A Laser Doppler Vibrometer (LDV) was used to measure flying height modulati
on (FHM) of sliders with sub-10 nm flying-heights (FH), It was found that a
precise trigger, averaging, and suitable filtering are 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 B and C), Disks B and C had the same super-smooth substrate but diff
erent lubricants and carbon overcoats, It was observed that this slider fle
w steadily over disk A and disk C, but it could not fly over disk B, The re
peatable part of the FHM of the slider flying over disk A and disk C was ab
out 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 inv
estigated, and it was found that at the design condition (7200 RPM) the FHM
(peak-to-peak) was minimized for this particular slider/disk system. Howev
er, 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 Fr
equencies, but the ratio of FHM to FH stays relatively constant. Decreasing
RPM increases FHM due to intermittent contacts and excitation of the air-b
earing.