Mechanical degrandation mechanism of aluminum-alloy structural films evaluated by environment-controlled tensile testing

This paper describes the mechanical degradation mechanism of sputtered aluminum-alloy (Al-alloy) film used as a structural material in microelectromechanical systems (MEMS). The environment-controlled uniaxial tensile test system with elongation measurement image analysis function was developed to investigate the material characteristics at temperatures ranging from room temperature (RT) to 358 K. From the quasi-static tensile test results, no specimen size effect on Young's modulus and yield stress was found, whereas the annealing and temperature influences were clearly observed. To investigate mechanical degradation to cycling loading, the cyclic loading tests were conducted under constant stress-and strain-amplitude modes. In constant stress-amplitude mode, stain amplitude increased with an increase of loading cycles due to creep-like deformation. Almost of the specimens fractured during the tests. Meanwhile, in constant strain-amplitude mode, stress amplitude gradually decreased with increasing cycles due to stress relaxation, but no fatigue failure was found. The cyclic loading and stress relaxation tests revealed that creep deformation was dominant in the degradation of Al-alloy film subjected to cyclic motion.