Phase Change Memory from Molecular Telluride Inks

Phase change memory (PCM) is an emerging data storage technology, where the information is stored by reversible switching of local bits between high-resistance amorphous and low-resistance crystalline phases of a material (logical “0” and “1”, respectively). The data is written by heating to the crystallization temperature (SET process). Vice versa, amorphization erases the data (RESET process).<br/><br/>Traditionally, phase-change material films are deposited via sputtering techniques, lithography, and lift-off. Solution-phase deposition of chalcogenides at ambient temperature and pressure provides a low-cost, scalable, and composition-flexible alternative. Additionally, thin film fabrication from the liquid phase gives access to new geometries of phase change memory devices (i.e., high-aspect ratio and multilayer arrays) and inexpensive high-throughput printing methods. One way to obtain such material inks is to dissolve bulk chalcogenides in an amine-thiol co-solvent. Annealing then forms compact crystalline thin films. This approach has shown its applicability for solar cells, thermoelectrics or resistive memory, but has not been researched for state-of-the-art telluride phase change applications yet.<br/><br/>Here, we synthesize a range of phase change memory material inks by dissolving bulk tellurides in an amine-thiol co-solvent formulation and subsequent purification steps. Deposition via spin-coating yields thin film telluride layers with tunable thickness, low surface roughness, and high crystallinity. We highlight the possibility to obtain stoichiometric binary materials (i.e., Sb₂Te₃, Sc₂Te₃ or Y₂Te₃) as well as composition-tunable ternary materials by admixing rare-earth telluride inks with antimony telluride. This yields homogenous doping in M_xSb_2-xTe₃ due to mixing on the molecular scale. We then demonstrate the benefits of ink formulations, e.g. deposition on patterned substrates like grooves and vias. Finally, we fabricate and test tailor-made prototype devices and quantify critical performance metrics such as I-V characteristics, switching behavior and speed, resistance contrast, power consumption, and cyclability of functional phase-change memory devices from molecular inks.