Critical Device Research Articles

(Invited) Dielectrics in Nanoelectronic Computing

As the CMOS scaling driven by the Moore’s Law approaching some fundamental limits, high power consumption and heat dissipation have been recognized as the most critical device challenges. The Nanoelectronics Research Initiative (NRI) was launched 14 years ago by the semiconductor industry to explore alternative switching devices with significantly lower power based on unconventional mechanisms, materials, and devices. NRI has investigated a broad range of devices, including steep-slop transistors, spintronics, van der Waals devices, as well as new architectures to utilize unique characteristics offered by these devices [1]. Novel materials, including various dielectrics, have been the foundation of NRI research. For example, dielectric layers for gating and electrical insulation have been a great challenge for low-dimensional devices; magnetic insulators are promising for low-power high-efficiency spintronic devices; ferroelectric materials have been utilized to realize the so-called “negative-capacitance” transistors for low-power applications [2]. Despite abundant scientific breakthroughs achieved in over a decade of research in NRI, no beyond-CMOS devices have been demonstrated to significantly outperform CMOS for Boolean logic and von Neumann architectures. Comprehensive benchmarking of beyond-CMOS devices conducted in NRI has revealed the limitations of these devices quantitatively [3].As the semiconductor industry shifts toward novel computing paradigms, beyond-CMOS materials and devices may find more suitable opportunities for applications beyond Boolean and von Neumann computing. In-memory computing and analog computing (including neuromorphic computing) have stood out in this promising direction. Ferroelectric materials, binary and complex oxides, and chalcogenides have been utilized in a wide range of nonvolatile memories and analog devices, which may enable highly efficient in-memory and analog computing solutions. However, stringent requirements exist for these devices to significantly outperform CMOS in these applications, e.g., high density, fast speed, low power, high endurance, long retention, wide analog tunability, etc. [4] More specific requirements also exist and vary from application to application. Device-architecture design and co-optimization can help to address some of these requirements, but more fundamental solutions are rooted in material engineering and optimization to enable devices capable of native implementation of these novel computing paradigms. This holistic approach from basic material exploration to device engineering and further up to architecture co-design has become the guiding principle of the follow-on program of NRI, known as nanoelectronic Computing Research (nCORE) [5].This paper will review NRI research and lessons learned, which laid the foundation for new directions and research in the nCORE program. The importance, challenges, and opportunities of dielectric materials in nanoelectronic research will be discussed in this context.

Analysis of the Impact of Process Variations and Manufacturing Defects on the Performance of Carbon-Nanotube FETs

Carbon-nanotube FETs (CNFETs) are potential successors to CMOS transistors; these emerging devices have a low intrinsic delay due to near-ballistic transport in carbon nanotubes (CNTs). As CNFETs are evaluated for circuit/system design, it is important to analyze variations in CNT process parameters. In this article, we present a systematic approach to quantify the impact of these imperfections on the transistor- and gate-level performances of CNT-based circuits. Process variations are investigated to identify the critical device parameters that have maximum impact on the device on-current. We also present a model that predicts the realistic CNFET yield in the presence of process variations. Finally, the impact of manufacturing defects, such as pinholes in the gate dielectric and parasitic CNFETs formed due to imperfect etching, are modeled and evaluated using HSPICE.

Pleasure or pain? An evaluation of the costs and utilities of bloatware applications in android smartphones

We investigate the privacy, security, and trust issues of the Android bloatware applications and evaluate the claims regarding their utility and the coverage of the functional needs of different end-user market segments. We analyze 17,179 bloatware applications, extracted from the firmware of 100 Android smartphones manufactured by nine leading original equipment manufacturers (OEMs), and conduct an online user study to validate the utility and coverage claims. We find an average of 172 bloatware applications in the firmware of examined smartphones. We discover that most of the bloatware applications can access sensitive data and critical device features in smartphones and perform critical functions. Their nature and abilities due to the use of Dangerous, Custom, and Signature Android Permissions can make privacy protection a complex task for the smartphone users, introduce trust issues, and expand the attack surface in the smartphones. We also provide a non-exhaustive set of examples of bloatware applications from smartphones of all nine brands that violate trust. Coming to their utilities, findings of our online user study involving 180 participants suggest that while most of the respondents agree that bloatware applications are useful to some extent, 39% of the respondents use 0–5 bloatware applications. An additional 35% of respondents use 6–10 bloatware applications. We also find that for their diverse functional needs, users depend more on applications acquired from different application markets. The results of our research suggest that while the pains of the bloatware applications are real, the claims regarding their pleasures need further investigation. We urge that the number and abilities of smartphone bloatware applications need to be constrained proportionally to their practical utilities for their users, and they must conform to security and privacy requirements for trustworthy systems.

