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Method in Tailoring ABS Roughness for Improved Slider Flyability Disclosure Number: IPCOM000124906D
Publication Date: 2005-May-11
Document File: 7 page(s) / 415K

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Due to ever demanding increase of aerial-density of magnetic Hard Disk Drive (HDD). Read and write magnetic element on a slider needs to fly lower and lower into the regime of near-contact recording (at 7 nm FH). Ever greater challenges in designing and fabricating sliders that fulfill such requirements include how to account for Van der Waals interaction between HDI interfaces, and stiction accompanied by the reduction of disk surface roughness required for lowering FH. There have been many proposed solutions for reducing ABS stiction in general including lithography methods for diamond-like carbon pads on ABS, and textured disc. For ultra-low FH applications, one of the proposed solution is to increase the roughness of ABS pad. An increase in ABS roughness is expected to reduce surface near-contact area when transient near-contact was encountered, during which stick-slip phenomenon can cause track mis-registration, spacing modulation and bit slip due to repeated stick-and-slide. In this disclosure, we describe a method to roughen the ABS surface by varying etch angle using an Ar plasma from an Ion Beam Source. The relative etch rate of TiC and Al2O3 in slider substrate is sensitively related to angle of ion beam incidence angle. Tuning this relative etch rate will therefore adjust relative elevation of the two constituent on the substrate surface and roughening the ABS.

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Method in Tailoring ABS Roughness for Improved Slider Flyability

   When the slider flies on the disk, the spacing between the disk and slider can vary depending on the wavelength content of the disk surface. For a given wavy surface the spacing modulation is very dependent on its wavelength. Typically three wavelength regions can be identified. When the wavelength is very small the slider does not respond and the spacing modulation is due entirely to the disk waviness. Short length waviness is also called roughness or microroughness. When the disk wavelength approaches the resonant wavelength of the slider the slider oscillates and the spacing modulation reaches a maximum. Finally, when the wavelength is very long, the spacing is preserved because the slider response is quasi static, as when the slider responds to changes in crown curvature. In this regions dynamic effects are not important. These response regions can be illustarted in Figure 1 for a typical slider. Resonance occurs near one-hundred micrometers wavelength. Beyond five-thousand micrometer wavelength there is little spacing modulation.

In an actual disk all wavelengths exist together. However the amplitude of the waviness drops with reduced wavelengths. When the amplitude reduction follows a quadratic power law the disk surface is called Gaussian. The excitation produced by this surface on the slider can be obtained from Fig. 1 and is shown in Fig. 2. The spacing modulation is measured by its root mean square value or rms. Notice that the spacing modulation grows quickly around the resonance wavelength and that saturation occurs at about five-thousand microns wavelength.

Under very low fly height conditions the slider is not always separated from the disk. Contact with disk increases with low fly hight and rougher disks. The first plot above showed that in the low wavelength range the flying slider is not affected. However, under contact conditions the slider stability is greatly affected by the microroughness of the surface. Smooth surfaces produce high friction with the slider. High friction causes intermittent stiction and slip between the disk and the slider. This stick-slip behavior can cause instabilities in the slider to disk spacing that may lead to catastrophic failure. Rougher disk surfaces reduce the friction and thus diminish the likelihood of failure.

Similarly, friction and stiction benefit from low wavelength can be equally reduced by roughening the slider surface. A key contribution of the present invention is the ability to eliminate or mitigate stick-slip conditions between the disk and the slider by tailoring slider ABS roughness when the fly height is so low that disk contact is allowed. This is the case of many of our current and Future designs.


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Figure 1: Slider response to interface roughness, specifically to periodicity of disk waviness


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Figure 2: Accumulated slid...