Synaptic plasticity and memory mimicked in solution-processed K-doped CuI thin film transistors

Abstract

Low-voltage electric double layer p-type thin film transistors (TFTs) were fabricated on glass substrates with copper iodide doped with potassium iodide (Cu0.95K0.05Ix) as the channel and chitosan as the dielectric. Cu0.95K0.05Ix TFTs exhibited Ion/Ioff ratio of 2.5 × 104, subthreshold swing of 30 mV/dec, threshold voltage of 1.34 V, operating voltage of 2 V, and saturation field-effect mobility of 16.6 cm2 V−1 s−1. The relaxation phenomenon induced by ion migration was effectively utilized, enabling Cu0.95K0.05Ix TFTs to simulate various synaptic plasticity functions. When a pulse is applied, the drain current reaches a peak, but it takes more time for the current to return to its equilibrium position after the pulse is removed, demonstrating the short-term memory (STM) characteristics of Cu0.95K0.05Ix TFT. It was observed an increasing trend in excitatory postsynaptic current (EPSC) with enhanced pulse width and amplitude, and when the pulse amplitude increased to −10 V, the TFT transitioned from STM to long-term memory characteristics. Furthermore, the measurement of consecutive EPSC revealed the paired-pulse facilitation (PPF) characteristics, with a gradual decrease in the PPF coefficient as the time interval increased, and a selective stronger response to high-frequency signals. Based on the aforementioned research, by extending the device structure to a dual in-plane-gate structure configuration and applying different pulse voltage sequences on the dual gate, the NOR logic functionality was achieved. The study demonstrates the significant potential of p-type Cu0.95K0.05Ix TFTs in the field of synaptic bionics, simulating human learning and memory, and neural chips.