Simulation on metal-dielectric hybrid nano-antenna attached to semiconductor ring resonator for heat-assisted magnetic recording

Abstract

Heat-assisted magnetic recording (HAMR) is a promising technology to increase the recording density of hard disk drives to more than 10 Tb/inch2. In HAMR, a near-field transducer (NFT) is necessary to form a light spot with the order of 10 nm to heat the recording medium locally to reduce its coercivity during recording. The authors’ group has proposed a device for HAMR, in which a metal nano-antenna acting as an NFT is attached to a semiconductor ring resonator acting as a light source. Because the characteristics of near-field light are influenced by the material and structure of nano-antenna, we investigated a metal-dielectric hybrid nano-antenna in this study. Especially, a core-shell-type nano-antenna, in which a dielectric sphere as a core was embedded in a gold tip as a shell, was taken as an example, and how the core refractive index and core radius influence the energy density and spot size of near-field light was numerically simulated. The tip radius of nano-antenna was 25 nm. As a result, when the core radius was 20 nm, maximum energy density of about 25 times and minimum spot size of about 91% compared with conventional gold-only nano-antenna were obtained at the core refractive index of 4.4 and 4.8, respectively. As the core refractive index became higher, the optimum core radius became smaller. Moreover, the behavior of energy density could be understood by one-sphere model and that of spot size could be understood by two-sphere model, both of which are determined by the localized surface plasmons.