Study Of V, Ag And Mo-doped GST Phase-change Materials For Phase-change Random Access Memory

Phase change memory has been considered as one of the most promisingnonvolatile memory for its advantage in terms of scalability, power dissipation andcompatibility. However, several problems remain to be solved, such as its relativelylow date retention and high RESET current. For commercial feasibility, theseproperties must be improved. The meaning of this paper lies on solving theseproblems from the view of phase change meterials.Various concentration of V, Ag and Mo-doped Ge2Sb2Te5flims were preparedvia magnetron co-sputtering. These films were systemically investigated byelectrical resistivity measurement, X-ray diffraction techniques and advancedTransmission electron microscopy (TEM) techniques. We mainly focused on therelationship between the structure and the properties. The achievements arefollowing:1. Doping V into Ge2Sb2Te5improved the thermal stability. Theresistance-temperature measurement revealed that the crystallization temperatureincreased with the concentration of V. The V dopants suppressed the second phasetransition from fcc structure to hcp structure. Doping V to GST films within acertain amount enhanced the electrical resistance. However, when the V dopantconcentration exceeds a certain value, the extra carrier offered by V would lowerdown the electrical resistance.2. Doping Ag into Ge2Sb2Te5films enhanced the electrical resistance both inamorphous and crystalline structure. The electrical resistance increased with theconcentration of Ag. It can be attributed to the Ag dopants which suppressed thegrain growth. It does help in reducing energy consumption in PCM. The result thatthe Ag dopants suppressed the second phase transition from fcc structure to hcpstructure was confirmed by in-situ TEM.3. The Mo dopants suppressed the crystallization of Ge2Sb2Te5alloys. Throughcounting the grain size of Mo3.1(GST)96.7films after annealing at230℃, it is foundthat the average grain size of Mo3.1(GST)96.7was smaller than that of Ge2Sb2Te5. Itis conviced that the Mo dopants would suppress the grain growth. That the Agdopants suppressed the second phase transition from fcc structure to hcp structurewas confirmed by in-situ TEM.Te nanowires with varying length were precopitaedafter natural aging for2weeks, which is comfirmed by EDS, these nanowires wouldinfluence the loop phase change ability of materials.4. Through the investigation of V, Ag and Mo doped into Ge2Sb2Te5, it can besummarized that the second phase transition from fcc structure to hcp structure was suppressed with these metallic elements doped into GST. These dopants also resultan enhancement in crystalline electrical resistance by suppressing the grain growth.It does help in reducing the RESET current in PCM.