Susceptor-controlled speed-performance tradeoff in hybrid microwave annealing of CoFeB/MgO/CoFeB magnetic tunnel junctions

The influence of susceptor material on the hybrid microwave annealing (HMA) of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) is investigated using p-type Si and poly-SiC susceptors. Under 3 kW HMA, the poly-SiC susceptor enables the MTJs to reach a tunnel magnetoresistance (TMR) of 101.9% within 2.5 min, whereas the p-type Si susceptor yields a higher TMR of 120.3% after 5 min. The Si-susceptor-annealed samples also exhibit higher anisotropy field and anisotropy energy density, indicating improved anisotropy-related metrics under fixed blanket-film geometry, while the SiC-susceptor-annealed samples show lower coercivity. Permittivity measurements show that the SiC susceptor has an approximately 15% higher imaginary permittivity at 2.45 GHz. In the absence of direct in situ temperature measurements, the earlier TMR activation observed with the SiC susceptor is interpreted as being consistent with a larger effective microwave energy dissipation under the present HMA conditions. These results suggest that susceptor choice influences the accessible HMA process window and produces a speed-performance trade-off: poly-SiC favors rapid TMR activation but with a narrower usable process window, whereas p-type Si is more favorable for maximizing the final TMR and anisotropy-related metrics of HMA-processed MTJs.