Heterogeneous nanometer-scale Joule and Peltier effects in sub-25nm thin phase change memory devices

We measure heterogeneous power dissipation in phase change memory (PCM) films of 11 and 22nm thin Ge₂Sb₂Te₅ (GST) by scanning Joule expansion microscopy (SJEM), with sub-50nm spatial and ∼0.2K temperature resolution. The heterogeneous Joule and Peltier effects are explained using a finite element analysis (FEA) model with a mixture of hexagonal close-packed and face-centered cubic GST phases. Transfer length method measurements and effective media theory calculations yield the GST resistivity, GST-TiW contact resistivity, and crystal fraction of the GST films at different annealing temperatures. Further comparison of SJEM measurements and FEA modeling also predicts the thermopower of thin GST films. These measurements of nanometer-scale Joule, thermoelectric, and interface effects in PCM films could lead to energy-efficient designs of highly scaled PCM technology.