Low-Voltage Oxide-based Electric-Double-Layer Synaptic Transistors And Their Humidity Sensing Applications

The human brain is a highly complex neural network and information processing system.The field of brain-inspired neuromorphic computing can break the bottleneck of von Neumann and provide a new idea for ultra-high performance and ultra-low power consumption of electronic integrated systems.Synaptic electronics aim at constructing circuits like the human brain neural network from the physical level,achieving massively parallel computing and high plasticity,and developing new electronic devices that can perform functions related to synaptic bionics and neural computation.In the large-scale array construction,the three-terminal synaptic transistors can effectively avoid the hidden path phenomenon caused by parasitic current;they can also simplify the circuit to achieve multi-terminal input cooperative work.So the three-terminal synaptic transistors not only can simulate the synaptic plasticity function,but also conform to the high parallelism and highly tight requirements of neuromorphic engineering.Electric-Double-Layer Thin-Film-Transistors(EDL TFTs)are typical three-terminal synaptic transistors.The EDL TFTs can effectively achieve ultra-low voltage operation by using the large electric-double-layer capacitance of the electrolyte.The relaxation caused by the ion motion in EDL TFTs can be used to simulate synaptic plasticities.Moreover,it is easy for EDL TFTs to expand into a multi-gate structure to realize multi-input integration.EDL TFTs work in a similar way to neuronal dendritic integration,so they have attracted much attention in the field of neuromorphological engineering and biochemical sensing.The solid electrolyte gate dielectric has a large electric-double-layer capacitance and is easy to process and prepare.It is used as gate dielectric material of EDL TFTs,which can reduce the operating voltage of the device and has better structural stability.In this thesis,composite electrolyte films were used as the gate dielectric of EDL TFTs,and the oxide-based EDL TFTs synapse devices were fabricated.Various synaptic plasticities simulations of EDL TFTs were carried out,and their application in the field of humidity sensing were also studied.The specific work are as follows:1.Oxide-based EDL TFTs were prepared on glass substrate and flexible substrate by using chitosan/graphene oxide composite films as gate dielectric.The ion conductive behavior of the chitosan/graphene oxide composite films and the formation mechanism of the EDL capacitance were studied.The saturation field effect mobility of the IGZO-based synapse transistors on the glass substrate can reach 24.9 cm2V-1s-1.The synaptic device was successfully used to simulate a series of plasticities of photoelectric synapses,including EPSC,PPF and filtering characteristics of electrical stimulation synapses,and EPSC,PPF and time accumulation characteristics of light-stimulated synapses.The field effect mobility of IZO-based EDL TFTs on the paper substrate can reach 33.8 cm2V-1s-1.At the same time,a resistive load type inverter synapse device based on flexible IZO-based EDL TFTs is introduced.The "NAND"logic function can be implemented in laterally coupled dual-gate IZO-based EDL TFTs.The excitatory post-synaptic potential(EPSP)simulation was successfully implemented using the inverter synapse device.2.The polyvinyl alcohol/graphene oxide composite films were prepared by solution method with a large EDL capacitance at the specific frequency of 1 Hz,which can reach 2.62 μF/cm2.On the ITO glass substrate,the polyvinyl alcohol/graphene oxide composite films were used as the gate dielectric layer,and the IZO-based EDL synaptic transistors were successfully fabricated by "one-step method".The "AND" logic function can be implemented in laterally coupled dual-gate IZO-based EDL TFTs.The synaptic devices were used to successfully simulate a series of long-term plasticities of electrical synapses,including single-pulse long-erm plasticity,multi-pulse long-time plasticity and time integration,and spike-timing-dependent plasticity(STDP).Flexible IGZO-based EDL TFTs were prepared on the paper substrate using polyvinyl alcohol/graphene oxide composite films as the gate dielectric layer.And we also successfully simulated the excitatory post-synaptic potential(EPSP)under light pulse stimulation.An inverter synapse device with light pulse synaptic plasticities is constructed.3.The dynamic humidity sensing characteristics of IZO-based synaptic transistors with graphene oxide/chitosan composite electrolyte as gate dielectric were investigated in room temperature.The relative humidity is quantitatively characterized by short-term dynamic synaptic plasticity parameters such as excitatory post-synaptic current(EPSC),paired-pulse facilitation index(PPF index),and high-pass filter coefficients.The spiking humidity response time and energy consumption of the IZO-based synaptic transistors were 30 ms and 2.2 nJ,respectively.At the same time,a model of electrolyte humidity regulation and adsorption of water molecules on the surface of IZO channels was proposed.Flexible IGZO-based TFTs used polyvinyl alcohol/graphene oxide composite films as gate dielectric exhibit stable spike voltage sensing characteristics at low humidity.And the devices have good bending stability and can be used in flexible sensing,wearable devices,and flexible display panels.