Estimation of amorphous fraction in multilevel phase change memory cells

The effective thickness of the amorphous chalcogenide part within the active element of a phase change memory (PCM) cell is estimated through electrical measurements. Current-voltage characteristics obtained at various intermediate cell states are fitted with the trap-limited subthreshold transport model and the amorphous part thickness is then extracted. Several cell electrical measures, such as the resistance and the threshold voltage, are shown to closely relate to the estimated parameter. The results serve to further validate the trap-limited conduction model, as well as the series phase distribution hypothesis in the active layer of a PCM cell.