Black titanium oxynitride thin films prepared by nitrogen plasma-assisted pulsed laser deposition for flat-panel displays

Abstract

Preference for a classy black turn-off appearance and for distinct dark colors on flat-panel displays has led to a high demand for optically black materials. Titanium oxynitrides and tungsten-doped oxynitrides were prepared using nitrogen plasma assisted pulsed laser deposition, and their optical absorption properties were investigated. A selection of Ti-O-N films were prepared with different compositions by controlling the emission current (Ie) and discharge voltage (Vd) of the ion source. It was found that the nitrogen content of the Ti(O,N)x could be adjusted by controlling the Ie. The large, flat absorption coefficient of approximately 40 μm−1 in the visible range (400–700 nm) attained for the samples deposited at high Vd was attributed to tungsten doping from a W filament in the ion source. The 4.1 mol%W-doped Ti(O,N)x, which had a rock-salt-type structure, was optically jet-black. The origin of the flat wavelength dispersion in the W-doped Ti(O,N)x was attributed to the coexistence of semiconducting absorption and metallic absorption mechanisms. DFT calculations suggest that the 5d states achieved when using doped tungsten provide high absorption in the mid-wavelength range, whereas undoped-Ti(O,N)x was characterized by weak absorption.