Electric-Double-Layer Synaptic Transistors Coupled With Triboelectric Nanogenerators For Tactile Perception Research

As one of the basic sensation information,tactile information is of great significance for human and other organisms to perceive the external world and mak e a reaction to the changes in due course of time.Enlightened by this,constructing artificial sensory neurons to emulate biological tactile perception will predicatively promote bionic sensing technology and carve new paths to fabricate bioinspired robots,neuroprosthetics,human-machine interface elements and other perceptual intelligent products.Generally,tactile sensory neuron can be simplified into three main components:receptor,axon,and synapse.Receptors perceive tactile information and transmit it to synapse via axon.Synapse is the junction between neurons,the synaptic strength alters depending on the afferent signals,and further modulates the synaptic output.Therefore,artificial tactile sensory neuron requires sensors possessing delicate perceptual abilities similar to receptors and neuromorphic devices which can imitate the behaviors of synapse.Triboel ectric nanogenerator(TENG),which has attracted much attention in recent years,has the characteristic of self-power,can convert mechanical energy into electricity directly.It possesses preferable sensitivity and high response speed,and is thought to have the capacity to drive transistor using the electrostatic potential as the gate voltage.In the field of neuromorphology,a lot of devices are developed chasing for the imitation of synaptic behaviors.Among these devices,three-or multi-terminal devices(for example,electrolyte-gated transistors(EGTs))show clearer operation mechanism and more convenient synergistic modulation.In EGTs,lots of anions/cations move towards the positively/negatively charged electrodes due to the electrostatic coupling of condensed matter,leading to the formation of interfacial electric-double-layer(EDL),providing EGTs high gate dielectric capacitance and low operating voltage.Moreover,the accumulation/relaxation time of ions in EGTs is about several milliseconds,which is comparable with the ionic influx in biological synapse,so they’re very suitable for synaptic biomimetic devices.In this thesis,we present a tactile-sensing element composed of a TENG and EDL thin-film transistors(TFTs)to emulate the biological tactile sensory neuron.The specific implementation s are as follows:1.The EDL TFTs are fabricated on indium-tin-oxide(ITO)/glass substrates,chitosan serves as the gate electrolyte,indium-gallium-zinc-oxide(IGZO)and ITO are used as channel and source/drain electrodes,respectively.The capacitance of chitosan is about 10μF/cm~2 at the frequency of 1Hz.For the EDL TFTs,high ON/OFF ratio of～1.2×10~8 is achieved,which show excellent electrical properties.Then the feasibility of the EDL TFTs to be used as synaptic devices is explored,several synaptic plasticities including excitatory post-synaptic current(EPSC),paired–pulse facilitation(PPF)and high-pass filtering are emulated.2.A piece of ITO/PET film spin-coated with silk fibroin solution and another piece of ITO/PET substrate are bonded into an arched geomet ry with a gap of～2.0mm to fabricate TENG.The TENG responses quickly to dynamic pressure signals,and can generate different output signals according to various external pressure speeds,that is,it can identify the pressure frequencies.3.Effectively connect the prepared EDL TFTs and TENG as an energy-saving tactile sensing device.As the mechanoreceptor,the TENG converts pressure signals into voltage pulses directly.The EDL TFTs are used as neuromorphic devices which can reproduce synaptic behaviors.Functions of biological tactile neurons including EPSC,PPF and high-pass filtering triggered by external pressure stimuli with multidimensional information(intensity,amount,frequency)are simulated,which are of great significance for the collection and refinement of numerous complex sensory data.In addition,the ability of spiders that can identify prey through sensing the vibration of cobweb is emulated for the first time.Based on the low energy consumption of EDL TFTs and the superiorities of simple preparation process and self-power of TENG,our results provide a good example for tactile sensing devices with simple structure,high energy efficiency and easy operation,which shows huge potential for the prospective study in e-skins with multiple tactile-perception functions,and bionic products with artificial intelligence.