Effect Of Bending On The Resistive Switching Of Flexible ZnO-based Thin Films

With the development of information technology,the traditional memory devices can not satisfy the necessary due to hard to bending.At the same time,common organic flexible device has the problem of poor physical properties.Therefore,the introduction of flexible inorganic resistive random access memory is important.The RRAM film is deposited on a flexible plastic substrate so that it can combine the high-performance with the good ductility.This work regards metal oxide as an example to systematic discuss the mechanical stress effects on flexible RRAM resistance characteristics ZnO has lots of merits including the high electronic mobility,but also excellent transparent.In this work,the ZnO nanoparticles,ZnO-NiO composite and layered nano heterojunction were prepared using hydrothermal method.The influence of hydrothermal condition and interface microstructure on the resistive characteristics was investigated before and after bending test.The specific contents of the dissertation are as follows:First,the ZnO nanoparticles was prepared by hydrothermal method correspond to hexagonal phase with particle size of 109.5 nm.The nanoparticles obtained by hydrothermal growth at 200 ℃ for 2 h have the relatively high ON/OFF ratio and low set voltage which.By changing the number of bending and bending radius,we found thin film threshold voltage increases,the ON/OFF ratio reduce significantly.Through the Abaqus calculation and analysis,the effect of bend radius on the film/substrate system is that the ZnO layer cracks firstly because of its high elastic modulus.The applied mechanical stress increases with the decrease of radius,micro crack conceives in film and accumulates,which influence the device resistance characteristics.Second,we choose the typical P-type NiO to fabricate different molar ratio ZnO/NiO physical nanoparticles and study the resistive characteristics.By changing the number of bending and bending radius,since the inorganic membrane rupture generally occur in the grain boundary,then film crack initiation and propagation,grain boundary barrier increases,which lead to that threshold voltage of the device increases,ON/OFF ratio drops by two orders of magnitude.For the layered ZnO-NiO nanomaterials film,they introduce new interfacial potential barrier between the electrode and function layer,it lead the average threshold voltage and ON/OFF ratio of the NiO-ZnO-NiO layered film are the highest of about 3.7 V and 3644.We test resistance characteristics of device before and after bending.The results show that electrical properties of film are reduced after bending,but there are no change of electron transport mechanism and the switching mechanism.And the Abaqus calculation results show function layer thickness increasing makes the neutral axis of the film-substrate system offset to the functional layer,so the stress value decreases.On same condition,we researched the strain of different layered films,for the NiO-ZnO-NiO,the introduction of NiO layer makes mechanical mismatch strain between the ZnO and the ITO layer decrease,and at the same time the NiO as a cover to make applied mechanical stress system under the same radius is minimum,so the influence of mechanical bending stress on NiO-ZnO-NiO resistance characteristics is smallest.we conducted the theoretical calculation using the Materials Studio software and confirmed that the interface with different contact types can affect the crystal.The theoretical to explore the effect of different p-n interface on the resistive switching of ZnO-NiO layered films.According to the calculated results of the density of states(DOS)near the Fermi level of layered model,we got the conduction mechanism of layered films change from N to P type.As a result of the contact interface types are different,interface barrier changes,the conductivity of NiO-ZnO-NiO layered is the smallest,the result agreed with the experimental data.In summary,the preparation of zinc base nanoparticles still have repeatable resistance switching characteristics after bending test,although the ON/OFF ratio sharply drops,and the threshold voltage increases.This work can provide useful information for flexible inorganic nanoparticles memory devices.