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

Ruifan Tang,Junyong Kang,Hongkai Lai,Zhiming Wu,Cheng Li,Kai Huang

doi:10.1186/1556-276x-8-368

Abstract

This study characterizes the charge storage characteristics of metal/HfO2/Au nanocrystals (NCs)/SiO2/Si and significantly improves memory performance and retention time by annealing the HfO2 blocking layer in O2 ambient at 400°C. Experimental evidence shows that the underlying mechanism can be effectively applied to reduce oxygen vacancy and suppress unwanted electron trap-assisted tunneling. A memory window of 1 V at an applied sweeping voltage of ±2 V is also shown. The low program/erase voltage (±2 V) and the promising retention performances indicate the potential application of NCs in low-voltage, non-volatile memory devices.

Highlights

Nanocrystal (NC) floating gate memory devices have recently attracted much attention as a strong candidate for non-volatile memories given their scalability, fast write/ erase speeds, low operating voltages, and long retention times [1,2,3,4]
Numerous attempts have been made to develop non-volatile memory devices using metal NCs, such as Ni [5], Au [6], Ir [7], and Pt [8], because metal NCs have a higher density of states around the Fermi level, a wider range of available work functions, and smaller energy perturbation compared with their semiconductor counterparts [9]
Further improvement in memory performance can be achieved through the integration of metal NCs with high-κ dielectric materials, such as HfO2 [10] and Al2O3 [11]

Summary

Background

Nanocrystal (NC) floating gate memory devices have recently attracted much attention as a strong candidate for non-volatile memories given their scalability, fast write/ erase speeds, low operating voltages, and long retention times [1,2,3,4]. Further improvement in memory performance can be achieved through the integration of metal NCs with high-κ dielectric materials, such as HfO2 [10] and Al2O3 [11]. Electron trapping is seldom achieved because of the HfO2 blocking layer. The energy band diagram shows that electrons trapped in the NCs tend to leak into the gate electrode through trap-assisted tunneling, which is supported by the oxygen vacancy-related levels during programming. The structure of metal/HfO2 (as-annealed)/Au NCs/SiO2/ Si shows that both electrons and holes are stored. Given their memory window of 1 V at an applied sweeping voltage of ±2 V, low P/E voltage (±2 V), and promising retention performances, low-voltage NC memories have a strong potential for application in non-volatile memory devices

Methods

Results and discussion

Conclusions