Direct observation of padded slider tipping using the MRE cooling effect

The padded slider is a necessary design to extend the contact start-stop (CSS) solution to the regime of ultra-low head-disc spacing required for high areal density recording. In the design of a padded slider, the rear-most pads are recessed by an adequate amount from the slider trailing edge (TE), in order for the pads not to protrude below the read/write elements during flying. Such a geometry permits the head to rest on the disc in a tipped state, i.e., resting on its rear-most pads and the air-bearing surface TE. This may lead to stiction failure, as large high-pressure menisci may be formed underneath the nonpadded air-bearing surface near the TE. The occurrence of head tipping, while indirectly verified in earlier backward-forward disc rotation experiments, has never been directly observed. An elegant approach to directly monitor head tipping is to use the magneto-resistive element (MRE) cooling effect. The MRE is at a substantially higher temperature than the surrounding environment when a sensing current is passing through it. When a head with padded slider tips backward, its MRE is brought into close proximity to the disc surface, which leads to increased cooling of the MRE and, hence, a decrease in its resistance. Thus, by implementing a MRE resistance sensor, we have achieved the capability to determine the exact resting state of a padded slider, i.e., tipped or untipped, prior to each CSS cycle. Furthermore, by simultaneously monitoring the MRE resistance and stiction, we are able to conclusively establish the causal relationship between tipping and stiction failure of a padded slider interface.