Improving Magnetic Field Detection Limits of Spin Valve Sensors Using Magnetic Flux Guide Concentrators

Guedes, A.; Almeida, José; Cardoso, S.; Ferreira, Ricardo

doi:10.1109/tmag.2007.893119

Cited by 66 publications

(38 citation statements)

References 9 publications

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“…The domains can fluctuate both in size and in magnetization direction, and since the magnetoresistive response of a device is dependent on the domain configuration, and the domain magnetization direction, this causes noise in the output signal. Magnetic lowfrequency noise is strongly associated with conflicting magnetic anisotropies [10,11,17], for the PHEBs, e.g., in the sharp corners where the easy axis of the shape anisotropy changes direction and, also, in the PHEB branches where the shape anisotropy is partly opposed by the exchange bias and field-induced uniaxial anisotropies. Given the larger number of such corners, a PHEB with n>1 could have been expected to have worse detectivity than one with n=1 and equal length.…”

Section: Figure 4 Herementioning

confidence: 99%

“…7). The magnetic part of the noise is reduced if the magnetization is directed along an anisotropy axis [10,11,17], and the detectivity should therefore have local minima at θ=θ ex and θ S . This was confirmed by the measurements.…”

Section: Figure 4 Herementioning

confidence: 99%

“…For TMR devices, the latter contribution is often attributed to defects in the tunnel barrier resulting in electron trapping with thermally activated kinetics and a broad distribution of activation energies, but it should be noted that 1/f noise is also found in metals where carrier scattering by extrinsic defects has been pointed out as the source of the resistivity fluctuations [13]. Attempts to improve field detectivity at low frequencies include low temperature annealing [14,15] and using flux concentrators to amplify the magnetic field at the sensor [5,6,16,17]. An interesting suggestion is to use an ac microelectromechanical flux concentrator system to mitigate the nuisance of 1/f noise by modulating the sensor magnetic field to a higher frequency regime where the 1/f noise is lower [18].…”

Section: Introductionmentioning

confidence: 99%

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Low-frequency noise in planar Hall effect bridge sensors

Persson¹,

Bejhed²,

Nguyen³

et al. 2011

Sensors and Actuators A: Physical

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The low-frequency characteristics of planar Hall effect bridge sensors are investigated as function of the sensor bias current and the applied magnetic field. The noise spectra reveal a Johnson-like spectrum at high frequencies, and a 1/f-like excess noise spectrum at lower frequencies, with a knee frequency of around 400 Hz. The 1/f-like excess noise can be described by the phenomenological Hooge equation with a Hooge parameter of γ H =0.016. The detectivity is shown to depend on the total length, width and thickness of the bridge branches. Increasing the total length by a factor of 10 improves the detectivity by a factor of 10 1/2 . Moreover, the detectivity is shown to depend on the amplitude of the applied magnetic field, revealing a magnetic origin to part of the 1/f noise.

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Section: Figure 4 Herementioning

confidence: 99%

Section: Figure 4 Herementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Low-frequency noise in planar Hall effect bridge sensors

Persson¹,

Bejhed²,

Nguyen³

et al. 2011

Sensors and Actuators A: Physical

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“…3 Recently, flux modulation has been proposed to reduce the 1/f noise of MR sensors by Edelstein et al [4][5][6] In their prototypes, the detected magnetic field was modulated to higher frequency (tens of kHz) with a pair of flux concentrators driven by an electrostatic comb, which resulted in that the 1/f noise of a spin-valve GMR element was hundreds even thousands of times reduced. Subsequently, the electrostatic cantilevers and torsionators with flux guides were used to modulate the detected magnetostatic field (DMSF) by Guedes et al [7][8][9] So far, the 1/f noise of MR sensors has been reduced successfully, but the MSD ability still suffers from the poor modulation efficiency (mostly lower than 11%). Therefore, how to improve the modulation efficiency has become a critical problem.…”

Section: Introductionmentioning

confidence: 99%

Magnetostatic detection using magnetoresistive sensors with vertical motion flux modulation

Pan

Chen

et al. 2012

Review of Scientific Instruments

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Recently, the flux modulation has been presented to deal with the 1/f noise of magnetoresistive (MR) sensors. However, the efficiency of most flux modulation schemes with simple micro- electromechanical-system (MEMS) actuators is not satisfying yet. In this paper, the vertical motion flux modulation (VMFM) is proposed to improve the modulation efficiency. In VMFM, the soft magnetic film driven by a MEMS actuator vibrates vertically above the MR sensors with a pair of flux concentrators. Consequently, the detected magnetostatic field is modulated to the higher frequency where the 1/f noise is much lower. A VMFM prototype based on AA002 (multi-layered giant magnetoresistive sensors) was fabricated and its flux modulation efficiency can reach 18.7%, which exceeds most achieved efficiency with other schemes. Also, the magnetostatic detection ability is improved to 530 pT/√Hz.

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“…These can sense magnetic fields in the pico-Tesla range [2], [3] and nano-size magnetic beads, labeling biological molecules of medical interest [4]. Schematics of the device are shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

High Sensitivity Spin Valve Sensors With AF Coupled Flux Guides

Trindade

Teixeira²,

Fermento³

et al. 2008

IEEE Trans. Magn.

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Giant magnetoresistive (GMR) sensors can have their field sensitivity enhanced by many fold if located in the gap of two magnetically soft flux-guides (FG). In this paper, we present spin valve (SV) sensors, with saturation fields of less than 3 Oe and high linearity characterized by coercive forces of less than 0.5 Oe. FG require magnetically soft thin films with thicknesses in the range of 100-500 nm. In previous work, we prepared single-layer (SL) films of amorphous Co 90 7 (Zr-Nb) 9 3 that exhibited stripe domains (SD) when patterned into FG, causing Barkhausen noise and complete lost of linearity in the SV sensors response. In this article, single layer films of an amorphous alloy of Co 88 4 Zr 3 3 Nb 8 3 , patterned into flux guides, do not exhibit SD but well-behaved closure domains. Nevertheless, these induce hysteresis in the sensors response, characterized by a coercive force of 0.7 Oe. This hypothesis is corroborated by focused beam magneto-optic Kerr effect (MOKE) magnetometry, performed in the poles region the CZN FG. By contrast, FG integrating instead multilayer (ML) thin films consisting of ferromagnetic layers of permalloy weakly anti-ferromagnetically (AF) coupled through Ru interlayers cause a strong reduction of hysteresis in the SV sensors response. The sensors in the gap of AF coupled (NiFe/Ru)xn FG, exhibit saturation fields of about 2 Oe and coercive forces of 0.3 Oe, despite the fact that the isolated sensors exhibit coercive forces of 2 Oe.

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Improving Magnetic Field Detection Limits of Spin Valve Sensors Using Magnetic Flux Guide Concentrators

Cited by 66 publications

References 9 publications

Low-frequency noise in planar Hall effect bridge sensors

Low-frequency noise in planar Hall effect bridge sensors

Magnetostatic detection using magnetoresistive sensors with vertical motion flux modulation

High Sensitivity Spin Valve Sensors With AF Coupled Flux Guides

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