A novel method for reduction of the cross track profile asymmetry of MR head during self servo-writing

Cross track profile is used to provide a head positioning signal during the self servo-writing process. A symmetric off-track profile is preferred in this case. The asymmetry of the cross track profile of a SAL biased MR head is characterized in this work, referring to the point at which the MR head is at the track center. Results indicate that the profile can be rather asymmetrical for some MR heads. Different MR heads correspond to different degrees of asymmetry. Different skew angles also exhibit different degrees of asymmetry, even for the same MR head. As a result, the positioning accuracy of a MR head during self servo-writing is affected. A novel method is presented in this work. Instead of keeping the bias current in a fixed direction, the new method uses bias current in both positive and negative directions for the readback of the positioning bursts. Results indicate that the new method can reduce both the asymmetry and the variation of the profile at different skew angles, and improve the uniqueness of the normalized cross track profile significantly.