Residual stress analysis and control of multilayer flexible moisture barrier films with SiNx and Al2O3 layers

In this work, we investigated the residual film stress of barrier layers and its effect on moisture barrier property and flexibility. We have deposited silicon nitride (SiNx) layer by a plasma-enhanced chemical vapor deposition (PECVD) process and aluminum oxide (Al2O3) layer by a spatially-resolved atomic layer deposition (SR-ALD) process on polyethylene naphthalate (PEN) flexible substrates at temperature below 100 °C. Two different types of film structure were fabricated to relieve the residual stress. First, we deposited SiNx layers on the both sides of PEN substrates and investigated residual film stress, water vapor transmission rate (WVTR) and flexibility. The residual stress was greatly reduced from 824 MPa in the single-side deposited SiNx film to 39.54 MPa in the double-side SiNx deposited film at the same total thickness of 600 nm. WVTR was reduced by 68% to 5.93×10-4 g/(m2•day) with a double-sided film from 1.85×10-3 g/(m2•day) with a single-sided SiNx film. The WVTR of the double-sided film was increased by 33% after 1,000 bending at 1.5 cm of radius while that of the single-sided film was increased by 51 % after bending. Second, we fabricated the multilayer structure with alternating of SiNx and Al2O3 layers on one side of PEN substrates. The residual film stress is reduced by 28% from 595.1 MPa in bilayer structure to 432.5 MPa in the 2.5 dyad multilayer structure. The WVTR was also reduced to 1.55×10-4 g/(m2•day) with the 2.5 dyad multilayer structure from 2.6×10-4 g/(m2•day) with the bilayer structure.