Fabrication and properties of spin dependent tunneling junctions with CoFeHfO as free layers

Spin-dependent tunneling (SDT) structures of Ta-Cu-Ta-CoFeHfO-Al2O3-FeCo-Cr PtMn have been deposited by rf diode sputtering. The junctions have been fa bricated using photolithographic techniques. A junction magnetoresistive ra tio as high as 34% has been obtained after annealing the junctions at 250 d egreesC for 1 h. The junctions have a typical bias voltage of 475 mV at hal f-maximum magnetoresistance values. The resistance-area-product is about 1 M Ohm mum(2), and the dc breakdown voltage is about 1.5 V. AlN has also bee n investigated as a barrier for the junctions. CoFeHfO layers have a high i n-plane induced anisotropy field of 65 Oe and a high 4 pi Ms value of 1.2 T , leading to a ferromagnetic resonance frequency higher than 2 GHz. This ma terial has a high bulk resistivity of 1000 mu Ohm cm, resulting in a small eddy current effect. Therefore, a SDT device with CoFeHfO as the free layer is an attractive candidate for high-speed applications. (C) 2001 American Institute of Physics.