Study of charge distribution and charge loss in dual-layer metal-nanocrystal-embedded high-κ/SiO2 gate stack

Abstract

In this work, we present a comprehensive experimental study of charge loss mechanisms in a dual-layer metal nanocrystal (DL-MNC) embedded high-j/SiO 2 gate stack. Kelvin force microscopy characterization reveals that the internal-electric-field assisted tunneling could be a dominant charge loss mechanism in DL devices that mainly depends on the charge distribution in two MNC-layers and inter-layer dielectric (ILD) thickness between the two layers of nanocrystals. Our findings suggest that an optimized DL-MNCs embedded memory cell could be achieved by defining the ILD thickness larger than the average MNC-spacing for enhancement of retention ability in MNC embedded gate stacks. It implies the possibility of reducing MNC spacing in DL structure of scaled memory devices by controlling the thickness of ILD. V

Charge storage characteristics of Au nanocrystal memory improved by the oxygen vacancy-reduced HfO2 blocking layer

“…Given the existence of an oxygen vacancy-related level below the conduction band and the rise of electron potential because of electron trapping in the NCs [23], electrons trapped in Au NCs could possibly leak into the gate electrode through the trap-assisted tunneling method during the programming operation (Figure 3b). This method is similar to the multi-phonon-assisted tunneling model described in previous reports [24]. The trap-assisted tunneling effect may be responsible for the minimal electron storage.…”

“…The difference between the observed retention behavior of A 1 and A 4 could be explained by the energy band diagram, which is based on the existence of oxygen vacancy-related levels. Figure 7a shows that the electrons trapped in the Au NCs leak into the gate electrode through the HfO 2 layer via electron tunneling to the oxygen vacancy-related level, as proposed in [24]; therefore, discharging easily occurs. However, the reduced oxygen-related levels in sample A 4 HfO 2 layer suppress the unwanted trap-assisted tunneling (Figure 7b); thus, electron loss rate is reduced.…”