Field enhancement effect of nanocrystals in bandgap engineering of tunnel oxide for nonvolatile memory application

Abstract

Charge storage characteristics of metal-oxide-semiconductor (MOS) structures containing Au nanocrystals on tunnel oxide composed of Al2O3/HfO2/Al2O3 stacks in different thickness piling up sequences were investigated. A significant enhancement of charge injection efficiency for both electrons and holes without sacrificing charge retention performance was found in the sample with a relatively thicker (∼3 nm) Al2O3 sublayer adjacent to Au nanocrystals and a thinner (∼1 nm) Al2O3 sublayer in front of the Si substrate. It is attributed to the local enhancement of electric field induced by the embedded Au nanocrystals, which greatly modifies the effective barrier of tunnel oxide.

Thickness dependence of Al2O3/HfO2/Al2O3 stacked tunneling layers on gadolinium oxide nanocrystal nonvolatile memory

“…On the other hand, for the case of negative gate bias, the Gd 2 O 3 -NC memories with AHA stacked tunneling layers can also demonstrate a higher erasing characteristic, especially for the sample S3 with the thinnest top Al 2 O 3 film of AHA stacked layers. For the case of Au-NC memories with the electron and hole injection from Si substrate during the programming and erasing operation, respectively, a thin bottom Al 2 O 3 film of AHA stacked tunneling layers is much more appreciated [22]. Fig.…”

Applications of Nanotechnology in Next-Generation Nonvolatile Memories

“…However, since the early 2000s, the focus has turned toward the various metallic nanocrystals for their higher work function and higher density of states compared to semiconducting ones. Various metallic ncs like Ni [20][21][22], Ag [21,23,25], W [25,26], Pt [24,26], Au [22,24,27,28], and Ru [33] have been reported in recent literature. The higher work function of the metallic ncs make for deeper potential wells, and the higher density of states give them the capability of storing more electrons per nanocrystal, than semiconducting ncs [21][22][23][24][25][26][27][28][31][32][33][34].…”

“…A number of recent experimental works have been reported on stacks such as nc-TiW-embedded SiO 2 -Al 2 O 3 [39] nc-Au-embedded Al 2 O 3 -HfO 2 -Al 2 O 3 [28] …”

“…The ncs are initially fabricated by solvothermal methods [28]. The synthesized nanocrystals are then dispersed in liquid media (e.g., hexane, methanol) and successively centrifuged to obtain ncs of uniform size distribution.…”

Nanocrystal formation for non-volatile memory application

“…Equivalent circuit corresponding to the double-barrier tunnel junction (DBTJ). (Reprinted fromRef[90])105 The electronic structure properties of the nanocrystals can be studied from the tunneling spectra. The spectra obtained by probing individual nanocrystals typically show a zero conductivity gap with dI/dV=0, which is related to the energies of the first conduction and first valence band level, which forms.…”