Sensitivity/uncertainty comparison and similarity analysis between TMSR-LF1 and MSR models

TMSR-LF1 (Thorium-based Molten Salt Reactor-Liquid Fuel) is the reactor chosen to be developed in the “Thorium molten salt reactor nuclear energy system” project of the Strategic Priority Program launched by the Chinese Academy of Sciences. The software and data library adopted in its design needs to be verified and validated by using benchmarks. In order to guarantee the validity of the verification results, the being-designed reactor should have similarity (index Ck and E ≥ 0.8) with the benchmark reactor. Using TSUNAMI module and in SCALE 6.1, the Sensitivity/Uncertainty (S/U) analyses and similarity assessments were performed in TMSR-LF1 and the candidate benchmark reactors: MSRE (Molten Salt Reactor Experiment), MSBR (Molten Salt Breeder Reactor) and the Critical Experiment Device (hereafter the device). Uncertainty was calculated using both SCALE and TMSR 44-group covariance data. It is found that the total eigenvalue uncertainties deduced from covariance data in TMSR-LF1 and the candidate benchmark reactors satisfy the ±1% design accuracy requirement proposed by M. Ishikawa in 2008, except in MSBR. To meet the accuracy of ±0.3%, targeted experiments for TMSR are needed. The covariance data of 7Li, C-graphite, 58Ni and 19F were the main contributors to the uncertainty of effective multiplication factor as well as the covariance data of fuel nuclides. The calculated similarity indices indicated that there was a good similarity (Ck and E > 0.9) between TMSR-LF1 and MSRE, and a lesser similarity between TMSR-LF1 and the device (Ck and E > 0.8). The uncertainties should be improved and more benchmarks for the direct verification and validation should be provided by relevant experiments.

Role of stress/strain mapping and random dopant fluctuation in advanced CMOS process technology nodes

In this work, biaxial and uniaxial strain techniques are implemented in the channel for both p- and n-type FinFETs necessary for advanced CMOS applications. Stress/strain mapping in strained-Si (n-type) and strained-SiGe (p-type) channels (in trapezoidal tri-gate FinFET devices) are studied through three-dimensional (3D) numerical simulation, with particular focus on the enhancement of drain current. Following the strain/stress profiles simulated, the piezoresistive changes are implemented in the simulator to describe the strain effects on device operation. Further, we have investigated the impacts of random discrete dopant variability on the characteristics of a 14-nm gate length FinFET transistors (both n and p-type) using a 3D finite element quantum corrected drift-diffusion device simulator. We have also found the fluctuation of critical device parameters such as threshold voltage (VTH), sub-threshold slope (SS), on current (ION), and off state current (IOFF), etc., mainly originated from the randomness of distribution of the dopants.

Celebridade

O objetivo deste texto é discutir a possibilidade de refletir sobre as celebridades como um dispositivo interacional crítico. Partimos da ideia de que os sujeitos célebres podem ser pensados como sujeitos políticos que atuam no contexto social, revelando valores de uma sociedade e seus problemas públicos. A análise se volta para a postura assumida por Fernanda Lima no programa Amor & Sexo, destacando eixos temáticos a partir dos quais podemos apreender os posicionamentos desta celebridade: machismo e misoginia, racismo, LGBTfobia. A análise mostra como a apresentadora se constitui como um dispositivo interacional crítico e pode atuar no fomento a lutas emancipatórias e na reconstrução de gramáticas morais capazes de atuar na promoção da justiça.

Robust Ag/ZrO2/WS2/Pt Memristor for Neuromorphic Computing.

