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Order of magnitude improvement of nano-contact spin torque nano-oscillator performance
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.ORCID iD: 0000-0003-4253-357X
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.ORCID iD: 0000-0003-1271-1814
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
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2017 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 5, p. 1896-1900Article in journal (Refereed) Published
Abstract [en]

Spin torque nano-oscillators (STNO) represent a unique class of nano-scale microwave signal generators and offer a combination of intriguing properties, such as nano sized footprint, ultrafast modulation rates, and highly tunable microwave frequencies from 100 MHz to close to 100 GHz. However, their low output power and relatively high threshold current still limit their applicability and must be improved. In this study, we investigate the influence of the bottom Cu electrode thickness (t(Cu)) in nano-contact STNOs based on Co/Cu/NiFe GMR stacks and with nano-contact diameters ranging from 60 to 500 nm. Increasing t(Cu) from 10 to 70 nm results in a 40% reduction of the threshold current, an order of magnitude higher microwave output power, and close to two orders of magnitude better power conversion efficiency. Numerical simulations of the current distribution suggest that these dramatic improvements originate from a strongly reduced lateral current spread in the magneto-dynamically active region.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017. Vol. 9, no 5, p. 1896-1900
National Category
Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-204731DOI: 10.1039/c6nr07309cISI: 000395594300017PubMedID: 28094381Scopus ID: 2-s2.0-85011392741OAI: oai:DiVA.org:kth-204731DiVA, id: diva2:1104682
Funder
EU, European Research Council, 307144Swedish Research CouncilSwedish Foundation for Strategic Research Knut and Alice Wallenberg Foundation
Note

QC 20170601

Available from: 2017-06-01 Created: 2017-06-01 Last updated: 2018-05-24Bibliographically approved
In thesis
1. Determining and Optimizing the Current and Magnetic Field Dependence of Spin-Torque and Spin Hall Nano-Oscillators: Toward Next-Generation Nanoelectronic Devices and Systems
Open this publication in new window or tab >>Determining and Optimizing the Current and Magnetic Field Dependence of Spin-Torque and Spin Hall Nano-Oscillators: Toward Next-Generation Nanoelectronic Devices and Systems
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Spin-torque and spin Hall nano-oscillators are nanoscale devices (about 100 nm)capable of producing tunable broadband high-frequency microwave signals ranging from 0.1 GHz to over 65 GHz that several research groups trying to reach up to200 - 300 GHz. Their development is ongoing for applications in high-frequency nanoelectronic devices and systems, such as mobile phones, wireless networks, base stations, vehicle radars and even medical applications.

This thesis covers a wide range of characterizations of spin-torque and spin Hall nano-oscillator devices that aim to investigate their current and magnetic field dependency, as well as to suggest improvements in these devices to optimize their application in spintronics and magnonics. The work is primarily based on experimental methods for characterizing these devices by building up new measurement systems, but it also includes numerical and micromagnetic simulations.

Experimental techniques: In order to characterize the fabricated nanodevices in a detailed and accurate manner through their electrical and microwave responses, new measurement systems capable of full 3D control over the external magnetic fields will be described. In addition, a new method of probing an operational device using magnetic force microscopy (MFM) will be presented.

Spin-torque nano-oscillators: We will describe remarkable improvements in the performance of spin-torque nano-oscillators (STNOs) that enhance their integration capability with applications in microwave systems. In nanocontact (NC-)STNOs made from a conventional spin-valve stack, though with thicker bottom electrodes, it is found the auto-oscillations can be excited with higher frequencies at lower threshold currents, and with higher output powers. We also find that this idea is useful for tuning spin-wave resonance and also controlling the thermal budget. Furthermore, a detailed study of magnetic droplet solitons and spin-wave dynamics in NC-STNOs will be described. Finally, we demonstrate ultra-high frequency tunability in low-current STNOs based on perpendicular magnetic tunnel junctions(p-MTJs).

Spin Hall nano-oscillators: Characterizations of spin Hall nano-oscillator(SHNO) devices based on different structures and materials with both conventional and novel methods will be described. A detailed study of the current, temperature, and magnetic field profiles of nanogap SHNOs will be presented. In addition, we show the current and magnetic field dependence of nanoconstriction-based SHNOs.Moreover, it is shown that multiple SHNOs can be serially synchronized, thereby increasing their output power and enhancing the usage of these devices in applications such as neuromorphic computing. We show synchronization of multiple nanoconstriction SHNOs in the presence of a low in-plane magnetic field. Finally, there is a demonstration of the results of a novel method for probing an operationalSHNO using MFM.

