Quantum simulation investigation of work-function variation in nanowire tunnel FETs.

The variability induced by the work-function variation (WFV) in p-type ultra-scaled nanowire tunnel FET (TFET) has been studied by using the Non-Equilibrium Green's Function module implemented in University of Glasgow quantum transport simulator called NESS. To provide a thorough insight into the influence of WFV, we have simulated 250 atomistically different nanowire TFETs and the obtained results are compared to nanowire MOSFETs first. Our statistical simulations reveal that the threshold voltage (V th) variations of MOSFETs and TFETs are comparable, whereas the on-current (I on) and off-current (I off) variations of TFETs are smaller and higher, respectively in comparison to the MOSFET. Based on the results of the simulations, we have provided a physical insight into the variations of the I on and I off currents. Then, we compared the nanowire and Fin TFETs structures with different oxide thickness in terms of the WFV-induced variability. The results show that WFV has a strongest impact on the I off, and moderate effect on the I on and V th in nanowire TFET with smaller oxide thickness. Lastly, it is found that compared with the random discrete dopants, WFV is a relatively weaker variability source in ultra-scaled nanowire TFETs, especially from the point of view of I on variation.

Full-band quantum transport simulation in the presence of hole-phonon interactions using a mode-space k·p approach.

Fabrication techniques at the nanometer scale offer potential opportunities to access single-dopant features in nanoscale transistors. Here, we report full-band quantum transport simulations with hole-phonon interactions through a device consisting of two gates-all-around in series and a p-type Si nanowire channel with a single dopant within each gated region. For this purpose, we have developed and implemented a mode-space-based full-band quantum transport simulator with phonon scattering using the six-band k · p method. Based on the non-equilibrium Green's function formalism and self-consistent Born's approximation, an expression for the hole-phonon interaction self-energy within the mode-space representation is introduced.

Design and fabrication of memory devices based on nanoscale polyoxometalate clusters.

Flash memory devices--that is, non-volatile computer storage media that can be electrically erased and reprogrammed--are vital for portable electronics, but the scaling down of metal-oxide-semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory, but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory, there are a number of significant barriers to the realization of devices using conventional MOS technologies. Here we show that core-shell polyoxometalate (POM) molecules can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core-shell POM clusters, we show, at both the molecular and device level, that embedding [(Se(IV)O3)2](4-) as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se(v)2O6](2-) moiety containing a {Se(V)-Se(V)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call 'write-once-erase'. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour. This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit.

Towards polyoxometalate-cluster-based nano-electronics.

We explore the concept that the incorporation of polyoxometalates (POMs) into complementary metal oxide semiconductor (CMOS) technologies could offer a fundamentally better way to design and engineer new types of data storage devices, due to the enhanced electronic complementarity with SiO2, high redox potentials, and multiple redox states accessible to polyoxometalate clusters. To explore this we constructed a custom-built simulation domain bridge. Connecting DFT, for the quantum mechanical modelling part, and mesoscopic device modelling, confirms the theoretical basis for the proposed advantages of POMs in non-volatile molecular memories (NVMM) or flash-RAM.

How I do it: modified lichtenberger-brown tracheoesophageal puncture procedure.

BACKGROUND: Tracheoesophageal puncture (TEP) with use of a prosthesis is nowadays a standard for voice restoration after laryngectomy. Different TEP approaches exist. METHODS: We retrospectively reviewed our series of patients who underwent TEP by a novel technique, based partially on the Lichtenberger endo-extralaryngeal needle carrier. The instrument is covered with a protective Nelaton catheter and introduced via the mouth to the neopharynx/esophagus. No rigid endoscope is used for visualization of the TEP site. The tip is palpated through the stoma at the posterior tracheal wall and incision is done to the catheter tip. The prosthesis is introduced through the mouth and the neopharynx in a retrograde fashion. RESULTS: In 14 laryngectomees with postoperative radiation voice prosthesis was successfully placed with this technique. A total of 18 procedures were performed. One misplacement occurred. No other early or late complications were observed or any other TEP or prosthesis related problems. CONCLUSIONS: The rationale of our technique is to simplify the procedure, avoid risk-bearing approaches and instruments such as rigid endoscopes, simplify the armamentarium and reduce tissue trauma. The initial clinical experience in 18 TEPs confirmed it usefulness in both standard and anatomically challenging situations. TRIAL REGISTRATION: The current study obtained the ethical approval from the Faculty of Medicine at Medical University "Prof. Dr. Paraskev Stoyanov"-Varna, Bulgaria (Protocol 087/24.10.2019 (retrospectively registered).

