Neuromorphic Devices Based On Oxide Electric-Double-Layer Thin-Film Transistors

The human brain is a parallel intelligent computer with the characteristics of high efficiency and low energy consumption.Nowadays,to build a brain-inspired intelligent conputing system is the bright new way to solve "the Von Neumann bottleneck"problem.The development of the brain-inspired conputing system includes two parts,the artificial neural network based on software programming and the neuromorphic system based on hardwares.The potential of artificial neural network based on software is still limited by the hardwares in Von Neumann architecture.Therefore,building device systems emulating the brain is the only way to enables the parallel signal processing with learning/memory functions for lower power consumption.The synapse is the basic unit of the brain when transmiting and processing information.Hardware implementation of synapse by individual electric device is of great significance for realizing such neuromorphic computation.Among the synaptic bionic devices,the electric-double-layer thin-film transistors based on ion conducting gate dielectric has a very good prospect for application for synapse emulating.The conducting ions in the gate dielectric will form a stable electric double layer at the interface of electrolyte/channel,which lead to the huge specific capacitance of the electrolyte and make the device able to work at a low voltage.The ion dynamic process in the electric-double-layer dielectric can result in a synapse-like behaviors in the channel layer.Based on the research on electric-double-layer thin-film transistors,the following works are carried out in this thesis.1.Two electrolyte films are fabricated,including chitosan organic polymers and graphene oxide modified by KH550 silane coupling agent.The electrical characteristics of the two films are mearsured in devices of IZO electrode/electrolyte film/ITO electrode sandwich structures.The fabrications are all in solution processing in constant temperature and air environment.The electrical characteristics show that chitosan and modified graphene oxide films both have a high proton conductivity and electron insulativity.They are suitable candidates as the electrolyte material of electric-double-layer thin-film transistors.The fabrication process of electric-double-layer TFTs based on these two dielectric films is also introduced.The fabricated TFTs display low operation voltage,large current on/off ratio and high field-effect mobility.2.Synaptic behaviors are emulated by electric-double-layer thin-film transistors,inbcluding excitatory post-synaptic current/potential,paired-pulse facilitation,high-pass filter,temporal integration,spike timing-dependent plasticity,spike rate-dependent plasticity.The electric-double-layer thin-film transistors can also be connected in series with a resistor to form an inverter,which is also able to mimic synapse with output voltage.The mechanisms behind these are electrostatic coupling and electrochemical doping.3.Light stimulated synaptic behaviors are mimicked in inverters based on IGZO-based electric-double-layer TFTs.Furthurmore,the gate voltage is involved in device tuning.The artificial synapse exhibits different characteristic under different gate voltages.In this condition,long-term potentiation and long-term depression are reproduced in a single artificial synapse.This work may become the key to realize complex computing tasks in neuromorphic systems.