Abstract [sv]

Spinntroniska oscillatorer är ca 100 nm stora nano-komponenter som kan generera avstämningsbara mikrovågssignaler över ett mycket stort frekvensområde. Frekvensområdet sträcker sig i dagsläget från 0,1 GHz till över 65 GHz och flera forskningsgrupper försöker att nå upp till 200-300 GHz. De spinntroniska oscillatorerna baseras på en effekt som kallas spinnvridmoment och de första oscillatorerna kallades därför spinnvridmomentsnano-oscillatorer (eng. spin torque nano-oscillators) som vanligtvis förkortas STNO:er. De senaste åren har man även använt den s.k. spinn-Hall-effekten och oscillatorer baserade på detta förkortas därför SHNO:er. Båda sorternas oscillatorer är under kraftig utveckling för att kunna användas inom olika högfrekvenstillämpningar som t.ex. mobiltelefon, trådlösa nätverk, basstationer, fordonsradar och även medicinska tillämpningar.

Denna avhandling täcker ett brett spektrum av olika mätningar på STNO:er och SHNO:er för att bestämma deras ström- och magnetfältsberoenden samt föreslå förbättringar av deras design för att använda dem inom spinntronik och magnonik. Arbetet bygger i första hand på experimentella metoder för att utveckla nya mätsystem, men det innehåller också numeriska och mikromagnetiska simuleringar.

Experimentella tekniker: För att kunna göra detaljerade och noggranna mätningar, som funktion av ström genom komponenten samt magnetfält runt komponenten, har två nya mätuppställningar utvecklats, båda med målet att enkelt kunna variera styrka och riktning på det magnetiska fältet i tre dimensioner. Dessutom presenteras en ny metod för att studera komponenterna med s.k. magnetkraftsmikroskopi(MFM).

STNO:er: Avhandlingen presenterar väsentliga förbättringar av prestanda hos STNO:er genom att öka tjockleken på det understa metall-lager som hela STNO:n är uppbyggd på. I sådana förbättrade STNO:er kan mikrovågssignaler med högre frekvens, högre uteffekt, och lägre tröskelström realiseras. Dessutom får komponenterna bättre värmeledningsförmåga så att de kan klara högre drivströmmar. Vidare beskrivs en detaljerad studie av magnetdroppsolitoner och spinnvågsdynamik i STNO:er. Slutligen beskrivs en ultrahög frekvensavstämbarhet i STNO:er baserade på magnetiska tunnlingselement med s.k. vinkelrät anisotropi.

SHNO:er: Avhandlingen beskriver också mätningar på SHNO:er baserade på olika strukturer och material, studerade med både konventionella och nya metoder. En detaljerad studie av temperatur och magnetfältsprofiler i s.k. nano-gap SHNO:er presenteras. Dessutom presenterar avhandlingen detaljerade studier av magnetfältsberoendet hos s.k. nano-förträngnings-SHNO:er. Vidare har det visat sig att flera sådana SHNO:er kan synkroniseras seriellt och därigenom få en kraftigt ökad uteffekt. Detta möjliggör i förlängningen också s.k. neuromorfiska beräkningar. Avhandlingen visar att en kedja av sådana SHNO:er också kan synkroniseras även vid låga magnetfält. Slutligen beskrivs de första mätningarna på SHNO:er med hjälp av MFM.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 101
Series
TRITA-SCI-FOU ; 2018:26
Keywords
nanoelectronics, spintronics, nanomagnetism, ferromagnetic materials, microwave oscillators, magnetization dynamics, spin waves, giant magneto-resistance, spin Hall effect, spin-torque nano-oscillators, spin Hall nano-oscillators, numerical modeling, electrical characterization, microwave characterization, magnetic force microscopy.
National Category
Nano Technology Other Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing Physical Sciences Condensed Matter Physics
Research subject
Physics; Materials Science and Engineering; Information and Communication Technology; Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-228391 (URN)978-91-7729-824-3 (ISBN)
Public defence
2018-06-15, Sal B Electrum, Kistagången 16, Kista, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and MedicineSwedish Foundation for Strategic Research Knut and Alice Wallenberg FoundationEU, FP7, Seventh Framework Programme
Note

QC 20180524

Available from: 2018-05-24 Created: 2018-05-23 Last updated: 2018-05-24Bibliographically approved

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Banuazizi, Seyed Amir HosseinEklund, AndersNaiini, Maziar M.Chung, SunjaeMalm, B. GunnarÅkerman, Johan

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