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电压调控磁各向异性磁隧道结(voltage controlled magnetic anisotropy magnetic tunnel junction, VCMA-MTJ)作为磁随机存储器(magnetic random access memory, MRAM)的核心器件, 具有读写速度快、功耗低、与CMOS工艺相兼容等优点, 现已得到国内外学者的广泛关注. 然而随着VCMA-MTJ尺寸不断缩小、MRAM存储容量不断增大, 工艺偏差对MTJ性能的影响变得越来越显著, 甚至会引起VCMA-MTJ电路的读写错误. 本文在充分考虑磁控溅射薄膜生长工艺中自由层厚度偏差( γ tf)、氧化势垒层厚度偏差( γ tox)以及离子束刻蚀工艺中由侧壁再沉积层引入的刻蚀工艺稳定因子( α)偏差影响的情况下, 给出了基于工艺偏差的VCMA-MTJ电学模型, 并将该模型应用到VCMA-MTJ读写电路中, 研究了工艺偏差对上述电路读写错误率的影响. 结果表明: 当 γ tf≥ 13%, γ tox≥ 11%时, VCMA-MTJ将无法实现磁化状态的有效切换; 当 α≤ 0.7时, VCMA-MTJ磁化方向的进动过程变得不稳定. 进一步地, VCMA-MTJ电路的读错误率和写错误率也将随着工艺偏差的增大而增大. 研究表明, 通过增大外加电压( V b)和减小外加电压脉冲宽度( t pw)可有效降低VCMA-MTJ电路的写错误率, 增大电路的读驱动电压( V dd)可有效降低VCMA-MTJ电路的读错误率.As one of the primary elements in magnetoresistive random access memory (MRAM), voltage controlled magnetic anisotropy magnetic tunnel junction (VCMA-MTJ) has received wide attention due to its fast read and write speed, low power dissipation, and compatibility with standard CMOS technology. However, with the downscaling of VCMA-MTJ and the increasing of storage density of MRAM, the effect of process deviation on the characteristics of MTJ becomes more and more obvious, which even leads to Read/Write (R/W) error in VCMA-MTJ circuits. Taking into account the depth deviation of the free layer ( γ tf) and the depth deviation of the oxide barrier layer ( γ tox) in magnetron sputtering technique as well as the etching process stability factor ( α) caused by the sidewall re-deposition layer in the ion beam etching process, the electrical model of VCMA-MTJ with process deviation is presented in the paper. It is shown that the VCMA-MTJ cannot achieve the effective reversal of the magnetization direction when γ tf≥ 13% and γ tox≥ 11%. The precession of magnetization direction in VCMA-MTJ also becomes instable when α≤ 0.7. Furthermore, the electrical model of VCMA-MTJ with process deviation is also applied to the R/W circuit to study the effect of process deviation on the R/W error in the circuit. Considering the fact that all of γ tf, γ tox, and α follow Gauss distribution, The 3 σ/ μis adopted to represent the process deviation, with using Monte Carlo simulation, where σis the standard deviation, and μis the average value. It is shown that the write error of the circuit goes up to 30 % with 3 σ/ μof 0.05 and the voltage ( V b) of 1.15 V. At the same time, the read error of the circuit is 20% with 3 σ/ μof 0.05 and driving voltage ( V dd) of 0.6 V. Both the read error rate and the write error rate of the VCMA-MTJ circuit increase as process deviation increases. It is found that the write error rate can be effectively reduced by increasing V band reducing the voltage pulse width ( t pw). The increasing of V ddis helpful in reducing the read error rate effectively. Our research presents a useful guideline for designing and analyzing the VCMA-MTJ and VCMA-MTJ read/write circuits.
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Keywords:
- magnetic tunnel junction/
- voltage controlled magnetic anisotropy/
- process deviation/
- read/write circuits
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参数 符号 数值 单位 氧化势垒层厚度标准值 tox 1.4 nm 垂直磁各向异性系数 Ki 0.32 mJ/m2 电压调控磁各项异性系数 ξ 60 fJ/(V·m) 自由层厚度标准值 tf 1.1 nm 简化的旋磁比 γ 2.21 × 105 m/(A·s) 磁导率 μ0 1.256 × 10–6 H/m 吉尔伯特阻尼因子 αd 0.05 饱和磁化强度 Ms 0.625 × 106 A/m x,y轴退磁因子 Nx,y 0.0168 z轴退磁因子 Nz 0.966 外加磁场在x轴分量 Hx 31830 A/m 
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