Simultaneous structural and electrical measurements on Si-doped Ge2Sb2Te5 for PCRAM applications


Simultaneous structural and electrical measurements on Si-doped Ge2Sb2Te5 for PCRAM applications

Wilde, L.; Bähtz, C.; von Borany, J.; Krügener, J.; Teichert, S.

Ge2Sb2Te5 (GST) based materials can be easily transformed between amorphous and crystalline phase and vice versa. The dramatic differences in the electrical resistance of these structural states make these materials suitable for non-volatile memory applications (phase change RAM or PCRAM). In order to tune these materials to the desired working point (e.g. low melting temperature, fast crystallization speed), dopants such as Si, N or O are used. In this study, we investigated the influence of PVD deposited Si dopants in 100 nm thin GST films on the crystallisation temperature and on the electrical resistance as well. The dopant concentration was varied between 0% and 3.5% by tunig the RF sputtering power on the SiO2 target. The XRD measurements (ESRF: ROBL beamline @ 12keV) were carried out in a high temperature chamber equipped with a Be dome, that allowed simulaneous determination of the sheet resistance by an electrical 4-point measurement. The samples were heated up to 450°C under vacuum conditions.
All samples were amorphous after deposition. Depending on the Si content, all samples crystallize in a cubic phase in the range between 160°C – 200°C. At the crystallisation temperature the electrical resistance drops by two orders of magnitude. A second transformation to a hexagonal phase was observed only for samples with a Si concentration below 1.0%. The temperature of this phase transformation depends significantly on the Si content. The electrical measurements show a further decline of the resistance upon this phase transformation. The cooling curve of the resistance measurements indicates, that the hexagonal phase exhibits metallic behaviour, whereas the cubic phase exhibits semiconducting properties.

Keywords: phase change memory; phase transformation; high temperature XRD

  • Poster
    12th International Conference on the Formation of Semiconductor Interfaces, 05.-10.07.2009, Weimar, Germany

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