Study On Measurement And Effect Of Spin Orbit Torque For SOT-MRAM

The field of spintronics has attracted great attention recently because it can reduce the technical scale and solve the problem of increasing power dissipation in current electronic circuits.The structure based on spintronics makes use of the spin freedom of electrons,which makes it have the characteristics of zero standby leakage,low power consumption,good reading and writing performance,nonvolatile,and easy three-dimensional integration with current electronic circuits based on CMOS technology.All these advantages have promoted the active research activities of using spintronic devices in storage units and changed the concept of in memory processing architecture in the future.In thesis,the spin orbit torque(SOT)effect used in the new magnetic random access memory(MRAM)is explored,the preparation technology and test method of the spin orbit torque device are studied,and the giant spin Hall material used in the spin orbit torque device is explored.Firstly,based on the basic theory of spin orbit torque,the magnetization dynamics caused by spin orbit torque,the micro source of spin orbit torque and the test method of spin orbit torque are introduced.Spin orbit torque is the transfer of angular momentum between spin current and magnetization vector.The generation of spin current comes from two physical mechanisms:spin Hall effect of non-magnetic and inverse spin galvanic effect at the interface of non-magnetic layer/magnetic layer.Secondly,by deriving the theoretical formula of measuring the spin orbit torque of the device by the harmonic Hall voltage analysis method,the second harmonic Hall voltage test system is established,and the preparation process of the spin orbit torque device with perpendicular magnetic anisotropy is studied.The correctness of the test system is verified by comparing the measured second harmonic Hall voltage curve with the theoretical formula.Finally,the spin Hall materials for SOT-MRAM were studied.A novel Pt_1-x(TiO₂)_xnanocomposite with giant spin Hall effect was prepared by magnetron sputtering.The spin Hall angle of Pt_1-x(TiO₂)_xwas evaluated by spin pumping and inverse spin Hall effect.The resultant spin Hall angle can reach 1.6,which is an order of magnitude higher than that of pure Pt.The SOT effect of Pt_1-x(TiO₂)_xnanocomposites in Pt_1-x(TiO₂)_x/Co/Pt devices was investigated by the second harmonic Hall voltage method and current-induced magnetization switching.The second harmonic Hall voltage test results are consistent with the spin Hall angle evaluation results,and the critical magnetization switching current density of Pt_0.94(TiO₂)_0.06/Co/Pt is as low as 2.5×10~6A/cm~2,which is one order of magnitude lower than that of pure Pt.The large spin Hall angle,low resistivity and good compatibility with semiconductor process make Pt_1-x(TiO₂)_xhave a good application prospect in SOT-MRAM devices.Then,the source of the giant spin Hall effect in Pt_1-x(TiO₂)_xwas analyzed by the physical formula of the extrinsic mechanism of the spin Hall effect.The giant spin Hall effect in Pt_1-x(TiO₂)_xcame from the enhancement of the side-jump mechanism caused by TiO₂impurities in Pt.