Surface Corrosion of HDD Media and Subsidiary Particle Formation Due to SO2 Gas Adsorption

Abstract

The storage capacity of hard disk drives (HDDs) for personal computers has increased more than 10,000 times in the past decade. Meanwhile, the gap between the disk and the magnetic head (flying height) has decreased from sub-micrometers to a few nanometers. The lower flying height leads to more sensitive disk-to-surface contamination linked to fatal failures. Many studies have reported that disk surface contamination is related to the adsorption of volatile organic compounds (VOCs) and the corrosion of the magnetic layer of the disk. However, surface contamination derived from sulfur dioxide (SO2) gas in the surrounding area has been discussed insufficiently. In this work, to ascertain the mechanism of disk surface contamination and the subsidiary particle generation, HDD disks were intentionally exposed to SO2 gas, followed by an evaluation of disk operation performance during endurance testing. After the series of endurance tests, a large quantity of sulfate and nickel, which is a main component of the disk substrate layer, was detected on the SO2-contaminated disk surface, as well as a small quantity of cobalt, which is a main component of the magnetic layer. From these findings, the mechanism of surface contamination of HDD disks in the coexistence of SO2 and water was inferred. Nickel is supplied from the substrate layer to the top layer through holes and cracks in the films of disks because of the corrosion triggered by adsorbed water. High temperature and humidity causes the desorption of SO2 from SO2-contaminated disk surfaces to react with nickel. Eventually, the products of nickel sulfate are precipitated on the surface to be released in the form of particles by contact with the head.