MR sensor oxidation mechanism at high temperature

A lifetime stress experiment was done on MR heads, followed by TEM analysis to decide whether higher temperatures induced structural degradation in the MRE stack. After 160 hrs, of testing at various bias currents, it was found that heads with sensor operating temperatures below 280/spl deg/C had little or no resistance increase, heads operated between 280 and 340/spl deg/C had varying degrees of resistance increase, and all heads operated above 340/spl deg/C burned out. The immediate cause of the resistance increase is shown to be oxidation of the MR film. A combination of TEM and electrical data, along with thermodynamic analysis of the TaN cap and the alumina 2nd gap, indicates that the likely mechanism is attack of the TaN cap by water vapor released from the alumina, followed by oxidation of the MR film.