Severe Acute Myocarditis after the Third (Booster) Dose of mRNA COVID-19 Vaccination.

Vaccination with mRNA vaccines against coronavirus disease 2019 (COVID-19) has been associated with a risk of developing myocarditis and pericarditis, with an estimated standardized incidence ratio of myocarditis being 5.34 (95% CI, 4.48 to 6.40) as compared to the expected incidence based on historical data according to a large national study in Israel. Most cases of myocarditis in vaccine recipients occur in young males, particularly following the second dose, and the presentation is usually mild. Recently, the third (booster) dose has been shown to reduce confirmed infections and severe illness even against common variants of the virus. In Israel, over 4.4 million citizens (more than 45% of the population) have been vaccinated with the third dose of Pfizer-BioNTech vaccine BNT162b2. Herein, we report the first case of a histologically confirmed severe myocarditis following the third dose of BNT162b2 COVID-19 vaccine.

Self-Consistent Enhanced S/D Tunneling Implementation in a 2D MS-EMC Nanodevice Simulator.

The implementation of a source to drain tunneling in ultrascaled devices using MS-EMC has traditionally led to overestimated current levels in the subthreshold regime. In order to correct this issue and enhance the capabilities of this type of simulator, we discuss in this paper two alternative and self-consistent solutions focusing on different parts of the simulation flow. The first solution reformulates the tunneling probability computation by modulating the WKB approximation in a suitable way. The second corresponds to a change in the current calculation technique based on the utilization of the Landauer formalism. The results from both solutions are compared and contrasted to NEGF results from NESS. We conclude that the current computation modification constitutes the most suitable and advisable strategy to improve the MS-EMC tool.

Simulation and Modeling of Novel Electronic Device Architectures with NESS (Nano-Electronic Simulation Software): A Modular Nano TCAD Simulation Framework.

The modeling of nano-electronic devices is a cost-effective approach for optimizing the semiconductor device performance and for guiding the fabrication technology. In this paper, we present the capabilities of the new flexible multi-scale nano TCAD simulation software called Nano-Electronic Simulation Software (NESS). NESS is designed to study the charge transport in contemporary and novel ultra-scaled semiconductor devices. In order to simulate the charge transport in such ultra-scaled devices with complex architectures and design, we have developed numerous simulation modules based on various simulation approaches. Currently, NESS contains a drift-diffusion, Kubo-Greenwood, and non-equilibrium Green's function (NEGF) modules. All modules are numerical solvers which are implemented in the C++ programming language, and all of them are linked and solved self-consistently with the Poisson equation. Here, we have deployed some of those modules to showcase the capabilities of NESS to simulate advanced nano-scale semiconductor devices. The devices simulated in this paper are chosen to represent the current state-of-the-art and future technologies where quantum mechanical effects play an important role. Our examples include ultra-scaled nanowire transistors, tunnel transistors, resonant tunneling diodes, and negative capacitance transistors. Our results show that NESS is a robust, fast, and reliable simulation platform which can accurately predict and describe the underlying physics in novel ultra-scaled electronic devices.

Losing One's Voice to Save One's Life: A Brief History of Laryngectomy.

Laryngectomy is a surgical procedure that involves the surgical removal of the laryngeal complex, thereby separating the upper from the lower respiratory tracts, resulting in a tracheostomy. In this way, respiration is achieved at the expense of the patient's voice. A neopharynx is formed, serving only as a digestive passage between the mouth and the esophagus. Until the introduction of the procedure, patients with laryngeal cancer were considered terminally ill. Most often, the title of "First recorded laryngectomy" is held by Theodor Billroth in 1873; however, the outcome of the operation itself was doubtful, with later attempts having a 50% mortality rate. The first major leap in reducing patient mortality rates was the introduction of the two-step laryngectomy, performed by Themistocles Gluck in 1881. This achievement, along with the general advancements in the field of surgery at the time allowed his student Johannes Sørensen to perfect the method and further develop it into a modified single-stage laryngectomy. This procedure is the basis of contemporary methods.

Quantum Enhancement of a S/D Tunneling Model in a 2D MS-EMC Nanodevice Simulator: NEGF Comparison and Impact of Effective Mass Variation.

As complementary metal-oxide-semiconductor (CMOS) transistors approach the nanometer scale, it has become mandatory to incorporate suitable quantum formalism into electron transport simulators. In this work, we present the quantum enhancement of a 2D Multi-Subband Ensemble Monte Carlo (MS-EMC) simulator, which includes a novel module for the direct Source-to-Drain tunneling (S/D tunneling), and its verification in the simulation of Double-Gate Silicon-On-Insulator (DGSOI) transistors and FinFETs. Compared to ballistic Non-Equilibrium Green's Function (NEGF) simulations, our results show accurate I D vs. V G S and subthreshold characteristics for both devices. Besides, we investigate the impact of the effective masses extracted Density Functional Theory (DFT) simulations, showing that they are the key of not only the general thermionic emission behavior of simulated devices, but also the electron probability of experiencing tunneling phenomena.

