Frequency of contact between Head element and Disk increase with thermal flying height control (TFC) technology in Hard Disk Drive (HDD). It is very important for reliability of HDD to know wear depth of carbon overcoat (COC) around Head element when element contact with Disk. But there was no method to measure wear depth of COC around Head element quantitatively. Observation by means of scanning electron microscope (SEM) has good areal resolution but no method to know wear depth from SEM image. Atomic force microscope (AFM) can measure relative height on Head element but absolute depth cannot be obtained if whole area of Head element had been worn.
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