The effect of lapping method on the thermal reliability of a GMR head based on Black´s equation

The Black´s equation is used as the theoretical basis in this study to investigate the effect of a lapping technique on the thermal reliability of a GMR head. Current density is identified via experiments as the key parameter affecting the thermal reliability of a GMR head from the viewpoint of head lapping. Mathematical models are developed to connect the thermal reliability with the inherent features of the two lapping techniques: the electrical lapping guide (ELG) and the magnetic device resistance (device). It is found that in general the effect of lapping on thermal reliability is a function of the deviations of the stripe height, the GMRE resistance and the wafer process parameters, as well as the lead resistance. For constant I-biasing, wafer process variation has no effect on head thermal reliability for ELG lapping, but it does reduce the thermal life-time of a head for device lapping. On the other hand, wafer process variation deteriorates the thermal reliability for both ELG and device lapping if constant V-biasing is going to be used in a hard drive. Equal thermal reliability charts are provided to help select the lapping method for thermal reliability improvement based on the wafer process and lapping process capabilities