On-chip full bridge bipolar linear spin valve sensors through modified synthetic antiferromagnetic layers

Abstract

Realizing the rising demand for high-sensitivity magneto-resistive (MR) sensors in the industry, an attempt was made towards the fabrication of a spin valve (SV) based bipolar sensor on chip in the form of a full Wheatstone bridge with push–pull configuration. For a sensor with a push–pull configuration, the opposite arms are configured with opposite sense layers. To achieve this, either odd or even layers of synthetic antiferromagnetic (SAF) structure were introduced in the conventional spin valve structure, through which the magnetization orientation of the sensing layer was regulated by either negative or positive sensitivity to the applied field direction respectively. A detailed theoretical simulation was carried out to achieve the stable antiparallel magnetic state around zero fields by varying individual layer thicknesses in the case of single and double-layer SAF structures. With optimized conditions, experimental data were presented, and a bipolar device with a sensitivity of the order of 0.7 mV/V/Oe in the linear field range of ± 15 Oe was fabricated. The performance of the device was characterized by a wider temperature range and it was observed that the device has high thermal stability in the range of - 40 °C to 125 °C with a thermal coefficient of the voltage around 12 μV/V/∘C. Angular performance of the fabricated sensor with minimized orthogonality error was presented and it was observed that the sensor can measure the angle with an accuracy of +/-2 ° .