Synthesis and Characterization of Amorphous Carbon Films for Heat-Assisted Magnetic Storage

Heat-assisted magnetic recording (HAMR) is a promising technology for next-generation magnetic storage devices that has the potential to increase magnetic recording density by orders of magnitude (up to 10 Tb/in2). By focusing a laser beam to rapidly heat the magnetic media above the Curie temperature, the coercivity of the magnetic domains over a small area can be sufficiently reduced to allow changes in polarization at a finer scale, thus enabling the reading and writing of data at much greater densities. Several factors, however, have prevented this technology from reaching the market. One major issue is the thermal stability of the amorphous carbon (a-C) overcoat on the magnetic head and its ability to protect critical components, such as read and write poles, near-field transducer, and waveguide, when heated to high temperatures during drive operation./nThis dissertation focuses on the optimization of a-C overcoats (also referred to as tetrahedral amorphous carbon (ta-C) due to the relatively high content of tetrahedral (sp3) carbon atom hybridization) deposited at very short deposition times (6 sec) and investigates the effects of heating on the nanostructure and intermixing with underlayers. As the overcoat thickness approaches only a few atomic layers, its performance and continuity become of concern, especially when exposed to higher temperatures. Since the tribomechanical and corrosion properties of carbon films have been correlated to the type of carbon atom hybridization, the choice of deposition technique and parameters to control the relative bonding content is crucial. Among the various deposition techniques, filtered cathodic vacuum arc (FCVA) was chosen to develop a-C protective overcoats. The energetic C+ ions film precursors in FCVA are especially beneficial for depositing continuous ultrathin a-C films with low surface roughness. Deposition parameters explored include the ion incidence angle and pulse substrate bias voltage under optimized duty cycle and ion fluence FCVA conditions, with the intent of minimizing a-C film thickness while maintaining adequate mechanical performance./nCross-sectional high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) were used to reveal nanostructure variations along the through thickness of a-C films and carbon intermixing with the substrate. The optimized coatings were deposited on an assortment adhesion (NiCr), buffer (SiN, TaOx), and base layers (Au, FeCo) common to HAMR magnetic media and heated for 30 min to simulate accumulation of heating damage. For a-C films 2-3 nm thick, the highest sp3 content was found in the bulk layer and were synthesized under FCVA deposition conditions of 65% duty cycle and -25 to -75 V substrate bias. The HRTEM and EELS analysis revealed no changes in thickness and minor structural changes in the a-C overcoat and generally small amounts of intermixing between the overcoat and the underlayers when operated in an inert hot environment. The findings of this dissertation suggest that proper optimization of such layered coatings can provide a viable solution to thermal damage of HAMR heads.

Advisor: Komvopoulos, Kyriakos