Structural change with the resistance drift phenomenon in amorphous GeTe phase change materials' thin films

Ageing of the amorphous phase of chalcogenide phase change materials is characterized by a large increase of their resistivity with time. This phenomenon, known as resistance drift and commonly attributed to structural relaxation, the nature of which remains unknown, has until now hindered the development of ultra-high multilevel storage devices. The origin of the resistance drift of amorphous GeTe thin films is studied here by resistivity measurements and grazing incidence x-ray absorption spectroscopy (GIXAS). The local order around Ge atoms is investigated at the Ge K-edge on a-GeTe samples previously set at different resistance drift levels by thermal annealing. In all samples, Ge-Ge and Ge-Te bonds coexist. This study demonstrates that the drift phenomenon is concomitant with structural changes linked to Ge-Ge homopolar bonds.