Preparation Of CsBi₃I₁₀ Halide Perovskite Film And Its Resistive Switching Properties

The migration of halogen ions in calcium halides（HPs）biases the ions and vacancies within the material,resulting in current hysteresis during the current-voltage sweep of the device,and can meet the requirements for switching from high resistance（HRS）to low resistance（LRS）states in random access memory（RRAM）.In recent years,the research of RRAM based on halide perovskites has been widely reported.However,the number and size of conductive filaments formed by ion migration caused by uneven grain boundary distribution and high defect concentration in the film are random,which makes the cycle stability of the device poor and the high resistance state current too large.In this paper,CsBi₃I₁₀ film are used as the active layer of the RRAM.By changing the film preparation process,adding different polar anti-solvents and introducing citric acid into the precursor solution,the morphology,crystallinity,grain size and I^-migration process of the CsBi₃I₁₀ film are adjusted.The resistive parameters such as cycle stability,high resistance current and operating voltage fluctuation of the device are optimized.This dissertation is mainly focused on the following:（1）The process conditions of improving CsBi₃I₁₀ thin film by one-step solution method were systematically explored,including precursor concentration,anti-solvent dropping time and spin coating speed.It was found that these process parameters would affect the nucleation density of CsBi₃I₁₀ grains,the supersaturation concentration of the precursor film and the thickness of the film.The optimized results showed that the film exhibited uniform and dense surface morphology and good crystallinity under the conditions of precursor concentration of 0.5 M,spin coating speed of 5000 rpm and dropwise addition of anti-solvent at 35 s.The combined contribution of I^-conduction and electronic conduction of CsBi₃I₁₀ thin films under electric field was analyzed by voltage scanning cyclic I-V curve and selective blocking method.The ionic conductivity of the obtained CsBi₃I₁₀ thin films is 3.19×10^-6 S/m,the electronic conductivity is 3.97×10^-5 S/m and the activation energy of ion migration is 0.23 e V.（2）In halide chalcogenide materials,grain boundaries act as the main pathway for ion migration and directly influence the growth and fracture processes of conductive filaments in RRAM.In this paper,the microstructures of CsBi₃I₁₀ thin films obtained by different polar anti-solvents chlorobenzene,ethyl acetate and isopropanol were compared.CsBi₃I₁₀ thin films with the same crystal structure and different average grain sizes were obtained.The average particle size of CsBi₃I₁₀ thin film obtained by isopropanol anti-solvent is up to 424 nm.Because the large grain size reduces the number of grain boundaries,the migration path of I^-decreases,the randomness of the distribution of conductive filaments is improved,and the cycle stability of the device is improved.The device achieves a switching ratio of 10⁴ and a retention time of 10⁴ s in 400 cycles.The logic operations such as OR,NAND,NOR and AND are realized by designing and applying electrical pulses.（3）The resistance switching behavior of CsBi₃I₁₀ devices is related to the film quality and I^-defect migration.In this paper,citric acid with different molar mass was introduced into the precursor solution of CsBi₃I₁₀,and the nucleation sites of perovskite were controlled by the coordination of-COOH in citric acid with Bi³⁺,as to improve the morphology,crystal structure and electrical properties of perovskite films.The-OH in citric acid forms hydrogen bonds with I^-in the precursor solution,which inhibits the migration of some I^-,reduces the number of conductive filaments,and reduces the high resistance current of the device.When the amount of citric acid added is 0.1 mmol,the device has a large on/off ratio（10⁴）,stable cycling（400cycles）,and long-term retention characteristics（>10⁴ s）.