We report on the structural and electrical characterization of sputter-deposited tungsten (W) films, having thicknesses between 1.5 and 100 nm, before and after annealing in the temperature range between 200 and 800 degrees C. In the as-deposited the beta-W phase prevails, for all the thicknesses studied. A beta-W to alpha-W transition occurs upon annealing at a temperature that depends on film thickness and it is accompanied by a corresponding resistivity drop. Films with thickness lower or equal to 8 nm are composed predominately of beta-W phase after annealing at 300 degrees C, while the alpha-W phase prevails after annealing at 450 degrees C. Films with thickness higher or equal to 10 nm remain at the beta-W phase after annealing at 200 degrees C, but the alpha-W phase prevails after annealing at 300 degrees C. The resistivity behavior as a function of film thickness and annealing temperature are discussed. The minimum film resistivity is obtained for the 100 nm thick film after annealing at 800 degrees C and it is 17.0 mu Omega center dot cm. (C) 2016 Elsevier B.V. All rights reserved.