Temperature Effects On Resisitive Switching Of Flexible Polymer Films Embedded With Nanoparticles Under Bending Condition

Flexible electronics is one of the main themes in information technology.Future electronic applications place higher demands on the flexibility,wearability and lightness of device.Thus,it is an urgent task to look for a flexible,non-volatile,low-power new storage technology.Nowadays,a frontier research field is to build new hybrid polymer-nanoparticles nanoscale composite films for making high-density and flexible memories,which can combine the advantages of both polymer and nanoparticles(NPs).Previous studies indicate that the deterioration mechanism of resistive switching under repeated bending conditions is one of the key issues that need to be addressed.In this paper,hybrid polymer-NPs memory devices were systematically studied by altering polymer materials,changing the thickness of the functional layer,as well as controlling the temperature condition to provide deep insight into temperature effects on switching behavior and bending endurance of flexible memory device.Corresponding evolution process of deterioration mechanism of resistive switching is revealed.This work focuses on elucidating the physics of the resistive switching failure during mechanical bending under low temperature.Firstly,different polymer/NPs interfaces were built by embedding ZnO NPs in polymethylmethacrylate(PMMA),polyvinylcarbazole(PVK),poly[(9,9-di-n-octylfluorenyl-2,7diyl)-alt-(benzo[2,1,3]thiadia-zol-4,8-diyl)](PFBT)films,then Al/Polymer-ZnO NPs/Al devices were fabricated by spin-coating and vacuum evaporation coating to explore the effects of polymer properties on the resistive switching.The results show that Al/PFBT-ZnO NPs/Al device shows the best switching behavior with average ON/OFF ratio of 4×103 and threshold voltage of 1.4V.While Al/PMMA-ZnO NPs/Al device shows the worst switching performance with ON/OFF ratio of 2×103 and threshold voltage of 1.7V.Charge trapping and detrapping process can be used to explain the carrier transport in the device.Ohmic conduction dominates the charge transport of low bias range,while TCLC or SCLC is responsible for higher bias region in high resistance state.The First Principles results show that charge transfer occurs easier between ZnO NPs and conductive PVK and PFBT,which can promote carrier to be trapped by interface traps.However,for PMMA without special functional,the carrier is not easy to be trapped,resulting in larger threshold voltage and smaller ON/OFF ratio.Secondly,functional-layer thickness effect on resistive switching and bending resistance of the device were investigated by changing the layers from 2 to 6,and bending times from 0 to 5000.The results show that the 4-layer Al/PFBT-ZnO NPs/Al device has stable switching performance with larger ON/OFF ratio and better bending resistance.With the bending time increased,the number of valid traps in the active layer decreased,resulting in the ON/OFF ratio decreased by three orders of magnitude after bending for about 3000 times.The transport mechanism jointly dominated by OhmicTCLC is gradually transformed into Ohmic-SCLC.After 5000 times bending,only Ohmic conduction dominate the charge transport.The FEA results indicate that the interfacial micro cracks caused by severe bending may act as blocking layers and thus deteriorate the switching performance.Finally,temperature effect on the resistive switching performace of device under bending condation was investigated in order to obtain a deep underlying physics of how the polymer-NPs interface affects the charge transport and switching mechanisms.The results show that bending effects on the deterioration of switching performance is significantly stronger than temperature effects on charge transport when the temperature change from 40? to 10?.Under the same temperature,ON/OFF ratio decreases sharply with the increase of bending times,while the ON/OFF ratio increases slightly with the increase of temperature at the same bending times.Further reducing temperature,resisitive switching performance deteriorated significantly.Under-5? and-10?,the device can only bear 3000 bending times,while under-20?,the device can only bear 2000 bending times.However,when the temperature reduces to-40?,device will be complete failure after bending 2000 times.Thus,low temperature can deteriorate the switching performance.Temperature reduction will make organic and inorganic materials inside the device more brittle and less flexible.Surface microcracks and interfacial cracks may occur after such continuous mechanical bending under low temperature.These microscopic cracks and interfacial debonding will damage the charge transport path and degrade the device performance.In addition,inactive carrier takes more energy to jump between the two traps under low temperature,which aggravates the deterioration of device performance to some extent.