Simulation of the Impact of Ionized Impurity Scattering on the Total Mobility in Si Nanowire Transistors.

Nanowire transistors (NWTs) are being considered as possible candidates for replacing FinFETs, especially for CMOS scaling beyond the 5-nm node, due to their better electrostatic integrity. Hence, there is an urgent need to develop reliable simulation methods to provide deeper insight into NWTs' physics and operation, and unlock the devices' technological potential. One simulation approach that delivers reliable mobility values at low-field near-equilibrium conditions is the combination of the quantum confinement effects with the semi-classical Boltzmann transport equation, solved within the relaxation time approximation adopting the Kubo⁻Greenwood (KG) formalism, as implemented in this work. We consider the most relevant scattering mechanisms governing intraband and multi-subband transitions in NWTs, including phonon, surface roughness and ionized impurity scattering, whose rates have been calculated directly from the Fermi's Golden rule. In this paper, we couple multi-slice Poisson⁻Schrödinger solutions to the KG method to analyze the impact of various scattering mechanisms on the mobility of small diameter nanowire transistors. As demonstrated here, phonon and surface roughness scattering are strong mobility-limiting mechanisms in NWTs. However, scattering from ionized impurities has proved to be another important mobility-limiting mechanism, being mandatory for inclusion when simulating realistic and doped nanostructures, due to the short range Coulomb interaction with the carriers. We also illustrate the impact of the nanowire geometry, highlighting the advantage of using circular over square cross section shapes.

Investigation of resistance switching in SiO x RRAM cells using a 3D multi-scale kinetic Monte Carlo simulator.

We employ an advanced three-dimensional (3D) electro-thermal simulator to explore the physics and potential of oxide-based resistive random-access memory (RRAM) cells. The physical simulation model has been developed recently, and couples a kinetic Monte Carlo study of electron and ionic transport to the self-heating phenomenon while accounting carefully for the physics of vacancy generation and recombination, and trapping mechanisms. The simulation framework successfully captures resistance switching, including the electroforming, set and reset processes, by modeling the dynamics of conductive filaments in the 3D space. This work focuses on the promising yet less studied RRAM structures based on silicon-rich silica (SiO x ) RRAMs. We explain the intrinsic nature of resistance switching of the SiO x layer, analyze the effect of self-heating on device performance, highlight the role of the initial vacancy distributions acting as precursors for switching, and also stress the importance of using 3D physics-based models to capture accurately the switching processes. The simulation work is backed by experimental studies. The simulator is useful for improving our understanding of the little-known physics of SiO x resistive memory devices, as well as other oxide-based RRAM systems (e.g. transition metal oxide RRAMs), offering design and optimization capabilities with regard to the reliability and variability of memory cells.

Variability Predictions for the Next Technology Generations of n-type SixGe1-x Nanowire MOSFETs.

Using a state-of-the-art quantum transport simulator based on the effective mass approximation, we have thoroughly studied the impact of variability on Si x Ge 1 - x channel gate-all-around nanowire metal-oxide-semiconductor field-effect transistors (NWFETs) associated with random discrete dopants, line edge roughness, and metal gate granularity. Performance predictions of NWFETs with different cross-sectional shapes such as square, circle, and ellipse are also investigated. For each NWFETs, the effective masses have carefully been extracted from s p 3 d 5 s ∗ tight-binding band structures. In total, we have generated 7200 transistor samples and performed approximately 10,000 quantum transport simulations. Our statistical analysis reveals that metal gate granularity is dominant among the variability sources considered in this work. Assuming the parameters of the variability sources are the same, we have found that there is no significant difference of variability between SiGe and Si channel NWFETs.

Enabling cutting-edge semiconductor simulation through grid technology.

The progressive scaling of complementary metal oxide semiconductor (CMOS) transistors drives the success of the global semiconductor industry. Detailed knowledge of transistor behaviour is necessary to overcome the many fundamental challenges faced by chip and systems designers. Grid technology has enabled the unavoidable statistical variations introduced by scaling to be examined in unprecedented detail. Over 200 000 transistors have been simulated, the results of which provide detailed insight into underlying physical processes. This paper outlines recent scientific results of the nanoCMOS project and describes the way in which the scientific goals have been reflected in the grid-based e-Infrastructure.