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W IN Collective Effects Kang L. Wang Raytheon Distinguished Professor of Physical Electronics Device research Laboratory Device research Laboratory Center on Functional Engineered NanoArchitectonics -- FENA (www.fena.org) Western Institute of Nanoelectronics – WIN (www.win-nano.org) California NanoSystems Institute – CNSIwww.fena.orgwww.win-nano.org (www.cnsi.ucla.edu)www.cnsi.ucla.edu University of California - Los Angeles Kang L. Wang Raytheon Distinguished Professor of Physical Electronics Device research Laboratory Device research Laboratory Center on Functional Engineered NanoArchitectonics -- FENA (www.fena.org) Western Institute of Nanoelectronics – WIN (www.win-nano.org) California NanoSystems Institute – CNSIwww.fena.orgwww.win-nano.org (www.cnsi.ucla.edu)www.cnsi.ucla.edu University of California - Los Angeles

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2 W IN Outline Introduction Interaction in the space and the Order Parameter Collective effects and state variables Variability issues of spintronics versus nanoelectronics Examples: Spin wave bus MQCA SPIN FET Molecules and atoms Summary

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3 W IN Conventional Electronics employs indept electron entity and Coulomb interaction The solution: To switch to interactions other than Coulomb Charge State Variable (RT) As the size of the devices goes down, the Coulomb (electrostatic) Capacitance energy arises. Leading to the increase of the energy per one electron and thus to high variability as quantum fluctuations become important r u-nm Order Parameter

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4 W IN Whatever the new interaction will be it is going to the some part of the ELECTRODYNAMIC interaction: Single electron level Too weak to work with Corrections for Coulomb Energy ElectroDynamic Interaction = Coulomb + Corrections Dynamic: of relativistic origin including spins, magnetic, multi- ferroics Many-body or Quantum Effective interactions in many-electron collective variables Static: Multi-pole, short ranged ~ 1/r n, n>2 Ferroelectric Big Molecules (collective variables) E> KT

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5 W IN Many-electron collective variables for information processing These we can call a first level collective variables, they are actually fields in space Excitations of these can be called a second level collective variables Collective variable representing the state of many-electron system (e.g., position) Molecules Examples of the order parameters and collective variables

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6 W IN Excitations of the order parameters as the second level collective variables Domain walls in ferromagnets MTJ memory unit can be view as a domain-wall trap oxide layer off (no wall) Fixed layer Free layer on (1 wall) oxide layer Fixed layer Free layer Is it possible to use Ferroelectric or even MultiFerroic, Domain walls, Topological excitations, Goldstones? Are they advantageous in any way ? Topological excitations of the order parameters: for example ferromagnetic vortices off on Goldstone excitations of the order parameter: for example spin waves:

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7 W IN Electronics Spintronics The Same Principle for elemental Electrics and Spintronics circuit units (FET and spin-FET) Variability: Electronics vs Spintronics

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8 W IN 8 Variability Issues Electronics Spintronics Total range spin vector = 2S+1 Thermal fluctuations give Gaussians:

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9 W IN Quantum fluctuations from the quantization of the state variable Spin Fluctuation N a : number of atoms constituting the gate

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10 W IN Variability or a linear length of 77 nm or a linear size of 1.6 nm Charge Spin Room Temperature. Quantum fluctuations of the projection of the Spin Quantum fluctuations of charge Quantum fluctuations of the Total Spin Ovchinnikov and Wang, APL 2008 High enough energy Collective particles

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11 W IN 11 Spintronics for low power – Spin as a state variable For Single Spin B min 155 Tesla – Not practical! E=2 B B = 1.157×10 -4 eV at 1 T) For N Spins Datta, APL 90, (2007) Single electron or collective variables should be used to satisfy thermal stability and power dissipation requirements

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12 W IN Summary Comparison of Electronic, Spin and Optical State Computing Electronic Spin Optical 3kBT3kBT 70k B T 3600k B T 1 nm 20 nm 7 nm MechanismEnergySize Lower bound (Impractical Limit) Practical limit ~3-5 nm Practical limit >20 nm Practical limit >90 nm Victor Zhirnov Independent electrons

