Study of Warm Electron Injection in Double Gate SONOS by Full Band Monte Carlo Simulation

In this paper we investigate warm electron injection in a double gate SONOS memory by means of 2D full-band Monte Carlo simulations of the Boltzmann Transport Equation (BTE). Electrons are accelerated in the channel by a drain-to-source voltage VDS smaller than 3 V, so that programming occurs via electrons tunneling through a potential barrier whose height has been effectively reduced by the accumulated kinetic energy. Particle energy distribution at the semiconductor/oxide interface is studied for different bias conditions and different positions along the channel. The gate current is calculated with a continuum-based post-processing method as a function of the particle distribution obtained from Monte Carlo. Simulation results show that the gate current increases by several orders of magnitude with increasing drain bias and warm electron injection can be an interesting option for programming when short channel effects prohibit the application of larger drain bias

Tunneling Between Multimode Stacked Quantum Wires

Tunneling between vertically stacked quantum wires has been investigated. The wires are assumed to have the dimension perpendicular to the tunneling barrier much smaller than the other transverse dimension, so that only the lowest mode in such direction is to be taken into account, while many modes in the other direction are filled. A model with hard-wall confinement has been used for the investigation of the transport problem, and the tunneling conductance has been computed, via a recursive Green's functions procedure

Comparison of Iteration Schemes for the Solution of the Multidimensional Schrödinger-Poisson Equations

We present a fast and robust iterative method for obtaining self-consistent solutions to the coupled system of Schrödinger's and Poisson's equations in quantum structures. A simple expression describing the dependence of the quantum electron density on the electrostatic potential is used to implement a predictor – corrector type iteration scheme for the solution of the coupled system of differential equations. This approach simplifies the software implementation of the nonlinear problem, and provides excellent convergence speed and stability. We demonstrate the algorithm by presenting an example for the calculation ofthe two-dimensional bound electron states within the cross-section of a GaAs-AlGaAs based quantum wire. For this example, six times fewer iterations are needed when our predictor – corrector approach is applied, compared to a corresponding underrelaxation algorithm

Hierarchy of Full Band Structure Models for Monte Carlo Simulation

This paper discusses the various hierarchy levels that are possible when the full band structure is considered. At the highest level, the scatterings are treated using complete k-k' transition rates, which entail extremely memory intensive computational applications. At the lowest level, the scattering anisotropy is neglected and the scattering rate is considered to be a constant average value on energy isosurfaces of the bandstructure. This model is more practical for device simulation. In between the two extremes, it is possible to design intermediate models which preserve some essential features of both. At all levels of the band structure hierarchy of models, there are similar issues of numerical noise, related to the sampling of real and momentum space that the Monte Carlo method necessarily performs with a relatively small number of particles. We discuss here computationally efficient approaches based on the assignment of variable weights to the simulated particles, in conjunction with careful gatherscatter procedures to split particles of large weight and combine particles of small weight

Transient Analysis of Warm Electron Injection Programming of Double Gate SONOS Memories by means of Full Band Monte Carlo Simulation

In this paper we investigate "Warm Electron Injection" as a mechanism for NOR programming of double-gate SONOS memories through 2D full band Monte Carlo simulations. Warm electron injection is characterized by an applied VDS smaller than 3.15 V, so that electrons cannot easily accumulate a kinetic energy larger than the height of the Si/SiO2 barrier. We perform a time-dependent simulation of the program operation where the local gate current density is computed with a continuum-based method and is adiabatically separated from the 2D full Monte Carlo simulation used for obtaining the electron distribution in the phase space. In this way we are able to compute the time evolution of the charge stored in the nitride and of the threshold voltages corresponding to forward and reverse bias. We show that warm electron injection is a viable option for NOR programming in order to reduce power supply, preserve reliability and CMOS logic level compatibility. In addition, it provides a well localized charge, offering interesting perspectives for multi-level and dual bit operation, even in devices with negligible short channel effects

Two Dimensional Quantum Mechanical Modeling of Nanotransistors

Quantization in the inversion layer and phase coherent transport are anticipated to have significant impact on device performance in 'ballistic' nanoscale transistors. While the role of some quantum effects have been analyzed qualitatively using simple one dimensional ballistic models, two dimensional (2D) quantum mechanical simulation is important for quantitative results. In this paper, we present a framework for 2D quantum mechanical simulation of a nanotransistor / Metal Oxide Field Effect Transistor (MOSFET). This framework consists of the non equilibrium Green's function equations solved self-consistently with Poisson's equation. Solution of this set of equations is computationally intensive. An efficient algorithm to calculate the quantum mechanical 2D electron density has been developed. The method presented is comprehensive in that treatment includes the three open boundary conditions, where the narrow channel region opens into physically broad source, drain and gate regions. Results are presented for (i) drain current versus drain and gate voltages, (ii) comparison to results from Medici, and (iii) gate tunneling current, using 2D potential profiles. Methods to reduce the gate leakage current are also discussed based on simulation results.Comment: 12 figures. Journal of Applied Physics (to appear

Operational evaluation of the Mediterranean Monitoring and Forecasting Centre products: implementation and results

