Nitrogen-Doped Ge^sub 2^Sb^sub 2^Te^sub 5^ Films for Nonvolatile Memory

• Published in: Journal of electronic materials 2005-02, Vol.34 (2), p.176
• Main Authors: Lai, Yunfeng, Qiao, Baowei, Feng, Jie, Ling, Yun
• Format: Article
• Language: English
• Subjects: Information storage; Materials science; Multilayered thin films; Phase transitions; Semiconductor doping
• ISSN: 0361-5235; 1543-186X

Nitrogen-doped Ge^sub 2^Sb^sub 2^Te^sub 5^ (GST) films for nonvolatile memories were prepared by reactive sputtering with a GST alloy target. Doped nitrogen content was determined by using x-ray photoelectron spectroscopy (XPS). The crystallization behavior of the films was investigated by analyzing x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results show that nitrogen doping increases crystallization temperature, crystallization-activation energy, and phase transformation temperature from fee to hexagonal (hex) structure. Doped nitrogen probably exists in the grain vacancies or grain boundaries and suppresses grain growth. The electrical properties of the films were studied by analyzing the optical band gap and the dependence of the resistivity on the annealing temperature. The optical band gap of the nitrogen-doped GST film is slightly larger than that of the pure GST film. Energy band theory is used to analyze the effect of doped nitrogen on electrical properties of GST films. Studies reveal that nitrogen doping increases resistivity and produces three relatively stable resistivity states in the plot of resistivity versus annealing temperature, which makes GST-based multilevel storage possible. Current-voltage (I-V) characteristics of the devices show that nitrogen doping increases the memory's dynamic resistance, which reduces writing current from milliampere to microampere. [PUBLICATION ABSTRACT] Key words: Phase change, nonvolatile memory, nitrogen doping, Ge^sub 2^Sb^sub 2^Te^sub 5^ (GST), multilevel storage, writing current reduction