The effect of addition of Al in ZrO2 thin film on its resistance to cracking

The paper reports on the structure, mechanical and optical properties of sputtered Zr–Al–O films. The Zr–Al–O films with Zr/Al > 1 and Zr/Al < 1 were prepared by a reactive sputtering using ac pulse dual magnetrons. The magnetrons were equipped with a target composed of Al plate (∅ = 50 mm) fixed to the magnetron cathode by a Zr fixing ring with inner diameter ∅in. The content of Al in the Zr–Al–O film was controlled by ∅in. It makes possible to control effectively the structure of the Zr–Al–O film determined by a mixture of the crystalline ZrO2 phase and the amorphous Al2O3 phase. The effect of Al content on the structure, mechanical and optical properties of the Zr–Al–O film is investigated in detail. It was found that (i) the Zr–Al–O films with Zr/Al < 1 are X-ray amorphous and exhibit low hardness (H ≤ 13 GPa), an effective Youngʹs modulus E⁎ resulting in a low H/E⁎ < 0.1 ratio and low elastic recovery We ≤ 60 and (ii) the Zr–Al–O films with Zr/Al > 1 are crystalline and exhibit high hardness (H = 18 to 19 GPa), an E⁎ satisfying a high H/E⁎ ≥ 0.1 ratio, high We up to 78% and strongly enhanced resistance to cracking during bending even for thick films up to 5 μm.