The development of the information age has made resistive random access memory (RRAM) a critical nanoscale memristor device (MD). However, due to the randomness of the area formed by the conductive filaments (CFs), the RRAM MD still suffers from a problem of insufficient reliability. In this study, the memristor of Ag/ZrO2/WS2/Pt structure is proposed for the first time, and a layer of two-dimensional (2D) WS2 nanosheets was inserted into the MD to form 2D material and oxide double-layer MD (2DOMD) to improve the reliability of single-layer devices. The results indicate that the electrochemical metallization memory cell exhibits a highly stable memristive switching and concentrated ON- and OFF-state voltage distribution, high speed (∼10 ns), and robust endurance (>109 cycles). This result is superior to MDs with a single-layer ZrO2 or WS2 film because two layers have different ion transport rates, thereby limiting the rupture/rejuvenation of CFs to the bilayer interface region, which can greatly reduce the randomness of CFs in MDs. Moreover, we used the handwritten recognition dataset (i.e., the Modified National Institute of Standards and Technology (MNIST) database) for neuromorphic simulations. Furthermore, biosynaptic functions and plasticity, including spike-timing-dependent plasticity and paired-pulse facilitation, have been successfully achieved. By incorporating 2D materials and oxides into a double-layer MD, the practical application of RRAM MD can be significantly enhanced to facilitate the development of artificial synapses for brain-enhanced computing systems in the future.

Observation of mobility and velocity behaviors in ultra-scaled LG = 15 nm silicon nanowire field-effect transistors with different channel diameters

Experimentally, two critical device performance factors, apparent mobility (μapp) and virtual source velocity (vx0) were investigated down to effective channel length (Leff) = 15 nm silicon nanowire field-effect transistors (SNWFETs) by using virtual source (VS) model. Both μapp and vx0 decreased in n-SNWFETs but increased in p-SNWFETs as the nanowire diameter (DNW) shrank because of opposite effective mass (meff) dependency. The critical on-current booster, vx0 rather than μapp increased monotonically as Leff shrank, and it showed that vx0 boosting by Leff scaling is still valid to Leff = 15 nm in SNWFETs. Furthermore, p-SNWFETs had higher μapp and vx0 than n-SNWFETs because compressive stress from SiGe layer below source/drain improved the performance of p-SNWFETs. Interestingly, unpredicted non-linearity of Leff/μapp vs. 1/vx0 plot was observed in short channel p-SNWFETs and its origin was discussed. Finally, thermal limit velocity (vTx) and ballistic efficiency (Bsat) consisting vx0 were extracted from experimental data. The DNW dependence of vTx and Bsat was analyzed using stress effect, meff, critical length (LC), and mean free path (λ), which provides the way of vx0 boosting.

Peeking inside energy devices

How well batteries, solar cells, and fuel cells generate and store electricity often depends on hidden details of thin layers of engineered materials. The hows and whys of nanoscale changes in the structure or composition of a buried photoactive material or catalytic electrode, for example, can spell the difference between a blockbuster device and one that dies on the drawing board. To reveal those performance-controlling secrets, researchers are designing state-of-the-art microscopy and spectroscopy tools to probe critical device components—in many cases, while the device is hard at work. The devices around us that generate and store the energy that powers our electronics and propels our vehicles rely on intricate chemistry that often happens in tiny spaces. But those sometimes-nanoscale reactions are incredibly difficult to study, making scientists wish they could magically shrink to watch the chemistry in real time. For example, Jasna Jankovic, a specialist in imaging methods at the

Preparation of Low-Resistance and Residue-free ITO Films for Large-scale 3D Displays.

The large-sized naked-eye three-dimensional (3D) display is a critical device in the real-time topographic survey for deep-sea scientific research. As a core component, the low-impedance transparent conductive indium tin oxide (ITO) thin-film electrode lacks a reliable industrial preparation method. In the 3D display, the grating element with a low-resistance ITO film electrode should have a good binocular parallax to drive the display favorably. However, an increase in the ITO film temperature during deposition may induce its crystallization, and its etching residue may cause a short circuit between the ITO electrodes and abnormal display operation. In this work, we propose a simple and straightforward technique to produce amorphous thin ITO films by controlling the water vapor flow rate during the deposition process. The obtained ITO amorphous thick film (300 nm) can be etched without leaving residues on the display surface, ensuring vivid display performance of the 3D display. A field test employing the 3D display, consisting of a 3D parallax barrier and a two-dimensional (2D) display, does not exhibit a short-circuit phenomenon caused by residues encountered in previous devices. This work makes the 3D display applicable for the real-time topographic survey on the basis of both satisfying the nonetching residue and the decrease of the resistance value.

