CoFeB/MgO/CoFeB Magnetic Tunnel Junctions
John Read
Cornell University
J. J. Cha, P. Y. Huang, W. F. Egelhoff, Jr., D. A. Muller, and R. A. Buhrman
Thin films of ferromagnetic material filter the spin of electrons that pass through. By changing the relative orientation of the magnetizations of two thin ferromagnets, one can control the flow of these spin-polarized currents. The physics of such spin-dependent electron transport is central to the Giant Magnetoresistance (GMR) effect for which Albert Fert and Peter Grünberg won the Nobel Prize this year.
A magnetic tunnel junction (MTJ) consists of a thin insulating layer in between two ferromagnetic electrodes where electrons quantum mechanically tunnel from one electrode to the other. High and low resistance states occur when the magnetizations are anti-parallel and parallel, respectively, and the magnitude of the difference in resistance states is measured by the Tunneling Magnetoresistance (TMR) ratio. The MTJ forms the basic element (bit) for a magnetic random access memory (MRAM) and functions as a magnetic sensor.
The CoFeB/MgO/CoFeB MTJ structure yields very large TMR after annealing and provides many engineering advantages. Several questions remain about the relationship among the chemical, electronic, and structural properties of these devices before and after annealing. I will present results from several experiments performed by our research team that help illuminate the modifications that occur during the annealing process, provide insight concerning the materials physics of the CoFeB/MgO/CoFeB structure, and yield clues to pathways for further optimization and modification for new device structures.
