Optimization and evaluation of variability in the programming window of a flash cell with molecular metal-oxide storage

We report a modeling study of a conceptual nonvolatile memory cell based on inorganic molecular metal-oxide clusters as a storage media embedded in the gate dielectric of a MOSFET. For the purpose of this paper, we developed a multiscale simulation framework that enables the evaluation of variability in the programming window of a flash cell with sub-20-nm gate length. Furthermore, we studied the threshold voltage variability due to random dopant fluctuations and fluctuations in the distribution of the molecular clusters in the cell. The simulation framework and the general conclusions of our work are transferrable to flash cells based on alternative molecules used for a storage media

Molecular Based Flash Cell for Low Power Flash Application: Optimization and Variability Evaluation

The field of molecular electronics continues to spur interest in the quest for miniaturization and reduction of operational power of electron devices. Most of the systems described in the literature are based on organic molecules, such as benzene, ferrocene and fullerenes. However, the use of inorganic molecules known as polyoxometalates (POMs) (see Fig.l and Fig.2) could offer several important advantages over the conventional and organic based devices. Our present work shows that POMs are more compatible with existing CMOS processes than organic molecules and they can replace the polysilicon floating gate in contemporary flash cell devices [2]. The interest in POMs for flash cell applications stems from the fact that POMs are highly redox active molecules and that they can also be doped with electronically active heteroatoms [3]. They can undergo multiple reversible reductions/oxidations, which makes them attractive candidates for multi-bit storage in flash memory cells. The molecular charge storage is localised, thus minimising cross-cell capacitive coupling, which arises from charge redistribution on the sides of a poly-Si floating gate (FG) and is one of the most critical issues with flash memories. Although this benefit is presently realised in floating gates by charge-trapping dielectric or by a metallic nano-cluster array, both technologies exhibit large variability. Charge-trap memories suffer variation in trap-density and trap energy and the size and density of nano-clusters is difficult to control. This precludes their ultimate miniaturization. In fact, the concept of using molecules as storage centers has already been demonstrated for organic redox-active molecules [1]. Here, using full 3D simulations, we evaluate correlation between the device performance (in terms of threshold voltage VT) and statistical variability, arising from the random dopant fluctuations (RDF) and POM fluctuations (POMF)

Atomistic modeling of [W18O54(SeO3)2]4- polyoxometalates (POM) molecules in the presence of counter-cations

Polyoxometalates (POMs) are versatile molecular metal oxides explored for various applications. This case study focuses on [W18O54(SeO3)2]4− , a POM with potential for integration with molecular memory devices. The impact of counter-cations on its properties is investigated using Density Functional Theory (DFT). The study delves into the computational details of [W18O54(SeO3)2]4− optimization using DFT, considering counter-cations and solvents. Theoretical models reveal the significant influence of counter-cations on frontier orbital energies, especially in vacuum. Interestingly, the Continuum Solvent Model (COSMO) demonstrates that explicit counter-cations have a minor impact when solvents are considered. This finding has implications for computational efficiency in future POM studies. The study concludes by highlighting the importance of counter-cations in DFT modelling and proposes avenues for further research, including expanding the range of POMs and exploring POM-cation-surface interactions

First Principle Simulations of Current Flow in Inorganic Molecules: Polyoxometalates (POMs)

In this work we present a simulation study of current flow in inorganic molecular metal oxide clusters known as polyoxometalates (POMs). The simulations are carried out by using combination of the density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. To investigate the current flow in POMs, we investigate two possible ways to place the POM cluster between two gold (Au) electrodes - vertical and horizontal. Our results show that the position of the POM molecule and the contact between the molecule and the Au electrodes determines the current flow. Overall, the vertical configuration of the molecule between the two Au electrodes shows better current flow in comparison to the horizontal configuration. In this work we also establish a link between the underlying electronic structure and transmission spectra and conductance

Comparison between bulk and FDSOI POM flash cell: a multiscale simulation study

In this brief, we present a multiscale simulation study of a fully depleted silicon-on-insulator (FDSOI) nonvolatile memory cell based on polyoxometalates (POMs) inorganic molecular clusters used as a storage media embedded in the gate dielectric of flash cells. In particular, we focus our discussion on the threshold voltage variability introduced by random discrete dopants (random dopant fluctuation) and by fluctuations in the distribution of the POM molecules in the storage media (POM fluctuation). To highlight the advantages of the FDSOI POM flash cell, we provide a comparison with an equivalent cell based on conventional (BULK) transistors. The presented simulation framework and methodology is transferrable to flash cells based on alternative molecules used as a storage media

Investigating the formation of giant {Pd72}Prop and {Pd84}Gly macrocycles using NMR, HPLC and mass spectrometry

The formation of giant polyoxometalate (POM) species are relatively underexplored as their self-assembly process is complex due to the rapid kinetics. Polyoxopalladates (POPds) are a class of POMs based on Pd, the largest of which is the {Pd84}Ac wheel, and the slower kinetics mean the system is more amenable to systematic study. Here, we show it is possible to follow the assembly of two types of Pd-wheel; the {Pd84}Gly the smaller {Pd72}Prop wheel formed using glycolate and propionate ligands respectively. We analyzed the formation of {Pd72}Prop and {Pd84}Gly using mass spec-trometry (SEC-HPLC-MS and preparative desalting followed by MS). This was accompanied by studies that followed the chemical shift differences between the outer/inner ligands and the free ligand in solution for the {Pd84}Ac, {Pd72}Prop, and {Pd84}Gly species using NMR; this showed it was possible to track the formation of the wheels. Our findings confirm that the macrocycles assemble from smaller building blocks which react together to form the larger species over a period of days. These findings open the way for further structural derivatives and exploration of their host-guest chemistry

Famílies botàniques de plantes medicinals

Facultat de Farmàcia, Universitat de Barcelona. Ensenyament: Grau de Farmàcia, Assignatura: Botànica Farmacèutica, Curs: 2013-2014, Coordinadors: Joan Simon, Cèsar Blanché i Maria Bosch.Els materials que aquí es presenten són els recull de 175 treballs d’una família botànica d’interès medicinal realitzats de manera individual. Els treballs han estat realitzat per la totalitat dels estudiants dels grups M-2 i M-3 de l’assignatura Botànica Farmacèutica durant els mesos d’abril i maig del curs 2013-14. Tots els treballs s’han dut a terme a través de la plataforma de GoogleDocs i han estat tutoritzats pel professor de l’assignatura i revisats i finalment co-avaluats entre els propis estudiants. L’objectiu principal de l’activitat ha estat fomentar l’aprenentatge autònom i col·laboratiu en Botànica farmacèutica

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Transition metal oxide–based storage materials

Polyoxometalates (POMs) can also be referred to as molecular metal oxides due to their molecular composition and their position between monomeric entities and bulk oxides. In addition, silicon-based traditional electronic storage devices need to face the evolution that incorporating molecular metal oxides could provide. POMs, otherwise known as molecular metal oxides, have been known of for centuries but until the last hundred years our understanding of chemistry and engineering simply was not advanced enough to allow for sufficient analysis into their structures. In order to drive, direct and trap the self-assembly of molecular metal oxide dependent building blocks, clusters, and materials in solution, authors must acknowledge that such processes can be driven by redox reactions, ion exchange, metal unit substitution. It is worth noting that there has been a lot of research in recent years into determining position and effects of critical sizes and those POMs in general have been garnering attention for making strides in breaching the Nanoworld