Electrical characterization of memory capacitors for nonvolatile memory applications based on nanolaminated HfO2/Al2O3 and Al-doped HfO2 stacks

Abstract

Memory capacitors with atomic-layer-deposited HfO2/Al2O3 nanolaminated layers and Al-doped HfO2 charge trapping layers were investigated through capacitance-voltage (C-V) and current-voltage (I-V) measurements. The dielectric constant of the multi-dielectric stack comprising 20-nm Al2O3 blocking oxide, a HfO2-based layer and 2.4-nm tunnel SiO2 does not depend on the manner of Al-introduction in HfO2.The stacks exhibit a negative oxide charge of about -5.1×1011 cm−2 and -2.5×1011 cm−2 for the structures with nanolaminated and doped layers, respectively. The Al-doping of HfO2 is found to produce lower leakage currents. A sublinear behavior of the current-voltage curves is observed in the range of -20 ÷ +10 V for both HfO2-based stacks. Memory windows of ∼ 1 V when charging with ±27-V voltage pulses are obtained; the data suggests that electron trapping is better pronounced in the HfO2/Al2O3 nanolaminate, while positive charge accumulation prevails in the Al-doped HfO2 layers.