Thin-Film Superelastic Alloys for Stretchable Electronics

Abstract

Conductive serpentine interconnects comprise fundamental building blocks (e.g., electrodes, antennas, wires) of many stretchable electronic systems. Here we present the first numerical and experimental studies of freestanding thin-film TiNiCuCo superelastic alloys for stretchable interconnects. The electrical resistivity of the austenite phase of a Ti53.3Ni30.9Cu12.9Co2.9 thin-film at room temperature was measured to be 5.43×10-7 Ω m, which is larger than reported measurements for copper thin-films (1.87×10-8 Ω m). Structuring the superelastic conductor to limit localized strain using a serpentine geometry led to freestanding interconnects that could reach maximum serpentine elongations of up to 153%. Finite element analysis (FEA) simulations predicted that superelastic serpentine interconnects can achieve significantly larger (~5X–7X) elastic elongations than copper for the same serpentine geometry. FEA predictions for stress distribution along the TiNiCuCo serpentine interconnect were experimentally verified by infrared imaging and tensile testing experiments. The superior mechanical advantages of TiNiCuCo were paired with the high electronic conductivity of copper, to create Cu/TiNiCuCo/Cu serpentine composites that were demonstrated to serve as freestanding electrical interconnects between two LEDs. The results presented in this manuscript demonstrate that thin-film superelastic alloys are a promising material class to improve the performance of conductors in stretchable and flexible electronics.