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13 W IN Summary Comparison of Electronic, Spin and Optical State Computing Electronic Spin Optical 3kBT3kBT 3kBT3kBT 3600k B T 1 nm 20 nm 2 nm MechanismEnergySize Lower bound (Impractical Limit) Practical limit~20~70 nm Practical limit ~2~7 nm Practical limit >90 nm Correlated electrons

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14 W IN Spin Logic Devices 3-terminal Spin Waves Spin Valves/Spin Torque Magnetic Cellular Automata Sugahara- Tanaka Phase modulation/Amplification/ Superposition Paralle l Anti- Paralle l 0 R AP I1I1 I2I2 I3I3 output Spin FET

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15 W IN Spin Wave Bus -- Spin-Based Logic Device and transfer of information (Phasetronics) Three terminal device (three MOS with a common ferromagnetic film) Two inputs – One output The input is provided by a Source -Drain current pulse - I SD The output is the inductive voltage between two nearest source ( or drain) contacts - V SS

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16 W IN Experiment – Spin wave Propagation Signal/Pulse Generator circulator Oscilloscope 50 GHz 100 nm NiFe Time resolved inductive voltage measured

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17 W IN Prominent modulation by weak (10 50 Gauss) magnetic field Experimental Data – SW transport in CoFe film M. Bao, J-Y Lee, A Khitun, K. L Wang, D. W. Lee and S. Wang, 3-D mapping of spin wave propagation in CoFe thin film, (2007).

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18 W IN General Concept and Some Results Experimental data on amplitude and phase modulation for the structure with 100nm CoFe film in the frequency range (0.5 6 GHz) and magnetic field range (0 350G) Prominent power (8dB/20G) and phase modulation ( 60Deg/10G) in the specific frequency regions Experimental data on amplitude and phase modulation for the structure with 100nm CoFe film in the frequency range (0.5 6 GHz) and magnetic field range (0 350G) Prominent power (8dB/20G) and phase modulation ( 60Deg/10G) in the specific frequency regions AND, OR, NOT gates Maj

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19 W IN detection Input 1 Input 2 In-Phase Out-of-Phase In Phase: Amplification Out of Phase: Cancellation Prototype Three-Terminal Device A. Khitun, M. Bao, Y. Wu, J-Y Kim, A. Hong, A. Jacob, K. Galatsis, and K. L. Wang, Logic Devices with Spin Wave Buses – an Approach to Scalable Magneto-Electric Circuitry, Proceeding of MRS, (in press), 2008 Logic state - spin wave phase Spin wave interferometer Phase control by the direction of current in the excitation loop Only two phases 0 and Logic state - spin wave phase Spin wave interferometer Phase control by the direction of current in the excitation loop Only two phases 0 and

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20 W IN Mitigating eddy current losses in nanoscale devices Continuous metallic Insulating film Eddy current losses severely damp spin waves in a metallic film. 0.1 T CoFe; 100 nm Ferrite (Fe3O4) Continuous metallic 2, 4, or 8 m Eddy current loss can be reduced by laminations. CoFe; 100 nm Jim Allen – UCSB Fig. (1)Fig. (2)

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21 W IN Prototype Device by Kostylev et al: I, A / Kostylev, M.P., et al., Spin-wave logical gates. APL, (15): p Logic state - spin wave amplitude Spin wave interferometer Phase modulation by magnetic field Gradual phase shift control up to 2.5 Logic state - spin wave amplitude Spin wave interferometer Phase modulation by magnetic field Gradual phase shift control up to 2.5

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22 W IN Follow-up work by T. Schneider et al. T. Schneider, A.A. Serga, B. Leven, B. Hillebrands, R.L. Stamps and M.P. Kostylev, Realization of spin-wave logic gates, APL, 92, , 2008 The same device structure as for the prototype (Kostylev et al.) Logic state - spin wave amplitude Phase modulation by magnetic field (Input current 1200mA XNOR, NAND logic gates demonstrated The same device structure as for the prototype (Kostylev et al.) Logic state - spin wave amplitude Phase modulation by magnetic field (Input current 1200mA XNOR, NAND logic gates demonstrated

