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

Abstract

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 ∼0.5nm for each layer, before and after annealing treatment of 900°C for 1min in N2 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 ∼3.1 and ∼1.5eV, respectively. The conduction band offsets are found to be ∼1.7eV for HfO2 films and ∼0.9eV 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 ∼5V at gate voltage of ±5V, due to the charge storage in multilayer quantum wells. The hysteresis memory window of ∼1.3V at small gate voltage of ±1V is also observed. The high-k HfO2∕TiO2 multilayer memory structure can be used in future nanoscale flash memory device applications.