Modeling and Analysis of Virgin Ge-Rich GST Embedded Phase Change Memories

Germanium-rich alloys of Ge2Sb2Te5 have been developed to improve the reliability and performance of embedded phase change memory (PCM). Fast program operation, integration in the back end of the line (BEOL), and stability under high-temperature profiles make PCM with Ge-rich GST one of the prominent technologies for the embedded memory market. The Ge-rich alloy composition requires an initialization pulse, called forming, to uniformize the electrical characteristic of the cells from the virgin state at the end of production. This work will analyze the key features of virgin state Ge-rich GST PCM devices. Electron microscopy images and temperature-dependent electrical resistance data are reported. A modeling framework, based on the energy landscape theory, is presented to reproduce the electrical behavior as a function of temperature on the basis of the observed Ge-rich GST microstructure. The impact of the BEOL process on the poly-crystalline virgin state is assessed and the model is extended accordingly. The new model provides a valuable simulation tool for material-and physics-based simulation of PCM based on Ge-rich GST for memory, computing, and hardware security.