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

Abstract

Magnetic tunnel junction (MTJ) has attracted great interest due to its high tunneling magnetoresistance (TMR) ratio,1 where sputter deposition of MgO between CoFeB electrodes is a strong candidate. The improvement in TMR is believed to result from B diffusion into the MgO to form a polycrystalline Mg-B-O layer with a shaper interface after annealing.2 Decrease in trap states can lead to smaller leakage currents and improvement in tunneling conductance. Therefore, a thorough electrical characterization on the CoFeB/Mg-B-O quality is crucial to model the TMR increase and associated reliability. Although the trap charge in the MTJ structure will change the tunneling path and cause serious parametric drift, it is difficult to directly measure its magnitude. Instead, we made CoFeB/MgO/Si MOS capacitors with process flow illustrated in Fig. 1, which can independently determine the interface traps, oxide charge and stress-induced leakage current (SILC) through conductance, high-frequency capacitance-voltage (HFCV) and IV measurements. We can then characterize the boron diffusion and annealing effects on Mg-B-O.