Flyability and flying height modulation measurement of sliders with sub-10 nm flying heights

A Laser Doppler Vibrometer (LDV) was used to measure flying height modulation (FHM) of sliders with sub-10 nm flying-heights (FH). It was found that a precise trigger, averaging, and suitable filtering are the key to successfully measuring FHM by LDV. Also, more accurate results can be obtained from the LDV velocity output as opposed to the displacement output. The FHM's of a 7-nm FH slider flying over three different disks were measured. One of the disks had higher roughness and waviness values (disk A) than the other two (disks E and C). Disks B and C had the same super-smooth substrate but different lubricants and carbon overcoats. It was observed that this slider flew steadily over disk A and disk C, but it could not fly over disk B. The repeatable part of the FHM of the slider flying over disk A and disk C was about 0.45 nm and 0.37 nm (RMS), respectively, in the frequency range between 20 kHz and 300 kHz. Also, for disk C, the dependence of FHM on RPM was investigated, and it was found that at the design condition (7200 RPM) the FHM (peak-to-peak) was minimized for this particular slider/disk system. However, we do need to consider the ratio of FHM to FH. Increasing RPM increases FHM due to the disk surface topography and decreasing air-bearing modal frequencies, but the ratio of FHM to FH stays relatively constant. Decreasing RPM increases FHM due to intermittent contacts and excitation of the air-bearing.