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23 W IN Speed of Operation Internal delay time = propagation distance/group velocity Propagation distance: ~ (submicron) Group velocity: gr = d /dk (~ 10 7 cm/s ) Delay time ~ ps Experimental Data: 100nm CoFe film, RT Propagation distance: 2 Group velocity: ~10 5 m/s or 10 7 cm/s Experimental Data: 100nm CoFe film, RT Propagation distance: 2 Group velocity: ~10 5 m/s or 10 7 cm/s Current device: 1 ns Ultimate limit: <10 ps The fundamental limit for device operation speed – limited spin wave group velocity. operation speed by the scaling down the signal propagation distance (submicron) The fundamental limit for device operation speed – limited spin wave group velocity. operation speed by the scaling down the signal propagation distance (submicron)

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24 W IN Numerical modeling: Multifunctional MagnetoElectric Cell Sang-Koog Kim, Sung-Chul Shin, and Kwangsoo No Seoul National University, IEEE TRANSACTIONS ON MAGNETICS, VOL. 40, NO. 4, JULY 2004 m - the unit magnetization vector M s - the saturation magnetization - the gyro-magnetic ratio - the phenomenological Gilbert coefficient Landau-Lifshitz-Gilbert formalism A - the exchange constant K - the uniaxial anisotropy constant e - the unit vector along with the uniaxial direction H pulse - the pulse field V M

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25 W IN Spin Wave Modulation by Electric Field R. Ramesh (Berkeley) S. Wang (Stanford) Modulation via the exchange bias coupling in FM/MF structure K. Wang (UCLA) Work Integrated by Ajey P. Jacob (Intel)

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26 W IN Magnetic Nanofabric: Spin Wave multibit processor Piezoelectric Ferromagnetic Film Silicon Substrate Modulator f n ACPS Line (input f 1,f 2 3,…f n ) ME Cell f n ACPS Line (output f 1,f 2 3,…f n ) Silicon Oxide Equivalent circuit

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27 W IN 2/6/20142/6/20142/6/20142/6/2014 PAGE 27 Magnetic Nanofabrics:- Spin Wave devices building blocks- A. Khitun, M. Bao and K. L. Wang (UCLA) (1)(2)

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28 W IN Physical ParameterEstimated Range Energy per bitSpin wave energy1kT – 100kT (H ext ~ 100Oe, V SW : 0.1um um 2 ) Energy to excite spin wave a) External magnetic field (e.g. coil) b) Internal excitation (e.g. spin torque) Energy to create a magnetic field a) 10 2 kT – 10 4 kT ( M/M ~0.01, ~10 7 rad/s/Oe, Z~50Ohm, ~ s) h: 1um – 10nm Ref.1 Number of functions without restoration (amplification) Spin wave coherence length /wavelength (L ~ : 100nm-10nm Signal restoration energy Electromagnetic coupling10 2 kT-10 5 kT - magnetoelectric coupling range from 10 to 1000 mV/(cm Oe) Ref.2 Signal propagation speedSpin wave group velocity10 6 cm/s cm/s (function of film thickness) Time delayPropagation length/Spin wave velocity0.05ns-1ns d range from 1um to 100nm Scaling factor and Defect Tolerance Spin wavelength 10nm - 100nm (insensitive to defects with size << ) Operation frequencySpin wave frequency 1GHz - 200GHz (NiFe, CoFe) Ref.3,4 (depends on the material structure) SW Logic Efficiency Estimates 1) Khitun A., Nikonov D.E., Bao M., Galatsis K., and Wang K.L., Feasibility study of logic circuits with spin wave bus. Nanotechnology 18, p , ) Eerenstein, W., N.D. Mathur, and J.F. Scott, Multiferroic and magnetoelectric materials. Nature, (17): p ) Covington, M., T.M. Crawford, and G.J. Parker, Time-resolved measurement of propagating spin waves in ferromagnetic thin films. Physical Review Letters, (23): p ) Vasiliev S.V., Kruglyak V.V.,Sokolovskii M.L., and Kuchko A.N., Spin wave interferometer employing a local nonuniformity of the effective magnetic field, JOURNAL OF APPLIED PHYSICS 101, p (2007). 1) Khitun A., Nikonov D.E., Bao M., Galatsis K., and Wang K.L., Feasibility study of logic circuits with spin wave bus. Nanotechnology 18, p , ) Eerenstein, W., N.D. Mathur, and J.F. Scott, Multiferroic and magnetoelectric materials. Nature, (17): p ) Covington, M., T.M. Crawford, and G.J. Parker, Time-resolved measurement of propagating spin waves in ferromagnetic thin films. Physical Review Letters, (23): p ) Vasiliev S.V., Kruglyak V.V.,Sokolovskii M.L., and Kuchko A.N., Spin wave interferometer employing a local nonuniformity of the effective magnetic field, JOURNAL OF APPLIED PHYSICS 101, p (2007).

