Electron Gun Induced ESD Damage on GMR Recording Heads

抄録

An investigation was conducted to determine if electron gun from Scanning Electron Microscope (abbr.SEM) induces electrostatic discharge (ESD) causing hard disk drive Giant-Magnetoresistive (abbr.GMR hereafter) sensor failure. We used both customer Shippable and returned single-spin valve (〜10 GB / sq.in areal density) head gimbal assembly (Abbr. HGAs) in this study. All shippable parts were first characterized on a magnetic test Spinstand as well as using quasi-static test bed. Results show that GMR sensor will melt as Low as 12 kV with brightness auto-contrast. However, this can not be reproduced consistently with the shippable control group which was subjected to even greater stress twice. We further examined all SEM work and concluded that they are lot dependent. This suggests some devices have sub-threshold ESD stress lebel which become enlarged by electron beam (abbr.E-beam) to become failed devices. We also searched through our archive and tabulated our ESD failures. Most appeared to come from HGAs that had low electrical head output at drive qualification already implying they may have been slightly EOS damaged or marginal. All returned heads for low head output amplitude are likely be destroyed during bombardment of electrons. It is recommended that proper care to connect the sample to ground through shunting to make it charge free is one way to minimize the ESD exposure. Three are those "sub-threshold" stressed GMR films: E-beam becomes a controlled energy source to stress the films as a failure analysis tool. Certain marginal heads when subject to the external field will weaken if not lead to catastrophic ESD failures. On the other hand, "high threshold" GMR heads are more robust.