Head reliability of AMR sensors based on thermal stress tests

摘要

Tape storage drives use robust shielded anisotropic magnetoresistive (AMR) read sensors. Under normal operating conditions, changes in sensor properties are undetectable. To estimate end-of-life conditions, sensors are exposed to elevated temperatures, and changes in relevant physical parameters are measured. Then, using thermodynamic models, these measurements are extrapolated to normal operating conditions. Thermal stress experiments using elevated electrical currents for heating were conducted on AMR read sensors designed for use up to about 200 Mb/in.2 in tape storage drives. Physical parameters that are relevant to tape-drive function include stripe resistance, AMR amplitudes and asymmetries, and stripe and shield oxidation. Changes in these parameters were measured as functions of time and temperature. The experimental results were fit to thermodynamic models, which were then used to extrapolate the observed changes to normal operating temperatures and extended times. The data shows that, at the lowest temperatures, the important processes are stripe oxidation and annealing-induced changes in magnetic characteristics. For the materials studied, the projected time-to- failure for use in a drive is greater than ten years.