Growth dominated crystallization of GeTe mushroom cells during partial SET operation

Abstract

Phase change memory devices are a leading candidate for non-volatile memory arrays, as artificial synapses in neuromorphic circuits, and for in-memory computing. These applications are hampered by a large cycle-to-cycle variation of resistance that is likely associated with the crystallization mechanism of phase change materials. This work presents a direct observation by transmission electron microscopy of the crystallization process during the SET operation of the GeTe 100 nm mushroom cell. The process proceeded purely by growth from the periphery of the amorphous dome without nucleation. It is invariably associated with partial melting of the GeTe layer. The growth-dominated SET operation can completely crystallize the GeTe functional layer only by a gradual sweep down of the voltage across the device. The experimental results were correlated with a finite element model of heat and charge flow and the crystallization dynamics.