Anisotropic stress mechanisms for different dielectric multi-layer films deposited by ion-beam assisted deposition on flexible substrates

Abstract

This study simulates and tests various prototype multi-layer films on polyethylene terephthalate (PET) and polycarbonate (PC) substrates. The optical and stress response properties of three commonly used optoelectronic anti-reflector (AR) coatings (TiO2/SiO2)2, (Ta2O5/SiO2)2 and (Nb2O5/SiO2)2 were determined. A lab-designed phase-shifting shadow moiré interferometer and Mohr circle approach were used to collect and interpret data. Results showed that the refractive indices of the four different dielectric films were 2.24(TiO2) > 2.23(Nb2O5) > 2.1(Ta2O5) > 1.44(SiO2). The transmittances of the three different AR coatings, in decreasing order, were 95.28%(Ta2O5/SiO2)2 > 94.86%(TiO2/SiO2)2 > 94.03%(Nb2O5/SiO2)2. The maximum shear stress of three different AR coatings, in decreasing size, were (Nb2O5/SiO2)2 > (Ta2O5/SiO2)2 > (TiO2/SiO2)2, for both the PET and PC substrate; however, the maximum principal stresses of three different AR coatings were tensors for the PET substrate, and compressive for the PC substrate. The principal stresses recorded were -916 MPa (Nb2O5/SiO2)2 > 438 MPa (Ta2O5/SiO2)2 > 346 MPa (TiO2/SiO2)2 for PET, and -951 MPa (Nb2O5/SiO2)2 > -838 MPa (Ta2O5/SiO2)2 > -766 MPa (TiO2/SiO2)2 for PC. The different elasticity moduli (ΔE) and relative elasticity between the different film layers may potentially be used to mitigate stress relief in multilayer coatings.