Deborah S. Schnur

Inspection of pole tip diamondlike carbon wear due to heater-induced head-disc contact

Heater-induced head-disc contacts can cause highly localized wear of the pole tip. We found that scanning electron microscopy and low beam-current focused ion beam imaging are suited at providing a map of the entire pole tip surface and quickly identify the location and shape of heater-induced wear. For longitudinal heads, the imaging can reveal detailed structure near the writer gap. By measuring the topography near the pole tip using atomic force microscopy (AFM), one can retrieve quantitative wear information. Using unburnished parts as controls, the accuracy of the AFM method reported here is about 1nm. We found transmission electron microscopy and Auger electron spectroscopy to be less effective in quantifying wear.

Discharge mechanism for electrostatic fly control

Electrostatic force has been proposed for use in fly height reduction and control. The dominant failure mode is electrical discharge at the head-disk interface (HDI) due to field emission. Ballast resistor films have been used for limiting field emission. We applied this idea to the HDI by depositing a thick coating of diamond-like carbon (DLC) on the slider. A typical slider has 25 /spl Aring/ of DLC and exhibits breakdown voltage of less than 3 V on product media. When the coating thickness was increased to 430 /spl Aring/, it was sufficient to prevent discharge up to 6 V and allowed approximately 33% clearance reduction without crashing or discharging. The result is in good agreement with fly height modeling, which takes into account the head-disk electrostatic force.

Electrical Breakdown in Electrostatic Fly Control

As areal density increases and fly height decreases in hard disc drives, it becomes more difficult to achieve a reliable flying interface between the recording head and the disc. Manufacturing variations, environmental conditions and other factors can cause mechanical spacing losses. One method to compensate for these losses is to control slider clearance using electrostatic force. An attractive force between the slider and the disc can be generated by grounding the disc and applying voltage to the entire slider body or a dedicated electrode. If the applied voltage exceeds the breakdown voltage of the head-disc interface (HDI), however, the resulting current flow will cause damage to the head and disc and ultimately cause the head to crash. A series of experiments were performed on flying heads and a MEMS small-gap tester to determine the nature of the current flow and the effects of head coatings and disc lubricant on breakdown voltage. The results support field emission as the current flow mechanism. In addition, a thick diamond-like carbon (DLC) coating on the slider or electrode increases breakdown voltage and may prove to be an enabler for electrostatic fly control. In comparison, lube appears to have only a secondary effect on electrical breakdown.Copyright

Dynamic Take-Off Study Using An Optical Fly Height Tester

We showed a new method of measuring air bearing take-off performance. The procedure involves spindle speed ramp up as during CSS. The data revealed the intrinsic behaviors for different air bearing designs and are in good agreement with both air bearing modeling and CSS tests over magnetic media. The method is an effective tool in evaluating air bearing take off performance.