Study of Longitudinal Stabilization Using In-Stack Biasing

Ho, M.; Tsang, C.; Childress, J. R.; Fontana, R.E.; Katine, J. A.; Carey, K.

doi:10.1109/tmag.2003.821201

Cited by 8 publications

(3 citation statements)

References 4 publications

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“…Higher fields result in better sensing layer stability but also in lower field sensitivities. 9 In this work, the noise level of micron sized AlOx MTJs 10 is investigatedwhere the free layer magnetization is stabilized with a PM integrated in the sensor structure. The integration of the PM is achieved using an optimized microfabrication process that minimizes the process steps.…”

mentioning

confidence: 99%

Low aspect ratio micron size tunnel magnetoresistance sensors with permanent magnet biasing integrated in the top lead

Chaves

Cardoso

Ferreira

et al. 2011

Journal of Applied Physics

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Optimized single magnetic bead detection requires magnetic sensors with an improved field detection limit and a sensor area matching the bead cross section (micron size spatial resolution). This work shows that square micron sized tunnel magnetoresistance sensors can be fabricated with integrated longitudinal permanent magnet (PM) biasing that show a linearized field response and low noise. PMs (Co66Cr16Pt18) were integrated in the top lead of an AlOx based magnetic tunnel junction sensor for transfer curve linearization. Sensors patterned with dimensions down to 3 × 3 μm2 present field detection limits of 6 nT/Hz0.5 and 3 nT/Hz0.5 at 10 kHz and 500 kHz, respectively, corresponding to a field sensitivity of 1.8% per mT (linear field detection range ΔB = −8 mT + 8 mT) and αH = 3.9 ± 0.3 × 10−10 μm2 (RxA = 1.9 kΩ μm2).

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mentioning

confidence: 99%

Low aspect ratio micron size tunnel magnetoresistance sensors with permanent magnet biasing integrated in the top lead

Chaves

Cardoso

Ferreira

et al. 2011

Journal of Applied Physics

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“…The external field created by the PMs depends on the dimensions and also on the magnetic moment of the patterned element. On the one hand, high LB fields result in improved sensing layer stability, leading however to lower field sensitivities of the sensor [21]. The PMs were dimensioned to create a bias field (μ 0 H LB ) at the center of the magnets of ~1 mT.…”

Section: Biasing With Permanent Magnetsmentioning

confidence: 99%

Magnetic tunnel junction sensors with pTesla sensitivity for biomedical imaging

Cardoso¹,

Gameiro²,

Leitao³

et al. 2013

SPIE Proceedings

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Ultrasensitive magnetic field sensors at low frequencies are necessary for several biomedical applications. Suitable devices can be achieved by using large area magnetic tunnel junction sensors combined with permanent magnets to stabilize the magnetic configuration of the free layer and improve linearity. However, further increase in sensitivity and consequently detectivity are achieved by incorporating also soft ferromagnetic flux guides. A detailed study of tunnel junction sensors with variable areas and aspect ratios is presented in this work. In addition, the effect in the sensors transfer curve, namely in their coercivity and sensitivity, as a consequence of the incorporation of permanent magnets and flux guides is also thoroughly discussed. Using sensors with a tunnel magnetoresistance of ~200 %, incorporating both permanent magnets and flux guides sensitivities of 220-260 %/mT were obtained for high aspect ratio sensors, increasing to values larger than ~2000%/mT for large areas and low aspect ratio sensors. Measured noise levels of the final device at 10 Hz yield 3.9×10 -17 V 2 /Hz, leading to an improved lowest detectable field of ~ 94 pT/ Hz 0.5 .

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“…Another advantage is that, in the absence of electrical leads and hard bias on the sides of the sensor, the magnetic shield which is normally electroplated on top of the stack can be made to be conformal with the sensor itself, thus providing side shielding to the sensor (Fig. 18(a), (b)) which can improve narrow-track, high-track-density performance [36]. In the case of AF-pinned in-stack bias layer, the challenge is to balance the thickness of the in-stack bias layer (thicker bias layer provides more magnetic flux for free layer stabilization) and the strength of the pinning (thicker bias layer results in a decrease of the pinning exchange field).…”

Section: In-stack Biasing and Conformal Shielding In Cpp Geometrymentioning

confidence: 99%