Flying Height Modulation for a Dual Thermal Protrusion Slider in Heat Assisted Magnetic Recording (HAMR)

Thermal flying-height control (TFC) technology has been used in the last few years in hard disk drives (HDDs) to achieve a lower flying height for higher storage areal density. In this paper a slider with dual thermal protrusions, one produced by the laser used to heat the disk in HAMR and the other one used for TFC, is studied. The flying height modulations (FHM) due to disk waviness and external disturbances are compared for the dual protrusions, single protrusion and no protrusion sliders. The protrusions provide additional force and torque excitation to the slider. The protrusions can be viewed as a passive feedback loop to compensate the disturbance. The gain of the feedback loop depends on the stiffness of the protrusions, which is determined by the protrusions' heights and positions. Thus the complicated air bearing slider system with protrusions is simplified by casting the protrusion perturbation as a feedback loop and this simplified model helps to speed up the optimization of the TFC protrusion height and position. The numerical simulation results show that FHM of the dual protrusion slider is reduced significantly when the TFC protrusion height and location are optimized. External disturbance induced FHM can be suppressed as well. This scheme for dual protrusion optimization and analysis described in the work can benefit HAMR head design because the optimized dual protrusion provides a more consistent flying height and a greater ability to compensate external disturbances.