Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • 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
Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.ORCID iD: 0000-0003-1271-1814
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0001-9352-2411
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
Show others and affiliations
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 9, 092405- p.Article in journal (Refereed) Published
Abstract [en]

The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18-25GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films.

Place, publisher, year, edition, pages
2014. Vol. 104, no 9, 092405- p.
Keyword [en]
Amplitude-frequency, Measurement bandwidth, Metallic thin films, Spin-torque oscillator (STO), Spin-torque oscillators, Theoretical treatments, Time domain measurement, Tunable microwave
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-144370DOI: 10.1063/1.4867257ISI: 000332729200057Scopus ID: 2-s2.0-84896799716OAI: oai:DiVA.org:kth-144370DiVA: diva2:713304
Funder
Swedish Foundation for Strategic Research Swedish Research Council, 2009-4190Knut and Alice Wallenberg Foundation
Note

QC 20140422

Available from: 2014-04-22 Created: 2014-04-22 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Microwave Frequency Stability and Spin Wave Mode Structure in Nano-Contact Spin Torque Oscillators
Open this publication in new window or tab >>Microwave Frequency Stability and Spin Wave Mode Structure in Nano-Contact Spin Torque Oscillators
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The nano-contact spin torque oscillator (NC-STO) is an emerging device for highly tunable microwave frequency generation in the range from 0.1 GHz to above 65 GHz with an on-chip footprint on the scale of a few μm. The frequency is inherent to the magnetic material of the NC-STO and is excited by an electrical DC current by means of the spin torque transfer effect. Although the general operation is well understood, more detailed aspects such as a generally nonlinear frequency versus current relationship, mode-jumping and high device-to-device variability represent open questions. Further application-oriented questions are related to increasing the electrical output power through synchronization of multiple NC-STOs and integration with CMOS integrated circuits.

This thesis consists of an experimental part and a simulation part. Experimentally, for the frequency stability it is found that the slow but strong 1/f-type frequency fluctuations are related to the degree of nonlinearity and the presence of perturbing, unexcited modes. It is also found that the NC-STO can exhibit up to three propagating spin wave oscillation modes with different frequencies and can randomly jump between them. These findings were made possible through the development of a specialized microwave time-domain measurement circuit. Another instrumental achievement was made with synchrotron X-rays, where we image dynamically the magnetic internals of an operating NC-STO device and reveal a spin wave mode structure with a complexity significantly higher than the one predicted by the present theory.

In the simulations, we are able to reproduce the nonlinear current dependence by including spin wave-reflecting barriers in the nm-thick metallic, magnetic free layer. A physical model for the barriers is introduced in the form of metal grain boundaries with reduced magnetic exchange coupling. Using the experimentally measured average grain size of 30 nm, the spin wave mode structure resulting from the grain model is able to reproduce the experimentally found device nonlinearity and high device-to-device variability.

In conclusion, the results point out microscopic material grains in the metallic free layer as the reason behind the nonlinear frequency versus current behavior and multiple propagating spin wave modes and thereby as a source of device-to-device variability and frequency instability.

Abstract [sv]

Dagens snabba utveckling inom informationsteknik drivs på av ständigt växande informationsmängder och deras samhällsanvändning inom allt från resursoptimering till underhållning. Utvecklingen möjliggörs till stor del hårdvarumässigt av miniatyrisering och integrering av elektroniska komponenter samt trådlös kommunikation med allt större bandbredd och högre överföringshastighet. Det senare uppnås främst genom utnyttjande av högre radiofrekvenser i teknologiskt tidigare oåtkomliga delar av spektrumet. Frekvensutnyttjandet har det senaste årtiondet ökat markant i mikrovågsområdet med typiska frekvenser runt 2.4 GHz och 5.2-5.8 GHz.

I den spinntroniska oscillatorn (STO:n) möjliggörs frekvensgenerering i det breda området från 0.1 GHz upp till över 65 GHz av en komponent med mikrometerstorlek som kan integreras direkt i CMOS-mikrochip. Till skillnad från i konventionella radiokretsar med oscillatorer konstruerade av integrerade transistorer och spolar, genereras mikrovågsfrekvensen direkt i STO:ns magnetiska material och omvandlas därefter till en elektrisk signal genom komponentens magnetoresistans. Dessa materialegenskaper möjliggör ett tillgängligt frekvensband med extrem bredd i en och samma STO, som därtill kan frekvensmoduleras direkt genom sin styrström och på så sätt förenklar konstruktionen av sändarsystem. STO:ns icke-linjära egenskaper kan potentiellt också användas för att i en och samma komponent blanda ned mottagna mikrovågssignaler och på så sätt förenkla konstruktionen även av mikrovågsmottagare.

STO:ns signalegenskaper bestäms av det magnetiska materialets fysik i form av magnetiseringsdynamik driven av elektriskt genererade spinnströmmar. I denna avhandling studeras denna dynamik experimentellt med särskilt fokus på frekvensstabiliteten i den hittills mest stabila STO-typen; nanokontakts-STO:n. Genom mätningar i tidsdomän av STO:ns elektriska signaler runt 25 GHz har frekvensstabiliteten funnits hänga samman med den typ av icke-linjärt beteende som också funnits vara utmärkande för tillverkningsvariationen i komponenterna. Mikroskopiska undersökningar av materialet visar att en trolig källa till denna variation är den magnetiska metallens uppbyggnad i form av korn i storleksordningen 30 nm, och datorsimuleringar av en sådan materialstruktur har visats kunna reproducera de experimentella resultaten. Därtill har en metod utvecklats för att med röntgenstrålning direkt mäta de små, magnetiska mikrovågsrörelserna i materialet. Denna röntgenteknik möjliggör detaljerade experimentella studier av magnetiseringsdynamiken och kan användas för att verifiera och vidareutveckla den existerande teorin för mikrovågsspinntronik.

Sammantaget förs STO-teknologin genom denna studie ett steg närmare sina tänkbara samhällsbreda tillämpningar inom snabb, trådlös kommunikation för massproducerade produkter med integrerad sensor- och datorfunktionalitet.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 91 p.
Series
TRITA-ICT, 2016:18
Keyword
spintronics, microwave oscillators, magnetization dynamics, spin waves, phase noise, device modelling, electrical characterization, X-ray microscopy, STXM, XMCD
National Category
Condensed Matter Physics Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics; Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-188546 (URN)978-91-7729-045-2 (ISBN)
Public defence
2016-09-02, Sal C, Electrum, Isafjordsgatan 22, Kista, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2009-4190Swedish Research Council, 2012-5372
Note

QC 20160620

Available from: 2016-06-20 Created: 2016-06-13 Last updated: 2016-06-20Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Authority records BETA

Bonetti, StefanoBanuazizi, S. Amir HosseinMalm, B. Gunnar

Search in DiVA

By author/editor
Eklund, AndersBonetti, StefanoSani, Sohrab R.Mohseni, Seyed MajidChung, SunjaeBanuazizi, S. Amir HosseinÖstling, MikaelÅkerman, JohanMalm, B. Gunnar
By organisation
Integrated Devices and CircuitsMaterial Physics, MFMaterials- and Nano Physics
In the same journal
Applied Physics Letters
Other Physics Topics

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 230 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • 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