Effect of pulse mode in reactive magnetron sputtering on structure and properties of titanium dioxide films

The state of the art to obtain crystalline Ti02 layers by vacuum deposition methods is the use of elevated substrate temperature during deposition or annealing after deposition above 250 IC. Therefore these processes are limited to temperature resistant substrates like glass. On the other hand there is a call for photo catalytic and hydrophilic layers on temperature sensitive materials. An innov ative reactive pulse magnetron sputtering (PMS) system allowing to change the pulse mode (unipolar pulse, bipolar pulse or pulse packet) has been used for the high rate sputter deposition of transparent Ti02 films Investigations were carried out to determine the influence of the pulse mode on the substrate peak temperature during deposition for different substrate materials, on the film structure and on different film properties (hardness, Young's modulus, refractive index, surface roughness, photohydrophilic decrease of the water contact angle). The experimental results show that it is possible to achieve crystalline Ti02 films by pulse sputtering without heating the substrate prior to or annealing the substrate after the coating procedure. Bipolar powering as well as pulse packet powerin g tend to affect the structure of the layers towards rutile. On thermal sensitive polycarbonate substrates it was possible to deposit 500 nin thick amorphous Ti 02 films by unipolar pulse sputtering.