Dependences of Electrical Properties of Thin GeSbTe and AgInSbTe Films on Annealing

We studied the electrical properties of 20- and 50-nm-thick Ge2Sb2Te5 and AgInSbTe films for nonvolatile lateral transistor memory devices. Both kinds of thin films were prepared as film samples and device samples which were then annealed at temperatures from 140 to 415°C. It is known that crystal size can be effectively reduced with film thickness on the basis of X-ray diffraction analysis. The resistances of all film samples annealed at 140–415°C decreased by approximately 5–6 orders of magnitude. In the case of device samples, however, the source-drain resistances of Ge2Sb2Te5 samples were first reduced and then reversely increased and it seemed that the resistances of AgInSbTe samples did not drop. The abnormal resistance increase above the crystallization temperature may be caused by phase change and thermal expansion, as we analyzed in this paper. Finally, the resistance changes of device samples with channel lengths in the range of 0.4–3 µm were discussed from the point of view of miniaturizing the phase change memory device.