Characterization of the Reader Width Using the Micro-Track Test in Perpendicular Recording

Micro-track test is a valuable tool used to characterize the electrical reader width in perpendicular recording. The test is based on trimming both sides of a track written with a single tone and followed by a cross-track scan of the remaining track. The reader cross-track profile or read sensitivity function is characterized by a narrow band measurement of the read-back signal as a function of cross-track position. With increasing track density, the signal amplitude decreases due to incomplete media saturation and to an increase in the off-track noise due to percolation and opposite polarity media saturation. These effects cause a lump at the edge of the micro-track profile that changes the width of the profile (MT10 and MT50). Micro-magnetic analysis indicates that the off-track demagnetization field creates a track-edge section in the media with opposite polarity relative to the originally written track. This section is coherent with the main track and decreases the read-back signal during the scan of the micro-track. Consequently, the shape of the cross-track read sensitivity function becomes distorted, causing a reduction in MT10 and a side lump. The solution to this problem is to increase the amplitude of the micro-track read-back signal by reduced trimming and by the use of a higher density (KFCI) in the main track that minimizes the off-track demagnetization field. These test improvements are shown to preserve the integrity of the micro-track profile and to enable an accurate measurement of MT10 and MT50. Optimizing reader and writer widths in perpendicular recording requires an accurate measurement of these parameters.