Applied Surface Science, Vol.268, 416-424, 2013
Defect analysis and mechanical performance of plasma-deposited thin films on flexible polycarbonate substrates
A simple solvent-etch based technique is developed to visualize and quantify defects in transparent thin films deposited on flexible polymer substrates. This approach is used to characterize defects in as-deposited films and to monitor their evolution as a function of applied and repetitive bending. Thin films investigated include sputtered indium tin oxide (ITO) and alumina-silicone nanolaminates fabricated by plasma-enhanced chemical vapor deposition. It is shown that the use of nanolaminate architectures reduces the defect density by two orders of magnitude relative to a single alumina layer. The pinhole density increases when nanolaminates are subjected to applied stress, and at a critical density of similar to 10/mm(2) the isolated defects coalesce into macroscopic cracks. In the case of ITO an optimum film thickness is identified that balances electronic performance with mechanical integrity. Conductivity correlates with defect density, and the films displayed very similar performance under tensile and compressive strain. A critical radius of curvature of 0.75 in. was identified, but films cycled below the threshold strain demonstrated robust performance, with only negligible changes in resistivity through 2000 bending cycles. The strong performance under strain is attributed to the amorphous nature of the sputtered ITO. (C) 2012 Elsevier B.V. All rights reserved.