Experimental Study of Structural Zone Model for Composite Thin Films in Magnetic Recording Media Application

Composite thin films are a new area of study with many applications, e.g. metal + oxide thin films in high density magnetic recording media. Engineering the processing, microstructure and properties of these thin films is of great importance. It has been found that microstructures of the thin films depend strongly on the oxide volume fraction and pressure during sputtering. Surface diffusion and self-shadowing effects are found to play important roles in determining various thin film microstructures under different processing conditions. Four characteristic microstructural zones could be generally distinguished: “percolated type”(A), “maze-like type”(T), “granular columnar type”(B) and “embedded type”a microstructure with metal nanocrystals embedded in the amorphous matrix (C). This modified structural zone model of composite thin films has been proposed as a supplement to Thornton’s model for sputtered thin film system. This research has been sponsored by Seagate Technology and the DSSC of CMU. INTRODUCTION Composite thin films e.g. metal + oxide thin films are widely used in high density magnetic recording media. These films are composed of the crystalline metallic phase and a secondary amorphous phase. Engineering the processing, microstructure and properties of these thin films is of great importance. The studies about composite thin films are limited and nonsystematic in literature. In addition, the real microstructures of composite thin films can be very complicated by varying various factors. Even a slight change of microstructure could cause a significant degradation of film properties. As a result, it is important to have a comprehensive understanding of how the composite thin films grow and how their microstructures evolve during sputter deposition, especially for composite thin films fabricated at room temperature for current perpendicular magnetic recording media. In order to predict the microstructures of composite thin films, it will be informative to construct a phenomenological structural zone model which includes the relative volume fractions of the two phases present. This supplements Thornton’s structural zone models for the sputter deposited thin films. In this paper, the major results based on the composite Ru + oxide thin films for magnetic recording media application will be discussed in details. It has been found that microstructures of the thin films depend strongly on the oxide volume fraction and pressure during sputtering. Surface diffusion and self-shadowing effects are found to play an important role in determining various thin film microstructures under different processing conditions. Four characteristic microstructural zones could be generally distinguished: “percolated type”(A), “maze-like type”(T), “granular columnar type”(B) and