Band offsets and charge storage characteristics of atomic layer deposited high-k HfO2/TiO2 multilayers

The band offsets and charge storage characteristics of atomic layer deposited high-k HfO2/TiO2 multilayers with ten periods in p-Si/SiO2/(HfO2/TiO2)/Al2O3 structure have been investigated. The thickness of high-k HfO2 or TiO2 film is similar to 0.5 nm for each layer, before and after annealing treatment of 900 degrees C for 1 min in N-2 ambient. High-resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy measurements on high-k HfO2/TiO2 multilayers confirm the layer-by-layer structure after annealing treatment, suggesting the HfO2/TiO2 multilayer quantum wells. The valence band offsets of HfO2 and TiO2 films are found to be similar to 3.1 and similar to 1.5 eV, respectively. The conduction band offsets are found to be similar to 1.7 eV for HfO2 films and similar to 0.9 eV for TiO2 films. The high-k HfO2/TiO2 multilayers in p-Si/SiO2/(HfO2/TiO2)/Al2O3/aluminum memory capacitor show a large capacitance-voltage hysteresis memory window of similar to 5 V at gate voltage of +/- 5 V, due to the charge storage in multilayer quantum wells. The hysteresis memory window of similar to 1.3 V at small gate voltage of +/- 1 V is also observed. The high-k HfO2/TiO2 multilayer memory structure can be used in future nanoscale flash memory device applications. (c) 2007 American Institute of Physics.