ZrO2 films of thicknesses varied in the range of 3-30 nm were atomic layer deposited from ZrI4 and H2O-H2O2 on p-Si(100) substrates. The effects of film thickness and deposition temperature on the structure and dielectric properties of ZrO2 were investigated. At 272 and 325 degreesC, the growth of ZrO2 started with the formation of the cubic polymorph and continued with the formation of the tetragonal polymorph. The ratio between the lattice parameters increased with the film thickness and growth temperature. The effective permittivity, determined from the accumulation capacitance of Hg/ZrO2/Si capacitors, increased with the film thickness, reaching 15-17 in 25-nm-thick films. The permittivity decreased with the increasing growth temperature. The hysteresis of the capacitance-voltage curves was the narrowest for the films deposited at 325 degreesC, and increased towards both lower and higher deposition temperatures.