Magnetic, magnetoresistive and low-frequency noise properties of tunnel magnetoresistance sensor devices with amorphous CoFeBTa soft magnetic layers

Mahmoud Rasly, Tomoya Nakatani, Jiangnan Li, Hossein Sepehri-Amin, Hiroaki Sukegawa, Yuya Sakuraba

Research output: Contribution to journalArticlepeer-review

Abstract

Magnetic field sensors using the tunnel magnetoresistance (TMR) effect require linear resistance-magnetic field (R-H) response curves with small hysteresis, for which the soft magnetic property of the free layer (FL) is critical. In this work, we investigated amorphous CoFeBTa (CFBT) as a soft magnetic layer of the FL of CoFeB/MgO/CoFeB-based magnetic tunnel junctions in view of magnetic, TMR, and low-frequency noise properties. A two-step annealing process enabled an orthogonal magnetization configuration between the FL and the reference layer, by which linear R-H curves with small hysteresis were realized. The change in the shape of the R-H curve depending on annealing temperature is explained by the Stoner-Wohlfarth model. The highest TMR ratio of ∼160% and sensitivity of ∼70%/mT were obtained with a CFBT (20 nm)/Ta (0.3 nm)/CoFeB (3 nm) FL. The noise of the TMR devices are dominated by 1/f noise below ∼10 kHz in frequency, which limits the detectivity (D) of the magnetic field of the sensor. The sensor devices patterned to 50 µm diameter circular shapes showed a minimum D of ∼2 nT/at 10 Hz, which is superior to the previously reported values for the TMR sensors with NiFe soft magnetic layers.

Original languageEnglish
Article number095002
JournalJournal of Physics D: Applied Physics
Volume54
Issue number9
DOIs
Publication statusPublished - 2021 Mar 4
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Acoustics and Ultrasonics
  • Surfaces, Coatings and Films

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