Low-frequency resistance fluctuations in metal films under current stressing at low temperature(T<0.3Tmelting)

Abstract

In this paper, we report a systematic study of low frequency $1∕{f}^{\ensuremath{\alpha}}$ resistance fluctuation in thin metal films (Ag on Si) at different stages of damage process when the film is subjected to high current stressing. The resistance fluctuation (noise) measurement was carried out in situ using a small ac bias that has been mixed with the dc stressing current. The experiment has been carried out as a function of temperature in the range of $150--350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The experiment establishes that the current stressed film, as it undergoes damage due to various migration forces, develops an additional low-frequency noise spectral power that does not have the usual $1∕f$ spectral shape. The magnitude of extra term has an activated temperature dependence (activation energy of $\ensuremath{\approx}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) and has a $1∕{f}^{1.5}$ spectral dependence. The activation energy is the same as seen from the temperature dependence of the lifetime of the film. The extra $1∕{f}^{1.5}$ spectral power changes the spectral shape of the noise power as the damage process progress. The extra term likely arising from diffusion starts in the early stage of the migration process during current stressing and is noticeable much before any change can be detected in simultaneous resistance measurements. The experiment carried out over a large temperature range establish a strong correlation between the evolution of the migration process in a current stressed film and the low-frequency noise component that is not a $1∕f$ noise.