A Flexible KFCI Compensation for Head/Media Optimization in Perpendicular Disk Drives

Head/media matching is one of the key procedures used to ensure an acceptable performance, reliability and areal density of the perpendicular drives with multiple head/media pairs. To achieve the optimal bit error rate (BER) performance, head/media optimization is required to handle the BER variation of each pair within a single drive. Due to a large variation of the head/media performance, the mismatched KFCI slopes often lead the under- and over-compensation issues. In this paper, we derive the mathematical conditions of these problems as a function of the step adjustment size, the initial BER, the target BER and the KFCI slopes. The minimum number of adjustments for the weak and the maximum ones for the strong heads are determined. In addition, we perform an experiment on the perpendicular drives to study the BER variation of head/media. A new graphical explanation is proposed to clearly show how the under- and over-compensation issues occur. Finally, we propose a flexible KFCI compensation method based on the actual KFCI slopes. The experimental results on the failed drives from the current fixed-slope method show that the improvement in the BER performances is achieved using the proposed method.