SYNAPSE

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SYnthesis and functionality of chalcogenide NAnostructures for PhaSE change memories

The SYNAPSE project initially aimed at the metalorganic chemical vapor phase deposition (MOCVD) and study of chalcogenide single material, (core) and double material (core-shell) nanowires (NWs), for innovative multi-level phase change memories (PCM). If Ge-Sb-Te is the most studied material for PCM applications, In-based materials, like In-Sb-Te or In-Ge-Te alloys, are also promising, since they are featured by low reset current and high crystallization temperature, paving the way for performing data storage devices even in the automotive field. At the same time, a great attention is currently devoted to the chance to downscale PCM cells by employing chalcogenide NWs. In SYNAPSE, Ge-based and In-based single material (SM-NWs) is deposited by MOCVD on different substrates and using different bottom-up approaches, the vapor-liquid-solid (VLS) and the selective area growth (SAG). SM-NWs were originally expected to be in-situ MOCVD-coated by other phase change chalcogenides, to obtain core-shell nanowires (CS-NWs), both free-standing and buried in template matrix. Different material combinations (Ge-Sb-Te/In-Sb-Te/In-GeTe) had to be explored in the realization of the CS-NWs, in order to expand the memory level operational features of the obtainable PCM devices. After a necessary project redefinition, the focus is now redirected on exploring NWs of different chalcogenide alloys, including Ge-based and In-based telluride, for their application to PCM devices both as single nanocells and in ordered arrays, this representing an important contribution to the achievement of downsized and low-power consumption non-volatile memory cells.

The NW synthesis is therefore supported by the development and test of precursors for MOCVD. A detailed study of the NW phase switching behavior (reversible amorphous-crystalline transitions) is carried out and correlated. Special attention is devoted to the investigation of electrical and thermal properties of the NWs, their phase formation/crystallization dynamics, size-dependent effects and structural/chemical composition. Experimental work is supported by theoretical modeling and simulation of both crystallization dynamics and electro-thermal behavior.

The SYNAPSE consortium is finally formed by 6 participants (5 academic/research centers and 1 industry) from Italy (2), France (2), Germany (1) and Ireland (1). The Partner Micron Semiconductors Italia S.r.l. was initially present and terminated in November 2014.