TY - THES

T1 - The influence of high current densities on intact and cracked thin gold films on flexible polyimide substrate

AU - Putz, Barbara

N1 - embargoed until null

PY - 2014

Y1 - 2014

N2 - Thin metal films on compliant polymer substrates are of major interest for their use in flexible electronics, for applications as diverse as rollable displays or artificial skin. The operating current densities of today’s flexible electronic devices are low in the range of μA – mA/cm², but smaller and more powerful devices demand for higher current densities in future flexible electronics making electromigration, a current driven self-diffusion of metal atoms, a major reliability concern. This work investigates the effect of high current densities on intact and cracked gold thin films on a polyimide substrate and the possible occurrence of electromigration. Through thickness cracks perpendicular to the straining direction are introduced into 50 nm Au films with a 10 nm Cr interlayer by uniaxial straining. The cracking behaviour is investigated mechanically and electrically with fragmentation testing and in-situ 4 point probe resistance measurements, respectively. The Cr interlayer causes brittle behaviour of a normally ductile Au film. Artificial single cracks are generated in 50 nm gold films with and without Cr interlayer. Both sample configurations are subjected to various current densities over different time frames while the electrical resistance of the film is recorded. The electrical stability and the possible occurrence of electromigration are detected by measuring the variation of the electrical resistance of the film as well as by imaging of the sample surface before and after electrical treatment using scanning electron microscopy. Atomic force microscopy and energy dispersive X-ray analysis of different phenomena obtained during testing indicate the occurrence of electromigration. Finally, measures to improve electromigration testing of thin films on flexible polymer substrates are recommended.

AB - Thin metal films on compliant polymer substrates are of major interest for their use in flexible electronics, for applications as diverse as rollable displays or artificial skin. The operating current densities of today’s flexible electronic devices are low in the range of μA – mA/cm², but smaller and more powerful devices demand for higher current densities in future flexible electronics making electromigration, a current driven self-diffusion of metal atoms, a major reliability concern. This work investigates the effect of high current densities on intact and cracked gold thin films on a polyimide substrate and the possible occurrence of electromigration. Through thickness cracks perpendicular to the straining direction are introduced into 50 nm Au films with a 10 nm Cr interlayer by uniaxial straining. The cracking behaviour is investigated mechanically and electrically with fragmentation testing and in-situ 4 point probe resistance measurements, respectively. The Cr interlayer causes brittle behaviour of a normally ductile Au film. Artificial single cracks are generated in 50 nm gold films with and without Cr interlayer. Both sample configurations are subjected to various current densities over different time frames while the electrical resistance of the film is recorded. The electrical stability and the possible occurrence of electromigration are detected by measuring the variation of the electrical resistance of the film as well as by imaging of the sample surface before and after electrical treatment using scanning electron microscopy. Atomic force microscopy and energy dispersive X-ray analysis of different phenomena obtained during testing indicate the occurrence of electromigration. Finally, measures to improve electromigration testing of thin films on flexible polymer substrates are recommended.

KW - Flexible Elektronik

KW - Fragmentierungs-Test

KW - Adhesionsschicht

KW - Elektromigration

KW - Dünnfilm

KW - Dünnschicht

KW - flexible electronics

KW - thin films

KW - fragmentation test

KW - brittle interlayer

KW - adhesion improvement

KW - electromigration

M3 - Diploma Thesis

ER -