Determination and evolution of tunneling distances in Ge nanocrystal based memories

A Ge nanocrystal layer embedded in thin SiO2 was prepared by ion beam synthesis in direct-tunneling distance to the Si substrate. The write performance was investigated in metal-oxide-semiconductor capacitors by means of capacitance measurements. With the experimental data and calculations using a floating-gate-like approach, the distribution of the tunneling oxide thickness dtox can be obtained in high precision confirmed by high-angle annular dark-field scanning transmission electron microscopy imaging. The evolution of dtox during heat treatment is discussed in terms of Ostwald ripening; i.e., dtox increases with annealing time.