Magnetoresistance of Single and Double Tunnel Junctions Formed by Direct Sputtering Using Al₂O₃ Target

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Tunnel magnetoresistance (TMR) has been investigated in single (Ni-Fe/Al₂O₃/Co) and double (Ni-Fe/Al₂O₃/Co/ Al₂O₃/Co) tunnel junctions. The Al₂O₃ layer was formed by a direct sputtering method with an Al₂O₃ target. Metal masks were used to form a cross pattern geometry. In the single junctions the dependence of the tunnel resistance and the TMR ratio on the Al₂O₃ thickness was investigated. The tunnel resistance increased exponentially with increasing the Al₂O₃ thickness. A maximum TMR ratio was 4-5 %. In the double junctions the dependence of the tunnel resistance and the TMR ratio on the thickness of central Co layer was investigated. The tunnel resistance decreased with increasing the Co thickness. The maximum TMR ratio was 2%, which was smaller than the value of the single junctions.