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Modelling and design of planar Hall effect bridge sensors for low-frequency applications
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology. (ÅSTC)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Dept. of Micro- and Nanotechnology, Technical University of Denmark.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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2013 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, Vol. 189, 459-465 p.Article in journal (Refereed) Published
Abstract [en]

The applicability of miniaturized magnetic field sensors is being explored in several areas of magneticfield detection due to their integratability, low mass, and potentially low cost. In this respect, differentthin-film technologies, especially those employing magnetoresistance, show great potential, being compatible with batch micro- and nanofabrication techniques. For low-frequency magnetic field detection,sensors based on the planar Hall effect, especially planar Hall effect bridge (PHEB) sensors, show promising performance given their inherent low-field linearity, limited hysteresis and moderate noise figure. Inthis work, the applicability of such PHEB sensors to different areas is investigated. An analytical modelis constructed to estimate the performance of an arbitrary PHEB sensor geometry in terms of, e.g., sensitivity and detectivity. The model is valid for an ideal case, e.g., disregarding shape anisotropy effects, andalso incorporates some approximations. To validate the results, modelled data was compared to measurements on actual PHEBs and was found to predict the measured values within 13% for the investigatedgeometries. Subsequently, the model was used to establish a design process for optimizing a PHEB to aparticular set of requirements on the bandwidth, detectivity, compliance voltage and amplified signalto-noise ratio. By applying this design process, the size, sensitivity, resistance, bias current and powerconsumption of the PHEB can be estimated. The model indicates that PHEBs can be applicable to severaldifferent areas within science including satellite attitude determination and magnetic bead detection inlab-on-a-chip applications, where detectivities down towards 1 nT Hz−0.5at 1 Hz are required, andmaybeeven magnetic field measurements in scientific space missions and archaeological surveying, where thedetectivity has to be less than 100 pT Hz−0.5at 1 Hz.

Place, publisher, year, edition, pages
2013. Vol. 189, 459-465 p.
Keyword [en]
Magnetoresistance Planar Hall effect Low-frequency noise Detectivity
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Materials Science; Engineering Science with specialization in Microsystems Technology
URN: urn:nbn:se:uu:diva-188200DOI: 10.1016/j.sna.2012.10.037ISI: 000314622600055OAI: diva2:576768
Available from: 2012-12-14 Created: 2012-12-13 Last updated: 2015-02-03Bibliographically approved
In thesis
1. Biomolecular Recognition Based on Field Induced Magnetic Bead Dynamics
Open this publication in new window or tab >>Biomolecular Recognition Based on Field Induced Magnetic Bead Dynamics
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, three different read-out techniques for biomolecular recognition have been studied. All three techniques rely on the change in dynamic behaviour of probe functionalised magnetic beads after binding to a biomolecular target complementary to the probe.

In the first technique presented, the sample is exposed to an AC magnetic field while the response to this field is probed using a laser source and a photodetector positioned at opposite sides of the sample. Beads bound to the target entity will experience an increase in their hydrodynamic volume, and will not be able to respond as rapidly to an alternating field as free beads. Here, the target entity is either DNA coils formed by rolling circle amplification or biotinylated bovine serum albumin (bBSA). The change in dynamic behaviour is measured as a frequency dependent modulation of transmitted light. Limit of detections (LODs) of 5 pM DNA coils originating from a V. cholerae target and 100 pM of bBSA have been achieved.

In the second technique presented, the beads are magnetically transported across a probe functionalised detection area on a microchip. Beads bound to a target will be blocked from interaction with the detection area probes, whereas in the absence of a target, beads will be immobilised on the detection area. The LOD of biotin for this system proved to be in the range of 20 to 50 ng/ml.

In the third technique presented, the sample is microfluidically transported to a detection area on a microchip. The read-out is performed using a planar Hall effect bridge sensor. A sinusoidal current is applied to the bridge in one direction and the sensor output voltage is measured across the sensor in the perpendicular direction. The AC current induced bead magnetisation contributing to the sensor output will appear different for free beads compared to beads bound to a target. LODs of 500 B. globigii spores and 2 pM of V. cholerae DNA coils were achieved.

From a lab-on-a-chip point of view, all three techniques considered in this thesis show promising results with regards to sensitivity and integrability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 94 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1193
Magnetic biosensor, magnetic nanoparticle, DNA detection
National Category
Nano Technology Biochemistry and Molecular Biology Condensed Matter Physics
Research subject
Engineering Science
urn:nbn:se:uu:diva-234302 (URN)978-91-554-9077-5 (ISBN)
Public defence
2014-12-12, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Knut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2014-11-21 Created: 2014-10-15 Last updated: 2015-02-03

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