Characterization of nano-oxide layers fabricated by ion beam oxidation: application in specular spin-valves and tunnel junctions

Summary form only given. The oxidation of CoFe layers in specular spin-valves or thin Al layers (<10 /spl Aring/) in low resistance tunnel junctions is currently done either by natural oxidation (where no plasma is used) or by plasma oxidation. In this work, the spin valve and tunnel junctions were prepared by ion beam deposition, and the oxidation was done using a remote plasma (/spl sim/20 eV), created in the /spl Phi/25 cm assist source (100 W RF plasma, no voltage applied to the grids). In this experiment, the Ar and O/sub 2/ gas flow were varied to obtain oxidation pressures up to 2.4/spl times/10/sup -4/ Torr: The incidence angle of the ions was also varied. The oxide thickness was estimated by RBS measurements of simpler samples (Ta 50 /spl Aring//CoFe 100 /spl Aring//oxid./CoFe 100 /spl Aring//Ta 50 /spl Aring/. From the depth of the valley between the two CoFe peaks (/spl Delta/, see Figure 1) the relative oxide thickness can be estimated. From RBS, absolute thickness values could only be obtained if the oxide density is known. But assuming a mixed layer (not crystalline phase) the oxide thickness is estimated as 30 /spl Aring/ (/spl Delta/=20%) and 15 /spl Aring/ (/spl Delta/=10%). For reference, one sample was prepared by natural oxidation, with the loadlock vented for 15 minutes in a class 100 clean room environment (30% controlled humidity). This sample was analyzed by TEM and a continuous 10 /spl Aring/ thick oxide layer was observed. Spin valves fabricated with ion oxidation of the top-pinned CoFe layer show MR signals in excess of 11%, which are lower than those obtained by natural oxidation. The slightly thicker oxide thickness produced by ion oxidation may be advantageous in the fabrication of CPP spin-valves.