The effects of disk morphology on flying-height modulation: experiment and simulation

The effect of morphology on flying height modulation (FHM) of a sub-10 nm flying air bearing slider was studied for three different disks by experiment and simulation. The experimental measurement methods are discussed and a new single beam laser Doppler vibrometer (LDV) measurement method, which yielded the highest resolution with a 2 μm beam spot size, was introduced. Analysis was performed in three different frequency bandwidths-a geometric FHM from 10 to 100 kHz, a dynamically excited FHM from 100 to 500 kHz and the third being negligible compared to the other two bands, above 500 kHz. Transfer function analysis was carried out to investigate the FHM in the lowest frequency band. FHM in the first band was shown to be caused primarily by a phase shift between the sliders´ response and the disks´ morphology and secondarily by decreasing slider motion with decreasing morphology wavelength, which correlated well with previous work. For two of the disks investigated, the FHM due to the disks´ morphology showed air bearing excitation that resulted in an intolerable level of FHM. However, for one of the disks studied, the FHM was as low as the disk morphology for wavelengths of 2 μm and less, which was within tolerable limits. It is concluded that when designing a disk for low FHM, it is not sufficient to characterize the quality of a disk by a single number such as roughness or waviness. Proper design and optimization of both the disk and air bearing slider results in FHM that is lower than the disks´ morphology.