Electrical fluctuation spectra due to characteristic thermal diffusion in Ta thin films deposited by RF-magnetron sputtering

Abstract

In this study, we investigate electrical resistivity and resistance fluctuation of Ta thin films deposited by RF-magnetron sputtering, and discuss the relation between the crystal structure and resistance fluctuation. The resistance fluctuation in the films shows exponential behavior in power spectral densities (PSDs), and the exponents of the PSDs are dependent on the film thickness. While the PSDs and exponents of thin films less than 10 nm or more than 60 nm are lower, the intermediate thickness samples exhibit higher PSDs. The intermediate thickness samples have strained α- and β-phases, and a positive correlation is presumed between the power exponent and the crystalline strain. Additionally, the thermal diffusion path, which depends on the coexistence of the two strained phases, has a characteristic fractal-like dimension with less-than-2 dimensions in 2D thin films. Numerical simulation shows that the thermal diffusion path, which is derived from the coexistence of α- and β-Ta grains, is related to the exponent in the PSDs. The higher exponents originate from the strained phases, and measurement of the PSDs in these thin films enables the detection of crystalline strain.