A model for an amorphous semiconductor memory device

The amorphous semiconductor Ge₁₅Te₈₁X₄ may be switched from a high resistance (amorphous) state to a low resistance (crystalline) state and back again. The two different resistive states are stable and can serve as the basis of a memory device. Recent measurements using techniques such as scanning electron micrographs, electromigration, electrical noise, lifetime studies, and metallurgical characteristics have yielded a body of data and ideas from which a model has been synthesized. The essential features of the model incorporate the mechanisms of filament formation and the subsequent resetting of the material into the amorphous state plus residual conducting debris. The conducting debris can serve as the nucleus of subsequent filament formation. The statistical variation in recycling, combined with percolation concepts, will be shown to account for most of the experimental data relating to operation and device lifetime.