Wide range and tunable linear magnetic tunnel junction sensor using two exchange pinned electrodes

Abstract

A magnetic tunnel junction sensor is proposed, with both the detection and the reference layers pinned by IrMn. Using the differences in the blocking temperatures of the IrMn films with different thicknesses, crossed anisotropies can be induced between the detection and the reference electrodes. The pinning of the sensing electrode ensures a linear and reversible output.It also allows tuning both the sensitivity and the linear range of the sensor. The authors show that the sensitivity varies linearly with the ferromagnetic thickness of the detection electrode. It is demonstrated that an increased thickness leads to a rise of sensitivity and a reduction of the operating range.

Tunable linear magnetoresistance in MgO magnetic tunnel junction sensors using two pinned CoFeB electrodes

“…Recently, Negulescu et al 11 reported an MTJ sensor device with an Al 2 O 3 tunnel barrier using two exchange pinned electrodes, which improves the linear field range, but with a relatively small TMR and a low sensitivity. Good sensors should possess wide operating field range, as well as high field sensitivity and low noise detectivity.…”

Adjusting magnetic nanostructures for high-performance magnetic sensors

“…This indicates an additional reduction of the pinning strength after the third annealing process. One possible reason is that the AFM/FM coupling (Ir 20 We also observed the TMR ratios of 205% and 236% for the second and third annealing, respectively. These values are much higher than those calculated from the low-field magnetic field MR loop.…”

“…In recent years, a number of efforts to modify the magnetic tunnel junction layer structures have been discussed by several research groups. There are several concepts to modify the magnetic properties of the free layer in magnetic tunnel junctions such as using hard magnet or magnetic field bias, 18,19 using an orthogonal antiferromagnetic coupling layer, [20][21][22] using two-step orthogonal annealing. [23][24][25] In this study, we discuss the variation of the magnetic properties of the free layer by changing annealing conditions that are related to the performance of the magnetoresistive sensor.…”

Linearization strategies for high sensitivity magnetoresistive sensors

“…2.3) or iv. use of exchange biasing on the sensing layer, which upon annealing can be set orthogonal to the reference layer [62,82,83] (Fig. 12e, Sect.…”

“…The exchange bias vanishes above the blocking temperature (T b ), being close to the Neel temperature (T N ) for thick AFM films with large grain sizes, while for thin films T b << T N due to finite size effects [97]. Therefore, the T b value is not characteristic of the material but depends on the AFM thickness [62,97] Through consecutive annealing steps under orthogonal in-plane magnetic fields at different temperatures, the crossed configuration between the magnetization of reference and sensing layers is then defined [62,82,83,98]. The first annealing, performed at higher temperature, sets both AFM fixed layers magnetizations in the same direction, while the second annealing step at a lower temperature sets the soft pinned sensing layer magnetization at a perpendicular direction to the bottom one (Fig.…”