A Study of Electromigration Behaviors of Chalcogenide Thin-films and Their Thermal Properties to the Operational Properties of Phase-change Memory

• Main Authors: Huang, Yin-Hsien, 黃胤諴
• Other Authors: Hsieh, Tsung-Eong
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/33614821268687840016

博士 === 國立交通大學 === 材料科學與工程學系所 === 103 === 　　Ge2Sb2Te5 (GST) is the most common chalcogenide materials serving as the programming layer of phase-change memory (PCM). Since the signal recording of PCM is induced by the electrical heating, the electromigration (EM) behaviors and thermal properties of GST are hence the key issues affecting the device reliability. This dissertation studies the EM and thermal characteristics of pristine GST, nitrogen- and cerium-doped GSTs and their influence on the operational properties of PCM devices. The EM behaviors of pristine and doped GST thin-films under direct-current bias and pulse bias were investigated. The mean-time-to-failure (MTTF) analysis in conjunction with Black’s theory indicated that the decrease of activation energy in doped GST samples. This is ascribed to the increase number of grain boundaries due to the grain refinement in doped samples, which amplifies the short-circuit diffusion and accelerates the EM failure. Microstructure and composition analysis indicated doping alleviates the mass segregation in GST only in a moderate manner. The Blech-structure analysis illustrated that sample length affected the mechanism of EM failure: the electrostatic force dominates in short-strip samples while the electron-wind force dominates in long-strip samples. On the other hand, pulse bias analysis revealed that the average current model could be applied to delineate their EM failure at frequencies greater than 10 MHz and the surface diffusion might involve in EM failure mechanism of strip in nano-scale dimension. 　　In the study regarding of the thermal properties of GSTs and the operational properties of PCM, the 3-omega method was adopted to measure the thermal conductivity and thermal boundary resistances (TBR) of GSTs and thin-films involved in PCM. The measured results were then implanted in the finite-element simulation utilizing the three-dimensional fully coupled electric and thermal model for analyzing the operational properties of PCM devices. The simulation results indicated that the TBR at the interface of GST and titanium nitride contact layer impedes the heat propagation and suppresses the programming current and the programming efficiency in PCM could be optimized by modulating the aspect ratio and doping in GST programming layer.