Electromechanical Behavior of Al/Al2O3 Multilayers on Flexible Substrates: Insights from In Situ Film Stress and Resistance Measurements

A series of Al and Al/Al2O3 thin‐film multilayer structures on flexible polymer substrates are fabricated with a unique deposition chamber combining magnetron sputtering (Al) and atomic layer deposition (ALD, Al2O3, nominal thickness 2.4–9.4 nm) without breaking vacuum and thoroughly characterized using transmission electron microscopy (TEM). The electromechanical behavior of the multilayers and Al reference films is investigated in tension with in situ X‐ray diffraction (XRD) and four‐point probe resistance measurements. All films exhibit excellent interfacial adhesion, with no delamination in the investigated strain range (12%). For the first time, an adhesion‐promoting naturally forming amorphous interlayer is confirmed for thin films sputter deposited onto polymers under laboratory conditions. The evolution of Al film stresses and electrical resistance reveal changes in the deformation behavior as a function of oxide thickness. Strengthening of Al is observed with increasing oxide thickness. Significant embrittlement can be avoided for oxide layer thicknesses ≤2.4 nm. Magnetron sputtering and atomic layer deposition (ALD) are combined without breaking vacuum to fabricate metal/oxide multilayers on polymer substrates with unprecedented film thickness and modulation ratios in search of damage‐tolerant thin films. While the deformation of multilayers is often dominated by the most brittle component, Al/Al2O3 films exhibit strengthening without brittle cracking up to an oxide thickness of 2.4 nm.