Magnetic field sensors are widely used in many fields to measure field, current, position and more. MgO based MTJ is a good option for a room temperature low magnetic field sensor.
The production of high sensitivity sensors is focused on the development of linearization methods of large TMR CoFeB/MgO/CoFeB MTJs (TMR~200%) which are able to provide sensors with reduced coupling and coercive fields (Hc<1Oe, Hk<1Oe), sharp linear response (linear range tunable between 20-300 Oe) and stable domain distribution both in the large area limit (required for devices operating at very low frequency) and in the sub-micron range (required for large spatial resolution devices).
In INL we have developed a three annealing process of an MTJ with a weekly pinned free layer to linearize the sensor response. We manage to control the direction of the three anisotropies, the crystalline one and the two antiferromagnets (AFM) attached to the free and the pinned layer. At the end of the three annealings we leave the crystalline and the AFM of the free layer anisotropies parallel to each other and transverse to the pinned layer AFM. With this configuration we achieve a linear response in bulk so we can have any shape and size sensors. By changing the stack and the annealing conditions we are able to tune up the linear range.
Methods for the production of MTJ sensors on large area wafers (200 mm) with very tight dispersion (1-sigma dispersion of 2% in TMR) have been developed as well as methods for integration of Magnetic tunnel junctions with other types of technologies (magnetic sensors in MEMS structures and magnetic sensors in flexible substrates).
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