Nonvolatile phase change random access memory (PCRAM) is regarded as one of promising candidates for next-generation memory in the era of Big Data. The phase transition mechanism of phase change materials is the key scientific issue to be addressed for phase change memory. Moreover, obtaining homogeneous phase change materials with high speed, low power consumption, long life and good thermal stability is still the ultimate challenge for high-density three-dimensional (3D) PCRAM. In this paper, starting from the octahedral structure motifs (octahedrons) which are considered as the "gene" of phase change materials, a new view on the phase transition mechanism is proposed. Based on this mechanism, a homogeneous phase change material is developed by constructing three matched octahedrons, which achieved an overall improvement in performance, showing 180 ℃ ten-year data retention, 6 ns SET speed, one order of magnitude longer life time and 75% reduced power consumption compared with traditional Ge₂Sb₂Te₅ (GST) devices. It is of great significance to use it in 3D PCRAM chip and multi-level brain- inspired computing chip in the future.

There is a continuous demand to reduce the size of the devices that form a unit circuit, such as logic gates and memory, to reduce their footprint and increase device integration. In order to achieve a highly efficient circuit architecture, optimizations need to be made in terms of device processing. However, the time involved in the current reduction of device sizes according to Moore's Law has slowed down. Here, we propose a flexible transistor with ultra-thin IGZO (InGaZnO, indium-gallium-zinc-oxide) as the channel material, which not only scales down the footprints of multi-transistor logic gates but also combines the functions of the logic gates, memory, and sensors into a single cell. The transistor proposed here has an ultrathin semiconductor layer and can implement the typical functions of logic gates that conventionally have 2-6 transistors. Furthermore, it demonstrates the memory effect with a programming time as low as 5 ns. This design can also display various artificial synaptic behaviors. This new device design and structure can be adopted for the development of next-generation flexible electronics that require higher integration.

Although phase change memory technology has developed drastically in the past two decades, the cognition of the key switching materials still ignores an important member, the face-centered cubic Sb₂Te₃. Apart from the well-known equilibrium hexagonal Sb₂Te₃ crystal, we prove the metastable face-centered cubic Sb₂Te₃ phase does exist. Such a metastable crystal contains a large concentration of vacancies randomly occupying the cationic lattice sites. The face-centered cubic to hexagonal phase transformation of Sb₂Te₃, accompanied by vacancy aggregation, occurs at a quite lower temperature compared to that of Ge₂Sb₂Te₅ alloy. We prove that the covalent-like bonds prevail in the metastable Sb₂Te₃ crystal, deviating from the ideal resonant features. If a proper doping technique is adopted, the metastable Sb₂Te₃ phase could be promising for realizing reversibly swift and low-energy phase change memory applications. Our study may offer a new insight into commercialized Ge–Sb–Te systems and help in the design of novel phase change materials to boost the performances of the phase change memory device.