Electro-Fragmentation Analysis of Dielectric Thin Films on Flexible Polymer Substrates
- PDF / 801,602 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 30 Downloads / 245 Views
1030-G03-12
Electro-Fragmentation Analysis of Dielectric Thin Films on Flexible Polymer Substrates Albert Pinyol, Bastian Meylan, Damien Gilliéron, Aurélie Mottet, Vinodh Mewani, Yves Leterrier, and Jan-Anders E Månson Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 12, Lausanne, AL, CH-1015, Switzerland ABSTRACT A novel electro-fragmentation method was developed as a fast alternative to the time consuming fragmentation test carried out in situ in a microscope, to investigate the failure of dielectric coatings on polymer substrates using an ultrathin conductive layer. Focus was put on SiNx coatings on polyimide substrates. A careful selection of the conductive layer was carried out to avoid artifacts resulting for instance from a change of the residual stress state of the investigated coating. Au layers were found to be too ductile and Al-Ti layers altered the stress state of the nitride, which invalidated their use to probe the failure of the nitride coatings. In contrast, a 20 nm thick graphite layer was found to accurately reproduce the failure of the nitride, which was analyzed in terms of residual strain and cohesive properties of the graphite layer. An electro-fatigue device was built and preliminary results suggest that damage already develops in ultrathin coatings at relatively low strain levels under long-term fatigue loading.
INTRODUCTION Flexible electronics present a challenging problem in terms of mechanical integrity, a result of the considerable hygro-thermo-mechanical contrast between the inorganic, brittle device layers (e.g., SiNx, poly-Si and ITO) and the compliant polymer substrates [1]. Their mechanical analysis is usually carried out under quasi-static tensile, bending and compressive loadings, and it is greatly complicated by the nanometric nature of the investigated layers. Up to now, the analysis of damage processes in-situ in a microscope was the most accurate method to determine the limits of polymer substrates coated with inorganic films under tensile (the fragmentation test [2,3]) and compressive [4] strains. In case of conductive coatings, simultaneous measurement of electrical resistance and crack detection enabled obtaining the onset of tensile failure with excellent resolution [5] and overall damage evolution under fatigue [6]. The objective of this work is to extend this electro-fragmentation method for dielectric coatings using an additional conductive layer deposited on top of the coating of interest. This testing method would constitute a fast alternative to the time consuming observations under the microscope, providing that the conducting probe layer does not perturb the original structure, but rather accurately reproduces the cracking behavior of the dielectric coating. Special attention should therefore be paid to overcome artifacts arising, for instance, from the change in residual stress in the coating after deposition of the probe layer. The present investigation focuses on silicon nitride coatings de
Data Loading...
