Preparation Technology And Properties Of MgSb-based Composites For New Memory

In recent years,with the increasingly fierce trade war between the United States and China,the chip industry in China has been greatly affected,and a series of chip designs with independent intellectual property rights are particularly important.Compared with the current mainstream memory,phase change memory has obvious advantages in size,power consumption,speed,lifetime,compatibility and so on.It is considered to be the most promising next generation of new memory.In the current research,phase change memory has the following problems:it can not guarantee good data retention while the storage speed is fast,and the RESET current does not reach the expected low power consumption.These problems can be solved by phase change materials.In this thesis,we develop new phase change materials to solve the above problems.In this thesis,three kinds of Mg₃₅Sb₆₅ based phase change composite films were prepared by magnetron sputtering.They are Mg₃₅Sb₆₅/Sb,Mg₃₅Sb₆₅/Sn₁₅Sb₈₅ and Mg₃₅Sb₆₅/Ge₂Sb₂Te₅.The electrical properties,atomic microstructure,data retention force and surface morphology of the films were characterized by resistance temperature measurement system,X-ray diffraction,scanning electron microscope(SEM),transmission electron microscope,visible near infrared spectrophotometer(CRT),atomic force microscope,device electrical performance test system and Raman spectrometer.The specific conclusions are as follows:1.A high vacuum magnetron sputtering system was used to prepare phase change thin films.Through a large number of quality comparison for the films prepared with different parameters,including coating uniformity,adhesion to the substrate,grain size,surface roughness,performance stability,etc.,the process was constantly optimized,and the specific process parameters in the sputtering process were finally determined.2.Mg₃₅Sb₆₅ is a kind of amorphous material with good thermal stability.Sb is a material with very fast phase transition speed but poor thermal stability,Mg₃₅Sb₆₅/Sb composite can make full use of advantages and avoid disadvantages,and is expected to be used in high-speed memory.Therefore,the phase transition properties of Mg₃₅Sb₆₅/Sb multilayer films were studied systematically.The Mg₃₅Sb₆₅/Sb thin film has better amorphous stability and higher resistance when combined with Mg₃₅Sb₆₅layer.The unidimensional growth mechanism enables Mg₃₅Sb₆₅/Sb to have an ultra-fast phase transition speed.The grain growth and interfacial stress have little influence on the surface morphology during crystallization.The multilayer structure is determined by the distribution of elements on the cross section.The scratch test results show that the film is firmly bonded to the substrate,and the critical loads before and after phase transformation are 34.7 and 39.3 Mn,respectively.A reversible resistance switch is implemented on the[Mg₃₅Sb₆₅(7nm)/Sb(3nm)]₅-base device.The results show that Mg₃₅Sb₆₅/Sb multilayer composite film is a phase change memory material with high speed and low power consumption,and has the potential to be used in high-speed memory.3.Sn and Mg have low melting points,which can theoretically reduce the power consumption at Reset.It is expected that Mg₃₅Sb₆₅/Sn₁₅Sb₈₅ composite can be used in low-power memory.Therefore,the comprehensive properties of Mg₃₅Sb₆₅/Sn₁₅Sb₈₅superlattice thin films were systematically studied.Mg₃₅Sb₆₅ is a kind of material with good amorphous thermal stability,and the film composite with Sn₁₅Sb₈₅ has good amorphous thermal stability and high resistance.The fundamental reason of semiconductor resistance variation is explained.XRD Raman and TEM tests were performed on the films at different annealing temperatures.With the increase of temperature,the crystallinity of the films increased gradually,and a new phase Mg Sn phase was formed under the interaction of interface.A reversible resistance switch is implemented on a[Mg₃₅Sb₆₅(7nm)/Sn₁₅Sb₈₅(3nm)]₅-base device.The results show that Mg₃₅Sb₆₅/Sn₁₅Sb₈₅ superlattice is a phase change storage material with good thermal stability and low power consumption.4.Ge₂Sb₂Te₅ is the most widely studied and applied phase change storage material,and it is the first phase change storage material put into practical application.However,there are still problems such as poor thermal stability and slow crystallization rate.The film with better comprehensive performance can be obtained by combining with Mg₃₅Sb₆₅.In addition,compared with the single-layer film,the existence of multi-layer interface can scatter phonons and electrons,so as to improve the material resistivity and reduce the material thermal conductivity.This helps reduce the heat loss during the Joule heating process,speeding up heating and reducing the amount of current energy required,thereby reducing power consumption.Therefore,the influence of Mg₃₅Sb₆₅ layer on the thermal stability and thickness change rate of Ge₂Sb₂Te₅ in super-lattice thin films was studied.Compared with single-layer Ge₂Sb₂Te₅ films,Mg₃₅Sb₆₅/Ge₂Sb₂Te₅ multi-layer composite films have higher amorphous resistance and phase transition temperature,and the data preservation ability is significantly enhanced.The fundamental reason of the film resistance change is explained from the change of band gap.The crystallization process of the monolayer Ge₂Sb₂Te₅ and[Mg₃₅Sb₆₅(5nm)/Ge₂Sb₂Te₅(5nm)]₅ films was analyzed by XRD.It was found that Mg Sb may inhibit the GST phase transition.Based on the reliability of PCRAM,the change rate of film thickness was analyzed in detail.