Understanding Overreset Transition in Phase-Change Memory Characteristics

In a phase-change memory (PCM), the overreset phenomenon, namely, the resistance decrease at pulse amplitudes well beyond the reset current, may affect the resistance window and the device noise margin. We characterized overreset states in PCM devices by electrical testing and electron microscopy. Our analysis shows that overreset programmed cell presents changes in the electronic band structure of the amorphous phase, with no degradation in the programmed amorphous volume.