arXiv subjects

Arnout Beckers

Publications and source records attributed to Arnout Beckers.

14 recordsLinked to original sources

arXiv2025

Theoretical Limit of MOSFET Subthreshold Swing at Sub-Kelvin Temperatures

Fully conductive band tails cause the subthreshold swing to saturate at temperatures above 1 K. However, recent measurements indicate that below 1 K, the subthreshold swing in certain MOSFET structures resumes a linear scaling with temperature. Following this ultra-steep behavior, a new type of plateau has been measured below 1 K. In this letter, we show that hybrid band tails, with both traps and mobile states, explain this new plateau. Furthermore, hybrid band tails explain various non-saturating behaviors above 1 K. Remarkably, for entirely non-conductive band tails, the simulations and theory predict a third type of plateau below 10 mK. We hypothesize that this represents the lower bound of subthreshold swing at sub-Kelvin temperatures, which is a testable prediction from the theory.

cond-mat.mes-hall↗

arXiv2025

Subthreshold Swing Behavior in Amorphous Indium-Gallium-Zinc-Oxide Transistors from Room to Cryogenic Temperatures

While cryogenic-temperature subthreshold swing (SS) in crystalline semiconductors has been widely studied, a careful study on the temperature-dependent SS in amorphous oxide semiconductors remains lacking. In this paper, a comprehensive analysis of the SS in thin-film transistors with an amorphous indium gallium zinc oxide (IGZO) channel at temperatures from 300 K down to 4 K is presented. Main observations include: 1) At room temperature (300 K), the devices exhibit a SS of 61 mV/dec, and a low interface trap density (<1011 cm-2), among the best reported values for IGZO devices. 2) A SS saturation around 40 mV/dec is observed between 200 K and 100 K. It is well explained by the electron transport via band tail states with exponential decay (Wt) of 13 meV. 3) At deep-cryogenic temperature, SS increase significantly exceeding 200 mV/dec at 4 K. Such high SS values are actually limited by the measurement current range, confirmed by Id-Vg simulations based on the variable range hopping (VRH) model. This work not only elucidates the SS behavior in amorphous IGZO devices but also provides a deep understanding of the physical mechanisms of electron transport in amorphous semiconductors.

cond-mat.mtrl-sci↗

arXiv2023

Generalized Boltzmann relations in semiconductors including band tails

Boltzmann relations are widely used in semiconductor physics to express the charge-carrier densities as a function of the Fermi level and temperature. However, these simple exponential relations only apply to sharp band edges of the conduction and valence bands. In this article, we present a generalization of the Boltzmann relations accounting for exponential band tails. To this end, the required Fermi-Dirac integral is first recast as a Gauss hypergeometric function, followed by a suitable transformation of that special function, and a zeroth-order series expansion using the hypergeometric series. This results in simple relations for the electron and hole densities that each involve two exponentials. One exponential depends on the temperature and the other one on the band-tail parameter. The proposed relations tend to the Boltzmann relations if the band-tail parameters tend to zero. This work comes timely for the modeling of classical semiconductor devices at cryogenic temperatures for large-scale quantum computing.

physics.app-ph↗

arXiv2023

Inflection Phenomenon in Cryogenic MOSFET Behavior

This brief reports the analytical modeling and measurements of the inflection in the MOSFET transfer characteristics at cryogenic temperatures. Inflection is the inward bending of the drain current versus gate voltage, which reduces the current in weak and moderate inversion at a given gate voltage compared to the drift-diffusion current. This phenomenon is explained by introducing a Gaussian distribution of localized states centered around the band edge. The localized states are attributed to disorder and interface traps. The proposed model allows to extract the density of localized states at the interface from the dc current measurements.

