High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO ₂ films: The effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO ₂ thin films using dc dual magnetron (DM) sputtering in Ar + O ₂ mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature T _surf measured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency f _r was investigated in detail. It was found that the increase of f _r from 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate a _D of sputtered TiO ₂ films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO ₂ films can be sputtered on unheated glass substrates at a _D = 80 nm/min, T _surf < 180 °C when high value of f _r = 350 kHz was used. Properties of a thin hydrophilic TiO ₂ film deposited on a polycarbonate substrate are given.