Sodium-based nano-ionic synaptic transistor with improved retention characteristics.

We propose an all-solid-state Na ion-based synaptic transistor (NST) to overcome the low retention problem of the Li ion-based synaptic transistor (LST). Through our analysis, it was found that the retention instability in an ionic synaptic transistor originated from its high ionic diffusivity. As confirmed by cyclic voltammetry analysis, Na ions have a lower ionic diffusivity than Li ions in the WOx layer. The state retention of NST was found to be improved to 20 times that of LST. Furthermore, near-ideal synaptic behaviors, such as linear weight update and linear I-V characteristics, were also obtained by material engineering.