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

A nano-floating gate memory capacitor consisting of a stack of 3 nm-thick HfAlO_x tunneling layer, self-organized Ag nanocrystals (NCs), and a 6 nm-thick HfAlO_x control 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/cm² are well dispersed in the amorphous HfAlO_x matrix. Counterclockwise hysteresis capacitance–voltage curve with a memory window of ∼ 2 V, corresponding to a charge storage density of about 1.3 × 10¹³ electrons/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 10⁴ s, but the memory window gradually becomes narrower, and only 54% stored charges are retained in the Ag-NCs after 10⁵ s stressing. Defect-enhanced Poole–Frenkel tunneling is found to be responsible for the degradation of memory properties. - Highlights: • Dispersed Ag nanocrystals act as memory nodes. • Realize a 2 V memory window • Illustrate the memory degradation process • Identify a defect-enhanced tunneling mechanism