| Resistive random access memory(RRAM)is considered one of the most important candidates for the next generation non-volatile memory application.Compared with the organic material,inorganic RRAM have the characteristic of simple structure,low manufacturing cost,high density and good retention.With the development of technology,there are higher requirement about the property of flexibility.However,for the intrinsic of brittle in inorganic material,crack is easy to initiate and there are limit research about the effects of bending on resistive switching mechanism.This paper focus on the bending resistance of films and carrier transport characteristics by using Finite element method(FEM)and First-principles Calculations,and construct the optimal device structure by modifying the layer orders and changing different metal-top-electrode.Also,the different between effects of outer-bending and inner-bending was investigated.The specific contents of the dissertation are as follows:First,?-type NiO and n-type TiO2 were prepared under the specific condition based on the formal study in our group.The FEM was conducted to compare the difference of stress distribution in NiO and TiO2 films.NiO films behave the better bending-resistance compared with TiO2 films for the lager energy needed for the initiate of micro-cracks.In addition,the structure is prone to be destructed for NiO films,and then the gallium-indium droplets can permeate into the films leading the reducing of effective thickness and threshold voltage.For TiO2 films,the gallium-indium droplets cannot effect the property of the films for the scale of cracks,but the oxygen will permeant into the films and leading the increase of the threshold voltage.Second,the effects of varies metal-top-electrode were investigated.It is easy to generate an oxide layer for Al electrode,and the typical I-V curve rendered as hysteresis plot.When Au as top electrode,electronic needs relative larger bias to go over the barrier,and the diameter of the metal-filaments will be increased leading the devices hard to return the high resistant state.Using the evaporation method fabricate the Ag electrode will cause the penetration of the Ag ions,and makes the short circuit of the devices.Through the First-principles Calculations,we found that the p-n junction will induce the extra energy level.Thus,compared with single layer structure,the composite thin films will lower the ON/OFF ratio,but the stability can be improved by the changing of the layer structure.Finally,the difference between the effects of outer-bending and inner-bending was analysed.With the increase of the outer-bending times,the micro-crack induced and propagated leading the increase of the leaking currents and lower slope value of high resistance fitting with SCLC.The films is mainly bear with compressive stress under inner bending,making the decrease of the gap between the nanoparticles,and the devices switch to ohmic contact.The delamination is one of the main failure mechanism for inner-bending.Compared with the outer-bending,the inner-bending is more likely to make the devices destoried under the same condition.In conclusion,the leakage current increase,the films switch to ohmic contact,ON/OFF ratio decrease and threshold voltage increase after bending.Our work may provide some useful information to further understand bending effects of flexible resistive random access memory devices. |
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