Improvement of Switching Field in Magnetic Tunnel Junction Using Ru/Ta Capping Layer

In this report, we will demonstrate that by simply using a bilayer capping layer of Ru/Ta instead of usually used Ta, the switching field, as well as distribution of switching fields, of magnetic tunnel junctions (MTJ) can be considerably reduced. Two samples with the same MTJ stack of Ta/PtMn/SAF-pinned/AlO_x/CoFeB(2 nm) (bottom to top) but capped by different metal layers of Ta and Ru/Ta, correspondingly, were deposited on thermally oxidized Si substrates at room temperature using a UHV DC sputtering system. The R-H loops of 100 MTJs were measured at room temperature with a bias voltage of 0.1 volt for various fields. Results suggested that MTJs of high magnetoresistance (MR) ratio as well as low switching field with narrow distributions can be achieved by using CoFeB as free layer and Ru/Ta as capping layer.