The effect of addition of Al in ZrO ₂ 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 (θ=50mm) fixed to the magnetron cathode by a Zr fixing ring with inner diameter θ _in . The content of Al in the Zr-Al-O film was controlled by θ _in . It makes possible to control effectively the structure of the Zr-Al-O film determined by a mixture of the crystalline ZrO ₂ phase and the amorphous Al ₂ O ₃ 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≤13GPa), an effective Young's modulus E ^* resulting in a low H/E ^* <0.1 ratio and low elastic recovery W _e ≤60 and (ii) the Zr-Al-O films with Zr/Al>1 are crystalline and exhibit high hardness (H=18 to 19GPa), an E ^* satisfying a high H/E ^* ≥0.1 ratio, high W _e up to 78% and strongly enhanced resistance to cracking during bending even for thick films up to 5μm.