Chalcogenide phase change alloys (Ge2Sb2Te5, GeTe and related materials) are the subject of extensive experimental and theoretical research because of their use in optical (DVD) and electronic (phase change memories, PCM) storage devices [1]. Both applications rely on the fast and reversible transformation between the crystalline and amorphous phases induced by heating either via laser irradiation (DVD) or Joule effect (PCM). The two states of the memory can be discriminated thanks to the large difference in optical reflectivity and electronic conductivity of the two phases. In the last few years, molecular dynamics (MD) simulations based on density functional theory (DFT) have provided useful insights on the properties of phase change materials (see Ref. [1] for a review and Ref. [2] for some of our contributions). However, several key issues such as the crystallization dynamics and the thermal conductivity at the nanoscale, just to name a few, are presently beyond the reach of fully DFT simulations. A route to overcome the limitations in system size and time scale of DFT-MD is the development of classical interatomic potentials. Traditional approaches based on the fitting of simple functional forms are very challenging due to the complexity and variability of the chemical bonding in the crystal and amorphous phases revealed by DFT simulations. A possible solution has been demonstrated recently by Behler and Parrinello [3] who developed empirical interatomic potentials with close to DFT accuracy for several elemental systems by fitting a large DFT database with a Neural Network (NN) scheme. By means of this technique, we have recently developed an interatomic potential for GeTe [4] which is one of the compounds under scrutiny for applications in PCM. After a brief review of our main DFT results on the properties of amorphous Ge2Sb2Te5 and related materials, we will discuss large scale NN simulations (4000 atoms for 10 ns) of GeTe addressing several properties such as the fragility of the supercooled liquid close to the glass transition temperature [4] and the crystallization dynamics of the amorphous phase. [1] D. Lencer, M. Salinga, and M. Wuttig, Adv. Mat. 23, 2030 (2011); M. Wuttig and N. Yamada, Nature Mater. 6, 824 (2007). [2] S. Caravati et al., Appl. Phys. Lett. 91, 171906 (2007); Mazzarello et al., Phys. Rev. Lett. 104, 085503 (2010); G. C. Sosso et al., Phys. Rev. B 83, 134201 (2011). [3] J. Behler and M.Parrinello, Phys. Rev. Lett. 14, 146401 (2007) [4] G. C. Sosso et al., Phys. Rev. B 85, 174103 (2012); G. C. Sosso et al., Phys. Rev. B 86, 104301 (2012); Physica Status Solidi B 249, 1880 (2012).

Sosso, G., Miceli, G., Caravati, S., Behler, J., Bernasconi, M. (2013). Simulation of phase change materials for data storage. In Abstract Book.

Simulation of phase change materials for data storage

BERNASCONI, MARCO
2013

Abstract

Chalcogenide phase change alloys (Ge2Sb2Te5, GeTe and related materials) are the subject of extensive experimental and theoretical research because of their use in optical (DVD) and electronic (phase change memories, PCM) storage devices [1]. Both applications rely on the fast and reversible transformation between the crystalline and amorphous phases induced by heating either via laser irradiation (DVD) or Joule effect (PCM). The two states of the memory can be discriminated thanks to the large difference in optical reflectivity and electronic conductivity of the two phases. In the last few years, molecular dynamics (MD) simulations based on density functional theory (DFT) have provided useful insights on the properties of phase change materials (see Ref. [1] for a review and Ref. [2] for some of our contributions). However, several key issues such as the crystallization dynamics and the thermal conductivity at the nanoscale, just to name a few, are presently beyond the reach of fully DFT simulations. A route to overcome the limitations in system size and time scale of DFT-MD is the development of classical interatomic potentials. Traditional approaches based on the fitting of simple functional forms are very challenging due to the complexity and variability of the chemical bonding in the crystal and amorphous phases revealed by DFT simulations. A possible solution has been demonstrated recently by Behler and Parrinello [3] who developed empirical interatomic potentials with close to DFT accuracy for several elemental systems by fitting a large DFT database with a Neural Network (NN) scheme. By means of this technique, we have recently developed an interatomic potential for GeTe [4] which is one of the compounds under scrutiny for applications in PCM. After a brief review of our main DFT results on the properties of amorphous Ge2Sb2Te5 and related materials, we will discuss large scale NN simulations (4000 atoms for 10 ns) of GeTe addressing several properties such as the fragility of the supercooled liquid close to the glass transition temperature [4] and the crystallization dynamics of the amorphous phase. [1] D. Lencer, M. Salinga, and M. Wuttig, Adv. Mat. 23, 2030 (2011); M. Wuttig and N. Yamada, Nature Mater. 6, 824 (2007). [2] S. Caravati et al., Appl. Phys. Lett. 91, 171906 (2007); Mazzarello et al., Phys. Rev. Lett. 104, 085503 (2010); G. C. Sosso et al., Phys. Rev. B 83, 134201 (2011). [3] J. Behler and M.Parrinello, Phys. Rev. Lett. 14, 146401 (2007) [4] G. C. Sosso et al., Phys. Rev. B 85, 174103 (2012); G. C. Sosso et al., Phys. Rev. B 86, 104301 (2012); Physica Status Solidi B 249, 1880 (2012).
abstract + slide
phase change materials, molecular dynamis simulations, non-volatile memory, crystallization
English
16th International Workshop on Computational Physics and Materials Science: Total Energy and Force Methods
2013
Abstract Book
2013
none
Sosso, G., Miceli, G., Caravati, S., Behler, J., Bernasconi, M. (2013). Simulation of phase change materials for data storage. In Abstract Book.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/50215
Citazioni
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
Social impact