Production and characterization of asymmetric laser-textured bumps for magnetic media

Abstract

Asymmetric “S-shaped” bumps are formed in the presence of a significant temperature gradient on the disk surface during the laser-texture process. The production of S-shaped bumps is of particular interest for low-glide magnetic media, for which the desired high bump densities require the use of high spindle speeds. The formation of S-shaped bumps as a function of laser-pulse energy (0.1–4.5 μJ), pulse width (350–5000 ns), and rotation speed of the spindle (1184–4737 rpm) was investigated. The results show that within the accessible energy range the peak-to-mean bump height increases with the pulse energy. For a constant pulse energy, larger bump heights are obtained for shorter pulse widths. In addition, higher bumps are also obtained for slower spindle speeds if the pulse width is 2000 ns or longer, but this changes as the pulse width is reduced. The full-width-at-half-maximum diameter of the trailing bump cone monotonically increases with the pulse energy for 350–1000 ns pulse width, but shows a local minimum for 2000 and 5000 ns pulse width, which is shifted to smaller pulse energies as the spindle speed is reduced. An investigation of the height shrinkage during the sputter process showed that the shrinkage is larger for 15 nm high bumps textured with 500 ns pulse width and 0.26 μJ pulse energy than for bumps of the about the same height textured with 1000 ns pulse width and 0.40 μJ pulse energy.