The role of disk surface waviness on baseline instability of MR head

To investigate the role of disk surface waviness on the baseline instability (BLI) of the read-back signals from MR head, we measured the average height of surface waviness with a spatial wavelength of 0.4 to 5.0 mm using a white light inlerferometer instrument. We used an MR head over four sets of media to measure the baseline instability at OD and at MD. The results show that the baseline instability becomes worse as the surface waviness increases and that the baseline instability is linearly proportional to the surface waviness. The result further shows that the effect of bias current on the baseline instability is amplified on the disk with worse surface waviness. The surface waviness, therefore, can not be overlooked when evaluating the media for a high-performance hard disk drive.