Functional analysis of In-based nanowires for low power phase change memory applications

Phase change memories (PCMs), based on chalcogenide alloys (mainly Ge2Sb2Te5), are the most promising candidate for the realization of “Storage Class Memories”, which would fill the gap between ‘‘operation’’ and ‘‘storage’’ memories. PCMs are also one of the few currently available technologies for the implementation of nanoeletronic synapses in high density neuromorphic systems. The main improvements needed in order to exploit the full potential of PCMs in these innovative applications are the reduction of the programming currents and power consumption, and further cell downscaling. Thanks to their nano-sized active volume to be programmed and self-heating behavior, phase change nanowires (NWs) are expected to exhibit improved memory performances with respected to commonly used thin-film/heater-based structures. The Ph. D. Thesis of the candidate reports the study of the phase change properties of ultra-thin In-based NWs for low power consuming PCMs, exploring the more promising features of this class of materials with respect to the commonly considered Ge-Sb-Te alloys. In particular, the self-assembly of In-Sb-Te, In-doped Sb and In-Ge-Te NWs was successfully achieved by Metal Organic Chemical Vapour Deposition (MOCVD), coupled to vapour-liquid-solid mechanism, catalysed by catalyst nanoparticles. The parameters influencing the NW self-assembly were studied and the compositional, morphological and structural analysis of the grown structures was performed. In all cases, NWs of several μm in length and with diameters as small as 15 nm were obtained. The experimental contribution of the Ph. D. candidate to the NWs growth study was mainly related to the substrates preparation, catalyst deposition and, morphological and elemental analysis of the grown samples. Moreover, the Ph. D. candidate has performed the functional analysis of In3Sb1Te2 and In-doped Sb NW-based PCM devices. To conduct that analysis, a suitable fabrication procedure of the devices and an appropriate electrical measuring set-up have been identified. Reversible and well reproducible phase change memory switching was demonstrated for In3Sb1Te2 and In-doped Sb NW devices, showing low working parameters, such as “RESET” voltage, current and power. The obtained results support the conclusion that In-based ultra-thin NWs are potential building blocks for the realization of ultra-scaled, high performance PCM devices.