Charge storage and tunneling mechanism of Ni nanocrystals embedded HfOx film

Abstract

A nano-floating gate memory structure based on Ni nanocrystals (NCs) embedded HfOx film is deposited by means of radio-frequency magnetron sputtering. Microstructure investigations reveal that self-organized Ni-NCs with diameters of 4-8 nm are well dispersed in amorphous HfOx matrix. Pt/Ni-NCs embedded HfOx/Si/Ag capacitor structures exhibit voltage-dependent capacitance-voltage hysteresis, and a maximum flat-band voltage shift of 1.5 V, corresponding to a charge storage density of 6.0 × 1012 electrons/cm2, is achieved. These capacitor memory cells exhibit good endurance characteristic up to 4 × 104 cycles and excellent retention performance of 105 s, fulfilling the requirements of next generation non-volatile memory devices. Schottky tunneling is proven to be responsible for electrons tunneling in these capacitors.

Visible-light enhanced charge storage characteristics of amorphous Ni-doped HfO2 films

“…In addition, an unexpected 3 nm-thick amorphous interfacial layer can be observed between the HfO x film and the Si substrate, revealing interfacial reactions occurred at the HfO x /Si interface during film deposition/annealing processes. It is surprising that some dispersed Ni-clusters (marked with white dashed circles) rather than general Ni-nanocrystals [20] are observed to be embedded in the amorphous HfO x matrix. There are two possible reasons: one is the deposition temperature of Ni clusters is as low as 280 °C, the other is that Ni clusters in the HfO x matrix are too few to self-assembly form nano-crystal particles.…”