Dynamic in-situ measurements of head-to-disk spacing

Abstract

The read signal from a magnetoresistive (MR) head is used to measure the dynamic head-to-disk spacing (flying height) inside of an operating disk drive. Changes in flying height modulate both the envelope of the read signal and its mean value. While the envelope is related to the magnetic spacing, the mean value is a function of the thermal spacing. The thermal spacing signal is the result of Joule heating whereby some of the thermal energy generated in the MR head is dissipated into the air film between the head and disk. Changes in head flying height alter the heat transfer and hence the temperature and resistance of the head. The thermal and magnetic signals are separable and give complimentary information about the flying height. To accurately measure flying height changes using the thermal signal when the head is inside a disk drive requires that the signal distortion caused by the head preamplifier and high-pass filter be corrected. The thermal signal, unlike the magnetic signal, is not sensitive to track misregistration making it more accurate for dynamic flying height measurements. In-situ dynamic flying height measurement results using both thermal and magnetic methods are discussed.