Driving forces for elemental demixing of GeSbTe in phase-change memory: Computational study to design a durable device

Elemental separation in phase-change volume is critical for the endurance of phase-change memory (PCM). The joule heating-induced phase transformation, which is a switching mechanism of PCM, generates driving forces, such as a high-density current and a temperature gradient, for atomic migration. Although identifying and quantifying driving forces are important to design a reliable device, it is difficult to analyze these forces because the devices have tiny and complex configurations. In this study, we analytically investigated the driving forces for mass transport in PCM using a finite differential method, and we suggested the design rules for suppressing mass transport-driven failures in the device. The driving forces were divided into electrical-, thermal-, mechanical-, and chemical-driven forces and were quantified. The effects on driving forces of both the scale of device and the current density for switching were studied, and the changes in mass transport behavior were investigated. The results were used to suggest a margin of scaling and a range of reset current for high-endurance PCM devices.