Abstract
The intense laser heating in heat-assisted magnetic recording (HAMR) has been a major hindrance to HAMR technology from becoming commercially viable. Thermal damage of the near-field transducer (NFT) and write pole (WP) embedded in the trailing edge of the magnetic head due to failure of the protective carbon overcoat after prolonged heating at an elevated temperature are major obstacles. Therefore, the main objective of this study was to develop an effective coating method for HAMR heads. This was accomplished by introducing a new class of layered coatings consisting of ultrathin amorphous carbon (a-C) overcoat, adhesion (SiN) layer, and buffer (NiCr or TaOx) layer sequentially deposited onto Au and FeCo base layers to mimic the layer stacking of NFT and WP elements, respectively. The structural stability of the a-C overcoats and diffusion characteristics of each comprising layer under conditions of heating at 350 °C for 30 min in an Ar atmosphere were investigated by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). For most stacking configurations the HRTEM/STEM and EELS results generally revealed some layer intermixing and minute carbon atom rehybridization in the heated a-C overcoats. The findings of this investigation suggest that further optimization of the developed layered coatings can provide a viable solution to thermal damage of HAMR heads.
Highlights
Amorphous carbon (a-C) films are commonly used in commercial hard-disk drives as overcoats of both magnetic heads and hard disks to provide protection against corrosion and mitigate surface damage from intermittent impact events
High-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS) were used to examine changes in the amorphous carbon (a-C) overcoat nanostructure with respect to atomic carbon bond hybridization as well as overcoat intermixing with underlying adhesion, buffer, and base layers due to heating under conditions resembling those encountered during steady-state operation of a heat-assisted magnetic recording (HAMR) head
Structure and contrast differences in the HRTEM images reveal the presence of the a-C overcoat and Au base layer; it is difficult to distinguish the SiN and NiCr layers based on contrast differences alone
Summary
Amorphous carbon (a-C) films are commonly used in commercial hard-disk drives as overcoats of both magnetic heads and hard disks to provide protection against corrosion and mitigate surface damage from intermittent impact events. Carbon films may disintegrate (oxidize) at temperatures as low as 300 °C in an atmospheric environment[13,14], which is within the steady-state operating temperature range of a HAMR head Both the mechanical performance[15] and thermal stability of the carbon overcoat depends on the content of tetrahedral (sp3) and trigonal (sp2) carbon atom hybridization. High-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS) were used to examine changes in the a-C overcoat nanostructure with respect to atomic carbon bond hybridization as well as overcoat intermixing with underlying adhesion, buffer, and base layers due to heating under conditions resembling those encountered during steady-state operation of a HAMR head. The HRTEM/STEM and EELS results of various layered coating configurations, i.e., a-C/SiN/NiCr(TaOx)/Au(FeCo), are contrasted to assess the integrity and protective capability of these new class of coatings under thermal conditions typical of HAMR heads
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