Preparation And Stability Study Of Perovskite Resistive Random Access Memory

In recent years,with the development of the Internet of Things?IOT?and the era of big data,people have put forward higher requirements for information storage and data processing,which urgently requires the development of non-volatile resistive random access memory?RRAM?with simple preparation process,low power consumption,low cost and fast response time.Organic-inorganic hybrid perovskite materials?CH₃NH₃Pb X₃?become“super-star”in the areas of nanomaterials and optoelectronic devices due to its excellent optoelectronic properties such as adjustable band gap,high bipolar carrier mobility,long carrier diffusion length and low excitation energy.As a switching media,organic-inorganic hybrid perovskite films can be prepared by low-temperature solution processing,but it is faced with a huge challenge:the perovskite structure is prone to collapse due to its intrinsic instability and easy degradation under environmental conditions,which reduces the performance and stability of the resistive memory device.Meanwhile,it will further limit the development of commercialization.Therefore,in this paper,starting from improving the environmental stability of perovskite,the interface engineering and element engineering are used to prepare optimized perovskite RRAM devices and improve their resistive performance and environmental stability.In the first part of this thesis,interface engineering is utilized and PVAm·HI with flexible long chains is added to the perovskite precursor solution to effectively regulate the morphology and crystal structure of the perovskite film,thereby obtaining polymer perovskite resistive memory device with improved performance and long-term stability.PVAm·HI is introduced into the precursor solution partially replacing methylamine ions?MA⁺?to fabricate stable and flexible polymeric perovskite devices.On this occasion,PVAm·HI acts as nucleation sites and the crystallization template for MAPb I₃ crystalline growth to tune the microscopic perovskite structure.The adjacent crystalline grains are covalently immobilized by anchoring PVAm·HI on the surficial A-site of perovskite nanocrystals to improve the stability and flexibility of OHP RRAM devices,even the resistive switching performance.The optimized device exhibits fast and stable non-volatile resistive switching characteristics with an ON/OFF ratio of?10⁵ and a SET voltage of-0.45 V.The research on polymeric perovskites with different PVAm·HI content shows that the improvement of the resistive switching characteristics not only comes from the modification of the perovskite grain boundaries,but also from the adjustment of perovskite grain size under ambient conditions.The conduction mechanism in polymeric perovskite resistive memory devices is also studied.The results suggest that the space charge-limited current?SCLC?is the main conduction mechanism in HRS while the Ohmic behavior is dominant in LRS.Moreover,the unsealed optimized devices in air maintain stable storage performance after one year.In the second part of this thesis,low-dimensional lead-free perovskite quantumdots?Cs₃Bi₂Br₉ QDs?RRAM devices are prepared by element engineering.Compared with the three-dimensional perovskite in the first part,the low dimension perovskite can fully improve the stability of the perovskite itself.At the same time,replacing the heavy metal lead element with bismuth element can reduce the harm to the environment and is more conducive to commercial development.The as-prepared Al/Cs₃Bi₂Br₉ QDs/ITO device exhibits stable non-volatile resistive switching characteristics with an ON/OFF ratio of?10⁴ and a SET voltage of-0.40 V.Additionally,we also assessed the photonic memory's response to the optical signal due to the excellent optoelectronic properties of the perovskite.The results show that light intensity can increase the current of the device in HRS and LRS,and effectively reduce the SET voltage.Multi-level storage states can also be realized by adjusting the light intensity.What's more,the conduction mechanism indicates that both the photo-generated carriers and the carriers generated under the electric field contribute to the resistive switching behavior together.Finally,the device was continuously tested in ambient environment at room temperature?23?28°C?and a relative humidity of 50%?60%.After 50 days,the devices still show excellent RS behaviors and maintain great long-term RS performance.