Memory effect and retention property of Ge nanocrystal embedded Hf-aluminate high-k gate dielectric

The memory effect and retention characteristics of a Ge nanocrystal (NC) floating gate memory structure consisting of Hf-aluminate (HfAlO) tunnelling and control oxides have been investigated by means of high-frequency capacitance-voltage (C-V) and capacitance-time (C-t) measurements. The trilayer structure (HfAlO/Ge-NC/HfAlO) on Si was fabricated by pulsed-laser deposition at a relatively low temperature. A high-resolution transmission electron microscopy study revealed that the Ge nanocrystals are about 5 nm in diameter and are well distributed within the amorphous HfAlO matrix. The memory effect was revealed by the counter-clockwise hysteresis loop in the C-V curves and a high storage charge density of about 1 × 1013 cm-2 and a large flat-band voltage shift of 3.6 V have been achieved. An 8% decay in capacitance after 104 s in the C-t measurement suggests a promising retention property of Ge NC charge storage. The effects of size/density of the Ge NC, the tunnelling and control oxide layer thicknesses and their growth oxygen partial pressure to the charge storage and charge retention characteristics have been studied.