A web-based validation platform has been developed at the Istituto Nazionale di Geofisica e Vulcanologia (INGV) for the Near Real Time validation of the MyOcean-Mediterranean Monitoring and Forecasting Centre products (Med-MFC). A network for the collection of the in-situ observations, the nested sub-basin forecasting systems model data (provided by the partners of the Mediterranean Operational Oceanography Network, MOON) and the Sea Surface Temperature (SST) satellite data has been developed and is updated every day with the new available data. The network collects temperature, salinity, currents and sea level data. The validation of the biogeochemical forecast products is done by use of ocean colour satellite data produced for the Mediterranean Sea. All the data are organized in an ad hoc database interfaced with a dedicated software which allows interactive visualizations and statistics (CalVal SW). This tool allows to evaluate NRT products by comparison with independent observations for the first time. The heterogeneous distribution and the scarcity of moored observations reflect with large areas uncovered with measurements. Nevertheless, the evaluation of the forecast at the locations of observations could be very useful to discover sub-regions where the model performances can be improved, thus yielding an important complement to the basin-mean statistics regularly calculated for the Mediterranean MFC products using semi-independent observations

Development and Validation of a Comprehensive Model to Estimate Early Allograft Failure among Patients Requiring Early Liver Retransplant

Importance: Expansion of donor acceptance criteria for liver transplant increased the risk for early allograft failure (EAF), and although EAF prediction is pivotal to optimize transplant outcomes, there is no consensus on specific EAF indicators or timing to evaluate EAF. Recently, the Liver Graft Assessment Following Transplantation (L-GrAFT) algorithm, based on aspartate transaminase, bilirubin, platelet, and international normalized ratio kinetics, was developed from a single-center database gathered from 2002 to 2015. Objective: To develop and validate a simplified comprehensive model estimating at day 10 after liver transplant the EAF risk at day 90 (the Early Allograft Failure Simplified Estimation [EASE] score) and, secondarily, to identify early those patients with unsustainable EAF risk who are suitable for retransplant. Design, Setting, and Participants: This multicenter cohort study was designed to develop a score capturing a continuum from normal graft function to nonfunction after transplant. Both parenchymal and vascular factors, which provide an indication to list for retransplant, were included among the EAF determinants. The L-GrAFT kinetic approach was adopted and modified with fewer data entries and novel variables. The population included 1609 patients in Italy for the derivation set and 538 patients in the UK for the validation set; all were patients who underwent transplant in 2016 and 2017. Main Outcomes and Measures: Early allograft failure was defined as graft failure (codified by retransplant or death) for any reason within 90 days after transplant. Results: At day 90 after transplant, the incidence of EAF was 110 of 1609 patients (6.8%) in the derivation set and 41 of 538 patients (7.6%) in the external validation set. Median (interquartile range) ages were 57 (51-62) years in the derivation data set and 56 (49-62) years in the validation data set. The EASE score was developed through 17 entries derived from 8 variables, including the Model for End-stage Liver Disease score, blood transfusion, early thrombosis of hepatic vessels, and kinetic parameters of transaminases, platelet count, and bilirubin. Donor parameters (age, donation after cardiac death, and machine perfusion) were not associated with EAF risk. Results were adjusted for transplant center volume. In receiver operating characteristic curve analyses, the EASE score outperformed L-GrAFT, Model for Early Allograft Function, Early Allograft Dysfunction, Eurotransplant Donor Risk Index, donor age × Model for End-stage Liver Disease, and Donor Risk Index scores, estimating day 90 EAF in 87% (95% CI, 83%-91%) of cases in both the derivation data set and the internal validation data set. Patients could be stratified in 5 classes, with those in the highest class exhibiting unsustainable EAF risk. Conclusions and Relevance: This study found that the developed EASE score reliably estimated EAF risk. Knowledge of contributing factors may help clinicians to mitigate risk factors and guide them through the challenging clinical decision to allocate patients to early liver retransplant. The EASE score may be used in translational research across transplant centers

Pemetrexed single agent chemotherapy in previously treated patients with locally advanced or metastatic non-small cell lung cancer

<p>Abstract</p> <p>Background</p> <p>The main objective of this study was to evaluate the safety of second-line pemetrexed in Stage IIIB or IV NSCLC.</p> <p>Methods</p> <p>Overall, 95 patients received pemetrexed 500 mg/m²i.v. over Day 1 of a 21-day cycle. Patients also received oral dexamethasone, oral folic acid and i.m. vitamin B12 supplementation to reduce toxicity. NCI CTC 2.0 was used to rate toxicity. All the adverse events were graded in terms of severity and relation to study treatment. Dose was reduced in case of toxicity and treatment was delayed for up to 42 days from Day 1 of any cycle to allow recovering from study drug-related toxicities. Tumor response was measured using the RECIST criteria.</p> <p>Results</p> <p>Patients received a median number of 4 cycles and 97.8% of the planned dose. Overall, 75 patients (78.9% of treated) reported at least one adverse event: 34 (35.8%) had grade 3 as worst grade and only 5 (5.2%) had grade 4. Drug-related events occurred in 57.9% of patients. Neutropenia (8.4%) and leukopenia (6.3 %) were the most common grade 3/4 hematological toxicities. Grade 3 anemia and thrombocytopenia were reported in 3.2% and 2.1% of patients, respectively. Diarrhea (6.3%), fatigue (3.2%) and dyspnea (3.2%) were the most common grade 3/4 non-hematological toxicities. The most common drug-related toxicities (any grade) were pyrexia (11.6%), vomiting, nausea, diarrhea and asthenia (9.5%) and fatigue (8.4%). Tumor Response Rate (CR/PR) in treated patients was 9.2%. The survival at 4.5 months (median follow-up) was 79% and the median PFS was 3.1 months. Twenty patients (21.1%) died mainly because of disease progression.</p> <p>Conclusion</p> <p>Patients with locally advanced or metastatic NSCLC could benefit from second-line pemetrexed, with a low incidence of hematological and non-hematological toxicities.</p