Buried word line planarization and roughness control for tunnel junction magnetic random access memory switching

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Abstract
Spin dependent tunnel junctions were fabricated on top of buried word lines. This was achieved modifying an existent 1.2 μm complementary metal–oxide–semiconductor backend metalization process. The word lines are 0.2 μm thick and 4 μm wide. Roughness over the buried line was decreased to 0.2 nm (rms), performing a spin-on-glass local planarization step. Tunnel junctions with 9–13 Å plasma oxidized Al barriers were patterned on top of the word line with different aspect ratios from 3×2 μm2 to 7×1 μm2 areas. Magnetoresistance values reach over 20% for top free electrode configurations. In this inverted structure the magnetization of the free electrode can be fully reversed with the field from word line. The word line creates a field of 0.7 Oe per mA. Applying simultaneously two perpendicular fields reduces the threshold for magnetization switching. The fabricated structure can be used to assess the junction switching mechanism for tunnel junction magnetic random access memories.