Stress-gradient induced fatigue at ultra high frequencies in sub micron thin metal films

Abstract

Abstract Mechanical fatigue at frequencies in the GHz regime in submicron metal thin films is governed by size and frequency effects. The cyclic load can lead to damage formation also known as acoustomigration and determines the reliability of micro electro mechanical systems and surface acoustic wave devices. The size and frequency effects dramatically change the fatigue behavior compared to bulk material. The resulting damage structure is similar to electromigration experiments where void and extrusion formation lead to failure. Here, a dislocation based mechanism is presented which explains the damage formation. This mechanism is induced by gradients in cyclic shear stress which is induced by the short acoustic wave length at frequencies in the GHz regime. Discrete dislocation dynamic simulations are presented that reflect the dislocation behavior at these ultra high frequencies.