Materials with a non-volatile resistive transition for RRAM memories

The field of non-volatile memories is currently dominated by Flash memories, the technological limitations of integration will quickly slow down there expansion. Resistive Random Access Memories (ReRAMs) are one of the most promising candidates for the replacement of Flash technology. Since one decade, research on ReRAMs is an emerging field particularly active at international level. In ReRAMs, non volatile data storage is enabled by a reversible electric-pulse-induced resistive switching (RS) between two different resistance states. This phenomenon, observed in several classes of materials, was mostly so far explained by thermal and/or electrochemical effects.

Recently, IMN researchers discovered the existence of a volatile and a non-volatile resistive transition in single crystals of narrow gap Mott insulators AM₄Q₈ (A = Ga, Ge; M = V, Nb, Ta; Q = S, Se). The results indicate that the mechanism behind the resistive transition is quite original and based on an electronic avalanche, allowing to consider a new class of RRAM memories from AM₄Q₈ compounds (Patent CNRS- Nantes Univ. 2007). The application interest was investigated through thin film deposition by magnetron sputtering of GaV₄S₈ compound. The phenomenon of non-volatile resistive and reversible transition induced by electric pulses was validated on GaV₄S₈ thin layers which exhibit already memory performances superior to those of single crystals. These materials are now considered in the international roadmap for semiconductors (ITRS 2011 AND 2013) as promising candidates to replace flash memory.

Recent significant progresses on understanding the mechanism behind the resistive transition allowed extending this functionality to a whole class of materials: the narrow gap Mott insulators, and in particular the timed honored Mott insulator (V_1-xCr_x)₂O₃ (Patent CNRS- Nantes Univ. 2012). The use of thin layers of such materials paves the way to a new class of ReRAMs, the Mott memories.

In the framework of Madec Querré PhD (2012-2016), the deposition of (V1-xCrx)2O3 Mott insulator in thin film has been investigated in close collaboration with ISCR (Institute Of Chemical Sciences of Rennes).

Thin layers of crystalline V₂O₃ and (V_1-xCr_x)₂O₃ are obtained by two methods: pulsed laser ablation of a composite target composite V₂O₃/Cr₂O₃ (ISCR) and DC cathodic magnetron co-sputtering in reactive mode (Ar / O₂) of vanadium and chromium targets (IMN). Well controlled thin layers are obtained in terms of purity, crystal quality, chromium content and oxygen stoichiometry, which is highly challenging considering the numerous oxidation states of vanadium and the complexity vanadium oxides phase diagram.

 

Thin films of V2O3: Cr deposited by laser ablation (ISCR left, 90 nm) and co-sputtering (IMN right, 800 nm).

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People involved: Marie-Paule Besland, Madec Querré (2012-2016), PMN team: Laurent Cario, Benoit Corraze, Etienne Janod, SATT Ouest Valorisation: Julien Tranchant

Collaboration: Institute of Chemical Sciences of Rennes (ISCR), Rennes.

¹ L. Cario et al., Adv. Mater. 22, 5193 (2010); Corraze B. et al., Eur. Phys. J. Special Topics, 222, 1047 (2013); Guiot V., et al. Nat Commun 2013, 4, 1722; Janod E. et al. Adv. Funct. Mater. (2015).
² L. Cario et al. Patents PCT / EP2008 / 052968, PCT / EP2013 / 057500
³ M.-P. Besland et al. Patent PCT / EP2010 / 053442; Physica Status Solidi. - Rapid Research Letters 5, 53 (2011)
⁴ International Technological Roadmap for Semiconductors (ITRS). Emerging Research Devices (2011) - http://www.itrs.net/
⁵ Link to page PMN team http://www.cnrs-imn.fr/index.php/fr/themes-de-recherche-pmn/materiaux -complexes-a-properties-electronic-unconventional / 32-advanced-materials-for-novel-electric-pulse-induced-electronic-properties