Nano-texturing of magnetic recording sliders via laser ablation
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To increase the storage density of hard disk drives, the flying height of the slider needs to be reduced to <10 nm. This requires super-smooth surfaces of the disk and slider. As the roughness decreases, stiction and adhesion are found to increase substantially leading to failures of the head/disk interface. Texturing the slider surface is a well-known approach to this issue. In this study we investigated laser ablation as a potential process for texturing magnetic recording sliders. It was found that straight laser machining caused unwanted re-deposition of material. These deposits could be significantly reduced by using a chemical etching enhanced laser process.
KeywordsLaser Ablation Hard Disk Drive Silicon Sample Ablate Material White Light Interferometry
In present day hard disk drives, the maximum storage density is in the order of 150 Gbits/inch2. In order to increase the recording density to approximately 1 Tbit/inch2, a reduction in flying height from currently 10 nm to 3 nm is required. A flying height of 3 nm requires that the surface of the disk is very “smooth”, with a peak-to-valley roughness in the order of <1 nm. As the roughness of the disk is decreased, stiction and adhesion are found to increase substantially during contacts between slider and disk. Contacts between a “super-smooth” head and disk are undesirable since the increased adhesion resulting from contact between smooth surfaces can lead to failure of the head/disk interface.
2 Texturing of surfaces to reduce friction
The use of reactive ion beam etching for texturing sliders require masking of the read/write element to prevent damage of the magnetoresistive read element in the head. Masking is cumbersome and time-consuming, and leaves a step increase in the surface height of the slider in the area, where the read/write head was masked. Thus, the question arises whether other manufacturing methods would be available for texturing of sliders with high throughput and without the need for masking the read/write element.
This paper is directed toward the study of laser ablation as a potential process for texturing magnetic recording sliders. We first investigate the feasibility of laser ablation of Al2O3TiC and then explore methods to vary the depth and surface characteristics of textured surfaces. Finally, we investigate the effect of power variation and partial laser light absorption to control the height of the surface texture achievable.
3 Experimental procedure
3.1 Laser ablation with decreasing laser power density
In the first set of experiments, the power of the laser beam was kept constant. After completion of a test, the power of the beam was decreased and a new sample was exposed.
Reduction of energy density on sample surface with attenuator plates
Number of plates
Energy density (mJ/cm2)
3.2 Chemical etching enhanced laser ablation
Water with various concentrations of acid was tested. The attenuation of the laser beam was found to be about 70%, resulting in an energy density of 700 mJ/cm2.
Texturing of alumina/TiC and silicon samples using laser ablation and liquid assisted laser ablation was performed in this study. Straight laser ablation was found to result in textured alumina/TiC with high peak-to-peak surface roughness and a high amount of build-up of deposits, depending on power and number of the laser pulses. Chemical enhanced laser etching was found to result in textured silicon surfaces with reduced peak-to-peak roughness and significantly reduced deposits of laser ablated material. These results for silicon encourage the study of chemical enhanced laser etching for alumina/TiC which is a common material for magnetic recording sliders.
It is likely that the use of lasers with shorter-pulse length will further reduce the deposition of unwanted material and thus yield improved textured surfaces.
RMS roughness of common sliders: 0.1 nm or less.
This research was supported in part by a grant from the Bavaria Technology Center, Germany.
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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