Theory of 1/f noise in metal films and whiskers

The equilibrium thermal fluctuation in metal films is studied with careful consideration of the finite size of the specimen and the boundary conditions on the metal-vacuum and metal-substrate interfaces. For a freely suspended film, the noise spectrum due to bulk fluctuation has two parts, a frequency-independent part below a characteristic frequency and an f/sup -3/2/ part above that frequency. The characteristic frequency is the inverse of the diffusion time across the largest dimension of the specimen. The 1/f spectrum is obtained when two conditions are met : (i) the metal film is deposited on a substrate of very low bulk thermal conductivity; and (ii) the thermal fluctuation in the film is two dimensional and is mainly excited by the random flow of heat between the film and the substrate. In freely standing metal whiskers the 1/f spectrum can be obtained when the fluctuation is excited by white-noise sources at the ends