Jianzhong Xue

Ge2Sb2Te5/Sb superlattice-like thin film for high speed phase change memory application

In order to improve the operation speed of phase change memory (PCM), superlattice-like Ge2Sb2Te5/Sb (SLL GST/Sb) thin films were prepared in a sputtering method to explore the suitability as an active material for PCM application. Compared with GST, SLL GST/Sb thin film has a lower crystallization temperature, crystallization activation energy, thermal conductivity, and smaller crystalline grain size. A faster SET/RESET switching speed (10 ns) and a lower operation power consumption (the energy for RESET operation 9.1 × 10−13 J) are obtained. In addition, GST/Sb shows a good endurance of 8.3 × 104 cycles.

Improved thermal stability of N-doped Sb materials for high-speed phase change memory application

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.

Improvement of the thermal stability of Sb thin film through erbium doping

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.

N-doped Zn15Sb85 phase-change materials for higher thermal stability and lower power consumption

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.

Nitrogen-Doped Ge10Sb90 Phase Change Thin Films for High-Temperature Data Retention and High-Speed Application

The amorphous to crystalline phase change of nitrogen-doped Ge10Sb90 thin films were investigated by in␣situ film resistance measurements. The thermal stability and data retention increased with the increase of N doping concentration. Compared with Ge10Sb90, a higher crystalline resistance of N-doped Ge10Sb90 thin films was obtained, which is beneficial for the reduction of RESET operation consumption of phase change memory. The analysis of x-ray diffractomer indicated that nitrogen doping can refine the grain size. The measurement of atomic force microscopy revealed that the crystallization was inhibited and the surface of thin films became smoother after N doping. A reversible phase transition was realized by the picosecond laser pulses and the switching speed of crystallization was measured.

Influence of N-doping on the thermal stability and switching speed of Zn15Sb85 phase change material

The phase change characteristics of nitrogen doping Zn15Sb85 thin films were investigated by in situ film resistance measurements. The crystallization temperature and activation energy for crystallization of thin films increased with the increase of nitrogen doping concentration. Compared with Zn15Sb85, nitrogen doping Zn15Sb85 thin films exhibited higher crystalline resistance, which is beneficial for the reduction of writing current of phase change memory. The analysis of X-ray diffractomer indicates that the films with doping of nitrogen can refine the grain size. A smaller density change before and after phase change for N-doped Zn15Sb85 thin films was obtained from X-ray reflectivity. The phase transition speed between the amorphous and crystalline state was investigated by the picosecond laser pulses.

Improvement of the thermal stability and power consumption of Sb70Se30 through nitrogen doping

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.

N-doped GeTe phase change material for high-temperature data retention and low-power consumption

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.

N-doped Sn15Sb85 thin films for high speed and high thermal stability phase change memory application

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.