Planar Hall effect bridge geometries optimized for magnetic bead detection

Journal of Applied Physics

2016

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Articles you may be interested inThe stack composition in trilayer Planar Hall effect bridge sensors is investigated experimentally to identify the optimal stack for magnetic bead detection using the sensor self-field. The sensors were fabricated using exchange-biased stacks Ni 80 Fe 20 (t FM )/Cu(t Cu )/Mn 80 Ir 20 (10 nm) with t FM ¼ 10, 20, and 30 nm, and 0 t Cu 0.6 nm. The sensors were characterized by magnetic hysteresis measurements, by measurements of the sensor response vs. applied field, and by measurements of the sensor response to a suspension of magnetic beads magnetized by the sensor self-field due to the sensor bias current. The exchange bias field was found to decay exponentially with t Cu and inversely with t FM . The reduced exchange field for larger values of t FM and t Cu resulted in higher sensitivities to both magnetic fields and magnetic beads. We argue that the maximum magnetic bead signal is limited by Joule heating of the sensors and, thus, that the magnetic stacks should be compared at constant power consumption. For a fixed sensor geometry, the figure of merit for this comparison is the magnetic field sensitivity normalized by the sensor bias voltage. In this regard, we found that sensors with t FM ¼ 20 nm or 30 nm outperformed those with t FM ¼ 10 nm by a factor of approximately two, because the latter have a reduced AMR ratio. Further, the optimum layer thicknesses, t Cu % 0.6 nm and t FM ¼ 20-30 nm, gave a 90% higher signal compared to the corresponding sensors with t Cu ¼ 0 nm. V C 2016 AIP Publishing LLC.

Section: B Experimental Characterizationmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Planar Hall effect bridge sensors with NiFe/Cu/IrMn stack optimized for self-field magnetic bead detection

Henriksen

Journal of Applied Physics

2016

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“…For example, we have described a building block approach to the sensor design and its optimization for magnetic bead detection. 16 Also, the use of PHEB sensors for both volume-and surface-based biodetection schemes using only the field from the sensor bias current as magnetic field excitation has been demonstrated. [17][18][19] While these PHEB sensors showed improved signal-tonoise ratio, both ring shaped sensors with curved resistors ("ring sensors") 7,15 and diamond shaped sensors with straight resistors ("diamond sensors") 14,20 have been argued to be the superior design.…”

Section: Introductionmentioning

confidence: 99%

Experimental comparison of ring and diamond shaped planar Hall effect bridge magnetic field sensors

Henriksen

Journal of Applied Physics

2015

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Planar Hall effect magnetic field sensors with ring and diamond shaped geometries are experimentally compared with respect to their magnetic field sensitivity and total signal variation. Theoretically, diamond shaped sensors are predicted to be 41% more sensitive than corresponding ring shaped sensors for negligible shape anisotropy. To experimentally validate this, we have fabricated both sensor geometries in the exchange-biased stack Ni80Fe20(tFM)/Cu(tCu)/Mn80Ir20(10 nm) with tFM=10, 20, and 30 nm and tCu=0, 0.3, and 0.6 nm. Sensors from each stack were characterized by external magnetic field sweeps, which were analyzed in terms of a single domain model. The total signal variation of the diamond sensors was generally found to be about 40% higher than that for the ring sensors in agreement with theoretical predictions. However, for the low-field sensitivity, the corresponding improvement varied from 0% to 35% where the largest improvement was observed for sensor stacks with comparatively strong exchange bias. This is explained by the ring sensors being less affected by shape anisotropy than the diamond sensors. To study the effect of shape anisotropy, we also characterized sensors that were surrounded by the magnetic stack with a small gap of 3 μm. These sensors were found to be less affected by shape anisotropy and thus showed higher low-field sensitivities.

“…For the self-field contribution, however, the 254 contributions from the two current orientations are subtractive 255 and the signal is proportional to m − n. Thus, a meander 256 structure does not increase this signal unless one of the current 257 orientations is eliminated (n = 0), e.g., by using a non-258 magnetoresistive conductor [21].…”

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confidence: 99%

“…3), each element in R 1 and R 4 with orientation 245 α is matched by a corresponding element in R 2 and R 3 246 with orientation −α, i.e., we let R 2 = R 3 = mR(−π/4) + 247 nR(3π/4) [11], [21]. This design has a high degree of 248 symmetry.…”

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confidence: 99%

Exchange-Biased AMR Bridges for Magnetic Field Sensing and Biosensing

2017

IEEE Trans. Magn.

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We introduce magnetic field sensor bridges that are formed by combinations of stripes of an exchange-pinned magnetic stack displaying anisotropic magnetoresistance. We present a systematic overview on how the stripe geometries can be combined to form sensor bridges with a scalable signal and how these can be tailored towards detection of external magnetic fields and of magnetic beads over or tethered to the sensor surface. Particular attention is given to the case where the beads are magnetized by the sensor self-field due to the bias current passed through the sensor, which is interesting for magnetic bead sensing and where the static and dynamic magnetic bead response can be monitored in the 2nd harmonic sensor response to an oscillating bias current. The recent literature on applications of these sensors for detection of magnetic fields and of the dynamic and static response of magnetic beads in suspension and attached to the sensor surface is reviewed as well as the use of the sensors for magnetic biosensing in volumeand surface-based formats. We illustrate that the sensors can be flexibly designed and applied for a number of sensing applications with sensitive detection of magnetic fields down to the nT range.Index Terms-Magnetoresistive sensor, planar Hall effect, magnetic field sensor, magnetic biosensor.