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

Abstract

Spin-dependent tunneling (SDT) structures of Ta–Cu–Ta–CoFeHfO–Al2O3–FeCo–CrPtMn have been deposited by rf diode sputtering. The junctions have been fabricated using photolithographic techniques. A junction magnetoresistive ratio as high as 34% has been obtained after annealing the junctions at 250 °C for 1 h. The junctions have a typical bias voltage of 475 mV at half-maximum magnetoresistance values. The resistance–area–product is about 1 MΩ μm2, and the dc breakdown voltage is about 1.5 V. AlN has also been investigated as a barrier for the junctions. CoFeHfO layers have a high in-plane induced anisotropy field of 65 Oe and a high 4πMs value of 1.2 T, leading to a ferromagnetic resonance frequency higher than 2 GHz. This material has a high bulk resistivity of 1000 μΩ 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.