Electromechanical Behavior of Al/Al₂O₃Multilayers on Flexible Substrates: Insights from In Situ Film Stress and Resistance Measurements

Abstract

In recent years, nanoscale metal/ceramic multilayers have come into greater focus as they exhibit promising mechanical, physical, and chemical properties, useful for a wide range of thermal, mechanical, and environmental conditions. Main efforts include manufacturing and characterization [1][2][3][4][5][6] of such structures as well as different experimental [4,5,[7][8][9][10][11][12][13][14][15] and modeling [9,13,[16][17][18][19] approaches to understand their deformation mechanisms and optimize mechanical properties. Enhancement in both, multilayer hardness and ductility, is achieved compared to rule of mixture values, depending on the bilayer thickness, the thickness ratio between ceramic and metal layers, and interfacial properties. [9,13] For thin layers (>10 nm) the metal can undergo elasticplastic deformation while the ceramic layer deforms elastically until it fails due to cracking; [4] alternatively, highly localized shear deformation may occur as a result of localized stresses at the interfaces. [5,9,15,17,19] When the layer thickness is reduced to a few nanometers, ultra-thin ceramics can plastically co-deform with metal layers, as has been demonstrated for Al/TiN. [4,18] Substantial intrinsic ductility at small scales has also been demonstrated for amorphous oxides (40 nm Al 2 O 3 ) [20] provided that the material is dense and free of geometrical flaws, whereby mechanical characterization remains experimentally challenging.Metal/ceramic multilayers are of interest for flexible thin-film applications, providing a unique combination of high strength, good conductivity, and potential damage tolerance due to sublayer fragmentation and crack deflection at interfaces.