Engineering of effective back-contact barrier of CZTSe: Nanoscale Ge solar cells – MoSe2 defects implication

Using temperature-dependent measurements and device modeling, we systematically study the effective back-contact barrier of CZTSe devices to improve the property of the back-contact interface. By comparing with CZTSe devices with various nanoscale Ge configurations, CZTSe nanoscale Ge bi-layers devices show the improved power conversion efficiency by 1.1%. DC magnetron sputtering is used to fabricate CZTSe: nanolayer Ge devices. Critical device parameters are characterized to understand the impact of nanoscale Ge films on the back-contact device characteristics. Based on empirical results, modeling is performed for the influence of MoSe2 defects on the effective back-contact barrier. Analysis of experimental results of Ge bi-layers devices with the improved back-contact barrier makes a good agreement with modeling and Sentaurus TCAD simulation at the 95% confidence-level. The conversion efficiency of CZTSe: nanoscale Ge bi-layers devices is improved up to 8.3%.

The Textilesphere: The Threshold of Everyday Contacts

A sense of displacement pervades contemporary life, with the global crisis of forced migration, increasingly modular and distributed families, and remote social interactions replacing familiar ways of being in a space with others. This sentiment, together with the widening application of highly advanced textiles in many areas of the built environment, calls for an appraisal of textiles in relation to notions of home and belonging. Drawing on a range of academic and practitioner literature, brought together under “relational approaches,” this essay puts forward the “textile-sphere” as a new ontological category and a critical device for textiles thinking within this context of societal and technological changes. The textile-sphere is an affective spatiality generated by physical wear as indexical traces of everyday life, emphasizing sustained physical contact as an essential of home. It suggests a new way of thinking about textiles which transcends 2D–3D, human–nonhuman, and material–immaterial dichotomies, focusing, instead, on the flexible relations between surfaces. The textile-sphere is a useful tool for exploring the complexity of contemporary spatiality in relation to various physical and virtual surfaces, and the role textiles can play in interrogating this complexity, letting us contemplate what it means to be “in touch,” to be home.

(Invited) Effect of Junction Resistance on the Percolation Conductivity of Metal Nanowire Networks for Transparent Conductors

Random networks of one-dimensional (1D) nanoelements, such as carbon nanotubes, graphene nanoribbons, and metal nanowires, have attracted significant research interest recently for next-generation transparent conductors. As a result, these networks can be used in many device applications, such as touch screens, flat panel displays, solar cells, light-emitting diodes (LEDs), and wearable flexible electronics. Among these nanomaterials, metal nanowire networks, such as silver and copper, exhibit high optical transmittance, low sheet resistance, mechanical flexibility, and solution-based fast deposition. These unique properties make metal nanowire networks promising candidates to replace indium tin oxide (ITO), which suffers from brittleness, scarcity, high cost, and slow deposition. At high optical transmittance values required for transparent conductors, the conductivity of metal nanowire networks is governed by percolation transport, which deals with the formation of long-range connectivity in random networks. As a result, Monte Carlo simulations need to be employed to theoretically calculate, predict, and optimize the conductivity of metal nanowire networks [1,2]. Two types of resistance contributions determine the overall conductivity of the nanowire network. The first is the nanowire-nanowire junction resistance and the second is the resistance of the nanowire itself. In most Monte Carlo simulations, it is assumed that the nanowire-nanowire junction resistance is much larger than the nanowire resistance, resulting in a junction resistance-dominated network [2-4]. Although this is the case for carbon nanotube networks, recent experiments have shown that, for metal nanowire networks, the junction resistance can be significantly lowered by post-deposition treatments, such as thermal annealing, plasmonic welding, joule heating, and mechanical pressing. In such cases, the nanowire resistance becomes comparable to the junction resistance and it can no longer be ignored. When the junction resistance becomes much lower than the nanowire resistance, the network becomes nanowire resistance-dominated, which is the lowest resistance limit for a given set of nanowire and device parameters. Despite the significant role the junction resistance plays in determining the percolation conductivity of metal nanowire networks, a systematic study of the effect of nanowire-nanowire junction resistance on the network conductivity as a function of other nanowire and device parameters is currently lacking. In this work, we perform systematic Monte Carlo simulations to study the effect of the nanowire-nanowire junction resistance on the conductivity and percolation critical exponents of metal nanowire networks. We define a parameter called the resistance ratio, which is the ratio of the nanowire-nanowire junction resistance to the nanowire resistance per unit length. We perform Monte Carlo simulations of the nanowire network conductivity by varying the resistance ratio over a span of six orders of magnitude, ranging all the way from a junction resistance-dominated to a nanowire resistance-dominated network. First, we study the effect of the resistance ratio on the nanowire network conductivity at different values of the other nanowire and device parameters, such as nanowire density, nanowire length, device length, device width, nanowire alignment, and nanowire curviness. Next, we study the effect of the resistance ratio on the percolation critical exponents. Approaching the percolation threshold, conductivity exhibits a power law dependence on nanowire and device parameters, which is characterized by percolation critical exponents. We first extract the critical nanowire density, nanowire length, device width, and alignment angle at the percolation threshold by calculating the percolation probability as a function of each variable. Then, we extract the critical exponents as a function of the resistance ratio for nanowire density, nanowire length, device width, nanowire alignment, and nanowire curviness. We find that the resistance ratio plays a crucial role in determining both the conductivity and the percolation critical exponents of metal nanowire networks. This study illustrates how the junction resistance affects the macroscopic conductivity of transparent, conductive metal nanowire networks. It also shows that Monte Carlo simulations are an essential predictive tool for providing insights into percolation transport and optimizing the electronic properties of these networks. These results are not limited to metal nanowire networks, but can be extended to any two-dimensional (2D) or quasi-2D network, film, or nanocomposite consisting of 1D nanoelements.

