E*PCOS2009 Bridging carrier transport and

Physics of amorphous chalcogenides sets the scaling potentials of PCM elements and their perspectives in multi-bit storage. Carrier transport, threshold switching, structural relaxation and crystallization processes have key importance from the application standpoint. They also represent peculiar effects which have always attracted interest and speculations by decades. The paper reviews experimental and modeling analysis of threshold voltage and resistance transients in amorphous chalcogenides. Both variables show time evolutions characterized by a fast component in the 10’s of ns range, called recovery, followed by a slower drift on longer time scales, with a gradual increase of the amorphous resistivity and activation energy. This latter dependence, ascribed to structural relaxations (SR) in the amorphous, proceeds until crystallization takes place. Although these processes appear rather different, the Poole Frenkel model of carrier conduction in disordered materials is remarkably able to link consistently them all, explaining the kinetics over 17 decades of time. Moreover, the Arrhenius dependence of SR shows that the exponential pre-factor of the process obeys a Meyer–Neldel rule, pointing to many-body thermal excitations as responsible for the anomalous large values of the crystallization time pre-factor observed in chalcogenide glasses. Key words: Chalcogenide materials, nonvolatile memories, phase-change memories (PCMs), threshold switching