Exploration on in-situ diagnosis methods for the evaluation of mechanical and magnetic performance of hard disk drives

Abstract

Currently flying height has been driven down to sub 10 nm with 10% variation margin. Such a low flying height and small margin makes the drive level in-situ flying height measurement crucial because undesirable flying height variation would result in data loss. A new flying height error function is proposed to evaluate measurement errors in existing in-situ flying height measurement methods. Based on this error function, harmonic burst method, which selects optimum testing frequencies by minimizing measurement error, is proposed and successfully applied to investigate the influence of environmental changes on flying height in disk drive operating environment. It is proved that harmonic burst method has both the advantage of high harmonic amplitude and alternatives for testing frequencies. By choosing optimum ratio of testing frequencies and channel density, flying height error can be minimized as possible to achieve high measurement accuracy.