Research On Current Pulse Injection Mode In STT-MRAM

Electron has two quantum properties: charge and spin.With the discovery of many new effects of spin quantum physics in recent years,the application of spin properties has become an important mean to break the limitation of Moore’s law in the post-Moore era.Spin Transfer Torque Magnetic Radom Access Memory is one of the most likely devices to replace the traditional Static Random Access Memory and Dynamic Random Access Memory in the future due to its advantages of non-volatility,simple structure and fast speed.However,its high write current density restricts the development of its large-scale commercialization.In order to reduce the write current density and save energy consumption,there have been many methods such as changing the structure of the device,changing the working environment of the device or external circuit control,but these methods either reduce the reading and writing speed of the device,or increase the area of the device,or need harsh working environment,so they have not been applied on a large scale.Therefore,in order to solve this problem,this research proposed new drive current pulse modes to reduce the writing energy consumption of STT-MRAM without affecting other performance of the device.The specific research is as follows:Firstly,the micromagnetic simulation software Mu Max3 is used to simulate the switching behavior of the core Magnetic Tunnel Junction unit Co Fe B/Mg O/Co Fe B driven by the spin transfer torque.In this study,two new pulse injection forms,gradient and step,are proposed based on the current conventional mode of constant pulse driving magnetization switching.The simulation results show that the switching relaxation time and write power of MTJ unit can be significantly reduced by using the two new pulse current injection forms proposed in the study.Under 20,30 and 40 ns pulse operation time,41.61%,33.33% and 37.5% relaxation time and 7.37%,40.75% and 25% energy consumption savings can be achieved by using the gradient pulse,respectively.Step pulse injection can also reduce relaxation time by 8.33%-62.5% and energy consumption by2.12%-44.42% under different pulse action times.Therefore,the proposed two new spin pulse injection methods are effective to reduce the write power consumption of STTMRAM and increase the storage speed of the unit.Furthermore,in order to verify the simulation results,the pulse generation circuit system is constructed based on FPGA chip through Verilog language design,simulation and hardware rendering,and the output signal of the circuit system was optimized to improve the driving force and reduce the noise interference.Finally,the output with good constant conventional and gradient pulse waveform was realized.The current pulse amplitudes and widths can be adjusted according to the experiment requirements.On this basis,the MTJ unit with 70-nm vertical anisotropy corresponding to the simulation is selected for comparative testing.The results show that compared with the conventional pulse drive mode at 20,30 and 40 ns,the energy consumption of the gradient pulse can be reduced by 14.41%,34.73% and 25.26%,which is close to the simulation results.Therefore,the new pulse current drive modes proposed in this study can effectively reduce the energy consumption and switching relaxation time of the present STT-MRAM driving,and can promote its commercialization.