Impact of metal nano layer thickness on tunneling oxide and memory performance of core-shell iridium-oxide nanocrystals

Abstract

The impact of iridium-oxide (IrOx) nano layer thickness on the tunneling oxide and memory performance of IrOx metal nanocrystals in an n-Si/SiO2/Al2O3/IrOx/Al2O3/IrOx structure has been investigated. A thinner (1.5 nm) IrOx nano layer has shown better memory performance than that of a thicker one (2.5 nm). Core-shell IrOx nanocrystals with a small average diameter of 2.4 nm and a high density of ∼2 × 1012/cm2 have been observed by scanning transmission electron microscopy. The IrOx nanocrystals are confirmed by x-ray photoelectron spectroscopy. A large memory window of 3.0 V at a sweeping gate voltage of ±5 V and 7.2 V at a sweeping gate voltage of ± 8 V has been observed for the 1.5 nm-thick IrOx nano layer memory capacitors with a small equivalent oxide thickness of 8 nm. The electrons and holes are trapped in the core and annular regions of the IrOx nanocrystals, respectively, which is explained by Gibbs free energy. High electron and hole-trapping densities are found to be 1.5 × 1013/cm2 and 2 × 1013/cm2, respectively, due to the small size and high-density of IrOx nanocrystals. Excellent program/erase endurance of >106 cycles and good retention of 104 s with a good memory window of >1.2 V under a small operation voltage of ± 5 V are obtained. A large memory size of >10 Tbit/sq. in. can be designed by using the IrOx nanocrystals. This study is not only important for the IrOx nanocrystal charge-trapping memory investigation but it will also help to design future metal nanocrystal flash memory.