Switching Properties Of Magnetic Tunnel Junctions For Spin-transfer-torque Magnetoresistive Random Access Memory

Spin-Transfer-Torque Magnetoresistive Random Memory(STT-MRAM), anew generation of non-volatile data storage devices based on the effect of spintransfer torque, it seem to be a competitive candidate among future solid-statemulti-purpose data memories, which integrates the advantages of lower costthan DRAMs, higher speed than SRAM and non-volatility of Flash memories inorder to meet market demands for data storage deviceswith high density, highcapacity, high speed, low cost and small size. With the rapid development offabrication techniques of magnetic tunneling junctions (MTJ), it is of urgentneed and great significance to research into the methodology of scaling downthe devices, reducing the operating current and improving the switch speed andthermal stability of MTJ for STT-MRAM.Based on micromagnetic analysis solving the governing Landau-Lifshitz-Gilbert-Slonczewski(LLGS) equation, this paper presents an investigation ofthe switching properties in MTJ for STT-MRAM. In particular, the work can besummarized as follows:1. The development of the theoretic model is first introduced. The model can be used to describe the magnetization dynamics in the free layer of MTJ.Then, the dynamic equations is derived, and the physical interpretations ofeach terms macrospin model are presented.2. The magnetization switching dynamics in CoFeB/MgO based magnetictunnelling junctions (MTJ) under the influence of interfacial perpendicularanisotropy and the tilt angle of the free layer magnetization is discussed. Inparticular, the switching current density and switching time of such type ofMTJ with in-plane magnetization orientation in its free layer are studied indetails. It is demonstrated that the switching current and switching time canbe significantly reduced with decreasing free layer thickness as the effect ofinterfacial perpendicular anisotropy becomes more pronounced. Theswitching property may be further improved when the tilt angle of the freelayer magnetization increased with decreasing free layer thickness.3. The study of current-induced switching in magnetic tunnel junctions in thepresence of a field-like spin-transfer torque. It is demonstrated that thefield-like term may improve the switching properties such as reduction ofthe switching current density and switching time if it changes sign in thesame way as the Slonczewski term. Otherwise, it results in negative effect.The greater absolute value of field-like term, the greater the effect. Thethermal fluctuation effects at room temperature is also presented.