Flicker (1/f) noise in copper films due to radiation-induced defects

Changes were measured in the resistivity and 1/f noise in polycrystalline Cu films due to defects induced by 500-keV to 1.1-MeV electron irradiation or 1-MeV Kr⁺-ion irradiation. Irradiation with 500-keV electrons increased the noise level in films maintained at 90 K by as much as an order of magnitude, while the resistivity increased by at most 10%. When the films were annealed at progressively higher temperatures, both the 1/f noise and the resistivity were reduced; however, at lower annealing temperatures, the fractional reduction in the induced noise was substantially more than in the added resistivity. These results suggest that a large fraction of the induced noise is generated by ‘‘mobile’’ added defects that are more readily annealed than the majority of the added defects. The temperature dependence of the noise after irradiation and partial annealing indicated that the induced noise was thermally activated in a manner consistent with the Dutta-Dimon-Horn model. Isolated defects created by 1.1-MeV electron irradiation were found to produce substantially higher noise levels than clustered defects resulting from 1-MeV Kr⁺ion irradiation. Measurements on a number of films indicate that the induced 1/f noise is not sensitive to the type and quantity of interstitial traps. A model which attributes the noise to the motion of defects involving vacancies close to surfaces, grain boundaries, or dislocations is most consistent with the experimental results.