Study On The Lifetime And Failure Mechanism Of Dynamic Flying Height

Electromigration（EM）is defined as a mass transport phenomenon due to theelectrical current. It is one of the most dominant factors to cause the failure inmicroelectronic components. With miniaturization and complexity tendency of devices,the dimension has a significant shrink and the current density has risen sharply. Thevalue of the average current density in devices has exceeded the threshold of EM, andthermomigration（TM）is often accompanied by the occurrence of EM, so the study onEM behavior is of great significance.Dynamic Flying Height（DFH）is an important internal stucture in hard diskrecording head, and it is very important to do the reliability assessment for DFH,especially the lifetime prediction. The method of increasing stress （current andtemperature）, which is called “acceleration test”, is usually used to predict the lifetimein normal hard disk working conditions in engineering. The failure mechanism analysisof acceleration test under current and temperature coupling field takes a moreintensified analysis on EM problems.Two typical DFHs were selected: Ta/W/Ta DFH and Ta/NiCu/Ta DFH. In order tosummarize the role of EM and TM during the acceleration test and predict the lifetimeaccording to the Black equation, we study the failure model and mechanism of DFHthrough analysis and comparison between direct current（DC）acceleration test andalternating current（AC）acceleration test.By acceleration test study, the phenomenon was found that the failure mode ofTa/W/Ta DFH is typical EM. In DC accelerated stress test, Au atoms of DFH leadframemigrate from anode to cathode in directional movement by electronic wind force,resulting in Au hillocks on DFH coil surface and black holes in left corner of DFHleadframe. In AC accelerated stress test, the AC signal can entirely or largely suppressthe occurrence of EM, which means there is no Au hillocks and holes failure defects,this validate the conclusion that the failure mode of Ta/W/Ta DFH is typical EM.By acceleration test study, the phenomenon was found that the failure mode ofTa/NiCu/Ta DFH is electric and temperature coupling failure. In DC accelerated stresstest, some inner holes defects produced by Ni and Cu atoms migration in bothhorizontal and vertical directions were found, and their distribution has obviousorientation, that means the number of defects which closer to the cathode side are morethan the side closer to the anode. In AC accelerated stress test, AC signal also cancompletely or largely suppress EM phenomenon, so resistance curve of DFH showed asignificant delay, and lifetime has increased nearly three times. The distribution of voidsin AC test has no obvious orientation. According to Black equation, Ta/NiCu/Ta DFH was conducted a lifetime prediction, and its lifetime is beyond five-year basic electronicproduct life standards.