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.