Modelling Techniques for the Quantification of Some Electron Beam Induced Phenomena

This paper presents simulation models for quantifying the voltage contrast, cathodoluminescence and indirect specimen charging phenomena in the scanning electron microscope (SEM). The voltage contrast model comprises an electric field computation program using the finite-element approach, and a secondary electron trajectory tracking algorithm employing a linear electric field assumption. This trajectory tracking algorithm is more accurate than the conventional electron trajectory tracking algorithms which make use of a constant electric field assumption within each computation step. Using this model, results of qualitative voltage contrast effects on secondary electron trajectories in the specimen chamber of the SEM are shown. This model can also be used for quantitative voltage studies for designing low error voltage energy analysers. The cathodoluminescence (CL) model consists of programs for simulating the electron beam-specimen interaction via Monte Carlo analysis, excess carrier generation and distribution, and optical losses of the CL emission. This model has been used to simulate the CL intensity as a function of surface recombination velocity, diffusion length, and absorption coefficient. A model has also been developed to simulate indirect charging of specimens in the SEM. This model uses the finite-element method to solve for the self-consistent electric field due to the imposed boundary conditions, trapped and moving charges. Secondary electrons are tracked using the trajectory tracking scheme developed

Standards for the Characterization of Endurance in Resistive Switching Devices

Resistive switching (RS) devices are emerging electronic components that could have applications in multiple types of integrated circuits, including electronic memories, true random number generators, radiofrequency switches, neuromorphic vision sensors, and artificial neural networks. The main factor hindering the massive employment of RS devices in commercial circuits is related to variability and reliability issues, which are usually evaluated through switching endurance tests. However, we note that most studies that claimed high endurances >106 cycles were based on resistance versus cycle plots that contain very few data points (in many cases even <20), and which are collected in only one device. We recommend not to use such a characterization method because it is highly inaccurate and unreliable (i.e., it cannot reliably demonstrate that the device effectively switches in every cycle and it ignores cycle-to-cycle and device-to-device variability). This has created a blurry vision of the real performance of RS devices and in many cases has exaggerated their potential. This article proposes and describes a method for the correct characterization of switching endurance in RS devices; this method aims to construct endurance plots showing one data point per cycle and resistive state and combine data from multiple devices. Adopting this recommended method should result in more reliable literature in the field of RS technologies, which should accelerate their integration in commercial products

A functional alternative splicing mutation in human tryptophan hydroxylase-2

The brain serotonergic system has an essential role in the physiological functions of the central nervous system and dysregulation of serotonin (5-HT) homeostasis has been implicated in many neuropsychiatric disorders. The tryptophan hydroxylase-2 (TPH2) gene is the rate-limiting enzyme in brain 5-HT synthesis, and thus is an ideal candidate gene for understanding the role of dysregulation of brain serotonergic homeostasis. Here, we characterized a common, but functional single-nucleotide polymorphism (SNP rs1386493) in the TPH2 gene, which decreases efficiency of normal RNA splicing, resulting in a truncated TPH2 protein (TPH2-TR) by alternative splicing. TPH2-TR, which lacks TPH2 enzyme activity, dominant-negatively affects full-length TPH2 function, causing reduced 5-HT production. The predicted mRNA for TPH2-TR is present in postmortem brain of rs1386493 carriers. The rs13864923 variant does not appear to be overrepresented in either global or multiplex depression cohorts. However, in combination with other gene variants linked to 5-HT homeostasis, this variant may exhibit important epistatic influences

Tri-Level Resistive Switching in Metal-Nanocrystal-Based Al(2)O(3)/SiO(2) Gate Stack

Tri-level resistive switching behavior was observed in an Al(2)O(3)/SiO(2) gate stack with Ru metal nanocrystals embedded in the Al(2)O(3) layer. The device was successfully switched among three resistance states (high, medium, and low) after a forming process using a simple electrical method. The resistance ratio of the high-resistance state to the low-resistance state is more than 10(3). The insulator-to-conductor (and vice versa) transition of the Al(2)O(3) and SiO(2) dielectric layers is elucidated by a physical model, which invokes oxygen ion (O(2-)) trapping/detrapping at the metal-oxide interfaces, as well as O(2-) transport and annihilation with the oxygen vacancies in the breakdown percolation path. The switching transition of each individual dielectric layer is found to be dependent on the polarity of the gate bias. This new understanding opens the prospect of metal-nanocrystalbased Al(2)O(3)/SiO(2) gate stacks for a resistive switching memory application

Temperature-dependent relaxation current on single and dual layer Pt metal nanocrystal-based Al2O3/SiO2 gate stack

We present a systematic investigation of the temperature dependent relaxation current behavior for single layer and dual layer Pt metal nanocrystal (MNC)-based Al2O3/SiO2 flash memory gate stacks. Stacks containing single layer Pt MNC exhibit a dual-slope behavior in the log-log plots of the relaxation transient, whereas those with dual layer Pt MNC exhibit a single-slope behavior. We propose a physical model embodying two competing relaxation mechanisms to explain the Pt MNC induced relaxation current-thermionic emission and the quantum tunneling. Based on this model, the dual-slope behavior of single layer MNC-based gate stack can be ascribed to the dominance of thermionic emission at the initial part and quantum tunneling at the tail part. In contrast, the single slope behavior of the dual layer metal nanocrystal-based stack arises from the dominance of the quantum tunneling throughout the relaxation. In addition, we verify that stacks containing dual layer MNC show better retention property than their single layer counterparts. Our results demonstrate that relaxation current measurements offer a simple way to assess the charge retention capability for MNC-based gate stacks. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764873

Study of charge distribution and charge loss in dual-layer metal-nanocrystal-embedded high-kappa/SiO2 gate stack

In this work, we present a comprehensive experimental study of charge loss mechanisms in a dual-layer metal nanocrystal (DL-MNC) embedded high-kappa/SiO2 gate stack. Kelvin force microscopy characterization reveals that the internal-electric-field assisted tunneling could be a dominant charge loss mechanism in DL devices that mainly depends on the charge distribution in two MNC-layers and inter-layer dielectric (ILD) thickness between the two layers of nanocrystals. Our findings suggest that an optimized DL-MNCs embedded memory cell could be achieved by defining the ILD thickness larger than the average MNC-spacing for enhancement of retention ability in MNC embedded gate stacks. It implies the possibility of reducing MNC spacing in DL structure of scaled memory devices by controlling the thickness of ILD. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712565