Spin Transfer Switching in sub-100nm Magnetic Tunnel Junctions

摘要

When injected spin polarized electrons interact with the magnetic moment of a free layer, their angular momentum becomes transferred to the free layer [1, 2]. If sufficient current is applied, the exerted torque switches the free layer either parallel or anti-parallel to the pinned layer depending on the direction of flow of the current. This type of localized current switching is attractive for an MRAM application because it does not have the half-select problems of conventional MRAM. Moreover, current requirements for spin transfer switching go down as devices scale to smaller sizes, so current-induced spin transfer is a good potential scaling path for the MRAM write operation. While interesting initial spin-transfer switching demonstrations were done with spin valve structures [3,4], these devices have impractically low output voltages. Recent advances in high tunneling magnetoresistance TMR devices with MgO barriers [5,6], including devices with low resistance-area (RA) products [7], have yielded a materials system capable of achieving sufficient output voltage for read operations in spin transfer devices. Indeed very recently, a first demonstration of a 4-Kbit spin-momentum transfer MRAM utilizing ～100×150nm{sup}2 MgO devices was reported [8].