Servo Signal Data Processing for Flying Height Control in Hard Disk Drives

In recent years, thermal actuated flying height control has been implemented in Hard Disk Drives (HDD) to reduce the effect of flying height variations due to manufacturing tolerances or write current introduced pole tip protrusion (Fig. 1). A stable low flying height is necessary to achieve low bit error rates (BER) [1]. Thermal flying height control is used in a “static manner” in current disk drives. The principle of thermal flying height control is based on the application of a current to a resistance heater positioned in close proximity to the read write element, thereby causing a thermal deformation of the head which causes a reduction in the static flying height at the read write element. Dynamic flying height variations of a slider over a disk are composed of repeatable and non-repeatable contributions. As the name suggests, repeatable variations of flying height occur at the same angular and radial position of the slider above the disk [2]. Thus, the question arises as to whether a thermal flying height control slider can be used to dynamically control the flying height variations between slider and disk. The objective of this paper is to study whether a thermal actuator could be used to reduce the effect that disk waviness and vibrations have on the flying height modulation of the head disk interface. Our main goal is to investigate active flying height control of a thermal slider up to the kilohertz regime.