Mechanical assessment of suspended ALD thin films by bulge and shaft-loading techniques

We assessed mechanical properties of free-standing atomic-layer-deposited (ALD) Al2O3 thin films, mixed oxide (AlxTiyOz) films and Al2O3/TiO2 nanolaminates (75 and 200 nm). Using bulge and microelectromechanical system shaft-loading techniques, we evaluated the Young’s modulus, residual stress and ultimate tensile stress of these films and laminates. Fits to the load–displacement curves provided estimates for the residual stress and Young’s modulus. We extracted a residual stress of 347–403 MPa for Al2O3, 365–389 MPa for AlxTiyOz and 450–455 MPa for the nanolaminate. The Young’s modulus was 164–165 GPa for Al2O3, 151–154 GPa for mixed oxide and 148–169 GPa for the nanolaminate. Thin membranes exhibited an ultimate tensile strength of 1.57–2.56 GPa for Al2O3, 1.17–2.09 GPa for AlxTiyOz and 1.23–2.26 GPa for the nanolaminate. The ability to make thin, yet mechanically strong, suspended membranes is useful in micro- and nanosystem applications ranging from thermally insulated devices to large stroke mechanical actuators.