Nanoelectronics Advanced MRAM cells integrating perpendicular magnetization materials
The integration of perpendicular magnetization materials in CoFeB/MgO/CoFeB is being pursued in two contexts :
1) The development of magnetic field sensors sensitive to the magnetic field component perpendicular to the layers plane, enabling the manufacturing of integrated 3D-field magnetometers
2) The development of high performance MRAM cells based on Spin Transfer Torque (STT-MRAM), aiming at energy consumption in the range of 1E-14 J/bit and a thermal data retention factor KV/KbT>70. These goals should enable gigabyte density MRAM memories. This research line is pursued in collaboration with INESC-MN and IFIMUP.
STT-MRAM cells incorporating perpendicular magnetization materials are of particular importance because of the strong economic implications associated with gigabyte MRAM memories and also because these cells are fundamental building blocks to more sophisticated devices that will be pursued at INL in the future.
Two approaches will be followed to achieve the stated goals :
1) Perpendicular magnetization electrodes will be integrated in state of the art low RxA MgO based MTJs (TMR>100%; RxA~1-10 Ohm um2). In such perpendicular structures the switching current depends on the balance between the out-of-plane demagnetizing field and the out-of-plane anisotropy. A reduction of the critical switching current by at least one order of magnitude with respect to the best present results is expected, i.e., Jc~1E+5 A/cm2.
2) A perpendicular magnetization polarizer will be integrated in a standard MgO MTJ with in-plane magnetized electrodes (with TMR>100% and RxA~1-10 Ohm um2). The role of the polarizer is to pump perpendicular polarized current into the free electrode. Timing the write current pulses properly, the free layer should switch with times of the order of 0.1ns, which is far less than the typical 10ns settling times, thus reducing the energy required to write a cell.
This project is being pursuit in a joint collaboration between INL, INESC-MN and IFIMUP with the financial support of Fundação para a Ciência and Tecnologia.