Design Optimization of an Anisotropic Magnetoresistance Sensor for Detection of Magnetic Nanoparticles

Abstract

Recent studies have shown that the magnetic field sensitivity of an anisotropic magnetoresistance (AMR) sensor using a single-layer Ni₈₀Fe₂₀ thin film can be considerably improved by increasing the shape anisotropy of the film. In this work, an effective approach for improving the sensitivity and reducing the magnetic coercive field as well as the thermal noise contribution in an AMR Wheatstone bridge sensor is proposed by combining multiple resistors in the series–parallel combination circuits. Four different AMR sensor designs, consisting of a single resistor, three and five resistors in series and six resistors in series–parallel connection, were fabricated by using Ta (10 nm)/Ni₈₀Fe₂₀ (5 nm)/Ta (10 nm) films grown on thermally oxidized Si substrates under the presence and the absence of a biasing magnetic field (900 Oe). The results showed that the sensors based on series–parallel combination gain a magnetic sensitivity (S_H) 1.72 times higher than that of the sensor based on the series connection. This optimized sensor has improved the capacity of detecting various concentrations of magnetic nanoparticles with a detection limit of magnetic moments estimated to be about 0.56 μemu.