Resistive Switching Induced by Electric Pulses in a Single-Component Molecular Mott Insulator

Abstract

International audienceResistive random-access memory (ReRAM) made of organic materials has recently received much attention for application in flexible devices. In the latter, resistive switching is usually obtained thanks to electrochemical effects or charge trapping. This work shows that, under electric pulses, the crystalline molecular Mott insulator [Au(Et-thiazdt) 2 ] exhibits a resistive switching based on an insulator-to-metal transition (IMT). Electric pulses exceeding a threshold electric field of a few kilovolts/centimeter induce a volatile transition, due to an intrinsic, purely electronic effect related to an avalanche phenomenon. Moreover, the application of electric pulses of higher amplitude induces a nonvolatile and reversible resistive switching. Both two-level and multilevel switching between resistances R on and R off are observed. At room temperature, a R off /R on ratio >100 is obtained, which is very high for this kind of switching mechanism and quite promising for ReRAM applications. [Au(Et-thiazdt) 2 ] appears as the first molecular member of a new class of ReRAM called Mott memories. ■ INTRODUCTION The demand for organic-based electronic devices has recently increased due to their potential advantages over conventional inorganic electronics, such as their low fabrication cost, high mechanical flexibility, light weight, and ease of fabrication. 1,2 Flexible organic memories that would enable data processing, storage, and communication are essential components to achieve flexible electronics. 3−9 In that context, resistive random-access memory (ReRAM) made of organic materials has recently received much attention. 10−14 In ReRAM, information storage is enabled by a nonvolatile resistive switching between two different resistance states achieved by the application of short electric pulses. In organic ReRAM, resistive switching mechanisms generally involve electro-chemical effects associated with anion or cation migrations or charge trapping in metallic nanoparticles. 15−20 A new type of resistive switching was recently reported in several chalcogenide inorganic narrow-gap Mott insulators with formulation AM 4 Q 8 (A = Ga, Ge; M = V, Nb, Ta; Q = S, Se). 21−24 The application of short electric pulses on these compounds induces a new phenomenon of volatile and nonvolatile resistive switching related to the collapse of the Mott insulating state. The volatile transition appears above threshold electric fields of a few kilovolts/centimeter and is based on an electronic avalanche process. 22,23 For electric fields much higher than the threshold avalanche breakdown field (E th), the resistive switching turns nonvolatile. 21 The switching mechanism is closely related with their Mott insulator character, as the avalanche breakdown induces the collapse of the Mott insulating state at the local scale and triggers the formation of a granular conductive filament formed by metallic and superinsulating domains. 21−23,25 First identified in inorganic compounds, the generalization of this purely electronic in...

High Ambipolar Mobility in a Neutral Radical Gold Dithiolene Complex

“…The isomers can be distinguished by a 0.01 ppm difference between the dithiolene protons in the 1 H NMR, and the isomers do not appear to interconvert (Figure S1, Supporting Information). While rapid cis–trans isomerism in solution has been reported for asymmetric nickel dithiolene complexes, rapid interconversion for asymmetric gold dithiolene complexes has not been observed . In most cases, the isomers are separated after the oxidation to the neutral species by selective crystallization of one isomer over the other.…”

“…Metal dithiolene complexes have received a great deal of attention in recent years as potential molecular based functional materials, due to their high stability, magnetic, optical and conductive properties, which can be tuned through variation of the metal center or substitution pattern of the dithiolene ligands . In particular, neutral nickel and gold bis(1,2‐dithiolene) complexes have been studied as single component conductors, due to attractive features such as their square planar geometry and delocalized electronic structure, which leads to favorable intermolecular stacking interactions (a requirement for solid state conductivity) and reversible and tunable redox chemistry. Additionally, neutral gold dithiolene complexes can behave as Mott insulators, with one radical per site, resulting in an activation barrier for conductivity behavior that can be overcome with pressure .…”

“…In particular, neutral nickel and gold bis(1,2‐dithiolene) complexes have been studied as single component conductors, due to attractive features such as their square planar geometry and delocalized electronic structure, which leads to favorable intermolecular stacking interactions (a requirement for solid state conductivity) and reversible and tunable redox chemistry. Additionally, neutral gold dithiolene complexes can behave as Mott insulators, with one radical per site, resulting in an activation barrier for conductivity behavior that can be overcome with pressure . Since the first molecular superconductor based on a metal dithiolene complex was reported, a charge transfer salt (TTF)[Ni(dmit) 2 ] 2 , a large number of neutral complexes containing dithiolene ligands with a TTF backbone have been synthesized, such as Au(ptdt) 2 , and Au(tmdt) 2 , showing metallic or near metallic behavior at ambient temperature and pressure.…”

“…Neutral gold dithiolene complexes without TTF containing ligands have also been reported, such as Au(α‐tpdt) 2 and Au(bdt) 2 , showing a wide variety of conductive properties, from semiconductor to metallic . Several complexes in the thiazole dithiolate family have been reported showing activated conductivity under ambient conditions, with some showing metal‐like conductivity under pressure, and one showing metallic behavior under ambient conditions …”

Interplay between bandwidth-controlled and filling-controlled pressure-induced Mott insulator to metal transition in the molecular compound [Au(Et-thiazdt) 2]

“…RRam applications are made possible by the resistive switching phenomenon (resistive transition induced by electric pulses). Whereas the resistive switching is usually obtained by electro-chemical effects or charge trapping, it is based on a pure electronic intrinsic effect in inorganic Mott GaTa 4 Se 8 [22] and in [Au(Et-thiazdt) 2 ] [23]. This phenomenon could constitute a generic feature of Mott insulators.…”