2-Axis Magnetometers Based on Full Wheatstone Bridges Incorporating Magnetic Tunnel Junctions Connected in Series

Abstract

Full Wheatstone Bridge incorporating a serially connected ensemble of Magnetic tunnel junctions was produced, targeting an application as a magnetic field compass. To that end, MTJs with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm RxA}\sim 10\ {\rm k}\Omega\ \mu{\rm m}^{2}$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm TMR}\sim 150$</tex></formula> –200%, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Hf}=5\ {\rm Oe}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Hf}=5\ {\rm Oe}$</tex></formula> were produced. In order to achieve a full bridge signal, two stacks with an asymmetric SAF reference structure where used to produce MTJs with opposite dR/dH upon annealing in the same substrate. The resulting Bridges exhibit sensitivities between 13.5–32 mV/V/Oe depending on the field range and provide a significantly advantageous alternative to AMR and GMR based bridges.