Electronic mechanism for resistance drift in phase-change memory materials: Link to persistent photoconductivity
S. R. Elliott
Accepted
Phase-change memory materials are being actively researched for non-volatile resistive random-access memory (RRAM) applications. Multilevel programming, wherein several different resistance states can be stored in the memory material as different partially amorphous/crystalline regions, allows more than one bit to be stored per memory cell. However, this route to increasing data density, without recourse to size down-scaling, is threatened by the phenomenon of 'resistance drift', wherein the electrical resistance of the amorphous state slowly increases inexorably with time after being written with a voltage pulse. In this Letter, we identify resistance drift as being an equivalent manifestation of the phenomenon of persistent photoconductivity widely observed in disordered semiconductors, and we provide a new theoretical model for this electricallyinduced resistance-drift effect in amorphous phase-change materials in terms of the longtime deep-trap release and subsequent recombination of charge carriers. In principle, this insight could then allow for the resistance drift to be mitigated by suitable materials 'engineering' of the amorphous state of phase-change materials via control of the electronic band-tail states in the vicinity of the bandgap.