Regensburg 2002 – wissenschaftliches Programm
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SYME: Mechanical Properties of Thin Films
SYME 3: Mechanical Stresses and Plasticity
SYME 3.6: Vortrag
Dienstag, 12. März 2002, 12:45–13:00, H 4
Stresses and viscous flow in thin films of amorphous chalcogenides — •Johannes Kalb1, Frans Spaepen1, and Matthias Wuttig2 — 1Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA — 2I. Physikalisches Institut der RWTH Aachen, 52056 Aachen, Germany
Thin films of chalcogenides are being used for optical data storage in re-writeable CDs. They can be switched by laser power locally and reversibly from the amorphous to the crystalline state. Upon crystallization of the as-deposited amorphous films large mechanical stresses are observed which are due to the densification of the material. In the not yet crystallized amorphous part of the film these stresses relax by viscous flow. As the occurrence of these stresses reduces the durability (cyclability) of the material which is a severe drawback concerning the competition with magnetic hard disks the study of viscous flow in the amorphous phase is of great interest. Therefore, stress relaxation by viscous flow in thin films of amorphous Ge4Sb1Te5, Ge2Sb2Te5 and AgInSbTe ion-beam-sputtered on Si substrates was measured by determining the substrate curvature as a function of time using a Wafer Curvature Setup. The stress relaxation data at a constant temperature could be fitted best using a viscosity that increases linearly in time. This is due to bimolecular structural relaxation kinetics. From measurements of the temperature dependence of the viscosity in an isoconfigurational state the isoconfigurational activation energy could be determined to be 1.94 ± 0.09 eV for Ge4Sb1Te5, 1.76 ± 0.05 eV for Ge2Sb2Te5 and 1.44 ± 0.07 eV for AgInSbTe. These numbers scale with the absolute melting temperatures of the materials.