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We have fabricated Sb70Se30/HfO2 superlattice-like (SLL) structure thin films for phase change memory by magnetron sputtering method, and investigated the effect of the HfO2 layer on the crystalline characteristics and phase change behavior of Sb70Se30/HfO2 thin films. The experimental results show that as the HfO2 thickness increases, the crystallization temperature rises, the data retention capacity increases as well as the band gap widens, which is beneficial for improving the thermal stability and reliability of Sb70Se30/HfO2 thin films. It was also found that the HfO2 composite layer inhibited the grain growth of the Sb70Se30 thin film, reducing the grain size and resulting in a smoother surface. In addition, the volume fluctuation of the Sb70Se30/HfO2 thin films changes by only 5.58 % between amorphous and crystalline. The threshold and reset voltages of the cell based on Sb70Se30/HfO2 thin films are 1.52 V and 2.4 V respectively. We found that the HfO2 composite layer plays a significant role in improving thermal stability, refining grain size of Sb70Se30 phase change films and reducing device power consumption.

Ge–Cu–Te thin films were investigated experimentally for their initial crystallization characteristics and their correlation with electrical behaviors as phase-change materials for application in phase-change random access memory (PCRAM). Explosive crystallization (EC) with random orientation was observed as an initiating effect on crystallization during the early stage of crystallization for Ge–Cu–Te thin films. Both the tetrahedral coordination environment and triangular Cu atoms clusters consisting of threefold rings for Ge–Cu–Te thin films contribute to the initiation of EC. Crystallization progresses from the surface toward the bulk of the thin films, resulting in grain growth through the thickness of the thin films. Thicker films can encourage EC by reducing heat loss and producing a thicker liquid layer as a result of more significant temperature gradients near the phase-change front. Moreover, providing additional external heat by extending the annealing time also pushes EC. Finally, electrical transport measurements using the Hall system demonstrated that conductivity is increased by a more continuous EC network that concentrates more carriers. The authors consider that the above results are beneficial for understanding the phase-change mechanism of Ge–Cu–Te phase-change materials.

Ni-Co-W alloy is expected to be a potential material for applications in national defense, military industry and petroleum exploration. Texture has a significant influence on alloy properties. In the present work, a 44Ni-37W-19Co alloy was prepared by vacuum melting and annealed at 1200 °C for 1h after forging, baring and hot stamping. The microstructure and texture at different positions were analyzed by optical micrographs (OM), scanning electron microscopy (SEM), x-ray diffraction (XRD) and electron backscattering diffraction (EBSD) technique. The alloy presents equiaxial grains with an average size of ~90 μm and a nearly random texture. All the average pole intensity levels at surface, sub-surface and center are ~2. The anisotropy degree along the circumferential direction is less than that along the normal direction. The maximum and minimum differences of the radial pole intensity are 0.44 and 0.04, respectively. It is expected that this work will contribute to the controllable effects of microstructure and texture to improve the properties of hot-stamped high-density Ni-Co-W alloys.

Herein, a GeCu2Te2 alloy is proposed as a phase-change material for application in nonvolatile phase-change random access memory (PRAM). The crystallization kinetics and microchemical changes during phase transformation are investigated, and their correlation with the electrical behaviors of the GeCu2Te2 thin films are examined. The key findings are as follows: (ⅰ) the GeCu2Te2 alloy shows a higher crystallization temperature (~185°C) than the classic Ge2Sb2Te5 (GST) thin films, thus demonstrating superior thermal stability; (ⅱ) the crystallization kinetics demonstrate a decreasing in the Avrami exponent n from 4, which is related to the growth-dominated crystallization process evidenced by the micromorphology; (ⅲ) a massive redistribution of the chemical elements along the depth of the thin films during crystallization is considered to be driven by selective surface oxidation at amorphous state, and stress buildup during crystallization. In addition, the crystallization-induced stress is determined as ~168 MPa by utilizing the wafer curvature and X-ray diffraction methods for the GeCu2Te2 thin films. Finally, the lower threshold switching voltage ~1.72 V for amorphous GeCu2Te2 thin films is beneficial for reducing the SET operating power consumption. The authors believe that these results are valuable for the optimal phase change material design.