Repeatable and Non-repeatable FH Modulation Study Near Head Contact

The lower head-media spacing (HMS) is always expected for achieving better recoding performance at high linear density. Besides the efforts to reduce the overcoat thickness of head and media, the low flying height (FH) and smaller FH modulation (FHM) are necessary to ensure the low HMS and good interface reliability. In the current HDD, the FH change is measured from the readback signal by the Wallace spacing loss equation. The real-time dynamic FH signals consist of repeatable and non-repeatable FH changes, or FHM. The repeatable FHM (RFHM) correlates with the disk morphology variations. It usually has the variation of transition parameter a inside. Because the change of a is the noise of the RFHM, it has to be very careful for the compensation of the RFHM by thermal FH control. Otherwise, it may cause unexpected head-disk contact. The non-RFHM (NRFHM) measurement is able to remove the media-related noise, which has a good testing accuracy of around 1 Å. This paper studies both RFHM and NRFHM characteristics of four types of sliders with different air-bearing surface designs.