Freestanding Oxide-based Neuromorphic Transistors

Neuromorphic computing aims to emulate the information processing mode of biological brain and perceptual nervous system,and build an ultra-low power intelligent computer with autonomous learning and cognitive functions.Synapses,neurons and sensory receptors are the basic units of information processing in biological computing systems.Therefore,the first step in the hardware implementation of neuromorphic computing is to develop neuromorphic devices with the functions of synapses,neurons or sensory receptors.Emerging neuromorphic devices can realize complex neuromorphic functions with a single device,among which Electrolyte Gated Transistors(EGTs)have great potential in realizing neuromorphic functions.On the one hand,the gate dielectric material of EGTs contains a large number of mobile ions,which can effectively modulate the channel conductance under the action of the gate electric field.This property is not only similar to the way organisms transmit information through ions,and also endows EGTs with lower operation voltage and energy consumption.On the other hand,the lateral gate device structure of EGTs has scalable multi-input mode,which is suitable for emulating spatiotemporal related neuromorphic functions.At present,human society is entering the era of intelligent sensing,and developing flexible,portable and wearable intelligent bionic sensors and sensing devices is a research hotspot.The freestanding EGTs device with biopolymer electrolyte membrane has ultra-high sensitivity,which is suitable for neuromorphic sensing systems such as robots and electronic skin.In this paper,freestanding oxidebased dual-gate EGTs devices were prepared,artificial nociceptors were constructed,and the high-order synaptic plasticity was emulated,mainly including the following contents:(1)Using chitosan electrolyte membrane as gate dielectric layer and selfsupporting flexible substrate,indium zinc oxide(IZO)lateral dual-gate EGTs device was fabricated.The chitosan electrolyte membrane has low surface roughness(~2.4nm),high visible light transmittance(~80%),a large number of hydroxyl and carboxyl groups beneficial to proton conduction,and electrical double layer capacitance(EDLC)of about 10 μFcm-2 at low frequency.The transfer characteristic curve of IZO lateral dual-gate EGT device supported by chitosan electrolyte membrane is also tested.The results show that the device has low operation voltage,and a counterclockwise hysteresis which is beneficial to realize neuromorphic functions.The threshold voltage,subthreshold swing,on/off ratio and field effect mobility of the device are 0.5 V,114.4m V/decade,9.8 × 106 and 7.6 cm2V-1S-1,respectively.Besides,bending does not cause obvious degradation of the transfer characteristic of device.(2)Based on the chitosan freestanding IZO EGTs device,an artificial nociceptor was prepared.The electrical pulses are applied to the gate of EGTs to emulate the peripheral stimulation experienced by the biological nociceptor,and the electrical pulse response current is regarded as the response signal of nociceptor.Setting a baseline current line of 10 n A.Based on the accumulation kinetics of protons and the slow relaxation process of protons in chitosan electrolyte,the threshold characteristics(1.0V),no adapt characteristics,sensitization characteristics and relaxation characteristics of nociceptors can be realized.By introducing an additional modulation gate terminal,proton dynamics can be modulated through the dual-gate cooperative operation mode,thus realizing the adjustable sensitivity of nociceptors.The adjustable sensitivity is embodied in the adjustable pain threshold characteristics(0.4 V~1.4 V),sensitization characteristics and sensitivity during relaxation.(3)Based on the chitosan freestanding IZO EGTs device,the synaptic metaplasticity behavior was emulated.Based on the dual-gate structure of the device,the priming stimuli are firstly applied to one gate to emulate synaptic priming activity which can cause synaptic metaplasticity.After a period of time,main stimuli which can trigger synaptic short term plasticity are applied to the other gate.The results show that priming stimuli can effectively modulate single pulse responses(The peak value of EPSC can be modulated between 2 n A to 140 n A),paried-pulse responses(The paried pulse A2/A1 ratio can be modulated between 0.5 to 2.5)and multi-pulse responses(EPSC gain can be modulated between 0.2 to 5.0),thus emulating the modulation of synaptic metaplasticity on synaptic short term plasticity.Based on the relationship between proton relaxation time and initial synaptic weight,the adjustable synaptic potentiation and inhibition are explained in detail.