Aug 14, 2002
Ultrathin layers safeguard hard drives
Scientists have developed a technique for depositing ultrathin layers of nitrogenated carbon (CNx) onto hard-disk substrates. The researchers, from Northwestern University in the US, Tianjin Normal University, China, and IBM Storage Technology Division, US, used a pulsed d.c. magnetron sputtering system in which they both tilted and rotated the substrate.
"There are other ways to achieve smooth, dense and pinhole-free protective overcoats but none of them are compatible with current manufacturing practice," Yip-Wah Chung of Northwestern University told nanotechweb.org. "All of the major manufacturing steps in laying down coatings on hard disks are done by sputtering. The proposed method appears to extend the utility of sputtering to the one nanometre scale."
For the computer hard-disk industry to increase storage densities to 1 Tbit/sq. in., it must reduce the magnetic spacing - the distance between the read/write head and the top of the disk - to 6.5 nm. That means reducing the thickness of the protective overcoats on the head and the disk to about 1 nm.
If CNx is to be used in such thin layers, the coating must be of an excellent quality. With this in mind, the scientists optimized the growth conditions for CNx coatings during magnetron sputtering by altering the bias, tilt and rotation of the substrate.
The researchers found that tilting the substrate to 45°, rotating it at 20 rpm and applying a substrate bias in the -100 to -150 V range increased the smoothness of the coatings. What's more, 1 nm thick CNx coatings prepared with substrate tilt and rotation provided double the corrosion protection of coatings prepared with a standard substrate arrangement.
"This work has been funded by industrial members of the Information Storage Industry Consortium (INSIC), and we certainly hope that members will implement this in actual production lines, with minor modifications," said Chung. "Of course, we still have a few tricks up our sleeves, and we hope to further improve film properties with other enhancements."
About the author
Liz Kalaugher is editor of nanotechweb.org.