Electron trapping characteristics and scalability of HfO2 as a trapping layer in SONOS-type flash memories

To determine the potential of hafnium oxide (HfO₂) film as a charge-trapping layer for flash memories, distributions of electron traps, equivalent oxide thickness (EOT) scalability, and data-retention characteristics are investigated. Electrons are trapped at both top and bottom interfaces of oxide/HfO₂ and in the HfO₂ bulk. This distinguishes HfO₂ from silicon nitride (SiN), where electrons are mainly trapped at the two interfaces. The interface trap densities of electrons are of the order of 10¹³ cm^-2, and that of the HfO₂ bulk is of the order of 10¹⁸ cm^-3, which is one order larger than that of the SiN bulk. The oxygen vacancy is a possible origin of HfO₂ bulk traps. From the viewpoint of EOT scaling, HfO₂ is superior to SiN as a trapping layer. Moreover, retention characteristics of HfO₂ were better than those of SiN.