1. Collective Effects Kang L. Wang
Raytheon Distinguished Professor of Physical Electronics
Device research Laboratory Center on Functional Engineered NanoArchitectonics -- FENA ( Western Institute of Nanoelectronics – WIN ( California NanoSystems Institute – CNSI (
University of California - Los Angeles

2. Outline Introduction Collective effects and state variables
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
A collection of atoms may be MEMS devices.

3. Charge State Variable (RT)
Conventional Electronics employs indept electron entity and Coulomb interaction r
u-nm
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
Making order parameters such as phase transition, magnetism, etc.
Order Parameter
The solution:
To switch to interactions other than Coulomb

4. Corrections for Coulomb Energy
Whatever the new interaction will be it is going to the some part of the ELECTRODYNAMIC interaction:
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/rn, n>2
Ferroelectric
Big Molecules (collective variables)
Single electron level
E> KT
Too weak to work with

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

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

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

8. Variability Issues Electronics Spintronics
Total range spin vector = 2S+1
The total range spin vector is 2S+1
Thermal fluctuations give Gaussians:

9. Quantum fluctuations from the quantization of the state variable
Spin Fluctuation
Na: number of atoms constituting the gate
This is like to shot noise versus Johson’s noise.

10. Variability Charge Spin or a linear length of 77 nm
or a linear size of 1.6 nm
High enough energy
Collective particles
Quantum fluctuations of charge
For To= 300K we will have the limitation on the size:
or a linear length of 77 nm
or a linear size of 1.6 nm.
Quantum fluctuations of the Total Spin
Room Temperature.
Quantum fluctuations of the projection of the Spin
Ovchinnikov and Wang, APL 2008

11. Spintronics for low power – Spin as a state variable
For Single Spin
Bmin155 Tesla – Not practical!
(DE=2 mB 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
Depending on Gilbert damping factor. 11 11

12. Summary Comparison of Electronic, Spin and Optical State Computing
Independent electrons
Lower bound
(Impractical Limit)
Mechanism
Energy
Size
Electronic
3kBT
1 nm
Practical limit ~3-5 nm
Spin
70kBT
7 nm
Practical limit >20 nm
Optical
3600kBT
20 nm
Practical limit >90 nm
Victor Zhirnov

13. Summary Comparison of Electronic, Spin and Optical State Computing
Correlated electrons
Electronic
Spin
Optical
3kBT
3600kBT
1 nm
20 nm
2 nm
Mechanism
Energy
Size
Lower bound
(Impractical Limit)
Practical limit~20~70 nm
Practical limit ~2~7 nm
Practical limit >90 nm

14. Spin Logic Devices Spin Waves Magnetic Cellular Automata 3-terminal
Phase modulation/Amplification/
Superposition
Magnetic Cellular Automata I1 I2 I3
output
3-terminal
Spin FET
Sugahara- Tanaka
Parallel
Anti-
RAP
Spin Valves/Spin Torque

15. 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 - ISD
The output is the inductive voltage between two nearest source ( or drain) contacts - VSS
This structure is a modification of the previous one :
(i) The ferromagnetic film is placed on the top;
(ii) It is a three terminal device.
All technological parameters are the same as reported by Covington et all. (slide 5)

16. Experiment – Spin wave Propagation
Signal/Pulse
Generator
circulator
Oscilloscope
50 GHz
100 nm NiFe
The general idea of using inductively coupled circuits for information processing is to transmit information between the circuits using a magnetic flux without transmitting current via wires. According to the Faraday’s law, the change of the magnetic flux through the surface generates an inductive voltage proportional to the rate of the magnetic flux change. The change of magnetization in the magnetic material alters the outgoing magnetic flux and results in the inductive voltage signal. In this case, the change of magnetization is through the propagation of spin waves.
The figure shows the inductive voltage measured for the device – simulated and measured.
Time-resolved inductive voltage measurement technique used for measuring spin wave. The dashed line depicts the voltage pulse applied to the excitation line. The pulse characteristics are as follows: pulse amplitude 24.5V; rising time 1.2ns; and pulse length 20ns. The solid line depicts the inductive voltage signal detected by the detection line. One can see the inductive voltage oscillation at the detection line caused by the inductive coupling via the spin waves. The output voltage signal has maximum pulse amplitude 26mV, and the period of oscillation is 9ns.
Time resolved inductive voltage measured

17. Experimental Data – SW transport in CoFe film
Prominent modulation by weak (10  50 Gauss) magnetic field
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).

