Magnetoresistive devices for industrial applications: improvement of thermal robustness

This study optimizes magnetic tunnel junctions for industrial applications requiring high thermal stability and linear response. Focusing on synthetic antiferromagnets (SAFs) with MnNi for bottom pinning and MnIr for weak pinning, we determined that a Ru spacer thickness of 0.65 nm maximizes linearization, evidenced by broader plateaus in VSM measurements.

Fabricated TMR sensors with a CoFeB free layer thickness of 2.4 nm yielded a peak TMR ratio of 35.5%, which, after dual annealing at 330ºC and 165ºC, displayed 64.5% TMR at room temperature, gradually decreasing to 47% at 150ºC. However, linearity was lost at 175ºC, as VSM curves resembled samples annealed at 180ºC, both past the second annealing temperature.

An exploration of integration of sensors into a Wheatstone bridge showed an enhanced sensitivity of [mV/V]/Oe with a bipolar output from -V to +V, confirming the potential of MnNi-based SAFs for stable, high-performance sensing applications under thermal stress.