| Memristors,attributing to their fast response speed and high storage density,have become one of the ideal choices for next-generation non-volatile memory,non-volatile logic operations,and brain-like neuromorphic computing,which are the current research frontier.Memristors usually consist of a metal/resistive layer/metal sandwich structure.The choice of the material of the resistive layer,the design and the regulation of the device structure,will cause the change of the memristive characteristics.Today,organic-inorganic hybrid metal halide semiconductor materials with perovskite structure have entered the market because of their simple preparation methods,low cost,high carrier mobility,adjustable band gap,and rich ion conduction characteristics.However,the water-oxygen instability of organic-inorganic hybrid perovskite materials has prevented from its large-scale application.Compared with organic-inorganic hybrid perovskites,inorganic cesium lead iodine CsPbI3 perovskite has significantly improved water-oxygen stability.?-CsPbI3 is more stable at higher temperatures,while it easily changes into ?-CsPbI3 with a non-perovskite structure at room temperature.Compared with ?-CsPbI3,the phase stability of ?-CsPbI3 at room temperature is more excellent.When it is placed at the sourrounding with much water and oxygen,the material properties will not change at all.This characteristic is suitable to its operation as a memristor exposed to an air environment with water and oxygen for a long time.As we all know,the electrical characteristics of the resistive layer film are the key to determine the memristor performance of the device,and its electrical characteristics are often affected by the morphology of the film.In this paper,?-CsPbI3 was firstly prepared by a simple,low-cost one-step solution method.The ?-CsPbI3 thin film prepared by this method has small crystal grains,many pores,non-uniform film surface and low coverage.However,by adding PMMA to the precursor solution,the surface quality of the film is greatly improved,which is called a composite film PMMA@CsPbI3.By SEM,XRD,and infrared quantitative analysis methods,it was determined that the amount of the substance in the precursor solution was 0.6 M and the film quality was best when PMMA was added at about 2 mg.The experiment also obtained the same conclusion through XPS,infrared powder tableting and Raman test analysis.It's proved that due to the presence of PMMA,it interacts with lead ions in CsPbI3 or bends the Pb-I bond in CsPbI3.During the growth of the film,the formation of CsI·PMMA and PbI2·PMMA adducts will affect the nucleation site and reduce the surface tension,which is the basic of the ?-CsPbI3 to form a complete film with fewer pinholes when PMMA is added.Further testing of electrical performance revealed that when pure ?-CsPbI3 was used as the resistive layer,it was found that its switching ratio was only about 2-3(<10),so it did not have memristive characteristics.The switching ratio of the memristive device prepared by the composite film PMMA@CsPbI3 is greater than 102,the number of cycles can be more than 500,the retention time of each resistance state is 103 s.The device was placed in exposed air for 60 days.The ?-? characteristic curve did not change significantly.The design and regulation of the device structure will cause changes in the memristor characteristics.The material of the bottom electrode and the top electrode in the device structure can not only change the resistance of the entire device in the high-resistance state and the low-resistance state,but also affect the memristive characteristics exhibited by the entire device.(1)Replace the Ag electrode with the Au electrode for the top electrode.The entire device has changed from a WMRM device type to a WORM device type.However,the change of the top electrode fails to change the magnitude of resistance of the high-resistance state and the low-resistance state,that is,it has little effect on the conductance of the entire device.(2)The bottom electrode covers the FTO with naturally oxidized Ag.The high-resistance state resistance becomes larger,and the low-resistance state resistance becomes smaller,that is,the conductance of the entire device has changed significantly.However,when only a fresh silver electrode is used without oxidation,the bottom electrode can be used as a supply source for the silver conductive path and the device cannot be erased.The barrier layer amorphous oxide AgOx is obtained by natural oxidation of silver electrode.After blocking the supply of silver from the bottom electrode,the device can be erased and has excellent memristive performance.Switching speed is significantly improved;set and reset voltages are 0.07?0.10v and-0.04?-0.07v.respectively,with low power consumption,the endurance of 102 cycles;the retention time of 105s;ultra-high switching ratio of 106?107,greatly reducing the possibility of misreading. |
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