Interface and oxide quality of CoFeB/MgO/Si tunnel junctions

Abstract

CoFeB/MgO/Si MOS capacitors were characterized to study the oxide and interface quality of very thin MgO layer (< 2 nm) after various annealing protocols. The improvement in tunneling magneto-resistance (TMR) ratio of a CoFeB/MgO/CoFeB composite layer is believed to result from boron (B) diffusion into the MgO layer to form a polycrystalline Mg-B-O layer, which has a much sharper interface after annealing. By studying the stress-induced-leakage current and the oscillating component of the tunneling current in these MOS structures, we were able to monitor the trap density, interface quality, and endurance of the dielectric. With the CoFeB capping layer, the dielectric defect density is indeed smaller after annealing, which may help to explain the enhancement in TMR. While thermal annealing results in a sharper interface and superior endurance quality with the capping layer, the interface trap density is only marginally improved with annealing.