Preparation,Properties And Phase Change Behavior Of Ruthenium-doped Sb-Te Based Phase Change Storage Materials

Phase change memory（PCRAM）is considered as the most promising next-generation non-volatile general-purpose memory because of its high density,good microscale performance,compatibility with CMOS process,high cycle times,high speed reading and multilevel storage.However,the current phase change memory with Sb-Te and Ge₂Sb₂Te₅（GST）as storage media can not meet the requirements of DRAM or Flash in data retention,operation speed,power consumption and cycle life.In this paper,Ru-Sb-Te and Ru-GST new phase change materials and devices were prepared by focusing on the contradiction between operation speed and thermal stability.The influence of Ru doping concentration on thermal stability and phase structure of phase change materials was studied.The optimal components were screened out,and the electrical performance and fatigue life of the devices were analyzed.The mechanism of Ru in Sb-Te system was discussed.The following innovative achievements have been achieved:1.A Ru-Sb-Te phase change material with both thermal stability and operation speed was prepared.The crystallization temperature of Ru_0.06（Sb₂Te）_0.94and Ru_0.08（Sb₂Te₃）_0.92are above 220℃,and the ten-year data retention temperature is above 140℃.The crystallization activation energy is greater than 4e V,and the thermal stability of amorphous state is significantly improved.The crystalline structures are all single phase without phase separation.It is beneficial to the operation speed and reliability of phase change storage unit.Meanwhile,after Ru doping,the grain size is significantly refined to tens of nanometers,which improves the crystal resistance of the two phase change materials and helps to reduce the operation power consumption of devices.The devices can still achieve reversible cycle operation under the pulse width of 10ns,and the cycle life is>10⁵.Reset power consumption is on the same order of magnitude as commercial GST.2.Ru-GST phase change materials with low power consumption and high thermal stability were prepared.The optimal component Ru_0.05（GST）_0.95film has a crystallization temperature of 225℃and a ten-year data retention temperature of151℃.The thermal stability of the film is better than that of the pure GST phase change material in commercial application.The incorporation of Ru inhibits the transformation of GST film from FCC cubic structure to HEX structure and improves the phase structure stability of GST film.The density difference of the film before and after phase transformation is 3.3%.The high and low resistance ratio of the device unit is still>10²after 10⁶reversible cycles,which improves the stability and reliability of the device.Under the same conditions,that the power consumption of the device unit RESET is only 3%of GST,makes it a promising material for applications in the Internet of Things（IOT）field.3.The mechanism of Ru in Ru-Sb-Te phase change material was elucidated.In Ru-Sb-Te system,the formation energy of impurities is the lowest and the structure stability is the best.Ru is only possible to have Ru-Te bond in Sb₂Te₃,while Ru is possible to have Ru-Sb bond and Ru-Te bond in Sb₂Te.The doping of Ru instead of Sb increases the band gap and effective carrier mass of Sb₂Te and Sb₂Te₃,leading to the increase of crystalline resistance.The different effects of Ru incorporation on the mobility of Sb₂Te and Sb₂Te₃is the main reason for the abnormal changes of amorphous resistance.