Exploring the Compositional Ternary Diagram of Ge/S/Cu Glasses for Resistance Switching Memories

N Onofrio and TW Ko, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 9486-9495 (2019).

DOI: 10.1021/acs.jpcc.8b12020

Amorphous semiconductors with tailored ionic and electronic conductivities are central to the operation of emerging resistive memory. However, because of the large amount of potential candidates and compositions, only limited numbers of materials have been tested experimentally. To accelerate the search of efficient solid electrolytes for resistive switching devices, we developed parameters to describe copper-doped germanium sulfides based on ReaxFF, a reactive molecular dynamics framework. The force field was optimized against a training set of first-principle calculations including crystals, amorphous structures, some small molecules, and clusters to describe the atomic interactions among Ge, S, and Cu elements. Based on this novel atomistic model, we studied the mobility of Cu as a function of the ternary composition of amorphous GexSyCuz, and we investigated the corresponding atomic and electronic structures of each solid electrolyte in details. analysis led to semiconducting compositions with high Cu mobility and favoring the formation of Cu clusters. Molecular dynamics simulations of switching under an external potential show that devices based on electrolytes with high Cu mobility form thick metallic filaments, and an amorphous copper sulfide phase was observed at the interface. Such an atomistic model is critical to improve our understanding of the atomic mechanism of filamentary growth and can be used to improve retention and endurance of resistive switching devices, which are still limiting their widespread commercial use.

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