Detection of Sub-Nano-Tesla Magnetic Field by Integrated Magnetic Tunnel Junctions with Bottom Synthetic Antiferro-Coupled Free Layer

Fujiwara, Kosuke; Oogane, Mikihiko; Nishikawa, Takuo; Naganuma, Hiroshi; Ando, Yasuo

doi:10.7567/jjap.52.04cm07

Cited by 32 publications

(20 citation statements)

References 30 publications

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“…The prepared MTJ multilayer lms were microfabricated into MTJ arrays by photolithography and Ar ion milling. The TMR sensor has a structure in which 74 MTJs with device area of 50 × 50 µm 2 are connected in series to reduce the 1/f noise [29][30][31] and the length of the 74 MTJ array is 6.7 mm. After the microfabrication, the MTJ arrays were annealed using the double annealing process with a magnetic eld of 0.3 T to realize linear output response against the external magnetic eld 32 .…”

Section: Sefs Using Squid-megmentioning

confidence: 99%

Scalp attached tangential magnetoencephalography using tunnel magneto-resistive sensors

Kanno

Nakasato

Oogane

et al. 2021

Preprint

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Non-invasive human brain functional imaging with millisecond resolution can be achieved only with magnetoencephalography (MEG) and electroencephalography (EEG). MEG has better spatial resolution than EEG because signal distortion due to inhomogeneous head conductivity is negligible in MEG but serious in EEG. However, this advantage has been practically limited by the necessary setback distances between the sensors and scalp, because the Dewar vessel containing liquid helium for superconducting sensors requires a thick vacuum wall. Latest developments of high critical temperature (high-Tc) superconducting or optically pumped magnetometers have not allowed scalp-attached MEG due to cold or hot temperatures at the sensing point, respectively. Here we applied tunnel magneto-resistive (TMR) sensors that operate at room temperature. Improvement of TMR sensitivity with magnetic flux concentrators enabled scalp-attached and scalp-tangential MEG to target the largest signal component produced by the neural current below. In a healthy subject, our single-channel TMR-MEG system clearly demonstrated the N20m, the initial cortical component of the somatosensory evoked response after median nerve stimulation. Multisite measurement confirmed a spatially and temporally steep peak of N20m, immediately above the source at a latency around 20 ms, indicating a new approach to non-invasive functional brain imaging with millimeter and millisecond resolutions.

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Section: Sefs Using Squid-megmentioning

confidence: 99%

Scalp attached tangential magnetoencephalography using tunnel magneto-resistive sensors

Kanno

Nakasato

Oogane

et al. 2021

Preprint

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“…Research on the development of such new devices is being performed by collaborations of industry, government, and academia. [87][88][89] …”

Section: Detection Of Biomagnetic Fieldsmentioning

confidence: 99%

Spintronics technology and device development

Ando

2015

Jpn. J. Appl. Phys.

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Spintronics is an emerging field of research that has made great advances in the last two decades. During this period, various new outstanding spintronics-related phenomena and devices using these phenomena have been proposed. In recent years, the period from the discovery of new spintronics-related materials and phenomena to the development and commercialization of devices using such materials and phenomena has markedly shortened. The importance of understanding the fundamental principles of spintronics has been increasing. In this review, I will first overview the features of spintronics technologies. Then, I will summarize the key technologies applied in the development of spintronic devices and describe their future prospects.

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“…Based on the crystalline barrier, previous studies demonstrated that optimized MTJs with synthetic antiferromagnetic-free layers could provide high sensitivity to sensing the variations in external magnetic fields [ 21 ]. Moreover, thanks to excellent miniaturization, MTJs can be fabricated for submicrometer-sized devices and connected in a series, which can enhance detectivity to obtain a high signal-to-noise ratio (SNR) [ 22 , 23 ]. These study results suggest that developed MTJs enable us to design sensors with high sensitivity and high spatial resolution for MFL testing applications.…”

Section: Introductionmentioning

confidence: 99%

Serial MTJ-Based TMR Sensors in Bridge Configuration for Detection of Fractured Steel Bar in Magnetic Flux Leakage Testing

Jin

Sam

Oogane

et al. 2021

Sensors

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Thanks to high sensitivity, excellent scalability, and low power consumption, magnetic tunnel junction (MTJ)-based tunnel magnetoresistance (TMR) sensors have been widely implemented in various industrial fields. In nondestructive magnetic flux leakage testing, the magnetic sensor plays a significant role in the detection results. As highly sensitive sensors, integrated MTJs can suppress frequency-dependent noise and thereby decrease detectivity; therefore, serial MTJ-based sensors allow for the design of high-performance sensors to measure variations in magnetic fields. In the present work, we fabricated serial MTJ-based TMR sensors and connected them to a full Wheatstone bridge circuit. Because noise power can be suppressed by using bridge configuration, the TMR sensor with Wheatstone bridge configuration showed low noise spectral density (0.19 μV/Hz0.5) and excellent detectivity (5.29 × 10−8 Oe/Hz0.5) at a frequency of 1 Hz. Furthermore, in magnetic flux leakage testing, compared with one TMR sensor, the Wheatstone bridge TMR sensors provided a higher signal-to-noise ratio for inspection of a steel bar. The one TMR sensor system could provide a high defect signal due to its high sensitivity at low lift-off (4 cm). However, as a result of its excellent detectivity, the full Wheatstone bridge-based TMR sensor detected the defect even at high lift-off (20 cm). This suggests that the developed TMR sensor provides excellent detectivity, detecting weak field changes in magnetic flux leakage testing.

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Detection of Sub-Nano-Tesla Magnetic Field by Integrated Magnetic Tunnel Junctions with Bottom Synthetic Antiferro-Coupled Free Layer

Cited by 32 publications

References 30 publications

Scalp attached tangential magnetoencephalography using tunnel magneto-resistive sensors

Scalp attached tangential magnetoencephalography using tunnel magneto-resistive sensors

Spintronics technology and device development

Serial MTJ-Based TMR Sensors in Bridge Configuration for Detection of Fractured Steel Bar in Magnetic Flux Leakage Testing

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