Comparative study of optical near-field transducers for heat-assisted magnetic recording

Optical and thermal analysis of the light-heat conversion process employing an antenna-based hybrid plasmonic waveguide for HAMR

“…The full-width half-maximum (FWHM) of roughly 65 × 70 nm 2 for the thermal spot is closely given by the contour at 550 K. The thermal spot is reduced to approximately 30 × 35 nm 2 near the point where gradients reach a maximum between contours of 650 K and 750 K. It is at this position of elevated temperature gradients where ideally one would like to apply the external magnetic field for bit writing. The FWHM compares very well with those reported for antenna-based HAMR designs for the NFT review in [25] although no write pole had been included in their study. Noticeably, the down track temperature gradient shown in Fig.…”

“…Most notably is the change in temperature difference between the Au taper and recording layer between the two cases which reaches 35 K. This can yield a significant improvement in lifetime of the NFT. Values reported for the ratio of the temperature rise in the media compared to that in the Au at the steady state (ΔT Media /ΔT NFT ) are significantly higher than those found reported for antenna-based NFTs though lower compared aperture-based designs [25,38]. However, thermal gradients in antenna-based designs tend to be higher compared to aperture structures, for which the tapered NFT presented in this article has maximum values closely matching state-of-the-art [3,4] values between 10 and 15 K/nm with estimations in Au thermal conductivity and thermal spot size slightly varying.…”

“…Optimization of the taper length according to plasmon wavelength is fundamentally different than optimization via coupling length such as that seen in similar antenna-based NFTs proposed for HAMR and may extend the taper length by many microns making a less compact design [16,46]. A maximum optical absorption efficiency around 8.5% is obtained for L taper = 330 nm comparing well with other HAMR devices [1,22,25,38,47,48]. Though the back reflection into the Si waveguide is nearing a maximum at this point, further alterations can be made by abutting anti-reflective coatings or anti-reflective trenches which have been shown capable of improving optical efficiencies significantly in plasmonic NFTs [49].…”

“…In addition, in Fig. 7(b), we report maximum thermal gradients as a function of input power and those 20 K from the peak temperature for direct comparison with the NFTs in [25]. We surpass all gradient values reported except the cross-track gradient for the E-antenna, and all values (antenna or aperture based) reported for temperature rise per milliwatt.…”

“…Thermal data may not always be reported for NFTs suggested for HAMR, and none have been found reporting on the thermal behavior of the multilayered hybrid design proposed in this investigation; partly chosen for being straightforward to fabricate or make alterations to. We adopt the definition of thermal efficiency defined in [25] which provides a thorough review on many of NFTs mentioned above (triangle, lollipop, E-antennas, bow-tie and C apertures) though no magnetic write pole is included as we have done which can significantly alter results. They supply (1) thermal spot size data, (2) cross and down track temperature gradients, (3) maximum temperatures, along with (4) the peak temperature rises per unit of input power (K/mW) in the recording medium compared to the NFT.…”