Hard protective coatings on magnetic recording heads

Abstract

Recently, carbon nitride (CNx) has already emerged as a new material of both fundamental and application interest. In particular application of protective coatings on magnetic recording heads, CNx has potential to replace diamondlike carbon (DLC) which has been widely employed. In this study, the nitrogen content dependence of the structure and the mechanical properties of ion beam deposited CNx films was investigated. Results showed that when the nitrogen content increased from 0 to 22.8 at.%, a diamondlike-to-polymeric transition in the film structure occurred. Related to this structural change, a film with a higher N content has lower electrical conductivity, lower hardness, lower damage threshold in a scratch test, weaker adhesion to the silicon substrate, and may have higher toughness or ductility as consequences. By controlling the level of N incorporation, the electrical conductivity of the film could lie in a suitable range to prevent from failure in reading signals or dielectric bread down. The hardness of the film can also be adjusted within the range of 24.3 - 11.7 GPa to suit various requirements for surface protective of devices. Furthermore, CNx films with higher N content are less brittle, consequently suppress the formation of debris, and prolong the lifetime of the head. The friction of all the CNx films is as low as that of the hydrogenated diamondlike carbon (DLC) films. Low friction favors the reduction of stiction, which is the resistance against the rotation of the hard disk when it is just powered and in contact with the head. In addition, the mechanical properties of hydrogenated DLC films prepared by electron cyclotron resonance deposition and direct-ion-beam deposition were measured by the nanoindenter, which are currently used as protective coatings of magnetic devices. Moreover, the hardness of various kinds of films, expected to have great potential as protective coatings, were measured. They include CNx/TiN multilayers, cubic boron nitride (c-BN), boron-silicon-nitrogen (B-Si-N), boron-carbon-nitrogen (B-C-N) and boron-carbon-nitrogen-oxygen films (B-C-N-O).