Bending Strain and Bending Fatigue Lifetime of Flexible Metal Electrodes on Polymer Substrates

Abstract

As the technology of flexible electronics has remarkably advanced, the long-term reliability of flexible devices has attracted much attention, as it is an important factor for such devices in reaching real commercial viability. To guarantee the bending fatigue lifetime, the exact evaluation of bending strain and the change in electrical resistance is required. In this study, we investigated the bending strains of Cu thin films on flexible polyimide substrates with different thicknesses using monolayer and bilayer bending models and monitored the electrical resistance of the metal electrode during a bending fatigue test. For a thin metal electrode, the bending strain and fatigue lifetime were similar regardless of substrate thickness, but for a thick metal film, the fatigue lifetime was changed by different bending strains in the metal electrode according to substrate thickness. To obtain the exact bending strain distribution, we conducted a finite-element simulation and compared the bending strains of thin and thick metal structures. For thick metal electrodes, the real bending strain obtained from a bilayer model or simulation showed values much different from those from a simple monolayer model. This study can provide useful guidelines for developing highly reliable flexible electronics.

Strain‐Engineering of Contact Energy Barriers and Photoresponse Behaviors in Monolayer MoS2 Flexible Devices

“…To gain fundamental insight into the nature of the semiconductor‐metal junction under applied tensile strain, we first fabricated the two‐terminal MoS 2 monolayer device using gold electrode on a flexible polyimide (PI)/PET substrate ( Figure a; Figure S4, Supporting Information) and measured its electrical properties upon each applied tensile strain. It should be noted that the applied strain was limited to 0.7% to avoid sample slippage [ 29,30 ] and rupture of electrodes [ 31 ] and to sorely focus on the strain effects. Figure 2b shows the current, I , as a function of bias voltage, V b , on a logarithmic scale which is measured under tensile strain.…”

Fabrication of Piezoelectric ZnO Nanowires Energy Harvester on Flexible Substrate Coated with Various Seed Layer Structures

“…It is important to note that the adherence of metal electrodes to PDMS substrate is usually poor [31]. Furthermore, among materials generally used in electronics devices, a thin metal layer is one of the weakest parts against mechanical stress and has a potential problem of cracking when stressed because of the degradation of its morphological and electrical properties during repeated mechanical excitation [32][33][34][35]. This could result in bad electrical charge transfer and increase the electrical losses, preventing the metal layer from being a functional bottom electrode.…”

Direct Laser Writing of Graphene‐Based Electrical Interconnects for Printed Circuit Board Repair

“…Corresponding bending strains can be determined using the formulation provided in Figure S3, Supporting Information. [ 27 ] The measurements were carried out using an in‐house‐built apparatus. The fractional change in resistance ( R / R 0 ) was used as a measure of the printed resistor's stability when it is subjected to bending.…”