Process-Induced Chemical Reactions on Interfaces of Thin Film Ionic Materials

The success of ionic devices relies on the capability of miniaturizing them without compromising charge transport mechanisms and the optimum control of their interfacial properties, which remains as a challenge in this field. This study investigates autolithiation, wherein Li spontaneously transfers from growing dielectric layers (LiPON and Li₂O) with similar thermodynamic stability but different reaction pathways into an underlying layered oxide film (V₂O₅) commonly implemented in microbatteries and memory devices during magnetron sputtering.

Electrochemical impedance combined with ellipsometry, X-ray photoelectron spectroscopy, and Raman spectroscopy reveal that interface reactions continue throughout deposition and post processing. LiPON forms stable, electron-blocking overlayers as thin as 15 nm while lithiating the underlying V₂O₅ at rates equivalent to ∼1 μA/cm². In contrast, Li₂O deposition results in an overlayer growth of less than 2 nm with nearly complete Li transfer into the V₂O₅, achieving compositions approaching Li₃V₂O₅.

The results demonstrate that LiPON remains functional at nanoscale thicknesses despite concurrent autolithiation, while Li₂O sputtering provides rapid lithium insertion with minimal overlayer formation, enabling rational design of thin film fabrication sequences for energy storage and neuromorphic devices.