Humidity-dependent synaptic characteristics in gelatin-based organic transistors

Organic synaptic transistors based on gelatin gate dielectric exhibit humidity-dependent synaptic characteristics. The device showed excellent field-effect transistor behavior without hysteresis when measured in a vacuum and dry air, but clear pinched hysteresis loops appeared in a humid environment. A large difference in the hysteresis window was observed under a small scanning range of gate voltage in different humid conditions, while the difference vanished under a large scanning range of gate voltage. The excitatory postsynaptic current strongly relies on stimulus pulse width, which is more pronounced in high humidity conditions, suggesting that slow proton transportation through a sequence of hopping may be responsible for the less pronounced dependence of stimulus amplitude with a short stimulus pulse width. The simulation of an artificial neural network for handwritten digit recognition revealed that the ultimate recognition accuracy at high relative humidity is higher than that at low relative humidity due to the large nonlinearity factor resulting from inadequate and low transportation of protons in the gelatin film under ambient conditions with low relative humidity. This work provides valuable insights into the effects of humidity on the performance of gelatin-based organic synaptic transistors, which could be useful for the development of environment-dependent synaptic devices.