Nonlinear mechanism for1fnoise

A phenomenological theory of excess ($\frac{1}{f}$) voltage noise is suggested. The slowly fluctuating variable describing the noise and obeying a local conservation law in a linear approximation is introduced. The breakdown of the conservation law in a nonlinear approximation leads to the singularity ${\omega }^{-\frac{1}{2}}$ in the spectral noise power as $\omega \to 0$. At higher frequencies the model reduces to the temperature diffusion model of Voss and Clarke. The theory is compared with experimental data on metals with respect to the magnitude of noise, its temperature variation, and its dependence on the thermal properties of substrates. The relaxation law for fluctuations as a function of their initial amplitudes is investigated.