Thickness dependent mechanical behavior of submicron aluminum films

Mechanical behavior of thin metallic films has been investigated on aluminum films deposited on a flexible polyimide substrate. Aluminum thin films exhibit a higher tensile strength than bulk aluminum. As film thickness decreases from 480 to 60 nm tensile strength increases from 196 to 408 MPa. These mechanical behaviors are correlated with the microstructure and its evolution with the thickness of aluminum thin films. Films are consisted of fine columnar grains and average grain size increases monotonically with the film thickness. The volume fraction of (111)-textured grains increases and the dispersion of texture axis becomes narrow as the film thickens. The relative contributions of the film thickness, grain size, and texture to the strength of aluminum thin films are estimated using an empirical strengthening model. The result indicates that the high strength of aluminum thin films is due largely to their small grain size, followed by the strengthening due to the film thickness and texture.