Magnetic tunnel junction based out-of-plane field sensor with perpendicular magnetic anisotropy in reference layer

Abstract

A magnetic tunnel junction (MTJ) with orthogonal magnetic anisotropy and consisting of Ta X/Co40Fe40B20 1.2 (reference)/MgO 2.0/Co20Fe60B20 2.3 (sensing)/Ta 5/Ru 5 (thickness in nanometers), where X ranges from 15 to 30, is proposed and investigated in response to the demand for out-of-plane field sensors. The reference layer with perpendicular magnetic anisotropy (PMA) demonstrates tuneable coercivity ranging from 72 Oe to 175 Oe. The sensing layer exhibits in-plane anisotropy with the avoidance of exchange coupling from the PMA reference layer because of a thick MgO barrier layer. The magnetization reversal behavior of micron scale devices not only corresponds well to the sheet film, but is also independent in terms of shape and size. The magnetoresistance curve exhibits a ratio of ∼27% in the presence of a perpendicular field and is insensitive to the in-plane field. For perpendicular field sensing, the dynamic range with a sensitivity of ∼0.3%/Oe can achieve ±25 Oe with a coercive field of less than 3 Oe. Additionally, even when bias is applied up to 9.1 mV, magnetic fluctuation still stays below 0.15 mOe.