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 (H RTEM) to observe DC plasma oxidized Al2O3 barriers directly. We measured av erage, minimum, and maximum thicknesses for a variety of barriers. We studi ed the effects of plasma oxidation time, precursor Al thickness, and oxygen plasma conditions on barrier thickness and thickness spread. The barrier t hickness spread is important in the transport behavior of these junctions b ecause of the exponential dependence of tunneling current on barrier thickn ess. The thickness spread initially increases with time and then appears to remain constant. The relative spread initially remains constant with incre asing thickness. The precursor Al thickness does not affect the barrier thi ckness distribution significantly, although there may be some oxidation of the bottom electrode for thin (approximate to 10 Angstrom) precursors. As e xpected, the barrier oxidation rate and final barrier thickness can be redu ced significantly (approximate to 30 %) by changing the plasma parameters.