Creep-resistant aluminum alloys for use in MEMS

Creep is expected to be a reliability issue in MEMS where high temperatures and stresses are present in the moving part. In this paper, we describe a method of measuring the creep parameters, Delta F and tau, in metal thin films. Substrate curvature measurements were used to study different Al alloys-Al98.3Cu1.7, Al99.7V0.2Pd0.1, Al93.5Cu4.4Mg1.5Mn0.6 and Al99.6Cu0.4 films-during isothermal tensile stress relaxation. We show that there is a direct relation between the measured creep parameters and the coherency, size and spacing of precipitates observed by TEM and SEM in the alloys. Furthermore, we confirm that the plastic deformation is controlled by the motion of dislocations inside grains in the Al alloy films. A strengthening process called precipitation hardening was used to create stronger precipitates within the grains in Al99.6Cu0.4 to hinder the movement of dislocations more effectively and thus to make the alloy more creep resistant.