Nanotech 2010

Characterization of Nano diamonds development in hard disk manufacture

A.H. Tan, J.T. Chen, J.Y. Yang, C.K. Lee
Ching-Yun University, TW

Keywords: characterization, nano diamonds, hard disk manufacture


Magnetic storage hard disk drives (HDDs) have been used widely to provide storage of digital information in modern computer systems and consumer electronic products. Consequently, developing a higher recording density on the disk media with good head read/write performance becomes more important to meet future requirements. Hard disk substrates play a key role in the data storage process of HDDs. However, a potential failure mode exists to the head burnish induced clearance requirements by variation induced by substrate nano-asperities. These asperities are very small measuring 2-3nm high and 40-80nm wide. Developing a polish process to eliminate surface asperities and residual surface defects on the glass substrate media in Perpendicular Magnetic Recording (PMR) disks processing is therefore a necessity to meet the challenges of future technology. Currently, the most important leading candidate is nano cluster diamond (NCD) abrasive which is a synthetic diamond which is created in an explosion process. A great effort is now underway to modify these NCD clusters to reduce light scratches and asperities in the PMR media polish process. Three distinct diamonds of NCD-90, NCD-80 and NCD-70 were utilized in this study. The major difference among these three distinct cluster diamond types is the diamond contained percentage amounts. Because of the differing diamond percentage content, this in turn induces a different structure and changes the polish properties. HRTEM, XPS, Raman, BET, AFM, Optical Surface Analyzer and disk defect tester were used for the diamond particles, polished substrate and disk analysis. Based on analysis results, the percentage of crystalline diamond in NCD-90, NCD-80 and NCD-70 solutions is 90%, 80% and 70%, respectively. NCD-90, NCD-80 and NCD-70 diamond particles exhibit an average primary crystalline size of 8nm, 6nm and 6nm. The NCD-70 graphite/diamond ratio is 4.45 which is higher than that of NCD-80 (3.29) and NCD-90 (2.88). The NCD-70 slurry generates relatively smaller Ra’s as compared to NCD-90 and NCD-80. This is due to the lower diamond contained percentage with smaller particle density and higher particle surface area in NCD-70. Its lower polish penetration depth causes a smoother polish surface, which in turn reduces surface scratches thus improving the disk defect. Additionally, since the NCD-70 cluster is a looser bonded formation than NCD-90 and NCD-80, its clusters will break down when acted upon by shear stresses, reducing the potential for scratches. On the other hand, all of the three slurries show similar polish stock removal amounts. There are two reasons for this affect. First, the contribution of NCD to beneficial polish stock removal amount is inherent in its particle density. The second contributing factor to polish removal performance is controlled by the particle surface area itself.
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