Characterization of aluminum oxyfluoride barrier in magnetic tunnel junctions

Abstract

The electrical characteristics and the interface structure of magnetic tunnel junctions with aluminum oxyfluoride barrier were studied. Compared to conventional junctions with aluminum oxide tunnel barrier, junctions with aluminum oxyfluoride barrier exhibit larger and nearly constant tunneling magnetoresistance (TMR) values over a wide range of junction resistance and show a smaller bias dependence of TMR, a smaller temperature dependence of junction resistance, and higher effective barrier height. The cross sectional TEM image demonstrates that the junction with oxyfluoride barrier has excellent barrier flatness and smooth interfaces. X-ray photoelectron spectroscopy indicates that the fluorine forms an aluminum oxyfluoride barrier together with oxygen and that the growth of fluorine-rich oxyfluoride layer near the top surface of the barrier plays an important role in the formation of the highly insulating barrier, resulting in nearly ideal barrier/electrode interfaces without a detrimental magnetically dead layer.

Effect of F-inclusion in nm-thick MgO tunnel barrier

“…The reason for the high intensity of F ions at zero sputter depth is probably the excess F ions on the surface of the junction sample, which is believed to originate from the F ions on the chamber walls after the deposition. The SIMS data clearly indicates the F ions mainly reside on the surface of the MgOF tunnel barrier layer, as in the case of F ions in the AlOF tunnel barrier [7,8]. Fig.…”

“…The structure of MgO(F) tunnel junctions was Si(100)/SiO 2 /Mg(20 nm)/barrier(oxidation)/ Mg(20 nm) from the bottom. For oxyfluoridation method, as we reported in our previous reports [7,8], we used a teflon ring as a source for F. Teflon, a compound of C and F, is decomposed into C and F ions in the oxygen plasma, forming CO 2 and leaving F ions. We used an Mg ring as the rf bias ring.…”

“…1 shows resistances of junctions in group A and B as a function of oxidation time. For comparison, resistances of junctions with AlO x and AlOF were plotted as empty symbols from our previous paper [7]. All four sets of data approximately follow exponential dependence on the oxidation time.…”

“…Our previous reports [7,8] on aluminum oxyfluoride (AlOF) have found that incorporation of F during the rf oxidation process of Al layer took place mainly on the surface of Al layer, resulting in highly insulating barrier with barrier height as high as 3.76 eV.…”

Structures and thermodynamic properties of aluminum oxyhalides: a computational study

“…Recent studies have shown AlOCl to be useful as a coagulating agent for cleaning wastewater from organic impurities [3]. A curious occurrence of AlOF is in magnetic tunnel junctions, where they seem to have much better characteristics than the conventional aluminum oxide barriers [4].…”