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29 W IN Spin Wave Logic Devices Experimentally demonstrated devices: M.P. Kostylev, A.A. Serga, T. Schneider, B. Leven, B. Hillebrands, Spin-wave logical gates. APL, 87(15): p , T. Schneider, A.A. Serga, B. Leven, B. Hillebrands, R.L. Stamps and M.P. Kostylev, Realization of spin-wave logic gates, APL, 92, , 2008 A. Khitun, M. Bao, Y. Wu, J-Y Kim, A. Hong, A. Jacob, K. Galatsis, and K. L. Wang, Logic Devices with Spin Wave Buses – an Approach to Scalable Magneto-Electric Circuitry, Proceeding of MRS, (in press), 2008 Ferromagnetic resonance controlled by electric field: A.A. Semenov, S.F. Karmanenko, V.E. Demidov, B.A. Kalinikos, S. Grinivasan, A.N. Slavin, J.V. Mantese, Ferrite-ferroelectric layered structures for electrically and magnetically tunable microwave resonators. APL 88, , Spin wave modulation using multiferroics: None

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30 W IN Magnetic Logic - Cellular Automata NAND gates form the building blocks for circuits inside your computer

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31 W IN = Current state-of-the-art: the majority logic gate. Imre et al, Science 311, 205 (2006) Logic Gates using MQCA

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32 W IN Instability of bits Energy (normalized) vs. θ 0° is unstable

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33 W IN Vertical Lines The Problem – stray fields cause vertical bits to flip firstThe Solution – Add stabilizing bits to left and right

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34 W IN The B-gate (NAND function) D. Carlton, UCB

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35 W IN = these gates can be linked together to do logic... D. Carlton, UCB

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36 W IN Nano magnet Switching speed Direct observation of spin transfer switching by x-ray microscopy. Joachim Stöhr – SLAC with Yves Acremann d) 8.6 nse) 9.0 nsf) 9.6 ns g) 12.0 nsh) 12.2 ns i) 13.2 ns a) 0 nsb) 0.15 ns c) 0.6 ns a b c d e f i h g b c d e f g hh i Y. Acremann et al., PRL 96, /1-4 (2006) 20 nm CoPt free layer 5 nm Cu as a tunneling layer Fe as Fixed layer

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37 W IN 37 Spin FET Field Effect in DMS Confirmed Ge MnGe Al 2 O 3 Al JingJing Chen and KL Wang et al., App. Phys. Letts. 90, Schematic Spin gain FET structure with a MnGe/SiGe quantum well. Transistor with Memory

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38 W IN Molecular Building Blocks Phase ChangeMolecular MotionRotational Conformation Physical Molecular Change MEMORY MEMORY applications LOGIC applications

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39 W IN Metal carborane molecules electronic switching Atomic Scale: 90 rotation Cu(II) Cu(I) Molecular Rotation - metallacarboranes ONOFF Rotor Stator Tetrahedral Square planar I-V characteristics Negative differential resistance due to tunneling through molecular rotor Hysteresis due to rotation LUMO HOMO EFEF Metal EcEc EvEv EFEF P + Si 5.2eV 4.6eV 4.1eV

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40 W IN 40 Acknowledgments V Zhirnov and R Cavin A Jacob, J Allen, A Khitun, I Ovchinnikov, M Bao H Ohno, Tanaka, and K Ando All the FENA, WIN & CNSI participants All students, postdoctoral fellows, Faculty and visitors as well as collaborators around the world Support: DARPA, SRC, NSF, Marco, NERC, ARO, AFOSR, ONR, and many industrial companies

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