Atomic layer deposition (ALD) of TiO2 films from tetrakis(dimethylamido) titanium (TDMAT) or titanium tetraisopropoxide (TTIP) precursors was investigated. The growth kinetics, chemical composition, and crystallization behavior of the TiO2 films were compared for combinations of the two precursors with three different sources of oxygen [thermal ALD using H2O and plasma-enhanced ALD (PEALD) using H2O or O-2 plasma]. For TDMAT, the growth rate per cycle (GPC) decreased with increasing temperature; while for TTIP with either water plasma or O-2 plasma, a relatively constant growth rate per cycle was observed as a function of substrate temperature. It was found that the crystallization temperature of the TiO2 films depends both on film thickness and on the deposition conditions. A correlation was observed between the TiO2 crystallization temperature and the C impurity concentration in the film. The TiO2 films grown using a H2O plasma exhibit the lowest crystallization temperature and have no detectable C impurities. In situ X-ray diffraction measurements were used to test the diffusion barrier properties of the TiO2 layers and proved that all TiO2 films grown using either H2O or O-2 plasma are dense and continuous.