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The monobasic Sb thin films with different thicknesses were prepared by radio frequency magnetron sputtering. The evolutions of Sb thin film from the amorphous state to the crystalline state were studied by in situ resistance–temperature measurement system. The crystallization temperature, electrical resistance, crystallization activation energy, and data retention capacity of Sb thin films increase significantly with the decrease of film thickness. The optical band gap energy increases and the surface become smoother. The analysis of X-ray diffraction indicates that the grain size becomes smaller and the crystallization may be inhibited by decreasing the film thickness. The prototype phase-change memories based on Sb thin films with different thicknesses were fabricated by CMOS technology. The electrical performances of phase-change memory show that the thinner Sb films have the larger threshold switching voltage and smaller RESET operation voltage, which means the better thermal stability and lower power consumption. The outcomes of this work provide the guidance for designing high-density phase-change memory by reducing the size of Sb thin film.

Titanium-doped SnSb4 phase-change thin film has been experimentally investigated for phase-change random access memory (PCRAM) use. The crystallization temperature, amorphous/crystalline resistance, and data retention of the SnSb4 thin film can be significantly enhanced by doping with titanium, improving the thermal stability of the amorphous state and reducing power consumption. The effect of titanium doping on electrical transport in the thin film was explored using the Hall system. X-ray diffraction and transmission electron microscopy confirmed that the grain size of the thin film was reduced as the titanium content was increased. Grain refinement improved the density changes of the thin films before and after the phase transition. The consequent change in chemical bonding states after adding titanium indicated that Ti was bonded to Sb in the SnSb4 lattice structure, wrapping around the Sb grains in an amorphous state. PCRAM cells based on Ti0.10SnSb4 thin film can be realized with a whole operation window by a 50 ns width pulse, and the operating power consumption was lower than that of a Ge2Sb2Te5 (GST) PCRAM cell of similar dimensions.

The thermal properties of Sb-Ge superlattice-like thin films have been experimentally studied for phase change memory. The Sb-Ge superlattice-like thin films have a high crystallization temperature (223 °C). The interdiffusion coefficient Dλ was determined by measuring the intensity of the low-angle X-ray diffraction arising from the modulation as a function of annealing time. The temperature dependence in the temperature range 80–200 °C is described by Dλ = 8.3 × 10−24exp(-0.42 eV/kT) m2/s. The thermal stability of Sb-Ge superlattice-like thin films can also dramatically be improved with the increase of the temperature. The density variation of Sb-Ge superlattice-like thin films changes by only around 8% between amorphous and crystalline states, which is very important for device reliability. The threshold current and threshold voltage of a cell based on Sb-Ge are 8.15 μA, 1.07 V, respectively. The lower RESET power is presented in the PCM cells of Sb-Ge superlattice-like thin films, benefiting from its high resistivity.

Phase-change memory is regard as one of the most promising candidates for the next-generation non-volatile memory. In this work, we proposed a Sb7Te3/ZnSb multilayer thin films to improve the thermal stability of Sb-rich Sb3Te7. The sheet resistance ratio between amorphous and crystalline states reached up to 4 orders of magnitude. With regard to the thermal stability, the calculated temperature for 10-year data retention is about 127 °C. The threshold current and threshold voltage of a cell based on Sb7Te3/ZnSb are 6.9 μA and 1.9 V, respectively. The lower RESET power is presented in the PCM cells of Sb7Te3/ZnSb films, benefiting from its high resistivity.

Ge 2 Sb 2 Te 5 /ZnSb (GST/ZS) stacked thin films were proposed for high density phase change memories (PCM). Electrical and structural properties were studied by in - situ resistance measurements and X-ray diffraction (XRD), respectively. The films exhibited good thermal stability and two resistance steps during heating process. A picosecond laser pump-probe system was used to measure phase change speed. Phase change memory cells based on [GST(35 nm)/ZS(15 nm)] 1 thin film were fabricated to test and verify multi-level switch between set and reset states.

Compared with Sb 2 Se, Si–Sb–Se material is proved to be a promising candidate for phase change memory (PCM) use because of its higher crystallization temperature (~ 230 °C), larger crystallization activation energy (3.25 eV), and better data retention ability (168 °C for 10 years). Furthermore, the fast crystallization time 3.30 ns is obtained for Si 0.20 (Sb 2 Se) 0.80 material by the picosecond laser technique. The set switching is realized with low threshold current 6.9 μA and voltage 1.80 V, respectively. The reverse resistance transition can be achieved by an electric pulse as short as 8 ns for Si 0.20 (Sb 2 Se) 0.80 -based PCM cell.

The transition process of a pure Sb thin film from amorphous to crystalline is ultrafast but thermally unstable. We fabricated Er doped Sb thin films by magnetron sputtering for the first time. By measuring the in situ film resistance vs. temperature, it was found that the crystallization temperature increased from 105 °C to 208 °C with increasing Er content, resulting in a significant improvement in the thermal stability. The phase transition speed was investigated using picosecond laser pulses, showing an ultrafast speed of ∼2 ns. SEM, EDS and XRD analyses also demonstrated the existence of Er and the improvement in the thermal stability by increasing Er-doping. The enhanced thermal stability through Er doping onto Sb thin films was attributed to the formation of Sb–Er bonds in doped films measured by XPS. The main outcomes of this work enable a prediction that the Er doped Sb thin films are well suited for data storage applications.

