Anisotropic Heatsinks for Heat Assisted Magnetic Recording

The relevance of anisotropic heatsinks for heat-assisted magnetic recording (HAMR) is investigated. First, 3-D thermal modeling is used to demonstrate that the heatsink performance on a glass substrate is determined by the heatsink in-plane thermal conductivity. The out-of-plane thermal conductivity has almost no impact on the heatsink ability to carry heat away from the hot spot. As a result, an anisotropic heatsink can be a good alternative to some conventional isotropic heatsink materials when its in-plane thermal conductivity is larger than that of the isotropic material. Second, time-domain thermo-reflectance (TDTR) measurements are presented to extract both the in-plane and the out-of-plane thermal conductivities of a (Cu/Ta) multilayer heatsink. The sensitivity to in-plane thermal conductivity is achieved by using small laser beam sizes and by combining measurements at multiple modulation frequencies on both a low and a high thermally conductive substrate. The fitting of all TDTR spectra gives for the (Cu[5.1]/Ta[1.4]) multilayers an effective out-of-plane thermal conductivity of 11.5 W/mK and an in-plane thermal conductivity of 69 W/mK. These thermal properties make such multilayer material an interesting candidate as HAMR heatsink, equivalent to a 70 W/mK isotropic material.