Study On The Performance Of Titanium Doped HfO₂ Compound Thin Film And Flexible Selector

As a new type of non-volatile memory device,the resistance random access memory（RRAM）has the advantages of high speed,low power consumption,easy integration,simple structure,and compatibility with COMS.However,the leakage current will occur in three-dimensional integration（The problem of sneak current refers to the misreading of information caused by the current that does not flow through a specific cell according to the set path during the read operation of the cross-array memory）.It is the important challenge of RRAM at the circuit and architecture.To solve this problem,researchers have proposed some solutions such as 1T1R,1D1R,1S1R,and CRS.Among them,the 1S1R（a selector in series with a RRAM）structure is favored for its small feature size,non-destructive reading,and low preparation temperature.The paper first characterizes the material of titanium-doped HfO₂ composite films with different scores to explore their physical and chemical properties.In this paper,HfO₂composite thin films with different titanium doping contents were prepared by the method of magnetron co-sputtering via control the RF power and time.Scanning electron microscope,atomic force microscope and X-ray photoelectron spectroscopy were used to analyze the physical and chemical properties of the thin-film materials such as the cross-sectional thickness,surface roughness,content of each element and its combined state.The results show that the thickness of the films prepared by the magnetron sputtering are～20 nm,and the surface root-mean-square roughness are about～0.14 nm.More importantly,the content of the elements and its compound state in the films affect their ferroelectric and resistance switching characteristics.The thesis focuses on the flexible selector based on Hf_17.66Ti_13.79O_68.55 compound film.The research found that the Pt/Hf_17.66Ti_13.79O_68.55/ITO device has typical ovonic threshold switching characteristic.The threshold voltage(V_th)and hold voltage(V_hold)have excellent consistency,and the switching speed is within 60 ns.The pulse endurance reached 6×10⁷times.During the bending resistance test,it was found that the threshold switching characteristic of the selector under bending radii of 30 mm did not degrade,and when the number of bending times reached 1000,the selector could still work normally.Through fitting analysis of the current conduction mechanism,the device is Schottky emission mechanism at the OFF state and space charge limiting current at the ON state.Subsequently,Hf_17.66Ti_13.79O_68.55 compound film was analyzed by photoelectron spectroscopy and transmission electron microscopy.The results show that hafnium was not completely oxidized and a small portion of hafnium exists in the metallic form in the Hf_17.66Ti_13.79O_68.55compound film.Combining the analysis of the results of electrical properties and material characterization,we proposed the mechanism of selector is the synergy between Schottky barrier and the space charge limiting current conduction mechanism.At the end of the thesis,a RRAM device based on the Pb doped HfO₂ thin film in a cross-array structure is studied.Compared with Pt/HfO₂/ITO device,the memory window of Pt/Pb:HfO₂/ITO device has been increased from 10 to 1000.According to the fitting analysis of the current conduction mechanism,we explored the mechanism of increasing the resistance window value of Pt/Pb:HfO₂/ITO device.To sum up,this paper adjusts the electrical properties of the devices by changing the ratio of each element in the composite film,and in-depth exploration of the conduction mechanism of the devices.It provides experimental basis and theoretical basis for the application of HfO₂-based compound films in semiconductor devices,and has important scientific value.