cond-mat.mes-hall↗

arXiv2023

Physics-Based and Closed-Form Model for Cryo-CMOS Subthreshold Swing

Cryogenic semiconductor device models are essential in designing control systems for quantum devices and in benchmarking the benefits of cryogenic cooling for high-performance computing. In particular, the saturation of subthreshold swing due to band tails is an important phenomenon to include in low-temperature analytical MOSFET models as it predicts theoretical lower bounds on the leakage power and supply voltage in tailored cryogenic CMOS technologies with tuned threshold voltages. Previous physics-based modeling required to evaluate functions with no closed-form solutions, defeating the purpose of fast and efficient model evaluation. Thus far, only the empirically proposed expressions are in closed form. This article bridges this gap by deriving a physics-based and closed-form model for the full saturating trend of the subthreshold swing from room down to low temperature. The proposed model is compared against experimental data taken on some long and short devices from a commercial 28-nm bulk CMOS technology down to 4.2 K.

cond-mat.mes-hall↗

arXiv2022

Robust Simulation of Poisson's Equation in a P-N Diode Down to 1 μK

Semiconductor devices are notoriously difficult to simulate at deep-cryogenic temperatures. The lowest temperature that can be simulated today in commercial TCAD is around 4.2 K, possibly 100 mK, while most experimental quantum science is performed at 10 mK or lower. Besides the challenges in transport solvers, one of the main bottlenecks is the non-convergence in the electrostatics due to the extreme sensitivity to small variations in the potential. This article proposes to reformulate Poisson's equation to take out this extreme sensitivity and improve convergence. We solve the reformulated Poisson equation for a p-n diode using an iterative Newton-Raphson scheme, demonstrating convergence for the first time down to a record low temperature of one microkelvin using the standard IEEE-754 arithmetic with double precision. We plot the potential diagrams and resolve the rapid variation of the carrier densities near the edges of the depletion layer. The main Python functions are presented in the Appendix.

cond-mat.mes-hall↗

arXiv2022

Bounded Distribution Functions for Applied Physics, Especially Electron Device Simulation at Deep-Cryogenic Temperatures

Numerical underflow and overflow are major hurdles for rolling-out the modeling and simulation infrastructure for temperatures below about 50 K. Extending the numeric precision is computationally intensive and thus best avoided. The root cause of these numerical challenges lies in the Fermi-Dirac, Bose-Einstein, and Boltzmann distribution functions. To tackle their extreme values, bounded distribution functions are proposed which are numerically safe in a given precision, yet identical to the standard distributions at the physical level. These functions can help to develop electron device models and TCAD software handling deep-cryogenic temperatures in the default double precision, to keep pace with the rapid experimental progress. More broadly, they can apply to other branches of applied physics with similar numerical challenges as well.

cond-mat.mes-hall↗

arXiv2019

Revised theoretical limit of subthreshold swing in field-effect transistors

This letter reports a temperature-dependent limit for the subthreshold swing in MOSFETs that deviates from the Boltzmann limit at deep-cryogenic temperatures. Below a critical temperature, the derived limit saturates to a value that is independent of temperature and proportional to the extent of a band tail. Since the saturation is universally observed in different types of MOSFETs (regardless of dimension or semiconductor material), the band tail is attributed to the finite periodicity of the lattice in a semiconductor volume, and to a lesser extent to additional lattice perturbations such as defects or disorder.

cond-mat.mes-hall↗

arXiv2019

A Review on Quantum Computing: Qubits, Cryogenic Electronics and Cryogenic MOSFET Physics

Quantum computing (QC) has already entered the industrial landscape and several multinational corporations have initiated their own research efforts. So far, many of these efforts have been focusing on superconducting qubits, whose industrial progress is currently way ahead of all other qubit implementations. This paper briefly reviews the progress made on the silicon-based QC platform, which is highly promising to meet the scale-up challenges by leveraging the semiconductor industry. We look at different types of qubits, the advantages of silicon, and techniques for qubit manipulation in the solid state. Finally, we discuss the possibility of co-integrating silicon qubits with FET-based, cooled front-end electronics, and review the device physics of MOSFETs at deep cryogenic temperatures.

