Analysis of electrostatic discharges events in TMR and HGA levels

Electrostatic discharges (ESD) in the tunneling magnetoresistive (TMR) head and head gimbal assembly (HGA) levels are investigated. The quasi static testing (QST) on 40 HGA samples suggests the machine as a more aggressive ESD source than human. The average failure ESD voltage measured by the machine model (MM) is 0.78 V, lower than 1.94 V obtained by the human body model (HBM). This may well be understood by the higher failure current and higher energy drop in the TMR observed from the MM. The ESD equivalent circuits are then adjusted and modeled to generate the overdamped current profiles with similar peak currents to those obtained from the QST. The ESD simulation is further extended to the HGA level. It is found that the peak ESD currents are smaller than those in the TMR level. By a linear curve extrapolation, the predicted maximum ESD failure voltages are 0.95 V and 4.15 V for MM and HBM, respectively.