Two generations of phase-change memory devices: Differences and common problems

Abstract

Two generations of phase-change memory (PCM) devices are analyzed from the point of view of material requirements. The first generation of PCM devices was based on chalcogenide glasses. The lack of sufficient information on the physical and chemical processes within the material that occur during operation of the devices led to poor reliability of the first-generation PCM integrated circuits (ICs). The second generation of PCM devices uses memory switches based on crystalline chalcogenide alloys. The basic operating mechanisms of the first- and second-generation nonvolatile PCM devices are largely the same. The PCM ICs designers of either generation face the same problems: contradictory requirements toward the phase-change material, where both low SET and RESET power and high reliability of cells retention are important, the problem of the dispersions of cell characteristics in the SET and RESET states, the problem of the forming process of PCM elements and others. The analysis of the results allows the problems that need solving to be looked at to avoid making the same mistake twice and to create highly reliable PCM devices with acceptable power and geometrical characteristics.