Effect of tungsten on the phase-change properties of Ge₈Sb₂Te₁₁ thin films for the phase-change device

Abstract

In this study, the electrical, optical, and structural properties of tungsten (W)-doped Ge₈Sb₂Te₁₁ thin films were investigated. Previously, GeSbTe alloys were doped with various materials in an attempt to improve the thermal stability. Ge₈Sb₂Te₁₁ and W-doped Ge₈Sb₂Te₁₁ films with a thickness of 200 nm were fabricated by using an RF magnetron reactive co-sputtering system at room temperature on Si (p-type, 100) and glass substrate. The fabricated thin films were annealed in a furnace in the ~ 0 - 400 ◦ C temperature range. The optical properties were analyzed using a UV-Vis-IR spectrophotometer, and by using Beer’s Law equation, the optical-energy band gap (E _op ), slope B ^1/2, and slope 1/F were calculated. For the crystalline materials, an increase in the slope B ^1/2 and 1/F was observed, exhibiting a good effect on the thermal stability in the amorphous state after the phase change. The structural properties were analyzed by X-ray diffraction, and the result showed that the W-doped Ge₈Sb₂Te₁₁ had a face-centered-cubic (fcc) crystalline structure increased crystallization temperature (T _c ). An increase in the T _c increased the thermal stability in the amorphous state. The electrical properties were analyzed using a 4-point probe, exhibiting an increase in the sheet resistance (R _s ) in the amorphous and the crystalline states indicating a reduced programming current in the memory device.