Memory properties using nano-scale phase separation of HfO based dielectrics

We investigated the phase separation of HfO based high dielectric constant (k) material for the application to non-volatile memory devices. We found that Hf_0.5Si_0.5O₂ underwent phase separation upon annealing in the temperature range of 900degC to 1000degC: Hf_0.5Si_0.5O₂ rarr (0.5 - x)/(1 - x) HfO₂ + 0.5/(1 - x) Hf₂Si _1-xO₂ where 0 < x < 0.5. When an electric field was applied to the tunnel oxide, the programming of memory devices with the high-k trapping layer consisting of phases separated in nano-scale was faster than that using Si₃N₄, due to the higher electron capture efficiency of the phase separated structure. Also, the phase separated nano-structure resulted in better retention than pure HfO₂. Furthermore, it was found that the phase separation of HfO_x into Hf-rich HfO_y (y<x) crystals and O-rich amorphous matrix HfO_z (z>x) was effective to suppress the lateral migration of charges trapped in HfO_x. This article demonstrates the 2-bit memory property attained using the phase separation for the short channel devices with channel length down to 180nm