Low resistance spin-dependent tunnel junctions deposited with a vacuum break and radio frequency plasma oxidized

Abstract

Spin-dependent tunnel junctions with resistance-area products (RJ×A) down to 1.8 kΩ×μm2 and tunneling magnetoresistance (TMR)⩾15% were fabricated. Junction areas vary from 6 to 45 μm2. A systematic study of junction resistance and TMR versus deposited Al thickness (tAl=7, 9, 11, and 13 Å), and oxidation time (from 4 to 90 s) is presented. The TMR is maximum (25% to 27%) for tAl=11 Å, with 6 s oxidation time (RJ×A=10 to 20 kΩ×μm2). At 6–10 s oxidation time, reducing the Al thickness from 11 to 7 Å reduces the resistance-area products from 10–20 kΩ×μm2 to 1–3 kΩ×μm2, while TMR decreases from 22%–27% to 13%–17%. Excess oxidation or incomplete oxidation of the Al layer leads to current–voltage curve asymmetry.

Barrier thickness dependence of the magnetoresistance in TaOx magnetic tunnel junctions

“…For AlO x MTJs this behavior is well-known, and is attributed to the complete oxidation of the barrier layer, without oxidizing the underlying magnetic electrode. 16,17 The observed magnitude of the MR ratio is comparable to previously determined values. 9,10 The interesting feature to be seen in Fig.…”

Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

“…Its main parameters are a typical barrier height I Ϸ 2 eV, although values in the range 0.1-8.6 eV have been reported ͑Gundlach and Hölz, 1971;Kadlec and Kadlec, 1975;Lau and Coleman, 1981;Barner and Ruggiero, 1989͒, and a dielectric constant smaller than that of bulk Al 2 O 3 ͓4.5-8.9 at 295 K ͑Bolz and Tuve, 1983͔͒. Several methods are currently utilized to fabricate high-quality ͑i.e., highly uniform and pinhole-free͒ aluminum-oxide barriers such as in situ vacuum natural oxidation ͑Tsuge and Mitsuzuka, 1997; Matsuda et al, 1999;Parkin et al, 1999;Sun et al, 2000;Zhang et al, 2001͒, oxidation in air ͑Miyazaki and Tezuka, 1995͒, and plasma oxidation ͑Moodera et al, 1995Gallagher et al, 1997;Sun et al, 1999͒, of a thin Al layer ͑typically below 2 nm͒. The latter two methods lead, in general, to higher R c values ͑of the order of several k⍀ m 2 or larger͒ with respect to natural oxidation.…”

Evidence of a barrier oxidation dependence on the interfacial magnetism in Co/alumina based magnetic tunnel junctions

“…The trend in TMR with oxidation time for this series was found to be similar to other reports. 11,12 XAS and XMCD measurements at the Co L 2,3 edge were performed on these operable MTJs by allowing x rays to strike an area of the sample containing the lower ferromagnetic electrode structure covered with the alumina barrier ͑see inset to Fig. 1͒.…”