Superionic rubidium silver iodide gated low voltage synaptic transistor

Nonvolatile resistive switching based memristor and memtransistor devices have emerged as a leading platform in neuromorphic computing. In this work, we have fabricated a multifunctional synaptic transistor (ST) using a conjugated polymer P3HT channel and a superionic rubidium silver iodide (RbAg₄I₅) thin film coated over a polyethylene oxide (PEO) layer as the gate dielectric. Large hysteresis in the transfer curve represents the memristive behavior with at least 10⁵ current On/Off ratio. Enormously large specific capacitance induced by the electrical double layers at the interfaces of PEO/RbAg₄I₅ dielectric induces polaron (P3HT⁺) generation in the channel through bound states formation by the electrons with Ag⁺ ions and consequent movement of iodine (⁠$I−$⁠) counter ions toward the P3HT channel under a negative gate bias stress. This is strongly supported by the blue shift of the Raman peak from 1444.2 to 1447.9 cm⁻¹ and the appearance of a new peak at 1464.6 cm⁻¹. Interestingly, the proposed ST device exhibits various synaptic actions, which include an excitatory postsynaptic current, paired-pulse facilitation, and short-term potentiation to long-term potentiation after repeated rehearsal on top of standard nonvolatile data storage capability. Our ST also depicts an enhanced retention to 10³ s and more than 10³ discrete On- and Off-states during potentiation and depression function modulation, respectively, just by consuming a very low energy of about 2.0 pJ per synaptic event. These results are very significant to make this organic synaptic transistor as a potential candidate in terms of the desired metrics for neuromorphic computation at low cost and improved accuracy in the future.