Annealing Effects on the Charging–Discharging Mechanism in Trilayer Al₂O₃/Ge/Al₂O₃Memory Structures

For the development of memory devices for the continuous advancement of IT engineering, a good understanding of the charging–discharging mechanisms in nanocrystalline floating gate memories is crucial to overcoming the current limitations. The charging–discharging mechanism in Al 2 O 3 /Ge/Al 2 O 3 trilayer memory structures obtained by magnetron sputtering deposition is investigated as a function of the postdeposition annealing temperature, up to 900 °C. The change by annealing of C – V hysteresis curves from a clockwise type at low temperatures to counterclockwise one in a sample annealed within the intermediary temperature range of 550 to 650 °C, and then, a return to a clockwise type for annealing within the higher temperature range of 800–900 °C was observed. Up to 700 °C, memory performances are constantly improved reaching for 600 °C annealed samples, a memory window of 5.6 V for voltage sweep in the range −1 to +15 V, and good retention characteristics for 650 °C annealed structures, in which the charge loss is only ∼2% after 10 8 s. When the annealing temperature was increased above 700 °C, a rapid decrease in the memory performance takes place. The annealing-induced changes are explained based on the Ge fast diffusion and nanocrystallization process, in correlation with morphological and structural high-resolution transmission electron microscopy results.