A network traffic assignment model for autonomous vehicles with parking choices

AbstractThis article is the first in the literature to investigate the network traffic equilibrium for traveling and parking with autonomous vehicles (AVs) under a fully automated traffic environment. Given that AVs can drop off the travelers at their destinations and then drive to the parking spaces by themselves, we introduce the joint equilibrium of AV route choice and parking location choice, and develop a variational inequality (VI)‐based formulation for the proposed equilibrium. We prove the equivalence between the proposed VI model and the defined equilibrium conditions. We also show that the link flow solution at equilibrium is unique, even though both the route choices and parking choices are endogenous when human‐occupied AV trips (from origin to destination) and empty AV trips (from destination to parking) are interacting with each other on the same network. We then develop a solution methodology based on the parking‐route choice structure, where we adjust parking choices in the upper level and route choices in the lower level. Numerical analysis is conducted to explore insights from the introduced modeling framework for AV network equilibrium. The results reveal the significant difference in network equilibrium flows between the AV and non‐AV situations. The results also indicate the sensitivity of the AV traffic pattern to different factors, such as value of time, parking pricing, and supply. The proposed approach provides a critical modeling device for studying the traffic equilibrium under AV behavior patterns, which can be used for the assessment of parking policies and infrastructure development in the future era of AVs.

Neutron flux distribution and conversion ratio of Critical Experiment Device for molten salt reactor research

Critical Experiment Device (cold) was established for research on the physics characteristics of Molten Salt Reactor (MSR) in 1970s, at Shanghai Institute of Applied Physics, China. Neutron flux distribution was measured for different core structures and the conversion ratio of the core containing thorium fuel was determined on the basis of the preliminary criticality experiments. The purpose of this work is to compare the calculated flux distribution and thorium-uranium conversion ratio with the measured results in this device. Calculations were accomplished by using MCNP5 code with nuclear data from ENDF/B-VII.0, ENDF/B-VII.1, JEFF 3.2, JENDL 4.0, CENDL 3.1 and ROSFOND 2010 libraries. The results show that the calculated results are in good agreements with the experimental data. Findings in this work have a great significance to the design and benchmark verification of a cold MSR. However, more hot experiments are needed to study the nuclear properties of the liquid fuel MSR.

