Synthesis and memory effect study of Ge nanocrystals embedded in LaAlO₃ high-k dielectrics

Abstract

A floating gate memory structure utilizing Ge nanocrystals embedded in LaAlO₃ (LAO) high-k dielectric films has been fabricated by pulsed-laser deposition. A cross-sectional high-resolution transmission electron microscopy study revealed that the floating gate structure contains 5-nm-diam spherelike Ge nanocrystals embedded in amorphous LAO. A significant memory effect with a very high density of charge storage up to 2×10¹ ³/cm² in the Ge nanocrystals and a maximum flat band voltage shift of 3.2 V have been achieved for the trilayer structure of LAO(8 nm)/Ge/LAO(3 nm)/Si. The memory structure utilizing the Ge nanocrystals grown in 1 min showed excellent charge retention characteristics, whereas the decay in memory capacitance after 10⁴ s of stress under a flat band voltage was only 8%. These results suggest that this memory structure utilizing Ge nanocrystals embedded in a LAO dielectric offers a high potential for the further scaling of floating gate memory devices. In addition, the effects of Ge growth time, and thus the size and density of the Ge nanocrystals, to the charge storage and charge retention characteristics were also studied.