SPIN VALVE SENSOR ARRAYS FOR MAGNETIC BIO-LABEL DETECTION

A spin-valve based biosensor array designed for the detection of magnetic bio-labels has been developed. A Co/Cu/Co/NiFe spin-valve design with a bottom Co layer pinned by a Co/Ru/Co synthetic antiferromagnetic tri-layer was employed. The Ta/Ru/Co/Ru/Co/Cu/Co/Ni81Fe19/Ta multilayer stack was deposited using UHV magnetron sputtering system. An external magnetic biasing field was applied during deposition to magnetically bias Ni81Fe19 layer to further control magnetization orientation of the free (top) Co layer. The deposition conditions and thickness of individual layers were carefully optimized to maximize the GMR ratio to 13% in unpatterned films. In order to fabricate nano-scale GMR based biosensors from multi-layer stack, new processes including optical and e-beam lithography were designed and conducted. The use of a new electron beam bilayer resists comprised of poly-(4-hydroxystyrene) (PHOST) as the top layer and poly-(dimethylglutarimide) (PMGI) as the bottom layer is demonstrated. Twelve 400nm × 400nm sensors on a chip were built. GMR peaks corresponding to antiparallel magnetization configuration over a base line corresponding to parallel magnetization configuration of the Co layer in the spin-valve stack was observed. Several sizes and numbers of Fe3O4 nanoparticles attaching over sensor surface resulted in a significant change of the GMR peak profile. Micro-magnetic simulation was also conducted in attempt to explain magnetic behavior of particle-sensor interaction. The trend effect of a magnetic particle on sensor GMR profile was confirmed. The simulation results were strongly consistent with those from experiments.