Failure analysis of ultrasonic pitting and carbon voids on magnetic recording disks

In this study, a new electrical tagging pattern system was used in the failure analysis to mark defect sectors, and with Kerr magneto-effect imaging, the defective sectors were effectively located for further failure analysis. The results of the failure analysis of ultrasonic pits and carbon void defects on disks showed that there was 30–40% loss of the recorded magnetic bit signal due to an increase in the gap between a recording head and a hard disk surface with the defects. Furthermore, the experiments conducted to improve disk performance by reducing the ultrasonic pit defects showed that low ultrasonic power for disk cleaning reduced ultrasonic pits significantly. Moreover, removing the biasing voltage on the substrate reduced carbon void defects significantly. The average number of the carbon voids per surface was reduced from 4 to 0.5, and the average size of the carbon voids was reduced from 8 to 3.8 μm.