Electromechanical Behavior of Al/Al$_{2}$O$_{3}$ Multilayers on Flexible Substrates: Insights from In Situ Film Stress and Resistance Measurements

A series of Al and Al/Al$_{2}$O$_{3}$ thin-film multilayer structures on flexible polymer substrates are fabricated with a unique deposition chamber combining magnetron sputtering (Al) and atomic layer deposition (ALD, Al$_{2}$O$_{3}$, 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.