Research Of Non-volatile Bit Cell Based On STT Complementary Polarizer Magnetic Tunnel Junction

Spin-Transfer Torque Magnetic Random Access Memory(STT-MRAM)is a novel non-volatile memory technology based on magnetism.With high access speed close to that of SRAM,high density comparative with that of DRAM,infinite endurance and compatibility with CMOS fabrication process,STT-MRAM has spurred significant interests in the research and industry as one of the best candidates for future universal memory.This dissertation is mainly concerned with the bit cell of STT-MRAM at device-level and circuit-level.The author's major contributions are outlined as follows:1.The STT-based Magnetic Tunnel Junctions(STT-MTJs)and bit cells of STTMRAM have been studied;The advantages of STT-based Complementary Polarizer Magnetic Tunnel Junction(STT-CPMTJ)have been concluded;The first STT-CPMTJ-based CPSTT-MRAM is studied,and the main shortcoming of CPSTT-MRAM is presented: the high energy assumption owing to the per-charging of unselected columns for accidental writing.A novel disturbance-free read methodology is proposed based on STT-CPMTJ utilizing the cancellation of complementary polarized currents.2.Based on study of the modeling of STT-MTJ,a model structure reflecting the comprehensive physical effects in STT-MTJ is proposed.A SPICE model for STT-MTJ is realized based on the proposed model structure.The SPICE model of STT-CPMTJ is realized based on the same modeling theory and methodology for STT-MTJ.The functionality and accuracy of the models are validated by SPICE simulations and MATLAB respectively.3.The Object-Oriented Micro-Magnetic Framework(OOMMF)is studied and the micro-magnetic simulation framework for the evaluation of read disturbance of STTCPMTJ are established;The the cancellation of complementary-polarized currents is validated by micro-magnetic simulations of the read operations;The proposed methodology for disturbance-free read operation is validated and the enhanced method on material is further proposed.4.A novel separated-path bit cell,namely SCPSTT,is proposed for making full use of the structural advantages of STT-CPMTJ.SCPSTT-MRAM can eliminate the precharging operations in CPSTT-MRAM and can achieve disturbance-free read operations based on the proposed methodology.Micro-magnetic simulations and SPICE simulations results show that,compared with CPSTT-MRAM,SCPSTT-MRAM achieves 8%improvement in writing speed,8× improvement in average access energy efficiency and93% reduction in read disturbance rate.5.A novel Total-Mode Non-Volatile Flip-Flop(TMNVFF)is proposed based on SCPSTT.SPICE simulations shows that the proposed TMNVFF achieves 59% improvement in storing speed and 57% reduction in storing energy when compared with the conventional STT-MTJ-based TMNVFF.Furthermore,the proposed structure is modified at circuit level to integrate the advantages of TMNVFF and the Hybrid-Mode NVFF(HMNVFF).Monte-Carlo statistic simulations are carried out to validate the functionality and reliability of the proposed structure.