Artificial Synapses And Neuromorphic Computing Based On Three-terminal Organic Transistors

Given that traditional storage and computing systems cannot overcome the von Neumann bottleneck,it is crucial to develop hardware with bio-inspired computing function and low power consumption.Three-terminal synaptic transistors based on twodimensional materials,metal oxides or organic semiconductor materials have been used to simulate the biological synapses in the human brain due to higher plasticity,parallel computing,integrated storage and system information processing.Among them,organic semiconductor materials are considered as the most promising neural synaptic materials due to mechanical flexibility,low cost,good biocompatibility and ductility.However,organic synaptic transistors still face great challenges with the precise regulation of synaptic weight.At present,the mechanism of ion and electron redox reactions in organic materials is not fully studied,such as formation mechanism and precise regulation mechanism of weight under the effect of temperature and mechanical stress.At the same time,these redox reactions that affect the weight accuracy are difficult to accurately regulate the synaptic performance of devices,which further hinders the in-depth simulation of biological synapses and artificial neural network systems by organic synaptic transistors.This paper focuses on the above issues:Firstly,the interaction between ions and electrons in organic synaptic transistors is studied by controlling the chemistry and microstructure of organic materials,and achieve the organic neuromorphic devices with non-volatility,low power consumption,high dynamic range and linear conductance updating characteri stics;Subsequently,the effect of working temperature on the redox reaction of ions and electrons in organic synaptic transistors was studied.By studying the thermal and electrochemical effects of organic materials,high-precision organic synaptic transistor with heat resistance and ambient stability are realized;Finally,the effects of mechanical stress on redox reactions of ions and electrons in organic semiconductor materials was investigated.By exploiting the characteristics of organic semiconductor materials,we realize flexible organic synaptic transistors with high synaptic weight accuracy,and demonstrate their potential in neuromorphic computing.The main study contents and the results obtained are as follows:(1)To study the effects of donor engineering on the synaptic properties of threeterminal organic synaptic transistors.Strong electron-donating bis(3,4ethylenedioxythiophene)(PIBET-A)or weak electron-donating bis-thiophene(PIBT-A)groups were introduced into the isoindigo conjugate skeleton to prepare three-terminal organic synaptic transistors with different donor units.The synaptic properties of the device can be significantly improved by enhancing the electron-donating strength of donor units.The strong donor device PIBET-A exhibits low switching energy of 13 ff,excellent memory retention of over 5×103 s,high analog dynamic range of 170×,and high operational stability,retaining 99%of their original current after 100,000 writeread events in air.The excellent synaptic properties can be attributed to the introduction of the strong donor bis-EDOT unit enhancing the HOMO level,π-π stacking,and the interactions with dielectric ions.Our proposed donor engineering sets a precedent for advancing the field of organic neural synaptic devices.(2)To study the physical mechanism of side-chain engineering regulating the dynamic range of three-terminal organic synaptic transistors under the strong donor functionalization strategy.Alkyl chains,linear ethylene glycol chains(PIBET-O),and branched ethylene glycol chains(PIBET-BO)were introduced into the electron-rich isoindigo-bis-EDOT conjugated skeleton to prepare three-terminal organic synaptic transistors with different side chain structures.The introduction of ethylene glycol chains helps to enhance the ion mobility of the polymer films,which can significantly improve the analog dynamic range of the device.The branched ethylene glycol chainbased device PIBET-BO shows gate field-dependent multilevel memory characteristics and ultra-high analog switching range(1200×),which are greatly improved compared with linear ethylene glycol chain PIBET-O(110×)and alkyl chain PIBET-A(66×)devices.The ultra-high analog dynamic range of PIBET-BO devices can be attributed to the introduction of branched glycol chains enhancing the disordered conformation of polymer films,thus contributing to the p-type doping of TFSI-ions in organic semiconductor films.This high dynamic range is an important basis for realizing highprecision artificial neural network simulation.(3)Based on the microstmcture regulation strategy of organic semiconductor materials,the physical mechanism affecting the heat-resistance and ambient stability of three-terminal organic synaptic transistors is studied.The traditional ethylene glycol(EG)chains and more hydrophobic oligoether chains propylene glycol(PG)or butylene glycol(BG)were introduced into the electron-rich bithiophene-thienothiophene backbone to prepare three-terminal organic synaptic transistors with different microstructures.The design of more hydrophobic oligoether chains can improve the high-temperature stability and ambient stability of the device without affecting synaptic function.BG chain-based p(b2T-TT)device exhibits highest memory retention of 103 s and analog dynamic range of 10× at 180℃,representing the record-high hightemperature synaptic performance for reported to date.They also show ultra-high ambient stability,retaining 96%of their original EPSC values after 3 months in ambient conditions.The superior high-temperature and ambient stability originate from the introduction of novel BG chains that improve the hydrophobicity and rigidity of the polymer films,thus reducing the conformational changes of polymer chains and forming a stable film morphology.This oligoether chains chain molecular design strategy provides promising strategies for high-temperature neuromorphic applications.(4)Using the mechanical flexibility of organic semiconductor materials,the flexible and bendable three-terminal organic synaptic transistor was fabricated,and the mechanism of pore structure on the mechanical stability of devices was investigated.In this section,we designed a porous p(b2T-T)polymer film for flexible three-terminal organic synaptic transistors,in which the backbone is bidentate-thiophene skeleton and the side chain is butylene glycol chain.The performance of flexible p(b2T-T)device is affected by pore structure and stable conformation.Due to the porous structure,p(b2TT)devices exhibit excellent mechanical stability,and the stable film conformation leads to the realization of heat resistance.Based on the above characteristics,the flexible p(b2T-T)synaptic transistors can achieve analog dynamic range of 20x and excellent durability of over 20,000 write-read events under mechanical deformation with a bending radius of 3 mm and a high-temperature environment of 120℃.The simulation of biological synapse and high-precision artificial neural network demonstrate the potential applications of flexible three-terminal organic synaptic transistors in future wearable neuromorphic electronic devices,intelligent robots,and prostheses.