304 research outputs found
A simple and controlled single electron transistor based on doping modulation in silicon nanowires
A simple and highly reproducible single electron transistor (SET) has been
fabricated using gated silicon nanowires. The structure is a
metal-oxide-semiconductor field-effect transistor made on silicon-on-insulator
thin films. The channel of the transistor is the Coulomb island at low
temperature. Two silicon nitride spacers deposited on each side of the gate
create a modulation of doping along the nanowire that creates tunnel barriers.
Such barriers are fixed and controlled, like in metallic SETs. The period of
the Coulomb oscillations is set by the gate capacitance of the transistor and
therefore controlled by lithography. The source and drain capacitances have
also been characterized. This design could be used to build more complex SET
devices.Comment: to be published in Applied Physics Letter
Three-Dimensional Simulation of the Dependence of the Programming Window of SOI Nanocrystal Memories on the Channel Width
Individual charge traps in silicon nanowires: Measurements of location, spin and occupation number by Coulomb blockade spectroscopy
We study anomalies in the Coulomb blockade spectrum of a quantum dot formed
in a silicon nanowire. These anomalies are attributed to electrostatic
interaction with charge traps in the device. A simple model reproduces these
anomalies accurately and we show how the capacitance matrices of the traps can
be obtained from the shape of the anomalies. From these capacitance matrices we
deduce that the traps are located near or inside the wire. Based on the
occurrence of the anomalies in wires with different doping levels we infer that
most of the traps are arsenic dopant states. In some cases the anomalies are
accompanied by a random telegraph signal which allows time resolved monitoring
of the occupation of the trap. The spin of the trap states is determined via
the Zeeman shift.Comment: 9 pages, 8 figures, v2: section on RTS measurements added, many
improvement
Experimental approval of the extended flat bands and gapped subbands in rhombohedral multilayer graphene
Graphene layers are known to stack in two stable configurations, namely ABA
or ABC stacking, with drastically distinct electronic properties. Unlike the
ABA stacking, little has been done to experimentally investigate the electronic
properties of ABC graphene multilayers. Here, we report the first magneto
optical study of a large ABC domain in a graphene multilayers flake, with ABC
sequences exceeding 17 graphene sheets. The ABC-stacked multilayers can be
fingerprinted with a characteristic electronic Raman scattering response, which
persists even at room temperatures. Tracing the magnetic field evolution of the
inter Landau level excitations from this domain gives strong evidence to the
existence of a dispersionless electronic band near the Fermi level,
characteristic of such stacking. Our findings present a simple yet powerful
approach to probe ABC stacking in graphene multilayer flakes, where this highly
degenerated band appears as an appealing candidate to host strongly correlated
states.Comment: 8 pages, 4 figure
Background charges and quantum effects in quantum dots transport spectroscopy
We extend a simple model of a charge trap coupled to a single-electron box to
energy ranges and parameters such that it gives new insights and predictions
readily observable in many experimental systems. We show that a single
background charge is enough to give lines of differential conductance in the
stability diagram of the quantum dot, even within undistorted Coulomb diamonds.
It also suppresses the current near degeneracy of the impurity charge, and
yields negative differential lines far from this degeneracy. We compare this
picture to two other accepted explanations for lines in diamonds, based
respectively on the excitation spectrum of a quantum dot and on fluctuations of
the density-of-states in the contacts. In order to discriminate between these
models we emphasize the specific features related to environmental charge
traps. Finally we show that our model accounts very well for all the anomalous
features observed in silicon nanowire quantum dots.Comment: 7 pages, 6 figure
A self-adaptive hardware with resistive switching synapses for experience-based neurocomputing
: Neurobiological systems continually interact with the surrounding environment to refine their behaviour toward the best possible reward. Achieving such learning by experience is one of the main challenges of artificial intelligence, but currently it is hindered by the lack of hardware capable of plastic adaptation. Here, we propose a bio-inspired recurrent neural network, mastered by a digital system on chip with resistive-switching synaptic arrays of memory devices, which exploits homeostatic Hebbian learning for improved efficiency. All the results are discussed experimentally and theoretically, proposing a conceptual framework for benchmarking the main outcomes in terms of accuracy and resilience. To test the proposed architecture for reinforcement learning tasks, we study the autonomous exploration of continually evolving environments and verify the results for the Mars rover navigation. We also show that, compared to conventional deep learning techniques, our in-memory hardware has the potential to achieve a significant boost in speed and power-saving
Hardware calibrated learning to compensate heterogeneity in analog RRAM-based Spiking Neural Networks
Spiking Neural Networks (SNNs) can unleash the full power of analog Resistive Random Access Memories (RRAMs) based circuits for low power signal processing. Their inherent computational sparsity naturally results in energy efficiency benefits. The main challenge implementing robust SNNs is the intrinsic variability (heterogeneity) of both analog CMOS circuits and RRAM technology. In this work, we assessed the performance and variability of RRAM-based neuromorphic circuits that were designed and fabricated using a 130 nm technology node. Based on these results, we propose a Neuromorphic Hardware Calibrated (NHC) SNN, where the learning circuits are calibrated on the measured data. We show that by taking into account the measured heterogeneity characteristics in the off-chip learning phase, the NHC SNN self-corrects its hardware non-idealities and learns to solve benchmark tasks with high accuracy. This work demonstrates how to cope with the heterogeneity of neurons and synapses for increasing classification accuracy in temporal tasks
Effects of oxygen partial pressure and annealing temperature on the formation of sputtered tungsten oxide films
Thin films of tungsten oxide were deposited on silicon substrates using reactive radio frequency sputtering. The structure of the films strongly depends on the conditions of deposition and post-treatment. Important issues are the influences of oxygen pressure during deposition and annealing temperature on the morphology. Atomic force microscopy and scanning electron microscopy revealed that films were formed by grains. The sample deposited with an Ar:O(2) partial pressure ratio of 1: 1 showed the highest roughness and the smallest grains when annealed at 350degrees C. X-ray photoelectron spectroscopy analysis revealed that the films were close to their stoichiometric formulation irrespective of the oxygen partial pressure used during film deposition. The number of W=O bonds at the grain boundaries was found to be dependent on the oxygen partial pressure. Analysis by Raman spectroscopy suggested that the structure of the films was monoclinic. On the basis of these results, an annealing temperature of 350degrees C was selected as post-treatment for the fabrication of WO(3) gas sensors. These sensors were highly sensitive, highly selective to ammonia vapors, and moderately responsive to humidity. (C) 2002 The Electrochemical Society.1493H81H8
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