60 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
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
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
Expanding memory in recurrent spiking networks
Recurrent spiking neural networks (RSNNs) are notoriously difficult to train
because of the vanishing gradient problem that is enhanced by the binary nature
of the spikes. In this paper, we review the ability of the current
state-of-the-art RSNNs to solve long-term memory tasks, and show that they have
strong constraints both in performance, and for their implementation on
hardware analog neuromorphic processors. We present a novel spiking neural
network that circumvents these limitations. Our biologically inspired neural
network uses synaptic delays, branching factor regularization and a novel
surrogate derivative for the spiking function. The proposed network proves to
be more successful in using the recurrent connections on memory tasks
Conductive filament evolution dynamics revealed by cryogenic (1.5 K) multilevel switching of CMOS-compatible Al2O3/TiO2 resistive memories
This study demonstrates multilevel switching at 1.5 K of Al2O3/TiO2-x
resistive memory devices fabricated with CMOS-compatible processes and
materials. The I-V characteristics exhibit a negative differential resistance
(NDR) effect due to a Joule-heating-induced metal-insulator transition of the
Ti4O7 conductive filament. Carrier transport analysis of all multilevel
switching I-V curves show that while the insulating regime follows the space
charge limited current (SCLC) model for all resistance states, the conduction
in the metallic regime is dominated by SCLC and trap-assisted tunneling (TAT)
for low- and high-resistance states respectively. A non-monotonic conductance
evolution is observed in the insulating regime, as opposed to the continuous
and gradual conductance increase and decrease obtained in the metallic regime
during the multilevel SET and RESET operations. Cryogenic transport analysis
coupled to an analytical model accounting for the
metal-insulator-transition-induced NDR effects and the resistance states of the
device provide new insights on the conductive filament evolution dynamics and
resistive switching mechanisms. Our findings suggest that the non-monotonic
conductance evolution in the insulating regime is due to the combined effects
of longitudinal and radial variations of the Ti4O7 conductive filament during
the switching. This behavior results from the interplay between temperature-
and field-dependent geometrical and physical characteristics of the filament.Comment: 8 pages, 4 figure
Observation of Highly Nonlinear Resistive Switching of Al2O3/TiO2-x Memristors at Cryogenic Temperature (1.5 K)
In this work, we investigate the behavior of Al2O3/TiO2-x cross-point
memristors in cryogenic environment. We report successful resistive switching
of memristor devices from 300 K down to 1.5 K. The I-V curves exhibit negative
differential resistance effects between 130 and 1.5 K, attributed to a
metal-insulator transition (MIT) of the Ti4O7 conductive filament. The
resulting highly nonlinear behavior is associated to a maximum ION/IOFF ratio
of 84 at 1.5 K, paving the way to selector-free cryogenic passive crossbars.
Finally, temperature-dependant thermal activation energies related to the
conductance at low bias (20 mV) are extracted for memristors in low resistance
state, suggesting hopping-type conduction mechanisms.Comment: 4 pages, 4 figures, IEEE 14th Nanotechnology Materials & Devices
Conference (NMDC 2019
Signals to Spikes for Neuromorphic Regulated Reservoir Computing and EMG Hand Gesture Recognition
Surface electromyogram (sEMG) signals result from muscle movement and hence
they are an ideal candidate for benchmarking event-driven sensing and
computing. We propose a simple yet novel approach for optimizing the spike
encoding algorithm's hyper-parameters inspired by the readout layer concept in
reservoir computing. Using a simple machine learning algorithm after spike
encoding, we report performance higher than the state-of-the-art spiking neural
networks on two open-source datasets for hand gesture recognition. The spike
encoded data is processed through a spiking reservoir with a biologically
inspired topology and neuron model. When trained with the unsupervised activity
regulation CRITICAL algorithm to operate at the edge of chaos, the reservoir
yields better performance than state-of-the-art convolutional neural networks.
The reservoir performance with regulated activity was found to be 89.72% for
the Roshambo EMG dataset and 70.6% for the EMG subset of sensor fusion dataset.
Therefore, the biologically-inspired computing paradigm, which is known for
being power efficient, also proves to have a great potential when compared with
conventional AI algorithms.Comment: Accepted to International Conference on Neuromorphic Systems (ICONS
2021
Low voltage and time constant organic synapse-transistor
We report on an artificial synapse, an organic synapse-transistor (synapstor)
working at 1 volt and with a typical response time in the range 100-200 ms.
This device (also called NOMFET, Nanoparticle Organic Memory Field Effect
Transistor) combines a memory and a transistor effect in a single device. We
demonstrate that short-term plasticity (STP), a typical synaptic behavior, is
observed when stimulating the device with input spikes of 1 volt. Both
significant facilitating and depressing behaviors of this artificial synapse
are observed with a relative amplitude of about 50% and a dynamic response <
200 ms. From a series of in-situ experiments, i.e. measuring the
current-voltage characteristic curves in-situ and in real time, during the
growth of the pentacene over a network of gold nanoparticles, we elucidate
these results by analyzing the relationship between the organic film morphology
and the transport properties. This synapstor works at a low energy of about 2
nJ/spike. We discuss the implications of these results for the development of
neuro-inspired computing architectures and interfacing with biological neurons.Comment: Full paper with supporting informatio
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