Study On The Phase Change Behavior Of Nanocomposite Sb₄Te-VO₂ Applied To Phase Change Memory

Phase change memory(PCM)is recognized as a strong competitor of the next generation of non-volatile memory due to its fast operation speed,high storage density,and multi-level storage.The storage medium of PCM is a phase change material based on a chalcogenide compound,and its phase change properties determine the performance of the PCM.Ge₂Sb₂Te₅(GST),the widely studied phase change material,is still not ideal in thermal stability and crystallization speed,which limits the further commercialization of phase change memory.The phase change material of the Sb-rich Sb-Te system has an ultra-fast crystallization rate,but has poor thermal stability.Aiming at the problem of poor thermal stability of the Sb-rich Sb-Te system,this paper proposes doping modification with metal oxide VO₂,in order to optimize the components with high thermal stability and fast crystallization speed.The research results of this paper have reference and guidance significance for the subsequent development of phase change memory with fast speed,low power consumption,and good data retention.The main tasks are as follows:(1)Some composition Sb₄Te-VO₂ were prepared by magnetron sputtering.And The relationship between the in-situ heating resistance of Sb₄Te-VO₂ thin films with different compositions and the 10-year data retention were tested.The phase change crystallization temperature and 10-year data retention of the preferred component(Sb₄Te)₇₄(VO₂)₂₆ can reach220?and 133?,respectively.The crystallization activation energy which calculated by the result of in-situ heating resistance is further proved to improve the thermal stability of the film.Combined with the experimental results and formulas,the crystallization kinetic index of the film is calculated,which proves that the film-dominated crystallization mode is the nucleation-dominated crystallization mode.The crystallization rate of the thin film is estimated by Ozawa formula.In order to explore the microstructure of the film,we used Raman,XRD,TEM,AFM,XPS and other means to study the changes in structure and properties of the film during crystallization.(2)Sb₄Te-VO₂ sample films were irradiated with lasers of different energy densities,and Raman confirmed that laser irradiation would cause the film to crystallize.We used the scanning electron microscope to obtain the morphology and tested the element distribution.of the laser irradiation.The results show that the laser energy density of 40 m J/cm² will cause the phase transformation of Sb₄Te-VO₂ thin film,and the laser energy density higher than 40 m J/cm² will cause Sb₄Te-VO₂ to melt to different degrees.The element distribution image shows that the molten area finds that the Sb element is easy to migrate We used SEM to explore the microstructure of the film after laser irradiation.In addition,the optical properties of the film were tested using an ellipsometer,and the refractive index and extinction coefficient of the amorphous and crystalline state of the film were calculated through modeling.The characteristic absorption spectra of amorphous and crystalline films were tested using a spectrophotometer and the optical band gap of the film was calculated.The results show that doping VO₂ will increase the optical band gap of the film.