Electromigration behaviors of Ge₂Sb₂Te₅ chalcogenide thin films under DC bias

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• 作者：Yin-Hsien Huang ; Chi-Hang Hang ; Yu-Jen Huang ; Tsung-Eong Hsieh
• 关键词：Chalcogenides ; Electromigration ; Black&rsquo ; s theory ; Blech structure ; Phase-change random access memory
• 刊名：Journal of Alloys and Compounds
• 出版年：2013
• 出版时间：15 December, 2013
• 年：2013
• 卷：580
• 期：Complete
• 页码：449-456
• 全文大小：3290 K

文摘

Electromigration (EM) behaviors of pristine Ge₂Sb₂Te₅ (GST), nitrogen-doped GST (N-GST) and cerium-doped GST (Ce-GST) thin-film strips under DC bias are presented. The mean-time-to-failure (MTTF) analysis based on the Black equation found that the EM failure times at room temperature are 1.2 ¡Á 10⁴, 40 and 9.2 ¡Á 10² years and the activation energies (E_a) of EM process are 1.07, 0.57 and 0.68 eV for GST, N-GST and Ce-GST, respectively. Moreover, the calibration of the current density exponent, n, of Black¡¯s equation found n values are close to 2 for all samples, implying the dominance of grain boundary diffusion during the mass transport of EM process. For doped GSTs, the inferior EM failure lifespans and smaller E_a values were ascribed to the grain refinement effect which increases the number of grain boundaries in such samples. It consequently promoted the short-circuit diffusion and accelerated the EM failure in doped GSTs. The Blech-type tests on GSTs found that the threshold product, i.e., the product of current density and sample length ((j ? L)_th), is 200 A/cm for GST, 50 A/cm for N-GST and 66.67 A/cm for Ce-GST. Moreover, the product of diffusivity and effective charge number (i.e., DZ^*) for GST, N-GST and Ce-GST was 2.0 ¡Á 10^?7, 4.5 ¡Á 10^?6 and 3.8 ¡Á 10^?6 cm²/sec, respectively. Analytical results illustrated that the electrostatic force effect dominates the EM failure in samples with short strip lengths while the electron-wind force effect dominates the EM failure in samples with long strip lengths. Doping might alleviate the mass segregation in GST; however, its effect was moderate.