Magnetic field sensor with voltage-tunable sensing properties

Abstract

We report on a magnetic field sensor based on CoFeB/MgO/CoFeB magnetic tunnel junctions. By taking advantage of the perpendicular magnetic anisotropy of the CoFeB/MgO interface, the magnetization of the sensing layer is tilted out-of-plane which results in a linear response to in-plane magnetic fields. The application of a bias voltage across the MgO tunnel barrier of the field sensor affects the magnetic anisotropy and thereby its sensing properties. An increase of the maximum sensitivity and simultaneous decrease of the magnetic field operating range by a factor of two is measured. Based on these results, we propose a voltage-tunable sensor design that allows for active control of the sensitivity and the operating filed range with the strength and polarity of the applied bias voltage.Comment: 4 pages, 4 figures, lette

Linearization strategies for high sensitivity magnetoresistive sensors

“…The latter presents simultaneously both types of responses, sharp hysteretic ones with TMR values up to ∼200% (t > t critical ) and linear responses with TMR values down to 40%, translating the thin CoFeB evolution from the ferromagnetic to the SPMlike regime (t ≤ t critical ). This transition is also illustrated in the inset of Figure 20a with the abrupt drop in coercive field at t critical ∼ 1.45 nm which is in accordance with other reported values [79][80][81][92][93][94]. Tsai et al estimated ∼23 nm as the average lateral size of the ferromagnetic particles at the sensing layer [94] while Shen et al obtained 40-120 nm [95] which for the given t critical implies that the clusters have a pancake-like shape.…”

“…The latter can result in a linear response to in-plane magnetic fields [80,81]. Figure 20a shows the progress of patterned MTJ transfer curves with decreasing sensing layer thickness.…”

“…2.2); iii. reduction of the sensing layer thickness until the superparamagnetic limit (e.g., CoFeB thicknesses below 1.5 nm) [79][80][81] (Fig. 12d, Sect.…”

Spin-torque diode radio-frequency detector with voltage tuned resonance

“…To achieve the above objective, we have investigated MTJs with the following multilayer structure: SiO 2 (substrate) / 5 Ta / 30 CuN / 3 Ta / 30 CuN / 3 Ta / 16 Pt 38 Mn 62 / 2.1 Co 70 Fe 30 / 0.9 Ru / 2.3 Co 40 Fe 40 B 20 / 1.6 MgO / 1-2 Co 40 Fe 40 B 20 / 10 Ta / 7 Ru (thickness in nm). By varying thickness of the CoFeB free layer (FL), we observed a transition from in-plane to perpendicular anisotropy at a critical thickness of t c ≈ 1.35 nm [13]. After deposition, the MTJs were annealed at 250 • C in an in-plane magnetic field of 0.4 T in order to set the exchange bias direction and to improve the crystallization of the ferromagnetic electrodes.…”

“…). By varying thickness of the CoFeB free layer (FL), we observed a transition from in-plane to perpendicular anisotropy at a critical thickness of t c ≈ 1.35 nm [13]. After deposition, the MTJs were annealed at 250 • C in an in-plane magnetic field of 0.4 T in order to set the exchange bias direction and to improve the crystallization of the ferromagnetic electrodes.…”