR) model. The data collected based on TCAD simulations and literature reports was processed, trained, and tested on various ML models such as the Artificial Neural Networks (ANN), Support Vector Regression (SVR) and RFR. The calculated R2 of the proposed RFR model was better than ANN and SVR, with a much smaller MSE (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{3. 2 1} \times \mathbf{1 0}^{-\mathbf{7}}$</tex>) and an RMSE (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1. 7 9} \times \mathbf{1 0}^{-\mathbf{4}}$</tex>), showing that the model is robust and exhibits better generalization within the conditions of the devices used. Also, the ranking of intrinsic feature importance offered by RFR has a better interpretation rate and complies well with the previous findings on TCAD. These findings place RFR as a sound and efficient substitute for TFET modelling, with lower computational expense and intact physical stability, and thus add another facet and a practical approach to future device design optimization, assisted by a novel and powerful ML

This paper describes the point defect treatment in nanowire MOSFETs. The 3D Poisson equation is self-consistently coupled to the Schrodinger equation. We adopt the mode-space representation in which the 3D Schrodinger equation is divided into a 2D equation, including the confinement of the cross-section, and an ID equation describing the ballistic transport based on the nonequilibrium Green's function formalism (NEGF). We use the simplest form of the tight-binding theory, with one orbital per atom, and considering only the first-neighbor-interactions. In this framework, equivalent to the ellipsoidal energy band approximation, influence of point defects on electronic transport is discussed.

The electronic structure of transition metal tricarbonyl derivatives in the ground state and the cationic hole-states. A semiempirical indo mo investigation based on the Green's function formalism

This work evaluates the potential impact of interface traps on the interface of oxide and semiconductor on a 2-D-based ion-sensitive field-effect transistor (ISFET) using a surface potential-based model and Technology Computer-Aided Design (TCAD) simulation calibrated for pH sensing applications. The electrolyte/oxide interface in the proposed 2-D ISFET model is modeled using the Guoy-Chapman–Stern technique and the site binding association model. The baseline field-effect transistor (FET) of the ISFET is modeled using Fermi-Dirac statistics to obtain surface potential, which is further used to derive a compact drain current expression. The proposed ISFET model development is carried out by accounting for the interface trap effect. The voltage and current sensitivity of ISFET with and without interface traps are calculated to demonstrate the impact of interface traps in 2-D material-based pH sensors. It is observed that voltage sensitivity remains close to the Nernst limit (59 mV/pH), and a decrease in current sensitivity from 34 to 2 nA/pH is observed, as the density of interface traps is varied from 0 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${5}\times {10} {^{{12}}}$ </tex-math></inline-formula>cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-}2 $ </tex-math></inline-formula>eV<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-}1 $ </tex-math></inline-formula>. Another sensitivity metric, the transconductance to drain current ratio, is analyzed for its variation with changes in the density of interface traps. The noise level of ISFET in the presence of interface traps is analyzed, and its influence on the minimum resolvable pH is demonstrated. The proposed model prediction closely matches the TCAD simulation data obtained from a calibrated TCAD simulation setup. The model is suitable for implementation in Verilog-A for ISFET-based circuit simulation, and the impact of interface traps on the response time of ISFET-based circuits is also demonstrated.

A functionally enhanced transistor is a potential candidate for further advancing electronics and Moore's law beyond the classical scaling. This chapter discusses these kinds of multifunctional transistors called reconfigurable field-effect transistor (RFET) and reconfigurable tunnel field-effect transistor (RTFET). The RFET works on the principle of Schottky barrier tunneling, and the RTFET works on the principle of band-to-band tunneling. Both devices can be configured as an n-type and p-type device based on the biasing. This chapter explains the working and performance comparison of RFET and RTFET in detail with the help of technology computer-aided design (TCAD) simulations. Further, the potential and current models of a single-gated RFET and double-gated RTFET are presented in this chapter. The presented analytical models are compared and verified with TCAD simulations. The potential in the channel regions of RFET and RTFET is modeled by solving a two-dimensional (2D) Poisson's equation. Because the working principle of both devices is different, two different formulas are utilized for modeling the current in the device. The current model for the RFET is developed by integrating Landauer's formula, whereas the current model for RTFET is obtained by integrating band-to-band generation rate over the tunneling volume. The procedure, technique, and assumptions followed to obtain the potential and current models of RFET and RTFET are detailed in this chapter.

