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Hole mask colloidal lithography on magnetic multilayers for spin torque applications
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
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2010 (English)In: INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) / [ed] Goll, G; Lohneysen, HV; Loidl, A; Pruschke, T; Richter, M; Schultz, L; Surgers, C; Wosnitza, J, BRISTOL: IOP PUBLISHING LTD, DIRAC HOUSE , 2010, Vol. 200, UNSP 072078- p.Conference paper, Published paper (Refereed)
Abstract [en]

We demonstrate the fabrication of metallic nano-contacts on magnetic multilayers using a Hole Mask Colloidal Lithography technique (HCL) based on Polystyrene spheres. The method applies PMMA as a sacrificial layer upon which a hole pattern is formed after liftoff of the spheres. An Au layer functions as a hard mask for the PMMA and the PMMA subsequently masks the SiO(2) during its etching. The resulting pattern is a dense collection of randomly located nano-holes through a SiO(2) film. Final devices are made using traditional photolithography to define a 600 nm circular mesa with about 3 to 4 nano-holes per device, and patterning of a metallic top contact.

Place, publisher, year, edition, pages
BRISTOL: IOP PUBLISHING LTD, DIRAC HOUSE , 2010. Vol. 200, UNSP 072078- p.
Series
Journal of Physics Conference Series, ISSN 1742-6588 ; 200
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-39659DOI: 10.1088/1742-6596/200/7/072078ISI: 000291321303006Scopus ID: 2-s2.0-77957035820OAI: oai:DiVA.org:kth-39659DiVA: diva2:440172
Conference
International Conference on Magnetism (ICM 2009). Karlsruhe, GERMANY. JUL 26-31, 2009
Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2013-05-27Bibliographically approved
In thesis
1. Fabrication and Characterization of Nanocontact Spin-Torque Oscillators
Open this publication in new window or tab >>Fabrication and Characterization of Nanocontact Spin-Torque Oscillators
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The manufacturing of nanocontact-based spin-torque oscillators (NC-STOs)has opened the door for spintronic devices to play a part as active microwaveelements. The NC-STO has the capability of converting a direct current intoa microwave signal, and vice versa, by utilizing the spin transfer torque (STT)in ferromagnetic multilayer systems. However, the high-frequency operation ofNC-STOs typically requires high magnetic fields and the microwave power theygenerate is rather limited. As a result, NC-STOs are not yet commercially used,and they require improvements in both material systems and device geometriesbefore they can find actual use in microwave applications.

In order to improve and advance this technology, NC-STOs are requiredwith both different nanocontact (NC) sizes and geometries, and using differ- ent stacks of magnetic materials. This dissertation presents experimental in- vestigations into the manufacturing of such devices using different fabrication techniques and a number of different magnetic material stacks. Currently, the fabrication of NC-STOs is limited to advanced laboratories, because NC fabri- cation requires high-resolution lithography tools. In the present work, we have developed an alternative method of fabrication, which does not require such tools and has the capability of fabricating NC-STOs having one to hundreds of NCs in a variety of sizes, possibly  down to 20 nm. Devices fabricated with this method have shown mutual synchronization of three parallel-connected NCs, and pairwise synchronization in devices with four and five NCs.

Furthermore, the present work demonstrates low-field operation (down to0.02 Tesla) of NC-STOs at a record high frequency of 12 GHz. This wasachieved by implementing multilayers with a perpendicular magnetic anisotropy(PMA) material in the free layer of the NC-STO. In addition, the fabricateddevices revealed an unexpected dynamic regime under large external appliedfield (above 0.4 Tesla). The new dynamic regime was found to be due to anentirely novel nanomagnetic dynamic object â a so-called magnetic droplet soliton,predicted theoretically in 1977 but not experimentally observed until now.Detailed experiments and micromagnetic simulations show that the droplet hasvery rich dynamics.

Finally,  spin-torque-induced  transverse spin wave instabilities have beenstudied.  A NC-STO with  a material stack consisting of a single ferromag- netic metal sandwiched between two non-ferromagnetic metals was fabricated. Prior to this work, evidence of spin wave instabilities was reported as resis- tance switching in nanopillar- and mechanical point contact based STOs. In the present  work, the fabricated NC-STOs showed actual microwave  signals up to 3 GHz under zero applied field with strong current hysteresis. All  the fabricated NC-STOs open up new means of studying STT in different environ- ments, in order to resolve their current drawbacks for industrial applications.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xvi, 65 p.
Series
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2013:04
Keyword
Spin-torque oscillators, phase locking, spin wave, giant magnetoresistance, spin transfer torque, thin films.
National Category
Physical Sciences Nano Technology
Identifiers
urn:nbn:se:kth:diva-122292 (URN)978-91-7501-760-0 (ISBN)
Public defence
2013-06-14, Sal/Hall E, Foru KTH-ITC, Isafjordsgatan 39, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20130527

Available from: 2013-05-27 Created: 2013-05-17 Last updated: 2014-01-14Bibliographically approved

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Citation style
  • apa
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