Grain Boundaries, Phase Impurities, and Anisotropic Thermal Conduction in Phase-Change Memory

Thermal conduction strongly influences the programming energy and speed in phase-change-memory devices. The thermal conductivity of the crystalline phase of Ge 2 Sb 2 Te 5 can be strongly anisotropic due to phase impurities at grain boundaries. This letter models this effect using effective medium arguments, lends further support to the hypothesis that phase impurities are responsible for the anisotropy, and estimates the impact of anisotropic heat conduction on device performance. Electrothermal simulations predict that the reduced in-plane conductivity will allow closer spacing of lateral-cell devices and reduce the reset programming current by 20%-30%.