(The) effect of buffer layer on tunnel magnetoresistance and electric field effect in CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction

Abstract

Conventional memory device which has volatile property causes large electric power loss due to the increase of standby-current as the device scales down. Among next generation memories, MRAM based on magnetic materials has received a great attention due to non-volatile, field-free magnetization switching in spin-transfer torque (STT) operation, and lower magnetization switching current as the device density increases. However, the thermal stability of STT-MRAM is reduced as the device size decreases. To solve this problem, new buffer materials which have high anneal condition for perpendicular magnetic anisotropy (PMA) compared to conventional Ta were studied at first. Meanwhile, modification of magnetic anisotropy was recently observed when electric field is induced in ferromagnet/oxide structures. Thus, the electric field effect could maintain thermal stability of device and reduce the energy barrier of magnetization switching during switching operation only. In this thesis, we study the electromagnetic property of perpendicular magnetic tunnel junctions and the change of magnetic properties by the electric field effect through the introduction of new buffer materials having the perpendicular magnetic anisotropy at higher anneal temperature than that of the conventional Ta buffer layer.