Numerical Simulation of Touchdown Dynamics of Thermal Flying-Height Control Sliders

With the advent of thermal flying-height control (TFC) technology the physical spacing in magnetic hard disk drives is now reduced to sub-1 nm. At this spacing the tribological flyability and reliability become critical issues for the performance of the read-write head. In this paper a numerical approach is applied to study the touchdown dynamics of TFC sliders by expanding a 3-degree-of-freedom slider dynamics model to a 250-degree-of-freedom head-gimbal assembly dynamics model and considering several significant tribological effects at this ultra-low clearance (adhesion, tribo-charge, friction, contact, etc.). The simulation results show that the slider's vibration amplitude increases substantially at the beginning of touchdown, and it gets suppressed with further reduction in flying height. Analysis in the frequency domain shows the excitation of the second air-bearing pitch mode when instability occurs. The expansion of the dynamic system to include a realistic model of the suspension is shown to be important in determining the frequency of the excited mode. Adhesion force is shown to play an essential role in exciting the second air-bearing pitch mode and causing instability, while electrostatic force and friction force affect only some details of the slider's dynamics at instability. Friction force is also shown to be related to the excitation of the first air-bearing pitch mode.

I. Introduction

The physical clearance between the read-write head and disk in magnetic recording hard disk drives (HDDs) has been continuously decreasing in the past decades in order to meet the ever-increasing demand for higher areal density of stored data. In recent years, thermal flying-height control (TFC) technology has been widely used to achieve an ultra-low physical clearance at the read-write transducers. In this approach, the local area around the read-write transducers is heated during reading or writing operations by use of a heating element imbedded in the air-bearing slider body, resulting in a bulge at the transducer area. The clearance at the transducer location is thus reduced by several nanometers while other parts of the slider stay well separated from the disk [1]–[6]. With the application of TFC technology, current air-bearing sliders can fly at a clearance of nm where the slider is subject to increasing interactions with the disk and thus experiences a much more complicated dynamic.