Charge transport properties of a diffusive normal metal /triplet\nsuperconductor (DN/TS) junction are studied based on the Keldysh-Nambu\nquasiclassical Green's function formalism. % Contrary to the unconventional\nsinglet superconductor junction case, the mid gap Andreev resonant state (MARS)\nat the interface of the TS is shown to enhance the proximity effect in the DN.\n% The total resistance of the DN/TS junction is drastically reduced and is\ncompletely independent of the resistance of the DN in the extreme case. % Such\nanomalous transport accompanies a giant zero-bias peak in the conductance\nspectra and a zero-energy peak of the local density of states in the DN region.\n% These striking features manifest the presence of novel proximity effect\npeculiar to triplet superconductor junctions.\n

Second breakdown current (It2) is an important merit of Electrostatic discharge (ESD) protection devices, and it is especially critical for high voltage ESD design. The device physics involved in ESD phenomena are highly complex as ESD devices operate at high current condition within a short period of time. Technology Computer Aided Design (TCAD) simulation offers faster design optimization and quantitative evaluation of robustness, which can significantly improve ESD device’s robustness. However, an accurate TCAD simulation requires accurate modelling of sophisticated device physics. Due to the ESD’s high stress nature, understanding and modelling of such device physics are non-trivial. We applied TCAD 2D simulation to a high voltage Silicon-controlled Rectifier (SCR), 2D simulation to diode and 3D simulation to diode with different sizes. Based on comparisons of two ESD modes (HBM and CDM) and two transmission line pulses (TLP and VFTLP) simulation data, the simulation method is self-consistent and shows effective It2 prediction ability. The above-mentioned TCAD simulation method can help accelerate design iteration of ESD design and find more optimized ESD device structures.

In this paper, technology computer aided design (TCAD) was applied to optimize the fabrication process to reduce the parasitic capacitance of PMOS transistor at the source/drian (S/D) junction (Cj) in developing the 65 nm low leakage (65 nmLL) technology. It was found that Cj can be effectively reduced by combining relative high-energy well implant and proper threshold voltage (Vt) implant method. Through measured data and TCAD simulation, this paper also demonstrates a ?doping compensation effect? by tuning Vt and Halo implants with proper species, energy, and dosage, to achieve the Cj reduction.

We extend the self-consistent Green's functions formalism to take into account three-body interactions. We analyze the perturbative expansion in terms of Feynman diagrams and define effective one- and two-body interactions, which allows for a substantial reduction of the number of diagrams. The procedure can be taken as a generalization of the normal ordering of the Hamiltonian to fully correlated density matrices. We give examples up to third order in perturbation theory. To define nonperturbative approximations, we extend the equation of motion method in the presence of three-body interactions. We propose schemes that can provide nonperturbative resummation of three-body interactions. We also discuss two different extensions of the Koltun sum rule to compute the ground state of a many-body system.

Several ultrasound-based techniques for the estimation of soft tissue elasticity are currently being investigated. Most of them study the medium response to dynamic excitations. Such responses are usually modeled in a purely elastic medium using a Green's function solution of the motion equation. However, elasticity by itself is not necessarily a discriminant parameter for malignancy diagnosis. Modeling viscous properties of tissues could also be of great interest for tumor characterization. We report in this paper an explicit derivation of the Green's function in a viscous and elastic medium taking into account shear, bulk, and coupling waves. From this theoretical calculation, 3D simulations of mechanical waves in viscoelastic soft tissues are presented. The relevance of the viscoelastic Green's function is validated by comparing simulations with experimental data. The experiments were conducted using the supersonic shear imaging (SSI) technique which dynamically and remotely excites tissues using acoustic radiation force. We show that transient shear waves generated with SSI are modeled very precisely by the Green's function formalism. The combined influences of out-of-plane diffraction, beam shape, and shear viscosity on the shape of transient waves are carefully studied as they represent a major issue in ultrasound-based viscoelasticity imaging techniques.

The electron-gas problem is investigated by means of a self-consistent Green's-function formalism with the aim of developing practical approximation schemes for metallic densities. The work is based on the Dyson equation for the single-particle propagator $G[U]$ as a functional of an external potential $U$. The self-energy functional $\ensuremath{\Sigma}[U]$, appearing in the Dyson equation, is evaluated by perturbation theory in terms of the exact $G[U]$, thereby leading to a self-consistent problem. A hierarchy of approximations is generated by summing successively larger sets of graphs for $\ensuremath{\Sigma}[U]$. The Dyson equation is expanded in a functional Taylor series in $U$ and yields a nonlinear integral equation for the $U=0$ propagator as well as linear integral equations for the $U=0$ higher-order Green's functions, with kernels dependent on $\frac{\ensuremath{\delta}\ensuremath{\Sigma}}{\ensuremath{\delta}U}$. In applications of the theory, the emphasis is on calculating the longitudinal dielectric function $\ensuremath{\epsilon}$ in terms of the contracted four-point Green's function. The linear integral equation for the latter is solved after making a low-momentum dominance approximation to the kernel. The result is a general, but approximate, closed-form expression for $\ensuremath{\epsilon}$ which can be used for different choices of $\ensuremath{\Sigma}$. The following five approximations for $\ensuremath{\epsilon}$, based on different approximations for $\ensuremath{\Sigma}$, are presented: the Hartree-Fock, random-phase, generalized random-phase, second-stage random-phase, and low-high-density approximations. The last approximation is designed to work well at the two extremes of the density spectrum and, hopefully, also at metallic densities. The long-wavelength plasmon dispersion relations obtained from two different versions of the generalized random-phase approximation for $\ensuremath{\epsilon}$ agree closely with the results of Kanazawa et al. and of Singwi et al.