Conformal ZrO2 and HfO2 thin films were grown by atomic layer deposition using novel liquid cyclopentadienyl precursors at 300 degrees C or 350 degrees C on planar Si wafers and deep trenched Si with an aspect ratio of 60:1. The crystal growth and phase content in as-deposited films depended on the precursor, film thickness, and the material grown. The structural and electrical behaviour of the films were somewhat precursor-dependent, revealing better insulating properties in the films grown from oxygen-containing precursors. Also the HfO2 films showed lower leakage compared to ZrO2.