Figure 1
(a) Photograph of the GMR biosensor chip with a reaction well. Coin is US dime (17.9 mm diameter). (b) Left: Optical image of GMR biosensor array (8 × 8 array). Middle: Optical image of GMR biosensor element. Right: SEM image of the sensor stripes (750 nm width) with magnetic nanoparticles (50 nm diameter) bound on the surface. (c) Structure of the GMR biosensor stripe (not to scale). The layers of Seed layer/IrMn (8)/CoFe (2)/Ru (0.8)/CoFe (2)/Cu (2.3)/CoFe (4.5) (all thicknesses in nm) were deposited on Si/SiO2 substrate. The pinned layer and reference layer are coupled to maintain the magnetization in a direction. The magnetization in the free layer is aligned in the orthogonal direction due to shape anisotropy. (d) Different patterns of masks on GMR biosensor stripes (not to scale). The sensor stripes have a width of 750 nm (shown in blue) and the trench between two neighboring sensor stripes is 750 nm wide. The mask of Photoresist on Trench (PoT) covers the trenches with 850 nm wide photoresist patterns (shown in orange). The offset masks of +100 nm, +200 nm and +300 nm illustrate the masks shifted from the PoT mask by 100 nm, 200 nm and 300 nm, respectively. The Photoresist on Stripe (PoS) mask is 700 nm wide photoresist patterns located right on the top of sensor stripes. Similarly, the offset masks of +100 nm, +200 nm and +300 nm were shifted from mask of the PoS by 100 nm, 200 nm and 300 nm, respectively. (e) Schematics of magnetoresistance (MR) changes due to different locations of particles with respect to the sensor stripes. Left: The changes in MR increases with magnetic field sweeping if the particles are distributed in the trench. Right: If the particles are distributed on top of the sensor stripes, the changes in MR decrease.
