Influence of interlayers on the interfacial behavior of Ag films on polymer substrates

Abstract

With the wider use of flexible electronics and sensors it is necessary to better understand how the substrate chemistry as well as the use of relatively brittle interlayers influences the electro-mechanical and interfacial behavior of electrically conductive thin films. Here, silver (Ag) films sputter deposited on polyimide (PI) and polyethylene naphthalate (PEN) with and without a titanium (Ti) adhesion layer were studied with in-situ electrical resistance measurements during uniaxial straining to study the electro-mechanical response with the cracking factor. Additionally, a molybdenum (Mo) stressed overlayer was utilized with the tensile induced delamination method to quantitatively measure the adhesion energies of the different material systems. It is demonstrated that the substrate chemistry, in terms of the mechanical behavior and number of C = O groups, plays a significant role in how through thickness cracks elongate and how the Ag and Ti may chemically bond to the polymer substrates. In general, a Ti interlayer degrades the electrical behavior, but can improve the interface adhesion of Ag to PI substrates. For PEN substrates, Ti is found to lower the adhesion compared to Ag alone. This new knowledge on the material interactions can be used to improve future flexible electronic thin film systems.