Band offsets and charge storage characteristics of atomic layer deposited high-k HfO_2/TiO_2 multilayers

摘要

The band offsets and charge storage characteristics of atomic layer deposited high-k HfO_2/TiO_2 multilayers with ten periods in p-Si/SiO_2/(HfO_2/TiO_2)/Al_2O_3 structure have been investigated. The thickness of high-k HfO_2 or TiO_2 film is ～ 0.5 nm for each layer, before and after annealing treatment of 900℃ for 1 min in N_2 ambient. High-resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy measurements on high-k HfO_2/TiO_2 multilayers confirm the layer-by-layer structure after annealing treatment, suggesting the HfO_2/TiO_2 multilayer quantum wells. The valence band offsets of HfO_2 and TiO_2 films are found to be ～3.1 and ～1.5 eV, respectively. The conduction band offsets are found to be ～1.7 eV for HfO_2 films and ～ 0.9 eV for TiO_2 films. The high-k HfO_2/TiO_2 multilayers in p-Si/SiO_2/(HfO_2/TiO_2)/Al_2O_3/aluminum memory capacitor show a large capacitance-voltage hysteresis memory window of ～5 V at gate voltage of ±5 V, due to the charge storage in multilayer quantum wells. The hysteresis memory window of ～1.3 V at small gate voltage of ±1 V is also observed. The high-k HfO_2/TiO_2 multilayer memory structure can be used in future nanoscale flash memory device applications.