Study on Cu/Ni Nano Superlattice Conductors for Reduced RF Loss

Abstract

We report on Cu/Ni paired superlattice conductors featuring reduced radio frequency (RF) loss based on eddy current cancelling (ECC). Also, the effects of the width and the individual layer thickness of the superlattice conductors have been studied for improved RF performance. The usage of Ni as the ferromagnetic material in the non-ferromagnetic/ferromagnetic superlattice structure is advantageous as it has a high contrast between the in-plane and out-of-plane magnetic coercivity fields making it suitable for effective thin film superlattice ECC, is abundant, and does not require a stoichiometric control of composition as other alloy magnetic materials do. Ni's negative permeability is also able to effectively cancel out the positive permeability of copper in the frequency of interest. A transmission line consisting of 10 superlattice Cu/Ni layers, with each layer being of 150 nm/25 nm totaling 1.75 $\mu\text{m}$ shows the same resistance value as one consisting of 10 Cu/Ni layers with each being 600 nm/100 nm totaling 7 $\mu\text{m}$ thick at 13 GHz, revealing 75% conductor volume reduction. Experimental results show more than three times improvement in the figure of merit defined as frequency/effective resistivity, compared with other state-of-the-art devices.