Memory characteristics and tunneling mechanism of Ag nanocrystal embedded HfAlO_xfilms on Si₈₃Ge₁₇/Si substrate

A nano-floating gate memory capacitor consisting of a stack of 3 nm-thick HfAlOxtunneling layer, self-organized Ag nanocrystals (NCs), and a 6 nm-thick HfAlOxcontrol layer, has been fabricated on compressively strained p-type Si83Ge17/Si(100) substrates by radio-frequency magnetron sputtering. The Ag-NCs with a size of 5-8 nm and a density of 5.7 × 1012/cm2are well dispersed in the amorphous HfAlOxmatrix. Counterclockwise hysteresis capacitance-voltage curve with a memory window of ∼ 2 V, corresponding to a charge storage density of about 1.3 × 1013electrons/cm2, is observed in this memory capacitor. The accumulation capacitance of this memory capacitor has no obvious decrease during electrical stressing process within a period of 104s, but the memory window gradually becomes narrower, and only 54% stored charges are retained in the Ag-NCs after 105s stressing. Defect-enhanced Poole-Frenkel tunneling is found to be responsible for the degradation of memory properties.