Nitrogen doping is applied to improve the thermal stability and power consumption of Sb70Se30 phase change thin film. Comparing to un-doped Sb70Se30 thin film, N-doped Sb70Se30 thin film has a higher crystallization temperature and better data retention. The measurement of atomic force microscopy indicated that the crystallization is inhibited and the surface of thin films becomes smoother after N doping. The analysis of X-ray diffraction proved that nitrogen doping can suppress the grain growth of the films and limit the grain size. The phase transition speed between the amorphous and crystalline state was investigated by the picosecond laser pulses. Phase change memory devices based on N-doped thin films were fabricated to test and evaluate the electrical properties. The results indicate that nitrogen-doped Sb70Se30 films have the potential in phase change memory application.

Phase change behavior in Alx(Sn2Se3)1−x (x = 0.003, 0.010, 0.023) films were investigated by utilizing in situ resistance measurements. It is found that the crystallization temperatures and resistances increase with increasing of Al content. The analysis of X-ray diffraction indicates that the grain size decreases and the crystallization is suppressed by more Al doping. Al0.023(Sn2Se3)0.977 has an excellent thermal stability with the crystallization activation energy of 3.79 eV and the failure time is longer than that of Ge2Sb2Te5 film. The crystallization speed of Al0.023(Sn2Se3)0.977 film is faster than that of GST. The phase transition kinetics of Al0.023(Sn2Se3)0.977 films were investigated. The obtained values of Avrami indexes indicate that a one dimensional growth-dominated mechanism is responsible for the amorphous–crystalline transformation of Al0.023(Sn2Se3)0.977 film. We conclude that Al0.023(Sn2Se3)0.977 film is a good candidate for phase-change random-access memory applications with good thermal stability and high switching speed.

Comparing to un-doped Zn15Sb85 material, N-doped Zn15Sb85 material had higher crystallization temperature, lower conductivity and better data retention. The optical band gap was derived from the transmittance spectra and a significant increase was observed with increasing nitrogen doping concentration. The measurement of atomic force microscopy indicated that the crystallization was inhibited and the surface of thin films became smoother after N doping. Phase change memory devices based on N-doped Zn15Sb85 thin film were fabricated to test and verify their electrical properties.

The Sn15Sb85 alloy is characterized by its rapid phase transition. However, its poor thermal stability hinders its application as phase change memory material. After nitrogen doping, the crystallization temperature and 10-year data retention temperature of Sn15Sb85 thin films even reach 235‡C and 173°C, respectively. Both the crystallization activation energy and the amorphous resistance of the thin films increase as well. As a result, the material thermal stability is significant improved. The surface roughness of the films is evaluated by atomic force microscope (AFM). The phase change speed of the thin films, measured by the picosecond laser technique, remains fast.

The amorphous-to-crystalline transitions of N-doped GeTe films are investigated by in situ film resistance measurements. Both the crystallization temperature and resistance of the N-doped films increase. The analysis of X-ray diffraction (XRD) measurement indicates that the grain size of the films with more nitrogen content can be refined, leading to the improvement in the resistance and thermal stability of the phase change films. The N-doped GeTe films have higher activation energy for crystallization. The 10-year lifetime is raised from 90°C of undoped GeTe film to 138°C of the N-doped GeTe film. The better surface roughness is confirmed by atomic force microscopy. The phase change speed is evaluated by the picosecond laser pump-probe technology.

Ge2 Sb2 Te5 (GST)/Ge superlattice-like (SLL) films are investigated in the study. Reflection spectra measurements with polarized excitations and atomic force microscopy are carried out to investigate phase-change properties. Because of the Ge cladding films, GST phase-change properties could be improved. The thicker Ge cladding film is believed could lead to a relatively larger grain size. GST phase-change behaviors in the films can be adjusted by changing the layer thickness. We found the [GST(5 nm)/Ge(5 nm)]10 SLL film has the higher crystallization temperature, faster phase change speed, better thermal stability and relatively smooth surface. The GST/Ge SLL films may have the potential for commercial use.

Superlattice-like Ge50Te50/Ge8Sb92 (SLL GT/GS) thin film was systematically investigated for multi-level storage and ultra-fast switching phase-change memory application. In situ resistance measurement indicates that SLL GT/GS thin film exhibits two distinct resistance steps with elevated temperature. The thermal stability of the amorphous state and intermediate state were evaluated with the Kissinger and Arrhenius plots. The phase-structure evolution revealed that the amorphous SLL GT/GS thin film crystallized into rhombohedral Sb phase first, then the rhombohedral GeTe phase. The microstructure, layered structure, and interface stability of SLL GT/GS thin film was confirmed by using transmission electron microscopy. The transition speed of crystallization and amorphization was measured by the picosecond laser pump-probe system. The volume variation during the crystallization was obtained from x-ray reflectivity. Phase-change memory (PCM) cells based on SLL GT/GS thin film were fabricated to verify the multi-level switching under an electrical pulse as short as 30 ns. These results illustrate that the SLL GT/GS thin film has great potentiality in high-density and high-speed PCM applications.

Compared with pure Sb, N-doped Sb material was proved to be a promising candidate for the phase change memory (PCM) use because of its higher crystallization temperature (∼250 °C), larger crystallization activation energy (3.53 eV), and better data retention ability (166 °C for 10 years). N-doping also broadened the band gap and refined grain size. The reversible resistance transition could be achieved by an electric pulse as short as 8 ns for the PCM cell based on N-doped Sb material. A lower operation power consumption (the energy for RESET operation 2.2 × 10−12 J) was obtained. In addition, N-doped Sb material showed a good endurance of 1.8 × 105 cycles.