Large Scale Simulations of Phase Change Materials for Data Storage

DIPC Seminars

Marco Bernasconi (Department of Materials Science, University of Milano-Bicocca, Italy)
Donostia International Physics Center
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Large Scale Simulations of Phase Change Materials  for Data Storage **Large Scale Simulations of Phase Change Materials** ** for Data Storage** ** ** **Marco Bernasconi** ** ** Department of Materials Science University of Milano-Bicocca, Milano, Italy Chalcogenide compounds such as GeTe and GeSbTe alloys are attracting an increasing interest for their application in Phase Change Memories (PCM) [1]. This novel type of electronic non-volatile memory rests on a fast (2-100 ns) and reversible transformation between the crystalline and amorphous phase of a chalcogenide film due to Joule heating. The two phases corresponding to the two states of the memory can be discriminated because of their large difference in electronic conductivity. PCMs are emerging as a leading contender for the realization of the so-called storage class memories that are sought to fill the performance gap between volatile DRAM and non-volatile Flash memories [2]. Storage class memories are believed to usher in seminal changes in the memory and storage hierarchy for all computing platforms ranging up to high-performance computing. In the last few years, atomistic simulations based on density functional theory (DFT) have provided useful insights on the properties of chalcogenide alloys of interest for PCMs [3]. Still, large simulation cells and long simulation times beyond the reach of fully DFT simulations are needed to address several key issues of relevance for PCM performances. To overcome these limitations, we have developed an interatomic potential for the prototypical phase change compound GeTe by fitting a huge DFT database with a neural network (NN) scheme. Large scale (104 atoms) NN simulations allowed us to get insights on the thermal transport and on microscopic origin of the high crystallization speed of these materials [4]. In this talk, I will present the results of NN simulations on the kinetics of homogeneous and heterogeneous crystallization of GeTe and on the structural relaxations leading to the aging of the amorphous phase and to a drift in the electronic resistance which is a particularly critical issue for PCM operation. [1] M. Wuttig and N. Yamada, Nature Mater. 6, 824 (2007). [2] G. W. Burr et al., IBM J. Res. Dev. 52, 449 (2008). [3] S. Caravati et al, Appl. Phys. Lett. 91, 171906 (2007); Lencer et al., Adv. Mat. 23, 2030 (2011). [4] G. C. Sosso et al. J. Phys. Chem. Lett. 4, 4241 (2013); J. Phys. Chem. C 119, 6428 (2015);
J. Phys. Chem. B 118, 13621 (2014); Phys. Rev. B 86, 104301 (2012); ibidem 85, 174103 (2012).