Effect of Cu on the structure and phase-change characteristics of Sb2Te film for high-speed phase change random access memory

In this paper, in-situ X-ray diffratometer, Raman spectrometer, and X-ray reflectometer are employed to study the crystal structure, bonding states, and density change upon crystallization of Cu-Sb2Te films. It is shown that the crystallization temperature increases with increasing Cu content due to much more energy being required to overcome the rigid atomic network for the atoms rearrangement as a result of the complex branching and cross links. In X-ray diffraction pattern, both hexagonal Cu7Te4 and Sb2Te peaks have nearly the same peak positions, while the rhombohedral Sb peaks shift obviously their positions toward a small angle upon heating, suggesting a significant increase in lattice parameters of Sb phase. A Cu-Te bond is formed in Sb2Te films containing 10 at% and 14 at% Cu which are crystalized into hexagonal Cu7Te4, rhombohedral Sb and hexagonal Sb2Te three phases. When Cu concentration increases to 19 at%, Cu-Te bond becomes full, and the excess of Cu will bond with Sb. Compared with Ge2Sb2Te5 (GST), Sb2Te films with 10 at% and 14 at% Cu have lower density changes upon crystallization which are about 3.2% and 4.0%, respectively. Phase change random access memory (PCRAM) based on Cu-Sb2Te is successfully fabricated and characterized. Operations of set-reset can be realized in a 10 ns pulse for Cu-Sb2Te based PCRAM. The value of set and reset operation voltage decreases with increasing Cu content. The endurance test shows that the operation cycle numbers can reach 1.3×104 and 1.5×105 for the 10 at% and 14 at% Cu-based PCRAMs, respectively. The resistance ratio of reset and set states maintains a balance of about 100. Cu-Sb2Te film may be considered as one of the promising candidates for high-speed PCRAM.