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 th e MRE stack. After 160 hrs, of testing at various bias currents, it was fou nd that heads with sensor operating temperatures below 280 degrees C had li ttle or no resistance increase, heads operated between 280 and 340 degrees C had varying degrees of resistance increase, and all heads operated above 340 degrees 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 a thermodynamic analysis of the TaN cap and the alumina 2( nd) gap, indicates that the likely mechanism is attack of the TaN cap by wa ter vapor released from the alumina, followed by oxidation of the MR film.