Cu+ Migration and Resultant Tunable Rectification in CuInP2S6

The ferroelectric vdW material CuInP2S6 with ionic conductivity has shown great potential in multistate computation and mechanical–electrical coupling. The interplay between Cu+ migration and electric polarization in the unique quadruple potential well has led to various applications, such as memristors, ferroelectric transistors, and processing in memory (PIM) devices. It is thus important to study the migration-related phenomena in CuInP2S6. In this work, long-range Cu+ migration and continuous spatial evolution in a CuInP2S6 flake were observed after a poling process by electrostatic force microscopy and Kelvin probe force microscopy. The migration showed a significant voltage polarity dependence. Further study using conductive atomic force microscopy with sweeping voltage cycles revealed a tunable threshold voltage induced by directional Cu+ migration under an external field. The asymmetry for opposite voltage polarities was in corroboration with the electrostatic force microscopy results. This work sheds light on the electrical tunability of ionic conductive semiconductors and their applications for the next generation of information technology devices and neuromorphic computation.