GMR multilayer system and its investigation Konstanty Marszalek AGH University of Science &Technology
Outline Motivation GMR Objectives engineering of Co/Cu multilayers structure with the use of surfactants Processes during film growth Application of surfactants to modify multilayers structure Conclusions
molecule <1nm protein Nanotechnology bacterias erythrocytes ~5 μm leukocyte Investigation DNA 1 μm and application of structures 100 nm (1 nm nanometer = 1 nm = 10-9 m) scale 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 Transistor SOI width 0.12μm semiconducting nanocristal ~1 nm Nanotubes transistor IBM PowerPC 750 TM Mikroprocesor 7.56mm 8.799mm 6.35 10 6 transistors Integrated circuit Cu traps width. 0.1μm
Nanoworld Microworld
Random Access Method of Accounting and Control (RAMAC) 4 MB 50x24 plates 1200 rpm 100 ms access Tubes not transistors First computer disk drive built by IBM in 1956 as part of RAMAC. On the right side of the image, some of the 50 platters are seen. In the center of the image is a pneumatically controlled access mechanism.
10 years latter 1.6 meters
Magnetic read / write processes
1957 Semiconductor heterostructures : GaSb, InAs Z. I. ALFEROV H. KROEMER J. S. KILBY Applications: semiconducting lasers photodetectors, solar cells Integrated semiconducting optics chips 1987 Discover of the antiferromagnetic coupling In metallic heterostructures: FeCr, CoCu leading to giant magnetoresistivity M.N.Beibich et al PRL 61,2472,(1988) 2000 Nobel Applications: Magnetoresisting sensors of current, position, rotation read heads in hard disc storage MRAM
Interlayer antiferromagnetic coupling Source spin dependent scattering Giant magnetoresistance Giant magnetoresistance effect ΔMR=(MR-MR S )/MR S
Diffusion processes during thin film growth Claster degradation Cluster diffusion Diffusion along the edge Diffusion trough the edge Deposition Adsorption to the edge Surface diffusion Cluster creation
Ehrlich-Schwoebel Barier Ehrlich-Schwoebel barier: Does not permit adatoms to drop through edge Leads to 3D growth of the film
How to modify growth in the presence of Ehrlich-Schwoebel barrier? - to diminish barrier at the edge (ES barrier reduction) - to increase surface diffusion barrier (growth temperature) What surfactants make? Surfactants increase mass transport between layers by segregation to the surface change growth mode from 3D to 2D
Low angle x-ray reflectometry Information: thickness periodicity roughness (as a global parameter)
Structure of interface and surface of Co/Cu multilayers σ rms = 0.7 nm 100 nm σ rms = 0.85 nm 100 nm σ rms = 1.2 nm 100 nm
Surface and thin films laboratory Ultra-high vacuum setup for preparation of thin films and multilayers Chemical and structural analysis of surfaces Low Energy Electron Diffraction - LEED Auger Electron Spectroscopy - AES Atomic Force Microscopy - AFM Magnetic and magnetotransport properties Perturbed Angular Correlations spectr. - PAC Resistivity measurement in magnetic field with four point probe method Materials: metallic multilayers, thin films, nanostructures Preparation method: thermal evaporation from 4 sources with thickness control
Magneroresistance four probe method measurement +I -I - U + s 1 s 2 s 3 0 x1 x2 Substrate Podłoppp
Sample preparation 20 Si / x nm Pb / (Co / Cu) N X = 5, 10, 20, 30, 40 nm Vacuum conditions: 1 x 10-8 mbar 0.05 0.1 Ǻ/s
Multilayer system [Co/Cu] n Buffer layer: Ag, Cu, Pb (also Bi i In) The number of bilayer repetition Co/Cu n=5,10,20 Cu 2 nm Co 1 nm Buffer layer
...and how in case we use surfactants as a buffer layer Only buffer layer Multilayer system [Co/Cu] 20 Bi In Pb
What is the influence of the observed properties on the magnetoresistanc?
How the topografy of the surface is changing when we differ Pb film thickness?... 5 nm 20 nm 40 nm... and what when we increase repetition of Co/Cu bilayer d Pb = 5 nm N=5 N=10 N=20
How the magnetoresistance is changing?
Short resume: Application metals in the buffer layers well known as surfactans increases multilayer magnetoresistance but strongly modify growth Perturb its peridicity The use of surfactans transform multilayer systems in a granular alloy Where Pb is located?
How does the growth of the multilayer system look on 5 nm Pb film?
We start multilayer deposition from 1 nm Co......and next we deposit 2 nm Cu
Similar like in the case of thicker Pb buffer layer...(30 nm)
Summary: Application of metallic surfactants in a buffer layer Increases magnetoresistance of multilayer system but Strongly modifies its growth distroys its periodicity changes multilayer system in a granular alloy Lead always remains on the surface of the system.
