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Nano-competence for hard thin films

January 23, 2003

The good old magnetic disk drive is holding up well in the face of competition from optical storage media like CD-ROM and DVD and semiconductor flash and smart cards. Major advances are still being made, with typical storage densities doubling roughly every year and a half. When IBM launched the first magnetic disk drive on the market in 1956, it was a monstrous piece of equipment providing five megabytes of storage on a stack of 50 rotating disks, each 60 centimeters in diameter. By contrast, IBM's new microdrive is the smallest ever, no bigger than a matchbook and weighing only 16 grams, yet providing two hundred times more capacity, at one gigabyte. Manufacturers are still using hard disks in their products, not only in computers but also in video recorders, digital cameras and portable MP3 players, because of their quick access and high read and write speeds.

But the higher the storage density of the disk, the smaller the distance must be between the read / write head and the surface of the disk. This applies similarly to the protective coating applied to the magnetic medium to guard against mechanical contact with the head and in order to prevent deterioration caused by oxygen in the air. The technique most commonly used in the past is magnetron sputtering. It will soon no longer be adequate to the task of applying the new extremely thin coatings, only two or three nanometers thick, in the required quality. A new process being developed by scientists at the Nanotechnology Competence Center for ultrathin functional coatings in Dresden, in collaboration with IBM, is capable of producing the necessary robust, dense layers of diamond-like carbon. The coating's low mechanical friction is essential to many other applications in microsystems engineering - not only in the manufacture of hard disks.

"Instead of using carbon nitride, which was employed in the past for such protective coatings, we use a filtered arc discharge plasma generating system to deposit amorphous carbon," explains Dr. Peter Siemroth, project manager at the Fraunhofer Institute for Material and Beam Technology IWS, which has been coordinating the activities of the competence center for over four years. "In this method, an electric arc struck in a vacuum vaporizes material off the graphite electrodes, which then builds up as a super-hard coating on the disk in a controlled process." The plasma is directed using magnetic fields. Microscopic particles produced by the arc discharge, which would reduce the smoothness of the coating, can be completely filtered out with its aid.

Fraunhofer-Gesellschaft