Crystallization of Ion Amorphized Ge2Sb2Te5 Thin Films in Presence of Cubic or Hexagonal Phase (Contributo in atti di convegno)

Type
Label
  • Crystallization of Ion Amorphized Ge2Sb2Te5 Thin Films in Presence of Cubic or Hexagonal Phase (Contributo in atti di convegno) (literal)
Anno
  • 2010-01-01T00:00:00+01:00 (literal)
Alternative label
  • De Bastiani R, Carria E, Grimaldi MG, Nicotra G, Spinella C, Rimini E (2010)
    Crystallization of Ion Amorphized Ge2Sb2Te5 Thin Films in Presence of Cubic or Hexagonal Phase
    in MRS Spring Meeting: Symposium H: Phase-Change Materials for Memory and Reconfigurable Electronics Applications, San Francisco, California, USA
    (literal)
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  • De Bastiani R, Carria E, Grimaldi MG, Nicotra G, Spinella C, Rimini E (literal)
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  • Chalcogenide materials have been widely used as storage media for optical memory disks and have also been proposed for semiconductor non-volatile phase change random access memory (PCRAM). Studies so far have shown that Ge2Sb2Te5 (GST) has a good combination of electric and phase changing characteristics for PCRAM applications. The phase-change data storage technology is based on the reversible switching between the amorphous and the crystalline phases of chalcogenides alloys. The stability of the amorphous phase in presence of a crystalline substrate is therefore a point of great interest for technological applications. In this work we report on the crystallization kinetics of continuous amorphous GST thin films (50 nm thick) in contact, with a planar interface, with either cubic and hexagonal GST. Sample were prepared by pulsed laser or low energy Ge+ ion irradiation of cubic or hexagonal phase obtained by isothermal annealing at 150 °C and 400 °C respectively. By a suitable choice of the irradiation parameters a thin surface amorphous layer (25 nm thick) on top of crystalline material was obtained. For example, ion irradiation at the liquid nitrogen temperature by 28keV Ge+ at a fluence of 1014 at/cm2, produced a 30nm thick amorphous layer with a sharp amorphous-crystalline (a/c) interface. A similar configuration was realized by 10ns frequency-doubled Nd:YAG pulse at energy density of 50 mJ/cm2. The crystallization of the amorphous layer during isothermal annealing was investigated by in situ time resolved reflectivity measurements (TRR), transmission electron microscopy and by ex situ X-ray diffraction. The experimental results reveal that during isothermal annealing the crystallization of the amorphous layer, generated by laser or ion irradiation, is affected by the adjacent crystalline structure. In particular the regrowth of the amorphized layer for both crystals (cubic or hexagonal) was found to proceed from the a/c interface with the formation of a cubic state at a temperature below that required in the amorphous to crystal phase transition for the Ge2Sb2Te5 composition. The a/c interface plays the role of a continuous region of potential nucleation sites, making the crystallization process more efficient. (literal)
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  • 1. Dip. Fisica ed Astronomia, Università di Catania, Catania, Italy; 2. IMM-CNR, Catania, Italy. (literal)
Titolo
  • Crystallization of Ion Amorphized Ge2Sb2Te5 Thin Films in Presence of Cubic or Hexagonal Phase (literal)
Abstract
  • Chalcogenide materials have been widely used as storage media for optical memory disks and have also been proposed for semiconductor non-volatile phase change random access memory (PCRAM). Studies so far have shown that Ge2Sb2Te5 (GST) has a good combination of electric and phase changing characteristics for PCRAM applications. The phase-change data storage technology is based on the reversible switching between the amorphous and the crystalline phases of chalcogenides alloys. The stability of the amorphous phase in presence of a crystalline substrate is therefore a point of great interest for technological applications. In this work we report on the crystallization kinetics of continuous amorphous GST thin films (50 nm thick) in contact, with a planar interface, with either cubic and hexagonal GST. Sample were prepared by pulsed laser or low energy Ge+ ion irradiation of cubic or hexagonal phase obtained by isothermal annealing at 150 °C and 400 °C respectively. By a suitable choice of the irradiation parameters a thin surface amorphous layer (25 nm thick) on top of crystalline material was obtained. For example, ion irradiation at the liquid nitrogen temperature by 28keV Ge+ at a fluence of 1014 at/cm2, produced a 30nm thick amorphous layer with a sharp amorphous-crystalline (a/c) interface. A similar configuration was realized by 10ns frequency-doubled Nd:YAG pulse at energy density of 50 mJ/cm2. The crystallization of the amorphous layer during isothermal annealing was investigated by in situ time resolved reflectivity measurements (TRR), transmission electron microscopy and by ex situ X-ray diffraction. The experimental results reveal that during isothermal annealing the crystallization of the amorphous layer, generated by laser or ion irradiation, is affected by the adjacent crystalline structure. In particular the regrowth of the amorphized layer for both crystals (cubic or hexagonal) was found to proceed from the a/c interface with the formation of a cubic state at a temperature below that required in the amorphous to crystal phase transition for the Ge2Sb2Te5 composition. The a/c interface plays the role of a continuous region of potential nucleation sites, making the crystallization process more efficient. (literal)
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