Study of DC plasma oxidized Al₂O₃ barriers in spin dependent tunneling junctions using high resolution transmission electron microscopy

We used cross sectional high resolution transmission electron microscopy (HRTEM) to observe DC plasma oxidized Al₂O₃ barriers directly. We measured average, minimum, and maximum thicknesses for a variety of barriers. We studied the effects of plasma oxidation time, precursor Al thickness, and oxygen plasma conditions on barrier thickness and thickness spread. The barrier thickness spread is important in the transport behavior of these junctions because of the exponential dependence of tunneling current on barrier thickness. The thickness spread initially increases with time and then appears to remain constant. The relative spread initially remains constant with increasing thickness. The precursor Al thickness does not affect the barrier thickness distribution significantly, although there may be some oxidation of the bottom electrode for thin (≈ 10Å) precursors. As expected, the barrier oxidation rate and final barrier thickness can be reduced significantly (≈ 30%) by changing the plasma parameters.