Designing micro-patterned Ti films that survive up to 10% applied tensile strain

Abstract

Reducing the strain in brittle device layers is critical in the fabrication of robust flexible electronic devices. In this study, the cracking behavior of micro-patterned 500-nm-thick Ti films was investigated via uniaxial tensile testing by in situ SEM and 4-point probe measurements. Both visual observations by SEM and 4-pt resistance measurements showed that strategically patterned oval holes, off-set and rotated by 45°, had a significant effect on limiting the extent of cracking, specifically, in preventing cracks from converging. Failure with regard to electrical conduction was delayed from less than 2% to more than 10% strain.

Piezoresistive response of nano-architectured Ti x Cu y thin films for sensor applications

“…The set of properties obtained are commonly known as having some mechanical and tribological constrains, namely in terms of brittleness, ductility and adhesion, together with reduced possibilities in terms of cohesion and adhesion after mechanical deformation [22,23]. In this particular aspect, the coating of polymer-based materials reveals to be a major example of high complexity.…”

“…In the past few years, several attempts have been carried out to develop relatively complex systems that could accommodate these restrictions and some thin film deposition approaches revealed promising results. In fact, it has been shown that brittle metals used as adhesion promoters will fracture at low applied strains (<1%), leading to electrical failure, while ductile charge carrying thin films such as Au, Cu or Ag, will plastically deform at relatively higher applied strains (>3%) without electrical failure [22][23][24][25]. The ability to combine good adhesion and high strength for these flexible systems is a current challenge.…”

Measuring electro-mechanical properties of thin films on polymer substrates

“…Another in-situ fragmentation test measures the resistance of the film using the 4 point probe (4PP) geometry [20–23] . The advantage of this in-situ technique is that the exact fracture strain can be determined for brittle films.…”

Improved electro-mechanical performance of gold films on polyimide without adhesion layers

“…In order to get a high stretchability, a high fracture strain and good adhesion between the metal film and the substrate are required [4] . To achieve high fracture strains methods such as film structuring [5] and wrinkling [6,7] have been utilized. A common way to improve the adhesion of the ductile conductive metal layers such as Au is to use 5–10 nm of brittle Cr, Ti or Ta as adhesion layers [8,9] .…”

“…This work utilizes fragmentation testing [11–14] and in situ 4 point probe resistance measurements (in situ 4PP) [3,5,15,16] , both under uniaxial tensile strain, to determine the effect of a 10 nm Cr adhesion layer on the electro-mechanical behaviour of 50 nm Au films on a flexible polyimide substrate and to assess the suitability of these film systems for flexible electronic technologies. It will be shown that the use of brittle adhesion layers, while possibly promoting adhesion, actually decrease the electrical performance by inducing the formation of cracks in the ductile layer.…”