Self-Heating-Induced Deterioration of Electromechanical Performance in Polymer-Supported Metal Films for Flexible Electronics

Abstract

The retention of electrical performance under the combined conditions of mechanical strain and an electrical current is essential for flexible electronics. Here, we report that even below the critical current density required for electromigration, the electrical current can significantly deteriorate the electromechanical performance of metal film/polymer substrate systems. This leads to a loss of stretchability, and this effect becomes more severe with increasing strain as well as increasing current. The local increase of electrical resistance in the metal film caused by damage, such as localized deformations, cracks, etc., locally raises the temperature of the test sample via Joule heating. This weakens the deformation resistance of the polymer substrate, accelerating the necking instability, and consequently leading to a rapid loss of electrical conductivity with strain. To minimize such a current-induced deterioration of the polymer-supported metal films, we develop and demonstrate the feasibility of two methods that enhance the deformation resistance of the polymer substrate at elevated temperatures: increasing the thickness of the polymer substrate, and utilizing a polymer substrate with a high glass transition temperature.

Polymer nanofibre composite nonwovens with metal-like electrical conductivity

“…The joule heating is shown to affect the deformation of the low glass transition temperature (Tg) polymers, such as polyethylene terephthalate (PET) substrate (Tg~75°C) in literature. 41 In our case, there was no burning or distortion of sample observed even after three cycles of heating and cooling. This might be due to the fact that the maximum temperature did not exceed the Tg of PAN, the matrix polymer.…”

Engineering the Interface: Effects of Interfacial Adhesion and Substrate Thickness on the Ductility of Polymer-supported Metal Films

“…To characterize the Al/PET film ductility, tensile tests were conducted at a constant strain rate of 1.25 × 10 −3 s −1 and gage length of 20 mm. During the tensile tests, the electrical resistance of the Al films was monitored with an Agilent 34401A multimeter in a four-probe method using a probing current of 1 mA, which is low enough to not create the substrate softening effect of higher currents [7]. The electrical resistance of the samples is expected to change prior to fracture during the film deformation due to the dimensional changes caused by the tensile load and Poisson's effect.…”

“…The fundamental mechanism of the improvement in ductility is that the polymer substrate constrains the deformation of the metal film and retards local thinning [6]. However, various factors in the metal-polymer system, such as the film thickness and microstructure of the metal have been reported to contribute to the apparent ductility and participating mechanisms [7][8][9][10][11]. For instance, Jang et al demonstrated that the combination of the mechanical deformation and electrical currents deteriorated the stretchability of the metalpolymer laminates due to the softening of the polymer substrate caused by the localized increase in temperature via Joule heating [7].…”

“…However, various factors in the metal-polymer system, such as the film thickness and microstructure of the metal have been reported to contribute to the apparent ductility and participating mechanisms [7][8][9][10][11]. For instance, Jang et al demonstrated that the combination of the mechanical deformation and electrical currents deteriorated the stretchability of the metalpolymer laminates due to the softening of the polymer substrate caused by the localized increase in temperature via Joule heating [7]. Lu et al discussed the effect of the thickness of the metal films on the failure strain of metalpolymer composite by conducting a uniaxial tensile test of copper (Cu) films deposited on 12 μm-thick polyimide (PI) films.…”

Electrical and thermal effects on electromechanical performance of stretchable thin gold films on PDMS substrates for stretchable electronics

“…23 Although the stretchability mechanism of the stretchable gold film electrodes has been fully investigated, few studies have been reported on the electromechanical performance of the stretchable electrodes under working conditions such as electrical and thermal treatments. 24 Since reliable electrical conductivity is essential for the stretchable electronics in various applications and circumstances, in this work, the performance of the stretchable gold film on a PDMS substrate is comprehensively investigated under working conditions. Stress analysis and crack quantification are discussed in detail, with some interesting phenomena observed and explained.…”