uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Etch-stop technique for patterning of tunnel junctions for a magnetic field sensor
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
2011 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 21, no 4, 045014-045022 p.Article in journal (Refereed) Published
Abstract [en]

Spin-dependent tunnelling devices, e. g. magnetic random access memories and highly sensitive tunnelling magnetoresistance (TMR) sensors, often consist of a large number of magnetic tunnel junctions (MTJs) of uniform quality over the whole device. The uniformity and yield of the fabrication of such a device are therefore very important. A major source of yield loss is the short-circuiting of junctions by redeposition of etch residues. This can be prevented by terminating of the etch in the typically 1 nm thick tunnelling barrier. Here, electron spectroscopy for chemical analysis for monitoring the etching semi-continuously is proposed. The fabrication scheme employs Ar ion milling for etching the MTJs, and photoelectron spectroscopy for analysing the composition of the etched surface in situ. Junctions etched either to or through the barrier were used for this. The quality of the etch stop was investigated using transmission electron microscopy (TEM), and it was confirmed that the etch could be stopped in the MgO barrier. The TEM imaging also showed clear signs of redeposition. Such redeposition was attributed to being partly caused by the reduction of the TMR ratio of the junctions etched through the barrier, which was only 15% as compared with 150% for junctions etched to the barrier. Also, the latter junctions exhibited 2.7 times less noise in the low-frequency regime, resulting in a 27 times improvement of the signal-to-noise ratio with the etch stop. The barrier also proved effective in protecting the bottom contact from oxidation during the capping and contacting of the junctions.

Place, publisher, year, edition, pages
2011. Vol. 21, no 4, 045014-045022 p.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
URN: urn:nbn:se:uu:diva-151972DOI: 10.1088/0960-1317/21/4/045014ISI: 000288751400016OAI: oai:DiVA.org:uu-151972DiVA: diva2:412607
Available from: 2011-04-26 Created: 2011-04-20 Last updated: 2017-12-11Bibliographically 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

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Persson, AndersEricson, FredricThornell, GregerNguyen, Hugo

Search in DiVA

By author/editor
Persson, AndersEricson, FredricThornell, GregerNguyen, Hugo
By organisation
Microsystems Technology
In the same journal
Journal of Micromechanics and Microengineering
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 872 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf