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, 5-10 μs, use of high voltages, 5-10 V and complex design) will limit its development in the near future. Several alternatives, such as the Phase Change (PCRAM), Magnetic (MRAM) or Resistive (RERAM) Random Access Memories, are currently considered to overcome the main limitations of the Flash technology. In particular, RERAM’s, based on an Electric-Pulse-Induced Resistive Switching (EPIRS) effect, seem to be an appealing solution as they offer a better scalability, shorter writing times (10-100 ns) and a good endurance. Recently, non-volatile reversible EPIRS effects were uncovered on AM4X8 (A = Ga, Ge; M = V, Nb, Mo, Ta ; X = S, Se) single crystals at the Institut des Matériaux Jean Rouxel (IMN)1. In this chalcogenide compound, short low level electric pulses (100 ns, 500 V.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; however, a large scale integration of such material in device memory requires prior thin film deposition.

TECHNICAL DESCRIPTION

The patent proposed here describes the process to obtain a pure and polycrystalline thin film of GaV4S8, i.e. one member of the AM4X8 family, by RF magnetron sputtering, a widely used deposition process compatible with microelectronic technology. Thanks to the sintering of a target suitable for sputtering, thin layers, ranging from 100 nm to 2 μm, were obtained with a well controlled chemical composition and crystalline structure after a post-annealing at temperature as low as 450 °C in a sulfur rich atmosphere. This process allows obtaining simple MIM structures on silicon substrate exhibiting at room temperature the same electric-pulse-induced resistive switching, as the one observed in single crystals, i.e.:
1-the two resistance states are observed, with a relative variation (Rhigh-Rlow)/Rhigh up to 90%;
2-the application of a series of ± 2.5 V / 10 μs pulses induces a reversible resistive switching between the two resistance states. This demonstrates the possibility of write-erase cycles;
3-Up to 300 cycles between the two resistance states were observed without any significant fatigue effect.

The patent claims the whole process of thin layer preparation, fully compatible with industrial technologies, from the PVD target synthesis to the post-annealing step. The obtained thin layers display the resistive switching effect, which clearly represents an important step towards the use of this new class of compounds as active materials for non-volatile memory applications.

BENEFIT

– Compatibility with industrial processes: good scalability related to the simplicity of MIM structure,
– Potential transfer of the synthesis process to other members of the AM4X8 family,
– Chemistry similar to the one of PCRAM materials, despite a different physical mechanism.

For further information, please contact us (Ref 00946-02)