Abstract
Sensors play an important role in Internet of Things (IoT) industry and account for a rapidly growing market share. Among them, the magnetic sensor based on tunneling magnetoresistance (TMR) effect possesses great potential applications in the fields of biomedical, navigation, positioning, current detection, and non-destructive testing due to its extremely high sensitivity, small device size and low power consumption. In this paper, we focus on the development of TMR sensor technology routes, covering a series of research advances from a sensor transducer to three-dimensional magnetic field detection, and then to the applications. Firstly, we recall the development history of TMR sensors, explain its working principle, and discuss the method to improve the output linearity of single magnetic tunnel junction. Next, we state the Wheatstone-bridge structure, which can inhibit temperature drift in detail and review several methods of fabricating the full bridge of TMR sensors. Furthermore, for the market demand of three-dimensional magnetic field detection, we summarize the methods of designing and fabricating three-dimensional sensing structure of the TMR sensor. At the same time, we list several optimization schemes of TMR sensor performance in terms of sensitivity and noise level. Finally, we discuss two types of emerging applications of TMR sensors in recent years. The TMR sensors can also be used in intelligence healthcare due to their ultra-high sensitivity. In addition, devices from the combination of spin materials and MEMS structure have attracted wide attention, especially, because of the large commercial market of microphones, spin-MEMS microphones utilized TMR techniques will be the next research hotspot in this interdisciplinary field.
Highlights
In this paper, we focus on the development of tunneling magnetoresistance (TMR) sensor technology routes, covering a series of research advances from a sensor transducer to three-dimensional magnetic field detection, and then to the applications
Furthermore, for the market demand of three-dimensional magnetic field detection, we summarize the methods of designing and fabricating three-dimensional sensing structure of the TMR sensor
55 6700104 Hainz S, de la Torre E, Guettinger J 2021 AmE 2021Automotive Meets Electronics; 12th GMM-Symposium online, March 10–11, 2021 pp Rohrmann K, Sandner M, Meier P, Prochaska M 2018 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Houston TX USA, May 14 –17, 2018 pp Guo D, Cardoso F, Ferreira R, Paz E, Cardoso S, Freitas P 2014 J
Summary
GMR 效应自 1988 年被首次发现之后 [5,6] 很快便 得到了商业化应用, 应用于硬盘驱动器的数据读取 磁头, 极大提高了硬盘的面记录密度, 更重要的是 与互补金属氧化物半导体 (complementary metal oxide semiconductor, CMOS) 技术的高兼容性使 之获得广泛研究和应用. TMR 效应的发现早于 GMR 效应 [7], 但直到 1995 年, 室温下可重复的隧 穿磁阻效应被报道后 [8,9], 才唤起人们的研究热潮. 显然, TMR 传感器相对于其他几 类磁传感器, 有更高的灵敏度、更低的功耗和更宽 的线性范围, 被认为是构建磁传感器的理想器件, 并且在多个领域有广阔的应有前景. 在电流检测方面, TMR 传感器可支 撑频率高达 10 MHz 的交流电流以及直流电流的 测试 [20], 适用于无接触式的多线电缆中的电流检 测, 相较于传统的电流钳, 使用方便且无需过多维 护, 因此常被应用于智能电网监测或智能制造中的 功耗监测 [21]. 除此之外, 由于 TMR 传感器在高频 交变磁场中表现出来的高灵敏度以及其可以实现 非接触检测, 因此这类传感器也常用于导电材料中 的无损检测 [22]. 本文首先介绍 TMR 传感器的基本单元— 磁隧道结 (magnetic tunnel junction, MTJ), 阐述 其对磁场进行线性感应的原理, 介绍基于磁隧道结 的磁阻传感器结构设计以及工艺制备的关键技术, 并重点从灵敏度及噪声水平两方面探讨总结传感 器性能优化的方法, 最后从自旋麦克风、生物医疗 等新兴领域介绍 TMR 传感器应用情况, 对传感器 的发展前景和应用潜力进行展望. 如图 1(b) 所示, 隧道结 的电阻随着自由层与参考层之间相对磁化方向的 夹角改变, 电阻值可以通过 (1) 式 计算, R(θ) = Rp + (Rap − Rp)(1 − cos θ)/2, (1). 其中, Rp 与 Rap 分别表示两个铁磁层相对磁化方 向为平行和反平行时隧道结的电阻, q 为相对磁化 方向的夹角, 当自由层和参考层磁化方向反平行 时, 阻值最大, 磁化方向平行时阻值最小. Magnetic tunnel junction: (a) Schematic diagram of the MTJ stacks; (b) R-H loop curve. 图 2 为 TMR 传 感器的图形化工艺流程图, 包括光刻、刻蚀、去胶、 回填等加工步骤. 在图 2 中, 第 1 步光刻的目的是形成底电极 (bottom electrode, BE) 的图形结构, 首先通过光 刻显影将图形复制到光刻胶上, 再通过刻蚀工艺将 图形转移到底电极上并去胶. 第 2 步光刻是为了形 成多个磁隧道结的图形结构. 需要注意的是, 在这 一步刻蚀得到磁隧道结后需要回填 SiO2 或 者 Si3N4, 以此来保护磁隧道结不会在后续工艺中受
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
