Chitosan Gate-Controlled Organic Electrochemical Transistor Simulating Artificial Synapse And Its Direction Selection Circuit

The research progress of brain-computer interface,implantable/wearable devices,prosthetics and intelligent soft robots requires close interaction and integration between technology and nature.Since the basic elements of life are very different from those used in electronic equipment,the ability to connect man-made devices with biological systems is critical to success in these areas.The neuromorphological system which borrows the design concept of biological signal system is expected to bridge this gap.Although several software-based neuromorphological algorithms have been integrated into biomedical systems,hardware-based systems are closely related to living tissues,develop their functions based on biofeedback,and make use of event-based sensing.the processing capacity of biological systems is ultimately necessary.Neural morphological computation imitates the computational characteristics of the brain.The human brain is a neural network connected by synapses,which can process unstructured data in real time,such as video,image or speech recognition,and information retrieval.Synapses have different responses,which are the basis of learning and memory.Many researchers have tried to simulate biological synaptic functions to develop artificial synapses（ASS）and integrate them into highly parallel,extremely compact,multi-functional,fault-tolerant,autonomous learning,adapting to the new environment,energy efficient,and data storage and processing at the same time.With the development of software algorithm and network structure,neural morphological computing and artificial intelligence have made substantial progress.In recent years,research on the generation of organic synaptic devices has focused on simulating the biological functions of artificial nervous system.Artificial organic synapses simulate brain plasticity using simple structures,low manufacturing costs and low power consumption.It is hoped that the brain-like computing system will break through von Neumann’s bottleneck.Therefore,the generation of organic synapses is of great significance for the future development of neuromorphic systems.Based on the penetration of ions into organic semiconductor channels,organic electrochemical transistors（OECTs）have the ability to modulate large current and have the unique characteristics of high transconductance,low voltage and large capacitance.The high current at low voltage and its compatibility with the water environment make OECTs particularly suitable for bioelectronic applications such as biointerfaces,printed logic circuits and neuromorphological devices.Organic electrochemical transistors（OECTs）stand out as synaptic devices for synaptic bionics and neural computing in the field of biological applications.Animals need to detect movement,but they must also be highly sensitive to their direction.The ability to perceive the direction of motion requires neurons to respond differently to visual stimuli moving in the opposite direction.This element is often referred to as directional selective（DS）neurons.DS neurons associated with optical flow analysis have been described in different arthropods.These neurons usually have a wide receptive field,are very sensitive to the grid of a specific axis（horizontal or vertical）,excite to one direction of movement（priority direction）,and strongly inhibit the opposite direction（zero direction）.In this paper,OECTs based on DPPT-TT is proposed as a neural morphological device.Ion-conducting Chitosan electrolytes used as dielectrics can provide low-voltage operation and synaptic functions for the device through its double-layer（EDL）capacitance effect.In this paper,by changing the preparation conditions of active layer DPPT-TT and gate dielectric Chitosan,such as film preparation mode,annealing time,annealing temperature and so on,an optimal condition is obtained:Chitosan is uniformly dripped onto the substrate about 0.3ml,then transferred to a heating table at 90℃to heat 30min,and finally the device is naturally air-dried in air for 2 days;DPPT-TT is preannealed at 80℃for 5min,and then annealed at 150℃for 1 h.The device can work under the low voltage of 2V～-2V,and the working current I_DS can reach 768n A,the current switching ratio of the device is 4.28×10³,the threshold voltage in the saturation region is1.73V,and the subthreshold slope is 2.86V/dec.In addition,the device uses two wiring schemes to simulate two different types of short-term synaptic plasticity,including enhancement（STP）and suppression（STD）.Ten positive voltage pulses are continuously applied at the presynaptic input of the device,pulse amplitude is 3V,pulse width is 50ms,pulse period（35）t is 50ms,stimulation to the drain electrode and V_GS is-0.7V,imitating STP.Ten positive voltage pulses are continuously applied at the presynaptic input of the device,the pulse amplitude is 3V,the pulse width is 50ms,and the pulse period（35）t is 50ms,which is stimulated to the drain and gate electrodes.At the same time,the voltage V_GS is-2.0V biased to the gate.Simulating STD;is essential in the biological nervous system.Finally,through the same working mechanism of the biological vision system,the simulated STP and STD are integrated to achieve directional selectivity in a new neural morphological loop.This study proves the great potential of chitosan gated DPPT-TT transistors in the application of neural morphology,and is expected to accelerate the development of the next generation of artificial intelligence systems.