Electronic switching in amorphous silicon devices: properties of the conducting filament

It has been amply demonstrated that non-volatile memory switching in metal-hydrogenated amorphous silicon-metal structures is crucially dependent on the formation of a conducting filament during the very first switching operation. In this paper we review the evidence which shows that the filament is an inclusion in the amorphous silicon made up of metallic particles from the top contact dispersed in an insulating matrix and that its critical dimensions are on the scale of nanometres. Particular attention is given to recent work on metal nonmetal transitions and a dielectric anomaly associated with the filament. These and earlier experiments all provide consistent evidence for the mesoscopic dimensions of the active filament region in which switching occurs