Investigation of contact deformation and wear characteristics of discrete track recording media
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- Yoon, Y. & Talke, F.E. Microsyst Technol (2011) 17: 733. doi:10.1007/s00542-011-1239-5
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The contact deformation and wear characteristics of smooth and discrete track recording (DTR) media are investigated using nano-indentation and nano-scratch testing. Plastic deformation of the land areas between adjacent grooves was found to be substantially larger than in the smooth regions of the same disk. Reciprocating wear tests showed that wear was more severe for discrete track disks than for smooth disks. To improve the tribology of DTR media, planarization of discrete track disks appears to be necessary.
Discrete track recording (DTR) technology has recently received renewed interest as a promising approach to increase the areal density in hard disk drives (Weller and Moser 1999; Greaves and Muraoka 2006). In DTR, adjacent tracks are separated from each other by circular “grooves” causing a reduction in “cross-talk” and an improvement in the signal to noise ratio (SNR) (Wachenschwanz et al. 2005). DTR technology has the potential of achieving areal densities in excess of 1 Tbit/in2. One of the key requirements for achieving areal densities in excess of 1 Tbit/in2 is that the separation between the recording slider and the disk should be on the order of 1 nm (Juang et al. 2007). The reduction of flying height from presently 5 nm to the 1 nm regime increases the likelihood of intermittent contacts, loss of data and failure of a hard disk drive. To prevent failure, improvements in the wear characteristics of the head disk interface are essential. Many researchers have studied the effect of slider/disk contacts (Komvopoulos 2000; Wang et al. 2001; Kohira et al. 2001; Xu et al. 2002) for conventional “smooth” media. However, little information is available on the problem of slider/disk contacts in the case of DTR media. Gong and Komvopoulos investigated numerically the contact deformation of patterned media (Gong and Komvopoulos 2003). Using finite element analysis, they observed that high pressure peaks at the edges of the bit pattern are present. Nunez et al. (2008) simulated numerically the contact behavior of patterned media after planarization. They found that planarization improves the contact resistance compared to non-planarized patterned media since the planarization material participates in supporting the applied load during contact and reduces the contact stress of the patterned surface.
In this paper, the contact deformation and wear characteristics of smooth and DTR media are investigated using nano-indentation and nano-scratch testing (Jiang et al. 1995; Anoikin et al. 1998; Li and Bhushan 1999; Sundararajan and Bhushan 1999; Bai et al. 2000; Bhushan 1999; Huang et al. 2001). The deformation of the land area between adjacent grooves is investigated as a function of land width and applied load. Comparison of the results with smooth media is performed. The dependence of wear characteristics on track geometry is investigated. Atomic force microscopy (AFM), in situ scanning probe microscopy (SPM) (Bhushan 2001) and scanning electron microscopy (SEM) are used to investigate wear and damage of individual discrete tracks.
2 Experimental procedure
2.1 Contacts between slider and DTR disk
In DTR, a slider flies over thousands of parallel discrete tracks during reading and writing.
2.2 Nano-indentation and nano-scratch testing
2.3 Reciprocating wear testing
3 Experimental investigation
3.1 Wear of DTR media due to contacts between slider and disk
If similar touch-down experiments were repeated on the same disk in the area outside of the discrete track region, no damage or wear was observed. Since the material properties of the disk are the same in the DTR area and the “smooth” area, it is apparent that the presence of grooves affects the contact and wear characteristics of DTR disks.
3.2 Contact deformation of smooth and discrete track surfaces using nano-indentation and nano-scratch testing
Characteristics of two different types of discrete track disk surfaces
Discrete track A
Discrete track B
Land width (W)
Groove depth (D)
Track pitch (T)
Ratio (D/W) (groove depth/land width)
3.3 Wear characteristics of discrete track media using reciprocating wear testing
4 Numerical investigation of static contact behavior
To correlate our experimental results with numerical predictions, a finite element analysis was performed for the static contact deformation using the commercially available software LS-DYNA.
Material properties of diamond tip and different layers of discrete track disk (Ovcharenko et al. 2010)
Hard magnetic layer (20 nm)
Soft magnetic layer (60 nm)
NiP (200 nm)
Yield stress (GPa)
5 Summary and conclusions
An experimental investigation of contact deformation and wear characteristics of discrete track and smooth disk surfaces was performed. Damage was found to be much larger in the land areas of discrete track disks than the smooth areas of the same disks. It is apparent that the stresses in the land areas of a discrete track disk are higher than the stresses in the smooth region of a disk under identical loads. The land area showed substantially higher wear and damage than the smooth areas outside the discrete track region. The latter results are a consequence of the presence of the unsupported edges of the narrow land areas of individual discrete tracks. From the data obtained we conclude that wear and damage increase with decreasing land width of discrete track disks. Numerical calculations are in agreement with experimental observations.
The generation of wear particles in discrete track disks increases the possibility of failure of hard disk drives during contacts between slider and disk. Therefore, to improve reliability and durability of DTR media, contact deformation and wear characteristics of discrete track media must be improved. Planarization of discrete track disks appears to be a necessary step towards improving the tribological properties of discrete track disks.
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