Biased Target Ion Beam Deposition of GMR Multilayers

– Multilayers like those used in giant magnetoresistive spin-valves can be improved if better layer thickness uniformity, lower contamination levels, reduced interfacial roughness and less interlayer mixing can be achieved. Atomistic simulations have revealed that optimization of the energy of the depositing atoms and the application of very low energy inert gas ion assistance reduce both interfacial roughness and interlayer mixing. Modulation of the energy of these fluxes as each layer growth progresses has been predicted to give even better quality interfaces. Unfortunately, these concepts cannot be implemented in conventional physical vapor deposition (PVD) or ion beam deposition (IBD) processes 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 conventional IBD, it uses a low energy ion source. The higher ion energy required for the sputtering is obtained by applying a negative bias voltage to the metal targets. This system enables 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 enable control of the atomic assembly at interfaces. We have used BTIBD to grow model Ta (40 Å)/Ni80Fe20 (40 Å)/Co (15 Å)/Cu (tCu)/Co (45 Å)/FeMn (100 Å)/Cu (20 Å) spin-valves that show improved GMR ratios and coupling fields over traditional IBD grown multilayers.