In this work, we evaluated the structural, electrical and optical properties of Ge₈Sb₂Te₁₁ and Cu-doped Ge₈Sb₂Te₁₁ thin films prepared by rf-magnetron reactive sputtering. The 200-nm-thick deposited films were annealed in a range of 100~400℃ using a furnace in an N₂ atmosphere. The amorphous-to-crystalline phase changes of the thin films were investigated by X-ray diffraction (XRD), UV-Vis-IR spectrophotometry, a 4-point probe, and a source meter. A one-step phase transformation from amorphous to face-centered-cubic (fcc) and an increase of the crystallization temperature (T_c) was observed in the Cu-doped film, which indicates an enhanced thermal stability in the amorphous state. The difference in the optical energy band gap (E_op) between the amorphous and crystalline phases was relatively large, approximately 0.38~0.41 eV, which is beneficial for reducing the noise in the memory devices. The sheet resistance(R_s) of the amorphous phase in the Cu-doped film was about 1.5 orders larger than that in undoped film. A large R_s in the amorphous phase will reduce the programming current in the memory device. An increase of threshold voltage (V_th) was seen in the Cu-doped film, which implied a high thermal efficiency. This suggests that the Cu-doped Ge₈Sb₂Te₁₁ thin film is a good candidate for PRAM.

We evaluated the structural, electrical and optical properties of tungsten (W)-doped Ge₈Sb₂Te₁₁ thin films. In a previous work, GeSbTe alloys were doped with different materials in an attempt to improve thermal stability. 200 mm thick Ge₈Sb₂Te₁₁ and W-doped Ge₈Sb₂Te₁₁ films were deposited on p-type Si (100) and glass substrates using a magnetron co-sputtering system at room temperature. The fabricated films were annealed in a furnace in the 0~400℃ temperature range. The structural properties were analyzed using X-ray diffraction (X`pert PRO, Phillips). The results showed increased crystallization temperature (T_c) leading to thermal stability in the amorphous state. The optical properties were analyzed using an UV-Vis-IR spectrophotometer (Shimadzu, U-3501, range : 300~3,000 nm). The results showed an increase in the crystalline material optical energy band gap (E_op) and an increase in the Eop difference (△E_op). This is a good effect to reduce memory device noise. The electrical properties were analyzed using a 4-point probe (CNT-series). This showed increased sheet resistance (R_s), which reduces programming current in the memory device.

In this study, Ge8Se(2+x)Te(6-x) thin film amorphous-to-crystalline phase-change rate was evaluated in using a nano-pulse scanner. The focused laser beam with a diameter <10 μm was illuminated in the power (P) and pulse duration (t) ranges of 1-31 mW and 10-460 ns, respectively, with subsequent detection of the responsive signals reflected from the film surface. We also evaluated the material characteristics, such as optical absorption and energy gap, crystalline phases, and sheet resistance of as-deposited and annealed films. The result of experiments showed that the thermal stability of the Ge-Se-Te film is largely improved by adding Se.

An amorphous Ge2Sb2Te5 thin film is one of the most commonly used materials for phase-change data storage. In this study, Aux(Ge2Sb2Te5)1-x thin film amorphous-to-crystalline phase-change rate were evaluated in using 658 nm laser beam. The focused laser beam with a diameter <10 μm was illuminated in the power (P) and pulse duration (t) ranges of 1-17 mW and 10-460 ns, respectively, with subsequent detection of the responsive signals reflected from the film surface. We also evaluated the material characteristics, such as optical absorption and energy gap, crystalline phases, and sheet resistance of as-deposited and annealed films. The result of experiments showed that the thermal stability of the Ge2Sb2Te5 film is largely improved by adding Au.