After compositing with Si, the superlattice-like (SLL) Si/Sb thin film had higher crystallization temperature (~231 o C), larger crystallization activation energy (2.95 eV), and better data retention ability (126 o C for 10 years). The crystallization of Sb in SLL Si/Sb thin films was restrained by the multilayer interfaces. The reversible resistance transition could be achieved by an electric pulse as short as 10 ns for [Si(22nm)/Sb(2nm)] 2-based PCM cell. A lower operation power consumption of 0.02 mW and a good endurance of 1.0×10 5 cycles was achieved. In addition, SLL [Si(22nm)/Sb(2nm)] 2 thin film showed a low thermal conductivity of 0.11 W/(m•K).

In general, there is a trade off between the phase change speed and thermal stability in chalcogenide phase change materials, which leads to sacrifice the one in order to ensure the other. For improving the performance, doping is a widely applied technological process. Here, we fabricated Er doped Sn15Sb85 thin films by magnetron sputtering. Compared with the pure Sn15Sb85, we show that Er doped Sn15Sb85 thin films exhibit simultaneous improvement over the thermal stability and the phase change speed. Thus, our results suggest that Er doping provides the opportunity to solve the contradiction. The main reason for improvement of both thermal stability and crystallization speed is due to the existence of Er-Sb and Er-Sn bonds in Er doped Sn15Sb85 films. Hence, Er doped Sn15Sb85 thin films are promising candidates for the phase change memory application, and this method could be extended to other lanthanide-doped phase change materials.

In comparison to Ge 2 Sb 2 Te 5 (GST) and pure Sb 70 Se 30 (SbSe) thin films, superlattice-like (SLL) Ge/Sb 70 Se 30 (Ge/SbSe) has a higher crystallization temperature, larger crystallization activation energy, better data retention and lower power consumption. SLL Ge/SbSe thin films with different thickness of Ge and SbSe layers were prepared by magnetron sputtering system. The amorphous-to-crystalline transitions of SLL Ge/SbSe thin films were investigated through in situ film resistance measurement. The crystallization activation energy of SLL Ge/SbSe thin films was calculated from a Kissinger plot. The data retention time was estimated through isothermal timedependent resistance measurement by Arrhenius equation. The phase structure of the thin films annealed at different temperatures was investigated by using X-ray diffraction. Phase change memory cells based on the SLL [Ge(8 nm)/ SbSe(5 nm)] 4 thin films were fabricated to test and evaluate the switching speed and operation consumption.

The influence of nitrogen dopant on the structure of the phase-change material Sb has been investigated by ab initio molecular dynamics simulations. The doped N exist as SbN complex in amorphous phase and would not enter into the rhombohedra phase of crystalline Sb. During crystallization of the amorphous phase, no N 2 molecule is formed and part of the N-Sb bonds are broken to release Sb atoms which contribute to growth of crystal nuclei by forming more Sb-Sb bonds. Remaining N-Sb bonds would segregate at the grain boundaries and retard growth of crystal nuclei.

Effects of the titanium dopant on the physical properties and structure of SbSe thin films were systematically investigated by experiments and first-principles calculations. The amorphous-to-polycrystalline transformation induced by heat was examined by in situ electrical resistance measurements. With the incorporation of titanium atoms, both the crystallization temperature and electrical resistance increase, revealing the improvement of the amorphous thermal stability and programing energy consumption. X-ray diffraction, transmission electron microscopy, and density functional theory calculations illustrate that a small amount of titanium dopant can inhibit the grain growth and refine the crystal size. The shift of Raman modes associated Sb upon the crystallization was observed. X-ray reflectivity and atomic force microscopy results prove the smaller volume fluctuation and the smoother surface morphology, meaning the better interfacial property and reliability of titanium-doped SbSe materials. Phase change memory cells based on titanium-doped antimony-selenium were fabricated to evaluate the electrical performance as well. All these results indicate that the suitable incorporation of the titanium element will be an effective method to optimize the physical properties and tune the structure of the SbSe phase change material.