Applications Of Zinc Oxide Nanowire Transistors With Polymer Electret Layer

Zinc oxide(ZnO)nanowire has distinct optical and electrical properties owing to the features including direct band gap and large specific surface area.Recently,the applications of ZnO nanowire in many fields have been studied extensively,such as photodetection,gas sensing,biological sensing,storage and logic operation,synaptic simulation and so on.With simple device structure and diversification of application scenarios,ZnO nanowire transistor has become an important type of devices.Therefore,it is necessary to explore the potential applications of ZnO nano wire transistor in different fields furtherly and understand the underlying working mechanism.This is beneficial for device performance optimization and helps to lay a foundation for using in multi-application scenarios.In this work,polymer electret material was used to improve the device performance of single ZnO nanowire field-effect transistor.The application in ultraviolet detection and the capability of simulating synaptic behaviors were mainly studied.The specific contents include the following parts:(1)Since ZnO nanowire contains high density of unintentional defect-induced carriers,perceptible dark current is often observed in such kind of photodetectors,which restrict the key parameters such as detectivity.In this thesis,a PVN electret interlayer was introduced between ZnO nanowire and gate dielectric by a spinning coating method and the single ZnO nano wire transistor based on PVN layer was prepared.Under a large positive gate voltage,electrons in ZnO nanowire were transferred and stored in the deep defect states of PVN layer.The additional electric field generated by stored charges effectively reduced the dark current and the changed state had a good retention.In addition,charges stored in the PVN layer had little effect on photocurrent of the device,thus the photodetection performance has been greatly improved.Under a weak ultraviolet light intensity of 0.11 μW cm-2,value of responsivity is 1.2×106 A W-1,photoconductive gain is 4.0×106,and specific detectivity can reach 3.4×1018 Jones,which are beyond the performance parameters of similar ZnO nanowire photodetectors.To make a comparison,single ZnO nanowire transistor without PVN interlayer was also fabricated.The electrical properties and photodetection performance revealed that in the absence of PVN layer,the same gate voltage can only make few carriers captured by the surface defects of silicon dioxide layer which was volatile.This also confirmed the key role of PVN layer in suppressing dark current and improving the device performance.Based on the experimental results,the underlying mechanism of performance optimization was analyzed.Additional electric field generated by the stored electrons in PVN layer changed the band structure of device and affected electron transfer at the interface between metal electrodes and ZnO nanowire,which effectively reduced the carrier concentration in ZnO nanowire thus the suppression of dark current was realized.(2)The emerging brain-inspired neuromorphic system is promising to overcome the bottleneck of present Von Neumann architecture computer system and the synaptic devices play important role in development of neuromorphic system.To explore the potential application of ZnO nanowire transistor in synaptic simulation,light signal stimulation and electrical signal stimulation were applied to emulate the synaptic plasticity.The simulation included the basic behavior of excitatory postsynaptic current and inhibitory postsynaptic current.Meanwhile,the effects of the amplitude and duration of stimulus signals on postsynaptic current were also researched.Paired-pulse facilitation,an important behavior in synaptic short-term plasticity was also emulated and the relationship between facilitation behavior and pulse interval was explored.According to the response of device under different stimulus signals,the synaptic behavior of transistors under the optical signal stimulation in this experiment was probably related to the persistent photoconductivity effect while the synaptic behavior under the electrical signal stimulation was caused by the capture and storage of electrons in PVN layer.In conclusion,we introduced a polymer electret material into ZnO nanowire transistor and explored its potential applications in synaptic simulation and device performance optimization in ultraviolet detection field.The mechanism of device performance optimization was explained and a new strategy or the design of ultra-sensitive photodetectors was provided.Moreover,this device structure was also applied to emulate synaptic behaviors and offered valuable experiment references for the multi-functional application of ZnO nanowire transistors.