Magnetoresistive Performances in Exchange-Biased Spin Valve and Their Roles in Low-Field Magnetic Sensing Applications

The magnetoresistive properties of pinned spin valves (SV) and their roles in low-field sensing applications were characterized. The magnetoresistive parameters were extracted, including the exchange bias (Heb) field as a function of the iron content in the CoFe layer and the antiferromagnetic (AFM) thickness, the magnetoresistance (MR) ratio versus the spacer thickness, the coercivity (Hc) as a function of the seed layer, and the composite layer [NiFe/Co] used. These parameters are crucial in determining the features of the magnetic sensors. Eventually, the selected SV film structure of (Si/SiO2)/Ta(50 Å)/[NiFe(30 Å)/Co(15 Å)]/Cu(24 Å)/Co80Fe20(25 Å)/IrMn(100 Å)/Ta(50 Å) was found significant, and the SV elements were patterned using the lithographic lift-off method with the active cell dimensions of 2 μm × 150 μm. To define a pinning axis, a cool-field anneal was applied at 250 °C for 30 min in a magnetic field of 2 kOe. A Wheatstone half bridge was engineered using two SV elements and two external resistors. The operation point of the sensor was well tuned using a tiny permanent magnet. A sensitivity of 5 V/T was observed with a linear range of ±2 mT. To demonstrate the performance of the designed sensor, a measurement of the Earth magnetic field was carried out. The engineered SV sensor finds its usefulness in low-field magnetometer and electronic compass applications.