What are the next topics : Atomic break junctions Qubits Perpendicular magnetic anisotropy devices Magnetic semiconductors MEMS etc. The End
AGH University of Science and Technology Electrical Engineering Faculty Electronics Department Thin Film Groups Electronics Groups Sensors Photovoltaic Fiber optics Digital Signal Processing Magnetic storage Microwave Vacuum equipments Electronic circuits
In-line 7 chamber sputtering system for large area deposition
Batch, tree chamber sputtering deposition system Control unit Vacuum Part
Thank you for your attention
Thank you for your attention
The structure of the Co/Cu multilayer with In surfactant X-ray reflectometry Intensity [a. u.] 10 12 10 10 10 8 10 6 10 4 10 2 10 0 ρ, t, σ (top) ρ, t, σ (X) ρ, t, σ (C) ρ, t, σ (B) ρ, t, σ (A) ρ, σ (S) W. protekcyjna Warstwa X Warstwa C Warstwa B Warstwa A Intensity (cps) 10 7 10 6 10 5 10 4 10 3 10 2 10 1 10 0 [CoCuIn] 20 [CoCu] 20 calc. 0 1 2 3 4 5 6 7 8 Glancing angle ( o 2θ) 1 2 Podłoże 3 4 5 2Θ z
Jak wygląda topografia powierzchni bez warstwy buforowej oraz na warstwie buforowej Ag i Cu... Only buffer layer Multilayer system [Co/Cu] 20 Without buffer layer Ag Cu
Growth 1 nm Co on Si
Growth 5 nm Cu on Si
Groth 1 nm Co on 5 nm Cu
Growth 2 nm Cu on the bilayer 5nm Cu/1 nm Co
Giant magnetoresistance Cienkie warstwy ferromagnetyczne (Co, NiFe) oddzielone cienkimi warstwami niemagnetyczny mi (Cu, Au) Spin valve multilayers Granular alloys Resistance depends on magnetic field R AP >> R P
Quality of interface critical Processes on surfaces during film growth
Jak zmodyfikować wzrost w obecności bariery Ehrlicha-Schoebela? zmniejszyć barierę na stopniu/krawędzi zwiększyć barierę dyfuzji powierzchniowej Przez zastosowanie surfaktantów modyfikują wzrost 3D do 2 D pozostają na powierzchni warstwy zwiększają transport masy pomiędzy warstwami Jak? klasycznie -przeskakując barierę - νexp(-e a /kt) nietradycyjnie -wbudowując się w powierzchnię, zakopując lub wypychając adatomy
Co wpływa na własności układów wielowarstwowych? Charakter międzywierzchni: topografia szorstkość mieszanie/ podczas wzrostu lub po utworzeniu międzywierzchni Konkurencja pomiędzy kinetyką a termodynamiką/ energie aktywacji kontra bariery energetyczne
Spektroskopia elektronów Augera
What is the multilayer structure?
Sensory magnetoporowe Czujniki położenia Biosensory
Przykład 1 modyfikacja struktury warstw zastosowanie surfaktanta Bariera Ehrlicha-Schwoebela Surfaktant E S Warstwa nanoszona E D E A miękkie metale duża objętość atomowa szybka dyfuzja powierzchniowa niska energia powierzchniowa surfaktant
Przykład 1 -Topografia powierzchni wielowarstw Co/Cu modyfikowanych surfaktantem rejestrowana Skaningowym Mikroskopem Sił Wiązka laserowa Sprężysty uchwyt sample bez In Pomiar siły pomiędzy uchwytem a próbką poprzez rejestrację odchylenia wiązki laserowej odbitej przez Układ wielowarstwowy [Co(1 nm)/cu(2 nm)] sprężynkę ( miękka sprężynka k = 0.01 do 10 20 N/m). z In
Przykład 1 - W jaki sposób ind modyfikuje strukturę układów wielowarstwowych Co/Cu? Spektroskopia elektronów Auger 0,0015 0,0010 25A Ni/75A Gd T = -140 0 C 0,0005 dn/de 0,0000-0,0005-0,0010 Gd 1nm Cu Ni Ni - 74,7% Gd - 18,6% O - 3% C - 3,7% 0,0015 0,0010 C 25A Ni/75A Gd 0.06 nm In T = +480 0 C dn/de 0,0005 0,0000-0,0005-0,0010 Ni - 12,7% Gd - 74,4% O - 8,5% C - 4,4% 2nm Cu 1nm Co 0 200 400 600 800 1000 1200 E (ev) Si(100)
Techniki obrazowania powierzchni - mikroskopia Porównanie: STM AFM atomowa zdolność + - rozdzielcza próbki przewodzące + + izolatory - + topografia powierzchni + +