Title :
Electric Field Assisted Switching in Magnetic Random Access Memory
Author :
Guchang Han ; Jiancheng Huang ; Bingjin Chen ; Sze Ter Lim ; Tran, Michael
Author_Institution :
Data Storage Inst., Agency for Sci., Technol. & Res., Singapore, Singapore
Abstract :
Electric field (EF)-assisted magnetization reversal is investigated in both top-pinned and bottom-pinned CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). EF modulation in coercivity (Hc) shows an increasing dependence with the thickness of the free layer (tFL) at small tFL values. This abnormal variation was attributed to possible Ta diffusion through the free layer to the interface with MgO barrier. It is found that the bidirectional switching is not achievable using unipolar EF only in our MTJ devices, which is due to small spin-transfer torque (STT) effect and switching uncertainty due to unipolar feature of EF-induced Hc modulation. A bipolar external magnetic field should be applied to realize EF-controlled magnetic random access memory (MRAM). For quasistatic magnetization reversal, the required field can be as low as 10 Oe when Hc is effectively modulated to nearly zero. Switching field as a function of switching time shows that the magnetization switching is dominated by thermal activation. Simulation results show that switching time is mainly determined by the damping constant and the EF efficiency. Different from STT-MRAM, a large damping constant is desired to achieve fast switching. Using a sweeping field method, we show that MTJs with a thermal stability factor as high as 58 can be reliably switched using an EF-modulated anisotropy scheme with a bipolar magnetic field as low as 10 Oe.
Keywords :
MRAM devices; magnetic tunnelling; magnetisation reversal; thermal stability; EF efficiency; bidirectional switching; bipolar external magnetic field; bottom-pinned magnetic tunnel junctions; damping constant; electric field assisted switching; electric field-assisted magnetization reversal; magnetic random access memory; quasistatic magnetization reversal; spin-transfer torque; sweeping field method; switching uncertainty; thermal activation; thermal stability factor; top-pinned magnetic tunnel junctions; Electric fields; Magnetic anisotropy; Magnetic fields; Magnetic tunneling; Magnetization; Switches; Thermal stability; Electric field; Electric field (EF); MRAM; magnetic random access memory (MRAM); magnetization switching; spin transfer torque; spin transfer torque (STT);
Journal_Title :
Magnetics, IEEE Transactions on
DOI :
10.1109/TMAG.2015.2439734