Surface smoothing process for high-performance MgO-based magnetic tunnel junctions

We developed a surface smoothing technique for stacked Ta–B and Co–Fe–B amorphous layers in a magnetic tunnel junction (MTJ) to yield a higher magnetoresistance (MR) ratio and stronger synthetic anti-ferromagnetic (SAF) coupling. The technique yielded an ultra-smooth surface (Ra ~ 0.1 nm) for both amorphous films and gave rise to atomically flat interfaces at the subsequently deposited layers. Top-pin MTJs fabricated with the technique exhibited superior properties, such as an MR ratio up to 315% and strong SAF coupling exceeding 0.7 erg cm−3. The smoothing process for amorphous layers will be an important for fabricating the MTJs of high-performance spintronics devices.