Phase change memories (PCM) are non-volatile memories based on the change in electrical resistance of the storage material. This change in resistance depends on the amorphous or crystalline structure of the storage material. The resistive material used for information storage is chalcogenide, a material combination of germanium( Ge), antimony (Sb) and tellurium (Te). The resistance change is triggered by temperature changes in the PCM material.
A phase-change memory cell is bit-organized and consists of two metallic electrodes between which is the phase-change material, heated by a small heating electrode. The phase-change material can assume two states: The ground state and a high resistance state. The phase change material is brought into this state of amorphization by brief heating. This is done by a short current pulse of several hundred micro-amps and a pulse duration of about 50 ns. The rapid cooling causes the material to remain in the amorphous state, which is characterized by the high resistance value.
For resetting to the crystalline ground state, the phase change material is subjected to a slightly longer current pulse of about 100 ns duration and of a few micro-amps. Such a current pulse causes the amorphous phase-change material to be heated above the crystallization point and crystallization to begin. The information stored in the memory cell is determined by the current flow in the phase-change material, which is generated by an applied voltage.
Because the phase-change memories' state changes from 0 to 1 and vice versa can be executed directly, i.e., without prior erasure, phase-change memories have a relatively short latency, which is lower than that of flash memories. They also have the advantage of not requiring a power supply when powered down.
Phase-change memories are realized in phase-change RAMs( PRAM or PCRAM) and 3D XPoint memories, they can replace Dynamic RAMs ( DRAM) and Static RAMs( SRAM) and due to the fact that they are not volatile, they also represent an alternative to flash memories.