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Reactive Ion Beam Etching (RIBE) of MTJ Cell using H₂/NH₃ plasma for Magnetic Random Access Memories
김두산,김예은,장윤종,김인호,김형용,채명관,염근영 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2
MRAM을 구동하기 위해 Magnetic Tunnel Junction (MTJ)층이 사용되며, 일반적으로 MTJ 층은 fixed layer, free layer, barrier layer로 구성된다. MTJ의 자성층 재료로써 CoFeB 및 CoPt가 일반적으로 사용되고 있으며, 이러한 MTJ cell 식각을 위해서 halogen-based RIE가 이용된다. 그러나, halogen 기체와 자성재료가 반응하여 halogen compound를 형성할 경우, 이는 non-volatile한 화합물로써 화학적 손상을 주게 되며, 식각 과정에서 패턴의 측벽에 다시 재 증착 되는 문제 등으로 인해 쉽게 제거되지 않는다. 본 연구에서는 이러한 문제를 해결하기 위해 H<sub>2</sub>/NH<sub>3</sub> 가스조합을 이용한 RIBE를 통해 CoFeB 박막의 식각 특성을 확인하였다.
Technology of MRAM (Magneto-resistive Random Access Memory) Using MTJ(Magnetic Tunnel Junction) Cell
Park, Wanjun,Song, I-Hun,Park, Sangjin,Kim, Teawan The Institute of Electronics and Information Engin 2002 Journal of semiconductor technology and science Vol.2 No.3
DRAM, SRAM, and FLASH memory are three major memory devices currently used in most electronic applications. But, they have very distinct attributes, therefore, each memory could be used only for limited applications. MRAM (Magneto-resistive Random Access Memory) is a promising candidate for a universal memory that meets all application needs with non-volatile, fast operational speed, and low power consumption. The simplest architecture of MRAM cell is a series of MTJ (Magnetic Tunnel Junction) as a data storage part and MOS transistor as a data selection part. To be a commercially competitive memory device, scalability is an important factor as well. This paper is testing the actual electrical parameters and the scaling factors to limit MRAM technology in the semiconductor based memory device by an actual integration of MRAM core cell. Electrical tuning of MOS/MTJ, and control of resistance are important factors for data sensing, and control of magnetic switching for data writing.
Chun-Yeol You,Hyungsuk Kim 한국자기학회 2013 Journal of Magnetics Vol.18 No.4
We find a metastable vortex state of the perpendicular magnetic anisotropy free layer in spin transfer torque magnetic tunneling junctions by using micromagnetic simulations. The metastable vortex state does not exist in a single layer, and it is only found in the trilayer structure with the perpendicular magnetic anisotropy polarizer layer. It is revealed that the physical origin is the non-uniform stray field from the polarizer layer.
허진희,정일섭,Kyuhag Eum 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.6
In order to use the magnetic tunnel junction (MTJ) as a component for memory applications, we need to analyze it and to obtain a well defined switching field, in spite of variations in the sample size and position. We studied the switching field variation in terms of the sizes of sub-micron MTJ cells by measuring the I-V characteristics of the MTJ cells and the hysteresis in the I-H loop, which was obtained by measuring the tunneling current for a sweeping magnetic field.
A Programmable Logic-in-memory (LiM) based on Magnetic Tunneling Junction (MTJ)
Dooho Cho,Kyungmin Kim,Changsik Yoo 대한전자공학회 2018 Journal of semiconductor technology and science Vol.18 No.5
A programmable logic-in-memory (LiM) based on magnetic tunneling junction (MTJ) is proposed. The logic function of the LiM is programmable by storing different state, that is, parallel or anti-parallel state, on a MTJ of reference cell. The logic function is performed by comparing the resistance of the MTJs in the cells representing the operands with that of the reference cell. A 24x8 LiM array has been simulated with a 65-nm CMOS process. When the LiM array is programmed as 8-bit full adder, the operation is completed in less than 3.6- ns and the energy consumption is 0.25-pJ/bit.
