Preparation Of Sb-based And Se-based Phase Change Materials And Research On Device Performance

Phase change memory?PCRAM?is a new nonvolatile memory,which is considered to be the most likely to replace the flash memory?flash?in the near future as a mainstream nonvolatile memory.Compared with other memories,PCRAM has many advantages,such as good fatigue,fast writing speed,low power consumption and compatibility with CMOS process.However,there are still a lot of problems that need to be solved in PCRAM.The first,it is very difficult to make phase-change materials have both fast phase-change speed and high stability.The second,PCRAM has high power consumption in the reverse phase transition process?RESET?.The third,the reliability of the data retention of phase change materials should be improved.In view of the hot issues of PCRAM,the nano phase-change film materials with high performance are prepared by magnetron sputtering.The application prospects of thin film materials in PCRAM are systematically studied in ter ms of phase structure,micro-morphology and thermal stability.The following conclusions have been obtained:?1?A novel Cu-Sn-Se phase-change film was developed by doping Cu elements into SnSe thin films.The amorphous-to-crystalline transition was studied by in situ film resistance measurements.Cu-Sn-Se material had lower activation energy for crystallization?1.60 eV?and higher crystallization resistance than SnSe.The amorphous Cu-Sn-Se had a smaller band gap compared to SnSe.After the adding of Cu,the crystallization of Cu-Sn-Se material was inhibited and the grain structure became more compact.The picosecond laser pulse measurement indicated that Cu-Sn-Se material had a fast phase change speed?3.36 ns?.Cu-Sn-Se film has higher crystalline resistance than SnSe film,which is very important for the application of low power PCRAM.?2?A new SnSb-O phase change film was developed by adding O element into SnSb film.With the addition of O content,the amorphous and crystalline resistance of SnSb-O films increasees,and the crystallization temperature rises from 158 to 240°C,which improves the amorphous thermal stability and data retention capacity of the phase change films.There are above 2 orders of magnitude for crystallization resistance of SnSb-O thin film before and after crystallization.The band gap of SnSb-O films also increased from 1.19eV before O-doping to1.63eV after O-doping.After the addition of O content,the crystallization of the SnSb-O film is also gradually suppressed.The oxide of Sb is formed during the crystallization process,which reduces the grain size,increases the crystalline resistance and reduces the power consumption of the RESET process.With the increase of oxygen content,the root-mean-square?RMS?roughness of SnSb-O films decreases gradually,which improves the reliability of the devices.The melting point temperature of SnSb-O film is 494°C,which is lower than that of traditional phase change film Ge₂Sb₂Te₅,leading to reduce the power consumption of film in device application.In addition,it is also found that excessive oxygen doping can lead to loss of phase-change properties for SnSb-O thin films and can not be applied by devices.?3?GeSb/SiO₂ nano composite multilayer phase change films with different thickness ratios are developed.With the increase of the relative thickness of SiO₂ insulator,the crystallization temperature of GeSb/SiO₂ multilayer films increases gradually,and the thermal stability of the films enhances.After annealing,the root-mean-square surface roughness for GeSb?1nm?/SiO₂?9nm?thin film increases slightly from 0.45 to 0.53 nm.The amorphization time for GeSb?1nm?/SiO₂?9nm?thin film?2.29ns?is shorter than Ge₂Sb₂Te₅?3.56ns?.The threshold voltage of a cell based on GeSb?1nm?/SiO₂?9nm??3.57V?is smaller than Ge₂Sb₂Te₅?4.18 V?,which reduces power consumption during phase change process.