149 research outputs found
Filamentary Switching: Synaptic Plasticity through Device Volatility
Replicating the computational functionalities and performances of the brain
remains one of the biggest challenges for the future of information and
communication technologies. Such an ambitious goal requires research efforts
from the architecture level to the basic device level (i.e., investigating the
opportunities offered by emerging nanotechnologies to build such systems).
Nanodevices, or, more precisely, memory or memristive devices, have been
proposed for the implementation of synaptic functions, offering the required
features and integration in a single component. In this paper, we demonstrate
that the basic physics involved in the filamentary switching of electrochemical
metallization cells can reproduce important biological synaptic functions that
are key mechanisms for information processing and storage. The transition from
short- to long-term plasticity has been reported as a direct consequence of
filament growth (i.e., increased conductance) in filamentary memory devices. In
this paper, we show that a more complex filament shape, such as dendritic paths
of variable density and width, can permit the short- and long-term processes to
be controlled independently. Our solid-state device is strongly analogous to
biological synapses, as indicated by the interpretation of the results from the
framework of a phenomenological model developed for biological synapses. We
describe a single memristive element containing a rich panel of features, which
will be of benefit to future neuromorphic hardware systems
Evaluation of a gate capacitance in the sub-aF range for a chemical field-effect transistor with a silicon nanowire channel
An evaluation of the gate capacitance of a field-effect transitor (FET) whose
channel length and width are several ten nanometer, is a key point for sensors
applications. However, experimental and precise evaluation of capacitance in
the aF range or less has been extremely difficult. Here, we report an
extraction of the capacitance down to 0.55 aF for a silicon FET with a
nanoscale wire channel whose width and length are 15 and 50 nm, respectively.
The extraction can be achieved by using a combination of four kinds of
measurements: current characteristics modulated by double gates,
random-telegraph-signal noise induced by trapping and detrapping of a single
electron, dielectric polarization noise, and current characteristics showing
Coulomb blockade at low temperature. The extraction of such a small gate
capacitance enables us to evaluate electron mobility in a nanoscale wire using
a classical model of current characteristics of a FET.Comment: To be published in IEEE Trans. Nanotechno
Relaxation dynamics in covalently bonded organic monolayers on silicon
We study the dynamic electrical response of a silicon-molecular
monolayer-metal junctions and we observe two contributions in the admittance
spectroscopy data. These contributions are related to dipolar relaxation and
molecular organization in the monolayer in one hand, and the presence of
defects at the silicon/molecule interface in the other hand. We propose a small
signal equivalent circuit suitable for the simulations of these molecular
devices in commercial device simulators. Our results concern monolayers of
alkyl chains considered as a model system but can be extended to other
molecular monolayers. These results open door to a better control and
optimization of molecular devices.Comment: 1 pdf file including text, figures and tables. Phys. Rev. B, in pres
The Non-Ideal Organic Electrochemical Transistors Impedance
Organic electrochemical transistors offer powerful functionalities for
biosensors and neuroinspired electronics, with still much to understand on the
time dependent behavior of this electrochemical device. Here, we report on
distributed element modeling of the impedance of such microfabricated device,
systematically performed under a large concentration variation for KCl(aq) and
CaCl2(aq). We propose a new model which takes into account three main
deviations to ideality, that were systematically observed, caused by both the
materials and the device complexity, over large frequency range (1 Hz to 1
MHz). More than introducing more freedom degree, the introduction of these non
redundant parameters and the study of their behaviors as function of the
electrolyte concentration and applied voltage give a more detailed picture of
the OECT working principles. This optimized model can be further useful for
improving OECT performances in many applications (e.g. biosensors,
neuroinspired devices) and circuit simulations.Comment: Full paper with supporting informatio
Impact of dopant species on the interfacial trap density and mobility in amorphous In-X-Zn-O solution-processed thin-film transistors
Alloying of In/Zn oxides with various X atoms stabilizes the IXZO structures
but generates electron traps in the compounds, degrading the electron mobility.
To assess whether the latter is linked to the oxygen affinity or the ionic
radius, of the X element, several IXZO samples are synthesized by the sol-gel
process, with a large number (14) of X elements. The IXZOs are characterized by
XPS, SIMS, DRX, and UV-spectroscopy and used for fabricating thin film
transistors. Channel mobility and the interface defect density NST, extracted
from the TFT electrical characteristics and low frequency noise, followed an
increasing trend and the values of mobility and NST are linked by an
exponential relation. The highest mobility (8.5 cm2/Vs) is obtained in
In-Ga-Zn-O, and slightly lower value for Sb and Sn-doped IXZOs, with NST is
about 2E12 cm2/eV, close to that of the In-Zn-O reference TFT. This is
explained by a higher electronegativity of Ga, Sb, and Sn than Zn and In, their
ionic radius values being close to that of In and Zn. Consequently, Ga, Sb, and
Sn induce weaker perturbations of In-O and Zn-O sequences in the sol-gel
process, than the X elements having lower electronegativity and different ionic
radius. The TFTs with X = Ca, Al, Ni and Cu exhibited the lowest mobility and
NST > 1E13 cm2/eV, most likely because of metallic or oxide clusters formation
Tunnel current in self-assembled monolayers of 3-mercaptopropyltrimethoxysilane
The current density-voltage (J-V) characteristics of self assembled
monolayers of 3-mercaptopropyltrimethoxysilane (MPTMS) chemisorbed on the
native oxide surface of p+-doped Si demonstrate the excellent tunnel dielectric
behavior of organic monolayers down to 3 carbon atoms. The J-V characteristics
of MPTMS SAMs on Si are found to be asymmetric, and the direction of
rectification has been found to depend upon the applied voltage range. At
voltages < 2.45V, the reverse bias current was found to be higher than forward
bias current; while at higher voltages this trend was reversed. This result is
in agreement with Simmons theory. The tunnel barrier heights for this short
chain (2.56 and 2.14 eV respectively at Au and Si interfaces) are in good
agreement with the ones for longer chains (>10 carbon atoms) if the chain is
chemisorbed at the electrodes. These results extend all previous experiments on
such molecular tunnel dielectrics down to 3 carbon atoms. This suggests that
these molecular monolayers, having good tunnel behavior (up to 2.5 eV) over a
large bias range, can be used as gate dielectric well below the limits of
Si-based dielectrics.Comment: Small, in pres
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