Investigation of Nano-Phase Change for Phase Change Random Access Memory

Understanding of the phase change in nano-scale, or so-called nano-phase change, and its related issues are important for its applications on both optical recording and phase change random access memory (PCRAM). Nano-phase change can be classified into thickness-dependent and structure dependent types. For PCRAM device performance, the film thickness-dependent thermal profile and materials´ properties are the two important factors. In this work, the thickness dependence of nano-phase change for chalcogenide materials was studied by both simulation and experiments. A thermal model was built up to simulate the film thickness-dependent thermal profiles and its corresponding effects of line type PCRAM. The simulation results showed that the temperature profile, heating rate and cooling rate are strongly dependent on the thickness of phase change materials. Experiments had been conducted to investigate the thickness dependence of crystallization temperature for both nucleation-dominated and growth-dominated phase change material. It was found that the crystallization temperatures are function of the thickness for the both materials. Higher crystallization temperatures were obtained for thinner phase change films. The influence of above factors on the performance of PCRAM devices is discussed.