The Effect of the Interface Impurity in Fabrication of Spin Dependent Tunnel Junction

Abstract

Ferromagnetic-insulator-ferromagnetic tunneling was measured in two types of Co/Al2O3/Co/NiFe junctions. For type 1 junction (two times of interface exposure to air), the maximum tunnel junction magnetoresistance (TMR) ratio was 16.5% at room temperature. Junctions with a relatively thicker Al layer showed a lower resistance and a higher TMR ratio. Whereas, junctions with a relatively thinner Al layer showed a fast increase of barrier width. The passivation effect of Al2O3 in oxidation process enhanced the TMR ratio. As the oxidation time is increased, the coercivity of Co bottom electrode is also increased. So the effect of CoO formation in the interface of the Co bottom electrode and the Al2O3 is discussed in three possible assumptions. For type 2 junction (just one time of interface exposure to air), the maximum TMR ratio was 21% at room temperature. And the TMR ratio was decreased to half at 550 mV. These junctions have potential use as low-power field sensors and memory elements.