Excess Electrical Noise in Aluminum-Based Thin Films.

The excess electrical noise in aluminum and aluminum alloy thin films were measured. Magnitude, frequency exponent, and distribution of the activation energy, D(E) , for noise spectra of 1/f^{ alpha}, with alpha between 0.8 and 1.2 were measured as a function of the sample temperature. Dependence of the 1/f noise magnitude on the temperature implied that temperature independent Hooge's empirical formula was not applicable in computing magnitude of the noise in the thin films. The Dutta and Horn model, however, is partially successful in explaining 1/f noise but fails to explain some of the experimental observation in Al thin films. Studying 1/f noise measurements as a function of temperature showed that the value of alpha and D(E) closely resembled the same patterns as that of the excess noise magnitude. Normalized noise magnitude at different frequencies versus temperature were plotted. In contrast to the theoretical prediction, decrease in the value of alpha with frequency and an increase in the value of alpha with temperature was observed experimentally. These two observations were attributed to the contribution of the thermal noise and 1/f ^{alpha}, with alpha larger than 1.2, noise component to the excess noise spectra respectively. The measurement technique, the variance in D(E), and the existence of other components of excess noise with alpha > 1.2 explained the shape of normalized noise magnitude plots. Also, Heat treatment of Al samples resulted in decrease of noise magnitude and D(E) due to the removal of defects. As the current density or the ambient temperature of the Al and Al alloy film increased, the noise spectra of 1/f^alpha, with alpha between 1.2 and 2.2, were observed. The 1/f^2 noise was closely related to the electromigration in the Al thin films. For the first time different regions in plots of normalize 1/f ^2 noise magnitude versus inverse temperature were observed. The calculated activation energy in the lower temperature region was close to the grain boundary activation energy, while in the higher temperature region the calculated value was close to the bulk diffusion activation energy of Al. The time dependence experiment on excess noise of Al showed 1/f^{ alpha}, with alpha larger than 2.2, noise spectra during later stages of electromigration process. The resistance drift of the sample will produce this type of noise spectra.