Atomic Assembly of Magnetoresistive Multilayers

The continuing ability to create ever higher performance microelectronic and photonic devises has underpinned many of the most important technological developments of the last 50 years. Many of today's nanoscopically structured devices are made by controlling the condensation of an atomic or molecular vapor at the surface of a substrate. The shapes of the resulting objects and that of the numerous materials within them are controlled using patterning methods and selective etching methods which have been facilitated by rapid advances in lithographic technologies. As technologists seek to incorporate new materials with novel functionalities into their microsystems and devices, the structures they seek to grow have increased in both chemical and structural complexity. The nature of the interfaces between the dissimilar materials used in these devices has also become a critical issue. The research community has responded to these challenges by developing new vapor deposition tools that can precisely control the vapor plumes incident upon a patterned substrate. These tools also attempt to manipulate and control the subsequent chemical reactions and physical assembly processes that occur on and within the vapor deposited film. The complexity of this has motivated interest in techniques that permit the visualization of the assembly processes, either experimentally or by modeling and simulation.

This chapter is a case study in the application of atomistic modeling and simulation tools to the reactive, ion-assisted vapor deposition of multilayered structures. It is motivated by efforts over the past decade to create a new generation of microelectronic devises that exploit giant magnetoresistive materials. We describe the origins of this effect and the role of the atomic scale defects that can significantly reduce the performance of devices. We then introduce an atomistic modeling framework. It is based upon a coupling of precise representations of interatomic force laws for the material systems of interest with high performance molecular dynamics simulation techniques. These tools are used to systematically investigate the deposition of metallic multilayers and the growth of dielectric tunneling barriers linking the results with experimentally obtained high resolution images and other atomic scale characterizations of the materials. This has resulted in new insights into the ways in which defects are formed during the atomic assembly process which have led to the development of new deposition tools that seek to eliminate them. This aspect is also addressed in the chapter.