quant-ph↗

arXiv2019

Cryogenic MOSFET Threshold Voltage Model

This paper presents a physics-based model for the threshold voltage in bulk MOSFETs valid from room down to cryogenic temperature (4.2 K). The proposed model is derived from Poisson's equation including bandgap widening, intrinsic carrier-density scaling, and incomplete ionization. We demonstrate that accounting for incomplete ionization in the expression of the threshold voltage is critical for an accurate estimation of the current. The model is validated with our experimental results from nMOSFETs of a 28-nm CMOS process. The developed model is a key element for a cryo-CMOS compact model and can serve as a guide to optimize processes for high-performance cryo-computing and ultra-low-power quantum computing.

physics.app-ph↗

arXiv2018

Characterization and Modeling of 28-nm FDSOI CMOS Technology down to Cryogenic Temperatures

This paper presents an extensive characterization and modeling of a commercial 28-nm FDSOI CMOS process operating down to cryogenic temperatures. The important cryogenic phenomena influencing this technology are discussed. The low-temperature transfer characteristics including body-biasing are modeled over a wide temperature range (room temperature down to 4.2\,K) using the design-oriented simplified-EKV model. The trends of the free-carrier mobilities versus temperature in long and short-narrow devices are extracted from dc measurements down to 1.4\,K and 4.2\,K respectively, using a recently-proposed method based on the output conductance. A cryogenic-temperature-induced mobility degradation is observed on long pMOS, leading to a maximum hole mobility around 77\,K. This work sets the stage for preparing industrial design kits with physics-based cryogenic compact models, a prerequisite for the successful co-integration of FDSOI CMOS circuits with silicon qubits operating at deep-cryogenic temperatures.

cond-mat.mes-hall↗

arXiv2018

Design-oriented Modeling of 28 nm FDSOI CMOS Technology down to 4.2 K for Quantum Computing

In this paper a commercial 28-nm FDSOI CMOS technology is characterized and modeled from room temperature down to 4.2 K. Here we explain the influence of incomplete ionization and interface traps on this technology starting from the fundamental device physics. We then illustrate how these phenomena can be accounted for in circuit device-models. We find that the design-oriented simplified EKV model can accurately predict the impact of the temperature reduction on the transfer characteristics, back-gate sensitivity, and transconductance efficiency. The presented results aim at extending industry-standard compact models to cryogenic temperatures for the design of cryo- CMOS circuits implemented in a 28 nm FDSOI technology.

physics.app-ph↗

arXiv2018

Cryogenic MOS Transistor Model

This paper presents a physics-based analytical model for the MOS transistor operating continuously from room temperature down to liquid-helium temperature (4.2 K) from depletion to strong inversion and in the linear and saturation regimes. The model is developed relying on the 1D Poisson equation and the drift-diffusion transport mechanism. The validity of the Maxwell-Boltzmann approximation is demonstrated in the limit to zero Kelvin as a result of dopant freeze-out in cryogenic equilibrium. Explicit MOS transistor expressions are then derived including incomplete dopant-ionization, bandgap widening, mobility reduction, and interface charge traps. The temperature dependency of the interface-trapping process explains the discrepancy between the measured value of the subthreshold swing and the thermal limit at deep-cryogenic temperatures. The accuracy of the developed model is validated by experimental results on a commercially available 28-nm bulk CMOS process. The proposed model provides the core expressions for the development of physically-accurate compact models dedicated to low-temperature CMOS circuit simulation.

cond-mat.mes-hall↗

arXiv2018

Cryogenic Characterization of 28 nm Bulk CMOS Technology for Quantum Computing

This paper presents the first experimental investigation and physical discussion of the cryogenic behavior of a commercial 28 nm bulk CMOS technology. Here we extract the fundamental physical parameters of this technology at 300, 77 and 4.2 K based on DC measurement results. The extracted values are then used to demonstrate the impact of cryogenic temperatures on the essential analog design parameters. We find that the simplified charge-based EKV model can accurately predict the cryogenic behavior. This represents a main step towards the design of analog/RF circuits integrated in an advanced bulk CMOS process and operating at cryogenic temperature for quantum computing control systems.

cond-mat.mes-hall↗