Julien Tranchant

Universal Electric-Field-Driven Resistive Transition in Narrow-Gap Mott Insulators

A striking universality in the electric-field-driven resistive switching is shown in three prototypical narrow-gap Mott systems. This model, based on key theoretical features of the Mott phenomenon, reproduces the general behavior of this resistive switching and demonstrates that it can be associated with a dynamically directed avalanche. This model predicts non-trivial accumulation and relaxation times that are verified experimentally.

Deposition of GaV4S8 thin films by H2S/Ar reactive sputtering for ReRAM applications

The chalcogenide compound GaV4S8 is promising for applications as active materials in non-volatile memory applications. We report here a comprehensive study on the thin-film deposition of this compound using a stoichiometric GaV4S8 target and H2S/Ar reactive sputtering. We show that a fraction of 0.5% to 1% of H2S in the reactive plasma is sufficient to compensate the sulfur deficiency that appears in films deposited in pure Ar plasma. This reactive plasma method allows avoiding the addition of elemental sulfur during the annealing treatment required to obtain a crystallized and stoichiometric GaV4S8 layer. A simple Au/GaV4S8/Au structure presents a resistive switching behaviour well suited for non-volatile memory applications.

Electric Pulse Induced Resistive Switching in the Narrow Gap Mott Insulator GaMo4S8

We report here on resistive switching measurements on GaMo4S8 a lacunar spinel compound with tetrahedral Mo4 clusters filled with 11 electrons. Alike other clustered lacunar spinel compounds with 7 or 8 electrons per cluster, this narrow gap Mott Insulator exhibits both a volatile and a non-volatile unipolar resistive switching. We found that the volatile resistive switching appears above a threshold electric field in the 7 kV/cm range. For electric field much larger than this threshold, the resistive switching becomes non-volatile. Successive electric pulses allow switching back and forth between high and low resistance states. All these results demonstrate that the narrow gap Mott insulator compound GaMo4S8 could be a relevant candidate for a new type of non-volatile memory based on an electric field induced breakdown of the Mott insulating state.

Mott insulators: A large class of materials for Leaky Integrate and Fire (LIF) artificial neuron

A major challenge in the field of neurocomputing is to mimic the brains behavior by implementing artificial synapses and neurons directly in hardware. Toward that purpose, many researchers are exploring the potential of new materials and new physical phenomena. Recently, a new concept of the Leaky Integrate and Fire (LIF) artificial neuron was proposed based on the electric Mott transition in the inorganic Mott insulator GaTa4Se8. In this work, we report on the LIF behavior in simple two-terminal devices in three chemically very different compounds, the oxide (V0.89Cr0.11)2O3, the sulfide GaMo4S8, and the molecular system [Au(iPr-thiazdt)2] (C12H14AuN2S8), but sharing a common feature, their Mott insulator ground state. In all these devices, the application of an electric field induces a volatile resistive switching and a remarkable LIF behavior under a train of pulses. It suggests that the Mott LIF neuron is a general concept that can be extended to the large class of Mott insulators.A major challenge in the field of neurocomputing is to mimic the brains behavior by implementing artificial synapses and neurons directly in hardware. Toward that purpose, many researchers are exploring the potential of new materials and new physical phenomena. Recently, a new concept of the Leaky Integrate and Fire (LIF) artificial neuron was proposed based on the electric Mott transition in the inorganic Mott insulator GaTa4Se8. In this work, we report on the LIF behavior in simple two-terminal devices in three chemically very different compounds, the oxide (V0.89Cr0.11)2O3, the sulfide GaMo4S8, and the molecular system [Au(iPr-thiazdt)2] (C12H14AuN2S8), but sharing a common feature, their Mott insulator ground state. In all these devices, the application of an electric field induces a volatile resistive switching and a remarkable LIF behavior under a train of pulses. It suggests that the Mott LIF neuron is a general concept that can be extended to the large class of Mott insulators.

An Artificial Neuron Founded on Resistive Switching of Mott Insulators

Narrow-gap Mott insulators exhibit under electric field a resistive switching related to the formation of a conducting filamentary path made of metastable metallic domains. When this effect is non-volatile it can be used to build up a new type of Resistive Random Access Memory called Mott memory. But we show here that when the resistive switching remains volatile it is of great interest for neuromorphic applications different than artificial synapses implemented by the so-called Memristors. Specifically, we show that under electric field the dynamics of the creation and destruction of the metastable metallic domains implement the three basic functions Leaky Integrate and Fire of artificial neurons. The central result of the present work is therefore to demonstrate that a simple two terminal device made of Mott insulator can be considered as an analogue of an artificial Leaky Integrate and Fire neuron.

From Resistive Switching Mechanisms in AM4Q8 Mott Insulators to Mott Memories

The application of electrical pulses on Mott insulators AM4Q8 (A = Ga, Ge ; M = V, Nb, Ta, Mo; Q = S, Se) induces a new phenomenon of resistive switching (RS). Appearing above threshold electric fields of a few kV/cm, this volatile transition stabilizes into a non volatile RS for higher electric fields. A pulse protocol alternating short multi-pulses of high voltage with long single pulses of low voltage enables to control this reversible RS in crystals and thin films. The resulting cycling performances obtained on GaV4S8 miniaturized devices demonstrate the interest of these compounds towards Mott memory applications.