Magnetic Field Dependence of Energy Barrier of Perpendicular Nanomagnet
Kyungmi Song,Sung Chul Lee,Kyung-Jin Lee IEEE 2014 IEEE transactions on magnetics Vol.50 No.11
<P>Based on the nudged elastic band model, we investigate the thermal energy barrier and its field dependence of a circular-shaped perpendicular nanomagnet for various exchange constants and cell sizes. We find that the energy barrier depends not only on the cell size but also on the exchange stiffness constant when the switching is governed by the domain-wall nucleation and propagation. We show that analyzing the switching probability curve based on the field-dependent energy barrier equation for the single-domain switching can underestimate the energy barrier so that one has to use the correct field dependence of energy barrier, which can be obtained numerically.</P>
MgO 절연막을 갖는 자기 터널 접합구조에서의 급속 열처리 효과
민길준(Kiljoon Min),이경일(Kyungil Lee),김태완(Taewan Kim),장준연(Joonyeon Jang) 한국자기학회 2015 韓國磁氣學會誌 Vol.25 No.2
To achieve a high tunneling magneto resistance (TMR) of sputtered magnetic tunnel junctions (MTJs) with an MgO barrier, the annealing process is indispensable. The structural and compositional changes as consequences of the annealing greatly affect the spin-dependent transport properties of MTJs. Higher TMR could be obtained for MTJs annealed at higher annealing temperature. The diffusion of Ru, Mn and/or Ta in the MTJs may occur during annealing process, which is known to be detrimental to spin-dependent tunneling effect. The rapid thermal annealing (RTA) process was used for annealing the MTJs with synthetic antiferromagnets. To suppress the diffusion of Mn, Ru and/or Ta in the MTJs, the process time and temperature of RTA were minutely controlled.
Embedded Object-Oriented Micromagnetic Frame (OOMMF) for More Flexible Micromagnetic Simulations
Hyungsuk Kim,Chun-Yeol You 한국자기학회 2016 Journal of Magnetics Vol.21 No.4
We developed an embedded Object-Oriented Micromagnetic Frame (OOMMF) script schemes for more flexible simulations for complex and dynamic mircomagnetic behaviors. The OOMMF can be called from any kind of softwares by system calls, and we can interact with OOMMF by updating the input files for next step from the output files of the previous step of OOMMF. In our scheme, we set initial inputs for OOMMF simulation first, and run OOMMF for Δt by system calls from any kind of control programs. After executing the OOMMF during Δt, we can obtain magnetization configuration file, and we adjust input parameters, and call OOMMF again for another Δt running. We showed one example by using scripting embedded OOMMF scheme, tunneling magneto-resistance dependent switching time. We showed the simulation of tunneling magneto-resistance dependent switching process with non-uniform current density using the proposed framework as an example.
Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers
Chun-Yeol You 한국자기학회 2012 Journal of Magnetics Vol.17 No.2
We investigate spin transfer torque (STT) in magnetic multilayer structures using micromagnetic simulations. We implement the STT contribution for magnetic multilayer structures in addition to the Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. In addition to the Sloncewski STT term, the zero, first, and second order field-like terms are also considered as well as the effects of the Oersted field due to the running current are addressed. We determine the switching current densities of the free layer with the exchange biased synthetic ferrimagnetic reference layers for various cases.
Hyein Lim,Seungjun Lee,Hyungsoon Shin Institute of Electrical and Electronics Engineers 2015 IEEE transactions on electron devices Vol. No.
<P>A circuit-level model of a magnetic tunnel junction (MTJ) that accurately depicts the spin-transfer torque switching behavior of an MTJ along with its voltage/temperature dependency is presented. The unified switching model that was suggested in our previous work is suitable for the circuit-level model because the model seamlessly covers the entire current pulsewidth region. Based on this switching behavior model, a method of dynamic current monitoring is proposed for an advanced circuit-level model. The voltage/temperature characteristics of an MTJ are also integrated for a more accurate circuit-level simulation. The proposed model corresponds well with the experimental data for switching characteristics at different temperatures. The design margin in the read/write circuits with an MTJ is analyzed to demonstrate the effectiveness of the model.</P>