Plastic substrate preembossed 100 kbpi, 3.4 μm track width magnetic disk (abstract)

To achieve higher areal recording density and at the same time very low cost magnetic media, a preembossed disk is proposed in which servo marks, header signals, and ROM data are formed on a plastic substrate by an injection method. Those media give very attractive features to reduce track pitch comparable to optical disks. A very expensive and low throughput servo writer is not necessary by using such preembossed servo marks. To realize the preembossed disk, a magnetic layer should be prepared by low-temperature deposition. In this paper, we studied the sputtering process and suitable magnetic materials such as CoCrPt/Cr film on plastic substrate. Plastic substrate was made by amorphous polyolefin (APO). The under layer (Cr), magnetic layer (CoCrPt), protective layer (C) are formed by magnetron sputtering without substrate heating. Effects of Pt content, thicknesses of magnetic layer, and under layer were investigated. Results showed that coercivity was achieved to 1900 Oe at Pt about 20 at. %, 30-nm-thick magnetic layer and 200-nm-thick under layer. Recording characteristics of the disk were measured by an MR head. The head has a track width of 3.4 μm and a shield distance of 0.35 μm. The results were D50=100 kfci, C/N=47 dB (at 75kfci), and a resulting density of 0.7 Gb/in2. The signal output from the prepit shows 80% maximum value compared with conventional magnetic bits.