标题: 硫族合金薄膜之电迁移行为及其热性质对相变化记忆体操作性质之研究
A Study of Electromigration Behaviors of Chalcogenide Thin-films and Their Thermal Properties to the Operational Properties of Phase-change Memory
作者: 黄胤諴
Huang, Yin-Hsien
谢宗雍
Hsieh, Tsung-Eong
材料科学与工程学系所
关键字: 相变化记忆体;硫族合金;3ω法;有限元素模拟;电迁移;Black理论;Blech结构;Phase-change random access memory (PCM);Chalcogenides;3-omega method;finite-element simulation;Electromigration;Black’s theory;Blech-structure
公开日期: 2015
摘要:   锗锑鍗(Ge2Sb2Te5,GST)是相变化记忆体(Phase-change Memory,PCM)最常见之编程层(Programming Layer)材料。由于PCM之信号记录系由电致加热所致,GST之电迁移(Electromigration,EM)与热性质遂成PCM元件可靠度的关键。本论文探讨GST及掺杂氮氮(Nitrogen,N)与铈(Cerium,Ce)元素的GST薄膜在直流以及脉冲电流下之EM行为。在直流电场的作用下,平均故障时间(Mean-time-to-failure)与Black理论之分析显示掺杂降低了GST的EM活化能,此乃因掺杂所致的晶粒细化作用同时增加了晶界数量,而晶界为熟知之快速扩散(Short-circuit Diffusion)路径,反而加速了EM的毁坏,对应之微结构与组成分析亦显示了掺杂并不能大幅抑制GST元素之电致偏移。Blech结构分析显示EM驱动力与试片长度有关:短尺度试片之EM由静电场力(Electrostatic Force)主导,而长尺度试片之EM则由电子风力(Electron-wind Force)主导。在脉冲电场的作用下,当电脉冲频率大于10 MHz时,EM破坏行为可利用‘平均电流模型’描述之,当试片为奈米尺度,表面扩散可能参与试片之EM破坏。
  在GST的热性质对PCM操作性质的研究中,首先以3ω法(3-omega Method)量测GST及组成PCM的各种薄膜的热传导系数(Thermal Conductivity)与界面热阻(Thermal Boundary Resistances,TBR),将量测结果代入有限元素模拟分析,以三度空间全电热耦合模型求解PCM元件之操作性质,研究结果显示在GST与氮化钛(Titanium Nitride)接触层(Contact Layer)界面之TBR阻碍了热传导且抑制了元件编程电流,透过编程层之宽高比设计及GST之掺杂可完成PCM元件编程效率之最佳化。
  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.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079918809
http://hdl.handle.net/11536/125890
显示于类别:Thesis