Contact Wear-Tolerant Two-Stripes Nanoheater Assembly for Small-Spot Heating and Thermal-Assisted Magnetic Writing on Disk.
Original Publication Date: 2002-May-02
Included in the Prior Art Database: 2003-Jun-20
The use of contact or near-contact nano-heater stripes for thermally-assisted recording (TAR) is described. In TAR local heating of a spot on a high-Hc disk is utilized to facilitate bit writing by a magnetic field from a write head. The present invention illustrated schematically in Fig. 1 utilize heater stripes for simultaneous heat and magnetic field delivery to a small spot on the disk. Prior arts (for example ) rely on heater transfer across gaseous media via near-field coupling/gas conduction effects or use a sub-wavelength optical aperture illuminated with a laser or other forms of optical sources for localized heating of the disk. The present invention differs from prior arts in several respects: (a) Contact: Prior arts taught "low-flying" for nanoheater-type TAR. Contact heating, either solid-solid or solid-liquid lubricant-solid contact, provides much improved heat transfer efficiency from the moving nanoheater to the disk. Estimates show that conventional heat transfer mechanisms involving gas conduction or Planck's radiation heating are not sufficient to heat up the disk spot by more than about a hundred degrees C under normal circumstances of low flying at a few nm. Contact heating provides a much needed improvement of heat-transfer. However, contact has several problems, including wear and debris-generation. Wear can be greatly reduced by reducing the contact pressure and by designing the write head to be wear-tolerant, i.e., some degree of wearing is permissible by design and also by adjusting the operating conditions (like write current) as the wear goes on with time. (b) Wear-tolerant: The heater stripe(s) should be made of conductive yet good tribological materials that wears slowly and do not produce harmful debris. Carbonaceous materials, including diamond-like-carbon, graphite, and carbon nanotubes, would be ideal for such tribological materials, but metal alloys, e.g., Ni and Fe alloys may be acceptable. Less wear of the heater stripe(s) is achieved by lowering the gram load force of the stripe(s) onto the disk, and by lowering the frictional coefficient between the stripe(s) and the disk top surface. Furthermore, the stripe(s) heating design is wear tolerant in the sense that the heat and magnetic field delivered to the disk are not quite sensitive to the heights of the stripe(s) and some degree of compensation for the heat and field magnitudes can be achieved by adjusting the current(s) to the stripe(s). (c) Heat and field delivery: Although heat can be delivered by contact conduction from one heater stripe to the disk spot and typically a 1-mW heater of dimensions on the order of tens of nm would be enough to produce adequate heating of the disk spot (typically a few hundred degrees C peak temperature), the need to switch the current direction for writing produces temperature transients that lasts at least ~1 ns. Such excessive temperature transients illustrated in Figure 2 can be greatly reduced by having at least 2 current stripes, as shown schematically in Fig. 1. Here, the main heating is provided by Heater Stripe 1 (HS1) which can be heated by dc or ac heating. Following closely is Heater Stripe 2 (HS2), which is located near the trailing edge of the slider and provides both the heating boost and the magnetic field gradient that actually writes the transition at the proper overlap location of thermal gradient and field gradient. A simple estimate using Ampere's Law indicates that a current of say 30 mA at HS2 of stripe height about 30 nm can produce a field of thousands of Oe at a distance of say 3 nm away where we locate the magnetic layer of the disk in close proximity with HS2. Hence, HS2 can provide both the heating and the writing field. By locating HS2 near the trailing edge, the heating at HS2 is localized and efficient, and there is no significant downstream heating of the disk to cause appreciable thermal erasure. Figure 3 shows the predicted thermal erasure profiles for nano-heaters with a fixed width of 50 nm. As the effective length of the nano-heater increases, side track erasure becomes more severe. By using HS1 as the steady main heater, the temperature transient effect of current reversal at HS2 during the writing procedure is minimized.