Organic thin-film synaptic transistor for emulating artificial synapse and non-volatile memory*

Ion gels, solidified ionic liquid electrolytes by structuring polymer networks, have attracted significant attention in various applications due to their exceptional material properties. These properties include a high specific capacitance, remarkable thermal, and electrochemical stability, non-flammability and rubber-like mechanical robustness. Pressure sensors, which convert external mechanical deformations to electrical signals, find utility in a wide range of fields such as human skins, soft robotics. For these sensors, it is crucial to have high sensitivity, a broad sensing range, and a quick response time. In the case of capacitive sensors utilizing ion gels, they offer significant advantages for pressure sensors due to their stability, rapid response, and simple device designs. However, sensitivity of these pressure sensors is often insufficient, which limits their practicality and applicability. To address this, we incorporated organic thin-film transistors and high-capacitance ion gels and successfully fabricated highly sensitive pressure sensors. By employing thin-film transistor-based sensors, very small mechanical stimuli can be magnified into substantial electrical signals, resulting in a significant enhancement in sensitivity. Additionally, synaptic transistors demonstrated with the pressure sensors exhibited reversible transitions between short-term plasticity, long-term plasticity, and non-volatile memory functions.