Use of Metallic Interlayers to Promote Metal/Metal Epitaxial Growth

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The objective of this research is to investigate the potential for ultrathin, metal interlayers to stabilize the interface in multilayered, thin-film structures. The research will identify those metals which when deposited in monolayer amounts at the interface make possible abrupt, epitaxial interfaces in systems that are otherwise characterized by interdiffusion or roughness. The interlayer materials, unlike surfactants, will remain at the interface to promote chemical, thermal, and structural stability. The interlayer should be atomically thin, unlike conventional diffusion barriers, to minimize the impact on any magnetic properties of the device. Since current fabrication techniques for tunnel junctions involve the oxidation of Al films grown on various ferromagnetic metals (Fe, Co, Ni, and their alloys), the structure and thermal stability of these interfaces will be characterized first. The effect of the interlayer on these structures will then be studied. Previous work suggests that Ti, Zr, and perhaps Ta have the potential for serving as stabilizing, ultrathin interlayers in aluminum/transition metal interfaces. The structure and stability of these magnetic films on oxidized Al surfaces, with and without an interlayer, will be studied. The measurements will characterize the degree of ordered growth or interdiffusion at the interface using high-energy ion backscattering and channeling, low energy electron diffraction, low-energy ion scattering, and x-ray photoelectron diffraction. Core-level photoelectron binding energies will serve to identify compound formation at the interface. Monte Carlo computer simulations, using embedded atom potentials to calculate total energies, will guide the structure analysis. Test structures will be fabricated using those materials that appear to have the most stable and abrupt interfaces, and the magnetic switching and tunneling properties of these structures will be measured. %%%The results of this research will provide a better understanding of, and ability to predict and grow abrupt epitaxial metal/metal interfaces. The work is directed primarily at improving the interfaces in thin-film magnetic tunneling junctions and giant magnetoresistive structures being considered for magnetic memory or sensing applications, where it is felt that more abrupt interfaces will result in devices with better magnetic switching characteristics and lower total resistance.***