Memory Cell Design And Key Fabrication Technology For Phase Change Memory

This dissertation focuses on the study of key technologies used for nonvolatile phase change memory, including fabrication and characterization of phase change materials, fabrication and characterization of electrode materials, circuit simulation and optimization of cell structure.First of all, the history and development of semiconductor memory was briefly reviewed, and some important nonvolatile memories were introduced simply. Then, the principles of phase change memory were discussed, including materials analysis, cell structure and basic performances. By comparing with other nonvolatile memories, the major advantages of phase change memory were expatiated, then the newest research status all over the world and the key points of research was discussed. After that, researches on phase change materials, electrode materials and cell structure were carried on, both in experiments and theories. Main results are shown as below:1, The process of Ge₂Sb₂Te₅ thin film fabrication was optimized, and Ge₂Sb₂Te₅ phase change film with high quality was successfully fabricated. The structure, phase change phenomena and electrical properties were studied. Sputtering Power determinate the deposition rate, while sputtering pressure influenced the crystallization temperature of phase change from FCC to HCP, the higher pressure ,the lower crystallization temperature.2, Ag doping improves the crystallization temperature of Ge₂Sb₂Te₅ film, from 172.7 °C at 0% to 210.0 °C at 11.3%. Ag doping also improves the resistivity of Ge₂Sb₂Te₅ film at polycrystal state, which can benefit the reducing the reset current. Using a simply but useful method to test the I-V curves of Ge₂Sb₂Te₅ films, which demonstrates that Ag doping doesn't destroy the phase change phenomena of of Ge₂Sb₂Te₅ film, only increasing the threshold voltage.3, The W electrode fabricated by high vacuum electron beam evaporation has excellent thermal stability, which can stand by temperature up to 700 °C. And when adding a Ti buffer lay between W and Si, the fabricated W film is α-W, which has single...