Resistivity dependence of $\frac{1}{f}$ noise in metal films

The $\frac{1}{f}$ noise of a number of different types of metal films has been studied at room temperature. We find that the noise of nominally identical samples can vary by as much as a factor of 10, which is well outside the estimated experimental uncertainties for the quantities thought to be relevant in determining the noise. This suggests that some other variables play an important role in the noise process. Despite these sample-to-sample variations, we find that the minimum level of $\frac{1}{f}$ noise for a given metal is a fairly well-defined quantity. Moreover, the minimum noise level exhibits a systematic resistivity dependence which has not been observed previously, and which cannot be accounted for by the semiempirical formula of Hooge. These results are compared with those of previous workers, and a modification of Hooge's formula is suggested.