Variation in the properties of the interface in a CoFeB/MgO/CoFeB tunnel junction during thermal annealing

Abstract

Variation in the quality of the interface in a CoFeB/MgO/CoFeB tunnel junction during thermal annealing was investigated using x-ray photoemission spectroscopy. The formation of B oxide and the reduction of Fe oxide at the bottom interface after thermal annealing near T-a=300 degrees C were found to enhance the tunneling magnetoresistance ratio significantly. At the same time, an asymmetry of the conductance (dV/dI) in the bias polarity and a local minimum of conductance in a positive bias state were measured which were attributed to the presence of a minority state at the bottom interface. The authors believe that the existence of the Bloch state was also responsible for the failure of the application of the Brinkman-Dynes-Rowell or Simmons models to the CoFeB/MgO/CoFeB junction. (c) 2007 American Institute of Physics.