| We have developed a new dynamic measurement system to investigate the small damping in thin metal films. This system includes a vacuum chamber, in which a free-standing bilayer cantilever sample is driven to vibrate with an electrostatic force, and a laser interferometer to measure displacement and velocity of the sample. With this equipment, we can measure internal friction as low as 10-5 in micrometer thick metal films in a temperature range from 300K to 800K. Free-standing cantilevers with different frequencies are fabricated using well-established IC fabrication processes. The cantilevers consist of thin metal films on thicker Si substrates, which exhibit low damping.; From measurements of internal friction of Al thin films at various temperatures and frequencies, we were able to study relaxation processes associated with diffusion. An activation energy calculated from the damping data was 0.57eV, which was consistent with other references. This value suggests that the mechanism of internal friction in pure Al films involves grain boundary diffusion controlled grain boundary sliding. We developed a model to describe these damping effects. By deriving an expression for the diffusional strain rate using a two-dimensional Coble creep model, and modifying the conventional standard linear solid model for the case of bending, we were able to give a good account of the observed damping.; The internal friction of Cu thin films was also measured and the activation energy of 1.47eV was obtained from the internal friction peaks. Based on the dependence of the internal friction on the temperature, the frequency and the thickness of the film, we suggested that this activation energy points to a dragging mechanism of jogs accompanied by vacancy diffusion along the dislocation core. The proposed mechanism was modeled and compared with experimental results. |
