184 research outputs found
Perspective: Organic electronic materials and devices for neuromorphic engineering
Neuromorphic computing and engineering has been the focus of intense research
efforts that have been intensified recently by the mutation of Information and
Communication Technologies (ICT). In fact, new computing solutions and new
hardware platforms are expected to emerge to answer to the new needs and
challenges of our societies. In this revolution, lots of candidates
technologies are explored and will require leveraging of the pro and cons. In
this perspective paper belonging to the special issue on neuromorphic
engineering of Journal of Applied Physics, we focus on the current achievements
in the field of organic electronics and the potentialities and specificities of
this research field. We highlight how unique material features available
through organic materials can be used to engineer useful and promising
bioinspired devices and circuits. We also discuss about the opportunities that
organic electronic are offering for future research directions in the
neuromorphic engineering field
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
Cation Discrimination in Organic Electrochemical Transistors by Dual Frequency Sensing
In this work, we propose a strategy to sense quantitatively and specifically
cations, out of a single organic electrochemical transistor (OECT) device
exposed to an electrolyte. From the systematic study of six different chloride
salts over 12 different concentrations, we demonstrate that the impedance of
the OECT device is governed by either the channel dedoping at low frequency and
the electrolyte gate capacitive coupling at high frequency. Specific cationic
signatures, which originates from the different impact of the cations behavior
on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)
polymer and their conductivity in water, allow their discrimination at the same
molar concentrations. Dynamic analysis of the device impedance at different
frequencies could allow the identification of specific ionic flows which could
be of a great use in bioelectronics to further interpret complex mechanisms in
biological media such as in the brain.Comment: Full text and supporting informatio
1-octadecene monolayers on Si(111) hydrogen-terminated surfaces: effects of substrate doping
We have studied the electronic properties, in relation to their structural
properties, of monolayers of 1-octadecene attached on a hydrogen-terminated
(111) silicon surface. The molecules are attached using the free-radical
reaction between C=C and Si-H activated by an ultraviolet illumination. We have
compared the structural and electrical properties of monolayers formed on
silicon substrate of different types (n-type and p-type) and different doping
concentrations from low-doped (~1E14 cm-3) to highly doped (~1E19 cm-3) silicon
substrates. We show that the monolayers on n-, p- and p+ silicon are densely
packed and that they act as very good insulating films at a nanometer thickness
with leakage currents as low as ~1E-7 A.cm-2 and high quality
capacitance-voltage characteristics. The monolayers formed on n+-type silicon
are more disordered and therefore exhibit larger leakage current densities
(>1E-4 A.cm-2) when embedded in a silicon/monolayer/metal junction. The
inferior structural and electronic properties obtained with n+-type silicon
pinpoint the important role of surface potential and of the position of the
surface Fermi level during the chemisorption of the organic monolayers.Comment: 33 pages, 8 figures, to be published J. Appl. Phy
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
An artificial spiking synapse made of molecules and nanoparticles
Molecule-based devices are envisioned to complement silicon devices by providing new functions or already existing functions at a simpler process level and at a lower cost by virtue of their self-organization capabilities, moreover, they are not bound to von Neuman architecture and this may open the way to other architectural paradigms. Here we demonstrate a device made of conjugated molecules and metal nanoparticles (NPs) which behaves as a spiking synapse suitable for integration in neural network architectures. We demonstrate that this device exhibits the main behavior of a biological synapse. These results open the way to rate coding utilization of the NOMFET in perceptron and Hopfield networks. We can also envision the NOMFET as a building block of neuroelectronics for interfacing neurons or neuronal logic devices made from patterned neuronal cultures with solid-state devices and circuits
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
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