Tribological impact of touchdown detection on bit patterned media robustness

Abstract

Touchdown detection by thermal-flying height control (TFC) has been implemented to calibrate flying height (FH) of magnetic sliders for all hard disk drives. For bit patterned media (BPM) to be successful as a revolutionary technology to further increase recording areal density, it must experience the touchdown process with similar robustness as conventional continuous media. Here we numerically study the tribological impact of TFC touchdown detection on the continuous media and unplanarized BPM by three-dimensional (3D) transient finite-element models with the frictional heating and thermal-elastic-plastic materials included. Our results demonstrate that the continuous media exhibits no plastic deformation due to the TFC touchdown with an over-push as large as 2 nm, whereas the plastic strain of the BPM may reach 3 % at higher sliding velocities, and it exists over a wide range of bulge radius and disk velocity. Such plastic deformation can lead to permanent media damage and data loss. Besides, the temperature rise of the BPM (~27 K) is approximately 1.3 times of that of the continuous media (~21 K), and may have to be considered when designing a robust head-disk interface for BPM. Although planarization may improve slider's flyability performance, our analysis shows that planarizing BPM with SiO2 deteriorates the tribological robustness of the media in particular at a high disk velocity probably due to the inhomogeneous composition and mismatch of material properties between the filling material and recording material. Hence extreme caution must be exercised when choosing a filling material.