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MA: Fachverband Magnetismus

MA 37: Spin Dependent Transport Phenomena

MA 37.7: Vortrag

Donnerstag, 26. März 2009, 16:45–17:00, HSZ 403

Time dependent dielectric breakdown in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions. — •Ayaz Arif Khan, Jan Schmalhorst, Karsten Rott, Andy Thomas, and Günter Reiss — Thin films and physics of Nano structures Department of Physics, Bielefeld university, P. O. Box 100131, 33501 Bielefeld germany.

The reliability of magnetic tunnel junctions (MTJs) is a key issue for their application in sensing or storing devices. We have investigated the time dependent dielectric breakdown in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions deposited on thermally oxidized silicon wafers and focused on its dependence on the barrier thickness(1.8 to 4nm), junction area, polarity of the applied voltage, ramp speed and annealing temperature. Measurements with positive and negative polarities are carried out by a voltage ramp method. The junctions with an area from 15×15 to 25×25µm² were patterned using laser lithography process, leading to a tunneling magneto resistance (TMR) up to 174% with a 1.8 nm thick barrier. It is found that the TMR decreases with increasing barrier thickness and a 4 nm thick barrier shows no TMR at room temperature. The observed intrinsic failure due to voltage stress-induced degradation of an insulator is characterized by an abrupt decrease in resistance at the breakdown voltage. The junction studied show an average DC breakdown voltage from 1.72 to 3.48 V depending on barrier thickness and on polarity of the applied voltage.The breakdown voltage increases linearly with the MgO thickness and the resistance area product increases from 96kΩµm² to 461MΩµm² in this investigated thickness range.