Spin Tunnel Junctions Research Articles

The optimum oxidation state of AlO/sub x/ magnetic tunnel junctions

In this paper we present results on how both the resistance and the magnetoresistance of magnetic spin-tunnel junctions depend on the oxidation time used to form the AlO/sub x/ barrier. The bias voltage dependence of junctions with barriers created with different oxidation times is measured and found to be optimal when the oxidation time is chosen to give sufficient oxygen for the barrier to be stoichiometric Al/sub 2/O/sub 3/. The oxygen content of the barrier was determined by Rutherford backscattering spectrometry and elastic recoil detection.

Large tunneling magnetoresistance enhancement by thermal anneal

Spin tunnel junctions with tunneling magnetoresistance of 36.5%±0.5%, resistance-area product of 35±6 kΩ×μm2, and junction area between 6 and 75 μm2 were fabricated. The barrier height is 2.5±0.3 eV and the barrier thickness is 7.7±0.3 Å. Large tunneling magnetoresistance (TMR) values are obtained by vacuum anneal (at temperatures from 100 to 240 °C for over 5 h) of junctions prepared with as-deposited TMR of 21%±1.7%, and an as-deposited resistance-area product of 25±6 kΩ×μm2. Two regimes occur during anneal. The first one occurs for anneals up to 200 °C where TMR and junction resistance increase, but the barrier parameters are unaltered. The second occurs above 200 °C, where TMR increases faster, together with an increase in barrier height. At 240 °C, TMR starts to decrease. Rutherford backscattering analysis indicates an asymmetry in the oxygen distribution in the as-deposited barrier. The oxygen distribution becomes homogeneous for anneals above 150 °C.

Faster and denser spin-tunneling random access memory (STram)

The spin tunneling junctions Co/Al/sub 2/O/sub 3//Ni/sub 80/Fe/sub 20/ provide an excellent means of storing a binary datum in the hard component (Co), and sensing its remanent state by switching the soft component (NiFe) in such a way that the magnetic state of the hard component remains unaltered. In this paper, it is clarified by a dynamic model that the switching is caused by the incoherent rotation of the magnetization in the fine thin film pattern and the read access time for a micro-structured spin tunneling with area of 0.256 /spl mu/m/spl times/0.256 /spl mu/m is 0.9 ns. In addition, a magnetic flux closure design was found to reduce the crosstalk by about a factor of five, compared with a conventional keeper-less design, which will be the most favored approach for achieving 10/sup 9/ bits/cm/sup 2/ areal density.