From Mechanics to Electronics: Influence of ALD Interlayers on the Multiaxial Electro‐Mechanical Behavior of Metal–Oxide Bilayers

Abstract The applicability of metal‐polymer thin films in flexible electronics and space applications is fundamentally limited by the trade‐off between mechanical and functional performance. This study shows how atomic layer deposited (ALD) amorphous AlO x H y interlayers (0–25 nm) directly control the electro‐mechanical functionality of sputter‐deposited aluminum films on polyimide substrates. Using uni‐ and equi‐biaxial tensile testing with in situ XRD and electrical resistance measurements, it is demonstrated that interlayer thickness determines both deformation mechanisms and electrical strain limits. Adding an ALD layer between the polymer substrate and the metal thin film significantly improves the deformability of the system. While a single ALD cycle enhances ductility, surprisingly a 1 nm AlO x H y interlayer causes early electrical failure. Optimal performance—improved ductility, delayed cracking, and maintained electrical conductivity under large deformation—is achieved at 5–10 nm interlayer thickness. Beyond this range, embrittlement causes early electrical failure through oxide‐initiated cracking. The work establishes quantitative design rules linking the nanoscale interface structure to macroscale electro‐mechanical performance, enabling flexible electronics with tailored mechanical properties and enhanced electrical functionality. These findings provide a direct pathway from fundamental interface engineering to high‐performance flexible devices operating under multi‐axial deformation.