GMR-based single-domain magnetic sensor for 500nm single particle detection

Summary form only given. In this study, we develop a GMR-based single-domain magnetic sensor that presents the result digitally by two states: the absence and the presence of the magnetic labels. The proposed sensor not only shares all the desirable properties of standard magnetoresistive sensors, but achieves single magnetic nanoparticle detection as well. Moreover, our single-domain magnetic sensor is readily available for immediate integration with biomolecule applications. A GMR-based magnetic sensor consists of two synthetic antiferromagnetic layers separated by 6nm Cu layer is developed. Co 5nm/Ru 0.8nm/Co 5nm is chosen to be the pinned layer to retain the direction of magnetization during the measurement, and the free layer Co 5nm/Ru 1.4nm/Co 10nm is designed to switch in a relatively low magnetic field that the tester system can easily achieve. The GMR stack (Ta 2.5nm/Ru 5nm/ Co 5nm/Ru 0.8/Co 5nm/Cu 6nm/Co 5nm/Ru 1.4nm/Co 10nm/Ta 5nm) is sputtering deposited on silicon wafer with 500nm SiO
₂
. After deposition, the film is patterned into an array of 700 X 600 nm
²
rectangles by e-beam lithography system and 70 nm thick Cu is made as leads to pass current to the GMR sensors. The sensors are finally coated with a 100 nm thick pinhole-free alumina to prevent corrosion and serve as a base for attaching biomolecules.