Hard Disk Media - Lubrication Layer Thickness

The thickness of the uppermost lubrication layer is critical to avoid wear and crashes of the recording head. Too much lubrication may cause stiction, too little can cause premature head wear.

The technique of XPS is ideally suited for the measurement of lube thickness; both the protective DLC layer and the fluoropolymer lubrication layer are predominantly made from carbon although the carbon exists in quite different chemical environments. XPS has the ability to differentiate these two species of carbon. The C signal from the protective layer is attenuated by the lubrication layer therefore a quantitative measure of overlayer thickness can be made. The ability to routinely determine lube thickness is demonstrated by the carbon spectrum of the thin lubrication and protective layer The XPS spectrum indicates the uppermost lubrication layer is composed of a graphitic type carbon as would be expected in DLC as well as hydrocarbon (probably environmental contamination), with the spectra showing a C 1s peak at 285eV binding energy as well as the fluorocarbon overlayer, with a well resolved peak at 293eV. The asymmetry at the high binding energy of the 285eV C 1s peak implies that the surface polymer also contains oxygen. The delicate nature of the fluorocarbon overlayer is demonstrated by the second C 1s spectra. After a short argon ion sputter the fluorocarbon lubrication layer has been removed, exposing the diamond like carbon layer.

Figure 4:C 1s X-ray photoelectron spectra of hard disk media (a) prior to sputtering, and (b) after a 30s sputter.

Summary

A high quality elemental concentration profile for a computer hard disk has been recorded using the AMICUS X-ray photoelectron spectrometer.

The features demonstrated for AMICUS include:

•      Good interface depth resolution with no decrease in resolution as a function of sputter depth.
•      Chemical state information from thin surface layer enabling determination of lube thickness.