1/f noise of metals: A case for extrinsic origin

Small multiprobe resistors have been fabricated from continuous metal films of Ag, Al, Au, Cr, Cu, Mo, Nb, Ni, Pt, and W deposited under various conditions. Each shows some reproducible level of flicker (1/f) noise. This study implicates carrier scattering by extrinsic defects or impurities as the source of the resistivity fluctuations. The noise level appears to be determined by the number of defects introduced in the film during deposition. We introduce a new quantity, ρ_*²=fS_ρ(f)N_a, as an appropriate measure of the level of noise and relate it to the residual resistivity ratio ρ(300 K)/ρ(4.2 K), a measure of the extrinsic defect and impurity density. [Here f is the frequency in Hz, S_ρ(f) is the power spectral density of the resistivity fluctuations, and N_a is the number of atoms in the sample.]