Retrograde transcatheter aortic valve closure in an infant with failing Norwood stage I palliation: a case report

BackgroundAortic valve regurgitation leading to coronary steal phenomenon can severely impair cardiac function in hypoplastic left heart syndrome, thus worsening long-term outcome.Case presentationA German infant with borderline aortic and mitral valve, hypoplastic left ventricle, ventricular septal defect, and hypoplastic aortic arch with critical coarctation initially underwent aortic arch reconstruction and aortic valve dilation with the aim of biventricular correction later on. Unfortunately, severe cardiac dysfunction necessitated a change in strategy entailing modified stage I Norwood palliation. Increasing aortic regurgitation with coronary steal was revealed postoperatively, which required redo surgery to oversew the valve. However, pronounced aortic regurgitation recurred, causing severe cardiac decompensation with repeated resuscitation. As a bailout strategy, we performed aortic valve closure via transfemoral retrograde implantation of an Amplatzer Duct Occluder II device. This led to the patient’s rapid stabilization while circumventing highly risky renewed surgery in such a critically ill infant.ConclusionsRetrograde transcatheter aortic valve closure may be considered a feasible alternative in infants with a failing single ventricle due to aortic regurgitation, with critical device evaluation being crucial for successful device implantation in this young age group.

Technological Benchmark of Analog Synaptic Devices for Neuroinspired Architectures

Editor's note: In this article, the authors present a circuit-level macro model (“NeuroSim” simulator) to estimate circuit-level performance of neuroinspired architectures to facilitate design space exploration. The model is used to analyze the impact of analog synapse device characteristics on the performance of a two-layer multi-layer perceptron (MLP) neural network and identify critical device properties (on/off ratio and asymmetry, in this case) to guide technology development.-An Chen, Semiconductor Research Corporation.

Leakage and breakdown mechanisms of GaN vertical power FinFETs

This work studies the leakage and breakdown mechanisms of 1.2 kV GaN vertical power FinFETs with edge termination. Two competing leakage and breakdown mechanisms have been identified. The first mechanism is dominated by the electric field, with the leakage current dominated by the electric field in the drift region and destructive breakdown voltage by the peak electric field at the edge termination. The second leakage and breakdown mechanism is controlled by an energy (or potential) barrier in the fin channel. This energy barrier suffers from the drain-induced barrier lowering (DIBL) effect and is highly dependent on gate/drain biases, fin geometries, and GaN/oxide interface charges. The electrons injected into the drift region due to the DIBL effect further lead to trap-assisted space-charge-limited conduction, which results in a nondestructive early breakdown. The barrier height in the fin channel determines which mechanism is dominant; the same device could show either destructive or nondestructive breakdown at different gate biases. To enable the normally off power switching, it is important to suppress the leakage from the second mechanism and maintain a sufficiently high energy barrier in the fin channel up to high drain voltages. Finally, the key device parameters determining the energy barrier in the fin channel have been identified. The findings in this work provide critical device understanding and design guidelines for GaN vertical power FinFETs and other “junctionless” vertical high-voltage power transistors.

Induced quantum dot probe for material characterization.

We propose a non-destructive means of characterizing a semiconductor wafer via measuring parameters of an induced quantum dot on the material system of interest with a separate probe chip that can also house the measurement circuitry. We show that a single wire can create the dot, determine if an electron is present, and be used to measure critical device parameters. Adding more wires enables more complicated (potentially multi-dot) systems and measurements. As one application for this concept we consider silicon metal-oxide-semiconductor (MOS) and silicon/silicon-germanium quantum dot qubits relevant to quantum computing and show how to measure low-lying excited states (so-called "valley" states). This approach provides an alternative method for characterization of parameters that are critical for various semiconductor-based quantum dot devices without fabricating such devices.

France à fric: the CFA zone in Africa and neocolonialism

Over 50 years after 1960’s ‘Year of Africa’, most of Francophone Africa continues to be embedded in a set of associations that fit very well with Kwame Nkrumah’s description of neocolonialism, where postcolonial states are de jure independent but in reality constrained through their economic systems so that policy is directed from outside. This article scrutinises the functioning of the Communauté Financière Africaine (CFA), considering the role the currency has in persistent underdevelopment in most of Francophone Africa. In doing so, the article identifies the CFA as the most blatant example of functioning neocolonialism in Africa today and a critical device that promotes dependency in large parts of the continent. Mainstream analyses of the technical aspects of the CFA have generally focused on the exchange rate and other related matters. However, while important, the real importance of the CFA franc should not be seen as purely economic, but also political.