Abstract
Since the discovery of giant magnetoresistance (GMR) effect, it has been applied to many fields, including read heads of magnetic recording media and magnetic sensors, for its large resistance change, high sensitivity and wide operating range. If we carefully select the thickness of the non-magnetic layers in a ferromagnetic and non-magnetic metallic multilayer system, the magnetizations of neighboring ferromagnetic layers will align in antiparallel directions through antiferromagnetic coupling. Applying a magnetic field can turn them into parallel arrangement. The resistance of the system is much higher at antiparallel state than that at parallel state. Therefore, the system can transit between high and low resistance states by an external magnetic field. This phenomenon is called GMR effect. GMR devices have relatively simple structure, high resistance to shock, good temperature coefficient of electrical resistance, high tolerance of operating error and environment and are less affected by harsh conditions such as dust, oil, high humidity, so they are a good choice for using under nasty environments, such as automobile industry and industrial manufacturing. Since GMR devices can easily be integrated with semiconductor manufacturing processes, they also have great potential to be applied in consumer electronics and biotechnological industry. This study is aimed to obtain a GMR device with high stability and high magnetoresistance (MR) ratio from different materials and structures and improvements on fabrication processes. We sputtered ferromagnetic (Co, CoFe, NiFe, NiFeCo) /non-magnetic (Cu) multilayers and selected the thicknesses with the highest MR ratio and antiferromagnetic coupling, and we observed the effects of ferromagnetic materials on MR ratio and sensitivity. A buffer layer was introduced under the multilayers to adjust the roughness and lower the spin-independent scattering to raise MR ratio. We found that Co/Cu multilayers had the highest MR ratio an NiFeCo/Cu multilayers had the best sensitivity among the systems we investigated. We also designed layer structures with CoFe and NiFe in hopes of combing their high MR ratio and high sensitivity respectively. We fabricated NiFeCo/Cu GMR devices by lift-off and etching processes respectively to demonstrate their potentials of magnetic sensors. After verifying that the MR ratio was maintained through the fabrication processes, we showed the sensing capabilities of the devices with a patterned magnet array. The results are helpful for developing highly precise and sensitive GMR sensors, which are expected to be applied in plenty fields, e.g. instrumental measurements, automobile industries, automatic robotics, semiconductor industries, biomedical sensing and consumer electronics.