Study On Optical And Electrical Properties Of Sb-Se-based Thin Films For Phase Change Memory

Phase change memory（PCM）is considered to be one of the most feasible candidates for the next-generation nonvolatile memories.As the core of the PCM,phase-change material is quite important to optimize the device’s performances.The most studied phase change materials are traditional Te-based chalcogenide compounds.However,their low data-retention ability and high power consumption limit their wide application in PCM.In this dissertation,the novel Sb-Se-based phase change materials with low power and high stability were systematically investigated,including the binary Sb-Se films and the composite（VO₂）_x（Sb₂Se）_100-x films for tunable optical storage.It provides reference and guidance for the subsequent development of high thermal stability,low power and high-contrast optical switching phase change memory.The main results are as follows:1.Optimizing the Sb₄₇Se₅₃ component with excellent phase change performance in Sb-Se phase change film.The crystallization temperature（Tc）and the 10-years data retention temperature（T10-years）of the preferred Sb₄₇Se₅₃ film are as high as 241 ℃ and 141.8 ℃,respectively.It is indicated that the Sb-Se film has good thermal stability.Hall coefficients of all films are positive value,which indicate the Sb-Se films belong to p-type conduction.The decrease in crystalline optical band gap with increasing Sb indicates that a decrease in activation energy for electrical conduction,and the increase in amorphous optical band gap with increasing Se indicates that the better conductivity.The Sb-Se film has a large difference in optical band gap between amorphous and crystalline states,which is beneficial to improve the switching ratio of the device.In addition,the large refractive index difference between the two states in the 1.7-25 μm spectral range enables the film to apply to tunable photonic devices,such as optical switches and optical memory devices.2.The composite（VO₂）_x（Sb₂Se）_100-x film has been proposed for the optical tunable device in the UV-VIS-NIR region.The Tc and the T10-years of the thin films are as high as 240 ℃ and 162.4 ℃,respectively,indicating the excellent thermal stability of the（VO₂）_x（Sb₂Se）_100-x film.This results from the formation of Sb-V and Se-V bonds with large bond enthalpy in the（VO₂）_x（Sb₂Se）_100-x film,and the stable chemical bond is not easily destroyed during heating.The widening of band gap（0.820 e V）in the amorphous phase is of fundamental importance for the switching properties.The magnitude of the optical contrast between the two states of the composite（VO₂）_x（Sb₂Se）_100-x film depends mainly on the resonant bonding coefficient.The resonant bonding coefficient decreases with increasing VO₂,which leads to the reduction in the optical contrast between amorphous and crystalline states.By making it possible for the（VO₂）_x（Sb₂Se）_100-x film can be a promising candidate for tunable photonic applications due to a large optical ON/OFF ratio by optimizing the concentration between VO₂ and Sb₂Se.（VO₂）₂₀（Sb₂Se）₍800 and（VO₂）₂₅（Sb₂Se）₇₅ demonstrate an excellent phase-change properties and are recommended as optimized compositions.