Biased Target Ion Beam Deposition of Spin-Valves
Abstract– A further reduction of defect concentration in spin-valve multilayers is difficult in today’s growth processes. Multilayers with better layer thickness uniformity, lower contamination and reduced interfacial roughness and interlayer mixing can have significantly improved properties. Atomistic simulations revealed that a modulation of the energy of depositing atoms during deposition of each material layer or the application of very low energy inert gas ion assistance could reduce both interfacial roughness and interlayer mixing. These concepts, unfortunately, cannot be implemented in the conventional physical vapor deposition (PVD) or ion beam deposition (IBD) processes currently used to deposit these materials. A new biased target ion beam deposition (BTIBD) system that enables these conditions to be achieved has recently been developed. Unlike the conventional IBD, it uses low energy ion source. The high ion energy required for the sputtering is obtained by applying a negative bias voltage to the metal target. This system enables the low energy ion assistance at the growth surface. By modulating the bias voltage during each layer growth, it is also possible to change the average energy of the depositing atoms and therefore enables control of the atomic assembly at interfaces. We have used this approach to grow Ta (40 Å)/Ni80Fe20 (40 Å)/Co (15 Å)/Cu (tCu)/Co (45 Å)/FeMn (100 Å)/Cu (20 Å) spin-valves and show improved GMR ratio and coupling field over traditional IBD grown multilayers.