CONTEXT

Information storage and more specifically non-volatile memories represent strategic issues in the field of microelectronics. The huge non-volatile memory market is currently led by the Flash technology (Flash cards, Solid State Drives). However, the intrinsic drawbacks of this technology (long writing time, 5–10µs, use of high voltages, 5-10V and complex design) will limit its development in the near future. Several alternatives, such as the Phase Change (PCRAM), Magnetic (MRAM) or Resistive (RRAM)  Random Acces Memories, are currently considered to overcome the main limitations of the Flash technology. In particular, RRAM’s based on resistive switching effect, seem to be an attractive solution as they offer a better scalability, shorter writing time (10-100 ns) and a good endurance. Recently, resistive switching effects were uncovered at the “Institut des Materiaux Jean Rouxel” (IMN) on single crystals of the chalcogenide compounds AM₄X₈ ( A = Ga,Ge; M = V, Nb, Mo,Ta; X= S, Se ) (patent PCT/EP2008/052968). In these non-centrosymetric Mott Insulators, short low level electric pulses (down to 100 ns, and less than 10 kV.cm^-1) yield a non-volatile resistive switching between a high and a low resistance state. These results obtained on single crystals are very promising for RRAM applications, since the resistive switching effect was also obtained on polycristalline thin layers prepared thanks to a deposition method fully compatible with industrial technologies, from the PVD target synthesis to the post-annealing step (Patent 09-R15981-FR, 100901).

TECHNICAL DESCRIPTION

The patent proposed here describes the use of centrosymetric mott insulators for RRAM applications,. The existence of a resistive switching phenomenon induced by electrical pulse was discovered in the family of centrosymmetric Mott insulators at the Institut des Matériaux Jean Rouxel (IMN). The consecutive application of electrical pulses induces the variation of the resistance of these materials between at least two distinct resistance states in a reversible manner. These resistance states can constitute 0 and 1 states of a binary memory bit, as a reversible switching between both states can be achieved. The resistive transition can be either volatile or nonvolatile and can be promoted thanks to electric pulses exceeding a treshold field applied on the active material place between two electrodes, i.e. a simple MIM device (Metal / centrosymmetric Mott insulator / Metal). Any material among the family of centrosymmetric Mott insulators can be used as active material of this MIM device for data storage.
The observed resistive switching in these systems corresponds neither to a amorphous crystalline phase change nor to any of the phenomena (thermal, electronic injection or ionic electromigration) proposed so far to explain the resistive switching effect in materials envisioned for RRAM applications. Our recent results show that the application of an electric field larger than a treshold field generates in the material an avalanche effect, that shows some similarity with the avalanche breakdown observed in semi-conductors. Our work suggests that this avalanche effect in Mott Insulator induces an insulator to metal transition at the nanoscale, which could enable a high scalability below 30 nm.

BENEFITS

•  Compatibility with industrial processes : good scalability related to the simplicity of MIM structure
•  Competitive characteristics: short switching time (less than 100 ns), potential low-power consumption, potential scalability if deposited in thin layer (see patent 09-R15981-FR, 100901).

INDUSTRIAL APPLICATIONS

Non-volatile memory: Resistive-RAM for highly integrated systems with short switching time, short or long retention time and low power consumption.

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