A New AFM-Based Technique to Detect the NFT Protrusion on HAMR Head

Heat assisted magnetic recording (HAMR) is anticipated to increase the areal density in hard disk drives to multiple Tb/in². However, the newly introduced protrusions caused by additional heat sources must be taken into account in head-disk spacing control. The light absorption by the near field transducer (NFT) and the heat dissipation into the slider through the laser delivery system can result in the temperature rise well over a hundred degrees Celsius. In response to such a big temperature change, an instantaneous protrusion at the NFT region is expected. This protrusion has a direct impact on the head-magnetic spacing (HMS) and therefore affects writing performance. Due to its small lateral size below 1 micrometer, the NFT protrusion is difficult to probe. In this paper, we introduce a new technique, which is based on atomic force microscopy (AFM) and allows for a simultaneous topography imaging and NFT protrusion mapping on the air bearing surface (ABS) with a nano-scale resolution. The measured NFT protrusion profile of a nonflying head indicates the local min-fly point at the location predicted by our simulation results. A further quantitative analysis proves the dependence of NFT protrusion on the laser power, which agrees very well with modeling and can offer a good guidance to the head-disk interface management during recording.