A Method for Laser Zone Texturing of Glass Based Magnetic Media Using Nd:Yag Lasers
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consistent "bumps" in a precisely controlled location on the Ni-P plated aluminum substrate. The most common lasers in production use are high-repetition-rate Q-switched infrared lasers (Nd:YAG, Nd:YLF or Nd:YVO 4). These lasers provide stable pulses at high repetition rates. The results are production systems with good process control and high throughput. These infrared lasers (X = 1064 nm) are not suitable for direct use with glass or glassceramic substrates. A novel method was developed which allows the use of existing laser systems with alternate substrates such as glass and glass-ceramic. A sputtered film that coats the surface of the substrate provides a texturing layer that absorbs the laser pulse and controllably forms regular, small bumps. Disks fabricated using this form of zone texture exhibit low friction and stiction values, even after many tens of thousands of continuous start-stop (CSS) cycles. EXPERIMENT Alloys of nickel and niobium were chosen for investigation because they form nonmagnetic amorphous films over a broad composition range when sputter deposited [4]. In 0 addition, the amorphous films have reported glass transition temperatures above 400 C, which make them suitable for the subsequent sputtering of magnetic films at elevated process temperatures. Films are deposited by dc magnetron sputtering onto polished alumino-silicate or borosilicate glass substrates. The cathode power is kept constant at a level that results in a deposition rate of 40 A per second. Thickness is controlled by sputter time. The argon gas pressure is 6.5 mTorr. (0.86 Pa). Texturing is performed using Nd:YVO4 lasers with pulse widths of 14 ns or 65 ns and spot sizes of 11 Igm and 10 jgm, respectively. Bump heights are measured using an optical interferometer microscope, MicroXam, manufactured by Phase Shift Inc. The measurement of bump height as a function of laser power and its associated slope, the bump height sensitivity, is made by texturing individual tracks of bumps, each at a fixed laser power. Continuous start-stop (CSS) testing is performed by configuring a spindle, a head and suspension assembly with a strain-gauge. The test sequence is to spin-up to operating speed, in this case 7200 rpm, maintain this speed for a short period, about 2 seconds, and then spin-down to a complete stop. The cycle is then repeated. For each cycle, the maximum static or dynamic friction is determined. The CSS graph is the plot of the maximum value for each cycle. The time at which the head remains in static contact with the disk surface is a few seconds. However, at every 5,000th cycle (or at least four times during the test) the time of static contact is increased to 2 hours to assess the static friction after an extended parking duration. RESULTS When irradiated with suitable laser pulses, thin films of Ni-Nb on glass produce reproducible and uniform bumps. The shape of the bump is primarily conical. This compares with the crater (or ridge) and sombrero shapes that are formed on plated NiP/Al substrates. Cross-sections from op
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