Optical and stress properties of ZrO₂/SiO₂ and TiO₂/SiO₂ anti-reflective coatings deposited by ion-beam-assisted deposition on a flexible substrate

Dielectric films of ZrO 2 ,TiO 2 , and SiO 2 were deposited on flexible polycarbonate (PC) and polyethylene terephthalate (PET) substrates by using ion-beam-assisted deposition (IBAD). Each layer had a thickness ranging from 30 to 210 nm. The optical and anisotropic stress properties were investigated. Two anti-reflective coatings (ARCs), ZrO 2 /SiO 2 and TiO 2 /SiO 2 , were selected and deposited on the PET flexible substrate. The anisotropic stresses of the single layer and ARCs were measured using a phase-shifting moiré interferometer. Experimental results showed that the optimal oxygen flow rates for the ZrO 2 ,TiO 2 , and SiO 2 films deposited with IBAD were 10, 10, and 15 sccm, respectively. The refractive index ( n ) was TiO 2 (2.37)>ZrO 2 (2.05)>SiO 2 (1.46), and the extinction coefficient ( k ) for all samples was below 10 −3 . The thermal expansion coefficient of the PC substrate was three times that of the PET substrate, and the high-refraction ZrO 2 and TiO 2 single-layer films presented cracks and distortions on the PC substrate. Only the low-refractive-index SiO 2 sample did not present cracks. The three dielectric films did not crack or distort when deposited on the PET substrate. The anisotropic stress analysis provided the maximum principal and shear stresses for the three dielectric films on the PET substrate. Therefore, the maximum principal stress of the 210 nm single-layer film on a PET substrate is TiO 2 >ZrO 2 >SiO 2 . It was also discovered that the principal stress of the AR multilayer film is significantly decreased due to the damping stacking effect (DSE) of the high- and low-refractive-index materials, ZrO 2 /SiO 2 ARC (−297.3MPa)>TiO 2 /SiO 2 ARC(−132.6MPa). Thus, the high packing density of TiO 2 gives a better DSE than ZrO 2 .