Orientation-Dependent Behavior of Reversible Switching in Li-Ion Gated Devices

Inspired by the neural system, electrolyte-gated devices are expected to provide new computing paradigms for pattern recognition and machine learning. In this study, we demonstrate reversible switching in ionic-polymer gated devices fabricated on epitaxial LiCoO₂ (LCO) films with different crystal orientations. The epitaxial LCO films with different thicknesses (50 nm or 20 nm) were grown on (100), (110), and (111) SrTiO₃ (STO) substrates using the pulsed laser deposition method. After films were patterned into micrometer-scaled bridges, a Li-ion polymer was used to cover patterned films to complete the devices. By controlling the amplitude and the duration of the current or voltage pulse applied to the gate, reversible multi-level switching in the conductance was realized. In particular, we found that current pulses with a relatively low amplitude are sufficient to drive the switching in the conductance. Orientations of epitaxial LCO films are different on different STO substrates which allow for a systematic study of the relation between the diffusion path of Li ions and the crystal structure of the LCO film. The (104) oriented films demonstrate the fastest switching speed (less than 1 s), consistent with the fact that this is known to be the fast-diffusion direction in LCO.