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Simultaneous estimation of the temperature dependant thermal effusivity and thermal boundary resistance at the Al/Ge2Sb2Te5 interface using the time resolved pump probe technique and a Bayesian estimation approach


J. Battaglia1, O. Fudym2, H. Orlande3, V. Schick1, A. Kusiak1, C. Rossignol1 and C. Wiemer4

1Université de Bordeaux 1, France
2ENSTIMAC, France
3University of Rio de Janeiro, Brazil
4Laboratorio MDM , Italia

Keywords: time domain thermoreflectance
property: interface
material: inverse problem

The Phase Change Memories (PCMs), developed by semiconductor industry are based on rapid and reversible change from amorphous to crystalline phases of chalcogenide materials [1]. Switching between the amorphous and the crystalline phase yields a variation of the electrical resistance of the material [2]. The amorphous-to-crystalline transition is performed by heating the cell above the glass transition temperature. The crystalline-to-amorphous transition is performed by quenching the material to its amorphous phase, rapidly decreasing its temperature from the melting point. Among all the chalcogenide materials, the Ge2Sb2Te5 (GST-225) ternary compound is the most studied. GST-225 is characterized by a low melting point (Tmelt ~ 600 °C), an amorphous and two crystalline phases. The metastable face centered cubic phase develops at 150°C and the stable hexagonal close packed phase develops at 350°C and is stable at room temperature. The phase transitions have low activation energy. The Time Resolved Pump Probe (TRPP) technique has been implemented to study [3], as a function of temperature, the thermal and mechanical properties of GST-225 film deposited on a silicon substrate covered with SiO2 (10 nm). The GST-225 film is caped with 20 or 10 nm aluminum layer. Both the temperature dependant thermal effusivity of the GST layer and the Thermal Boundary Resistance (TBR) at the aluminum-GST interface are estimated simultaneously with a Bayesian estimation approach, so that the posterior probability distributions of these properties are retrieved. In a second stage, the behavior at very small times (some picoseconds after the pulse) is also investigated in order to estimate the temperature influence on the electron-phonon coupling factor in the aluminum layer starting from the two temperatures model.

References
  1. S. R. Ovchinsky. Phys. Rev. Lett. 21, 1450 (1968); J. Non-Cryst. Solids 2, 99 (1970).

  2. R. Fallica, J.-L. Battaglia, S. Cocco, C. Monguzzi, A. Teren, C. Wiemer, E. Varesi, M. Fanciulli. Int. J. of Chem. and Eng. Data 54, 1698 (2009).

  3. J.- L. Battaglia, A. Kusiak, C. Rossignol, N. Chigarev. Phys. Rev. B 76, 184110 (2007).

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