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Low-frequency noise in planar Hall effect bridge sensors
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

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 gH=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 101/2. 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.

Keyword [en]
Magnetoresistance, Planar Hall effect, Low-frequency noise, Detectivity
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Microsystems Technology
Identifiers
URN: urn:nbn:se:uu:diva-153314OAI: oai:DiVA.org:uu-153314DiVA: diva2:416044
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2011-07-01Bibliographically approved
In thesis
1. Magnetoresistance and Space: Micro- and Nanofeature Sensors Designed, Manufactured and Evaluated for Space Magnetic Field Investigations
Open this publication in new window or tab >>Magnetoresistance and Space: Micro- and Nanofeature Sensors Designed, Manufactured and Evaluated for Space Magnetic Field Investigations
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In recent years, the interest for miniaturization of spaceborne instruments and subsystems has increased steadily, as this enables development of small and lightweight satellite classes as well as more versatile payloads on traditional spacecraft.

In essence, this thesis work is an investigation of the applicability of magnetoresistive technology to a magnetometer intended for space. Two types of magnetoresistive sensors, promising with respect to performance competiveness also after considerable miniaturization, were developed and evaluated, namely magnetic tunnel junctions and planar Hall effect bridge sensors.

In the case of the magnetic tunnel junctions, much effort was put on the micromanufacturing process. Two schemes were developed and evaluated for sensor contouring: one employing focused ion beam processes for rapid prototyping, and the other combining sputtering and x-ray photoelectron spectroscopy for precise etch depth monitoring during ion etching. For the former, the resulting implantation damages were investigated with chemical analysis and correlated to the sensor properties. In the latter, the depth of the etching was monitored live with a resolution sufficient to stop the etching in the 1 nm thick tunneling barrier. The effect and extent of redeposition were investigated by transmission electron microscopy and micromagnetic analysis. With the knowledge so gained, the tunneling magnetoresistance of the manufactured junctions could be improved significantly and their inherent noise could be reduced. As a step in space flight qualification, the magnetic tunnel junctions were subjected to both g and particle radiation, leaving them unaffected by the first, but rendering them a reduced tunneling magnetoresistance ratio and an increased coercivity by the latter.

In the case of the planar Hall effect bridge sensors, their inherent noise was thoroughly investigated, revealing both electric and magnetic 1/f noise at low frequencies along with thermal noise at higher frequencies. In addition, an analytical model of the magnetic properties of the planar Hall effect bridges was developed, and a design process, based on the model, was established to optimize the bridges for a particular application.

In conclusion, both types of sensors show great promises for use in space. Of the two, the planar Hall effect bridge sensors had a better detection limit at low frequencies, whereas the magnetic tunnel junctions were more precise at higher frequencies. However, both sensors had a bandwidth greatly exceeding that of traditional spaceborne magnetometers. A magnetometer employing the magnetic tunnel junctions from this work is currently included as payload onboard the Vietnamese satellite F-1 scheduled for launch this year. A magnetometer using magnetoresistive sensors – planar Hall effect sensors, magnetic tunnel junctions, or both – enables a mass reduction of more than two orders of magnitudes compared with traditional systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 68 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 829
Keyword
Tunneling Magnetoresistance, Planar Hall effect, Magnetic tunnel junction, Magnetometer
National Category
Materials Engineering Other Engineering and Technologies
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-151832 (URN)978-91-554-8085-1 (ISBN)
Public defence
2011-06-01, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2011-05-11 Created: 2011-04-18 Last updated: 2011-07-01Bibliographically approved

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