18. 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
“AND”, “OR”, “NOT” gates
Maj

19. Prototype Three-Terminal Device
Logic state - spin wave phase
Spin wave interferometer
Phase control by the direction of current in the excitation loop
Only two phases 0 and 
detection
Input 1
Input 2
In-Phase
Out-of-Phase
In Phase: Amplification
Out of Phase: Cancellation
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

20. 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)
2, 4,
or 8 mm
Eddy current loss can be reduced by laminations.
Fig. (1)
Fig. (2)
Jim Allen – UCSB

21. Prototype Device by Kostylev et al:
Logic state - spin wave amplitude
Spin wave interferometer
Phase modulation by magnetic field
Gradual phase shift control up to 2.5
I, A
/
YIG (Yittrium iron Garnet) was used. L is 8 mm between the transducer and detector. Backward volume magnetostatic waves (BVMSW) and MSSW (magneto static spin waves)
Kostylev, M.P., et al., Spin-wave logical gates. APL, (15): p

22. Follow-up work by T. Schneider et al.
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
YIG (Yittrium iron Garnet) was used. Backward volume magnetostatic waves (BVMSW) and MSSW (magneto static spin waves)
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

23. Propagation distance: 2 Group velocity: ~105 m/s or 107cm/s
Speed of Operation
Internal delay time = propagation distance/group velocity
Propagation distance: ~ (submicron)
Group velocity: gr= d/dk (~ 107 cm/s )
Delay time ~ ps
Experimental Data:
100nm CoFe film, RT
Propagation distance: 2
Group velocity: ~105 m/s or 107cm/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)

24. Numerical modeling: Multifunctional MagnetoElectric Cell
m - the unit magnetization vector
Ms - 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
Hpulse - the pulse field M V
Sang-Koog Kim, Sung-Chul Shin, and Kwangsoo No Seoul National University, IEEE TRANSACTIONS ON MAGNETICS, VOL. 40, NO. 4, JULY 2004

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

26. Magnetic Nanofabric: Spin Wave multibit processor
Piezoelectric
Ferromagnetic Film
Silicon Substrate
Modulator f n
ACPS Line
(input 1 ,f 2 3
,…f )
ME Cell
(output
Silicon Oxide
Here we have a set of converters, modulators, and magneto-electric cells arranged in a sequence. Two antenna transmission lines on the edge are aimed to excite and detect spin wave signals on different frequencies. The pair of modulator and magneto-electric cell is adjusted to modulate/amplify spin wave signals on specific frequency.
At the bottom, we have an equivalent circuit.
Equivalent circuit

27. Magnetic Nanofabrics:- Spin Wave device’s building blocks- A. Khitun, M. Bao and K. L. Wang (UCLA)
(1)
(2)
The set of figures on the left are the basic elements that are developed for building magnetic circuits on the right.
so, (1) we have a converter to translate input voltage pulse into spin wave signal and vice versa.
(2) Spin wave guides to transmit spin wave signal through the circuit. Depending on the design, we could make a splitter or a combiner of the spin wave.
(3) Modulator to provide pi-phase shift to the propagating spin wave.
(4) Magneto-electric cell – multifunctional element to serve as a memory and an amplifier for spin wave signal
(5) this is the simple circuit of a one-bit logic comprising of input converter, modulator, magneto electric cell and output converter.
(6) Three input majority gate that has a converters, combiner and the magnetoelectric cell.
(7) Multifunctional logic gate built on the base of the majority gate by introducing two modulators. Depending on the control voltages applied to the modulators, the gate operates as AND, OR, NAND, and NOR logic gates.
3/27/20173/27/20173/27/20173/27/20173/27/2017

28. SW Logic Efficiency Estimates
Physical Parameter
Estimated Range
Energy per bit
Spin wave energy
1kT – 100kT
(Hext ~ 100Oe, VSW: 0.1um um2)
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)
102kT – 104kT
(M/M ~0.01, ~107 rad/s/Oe, Z~50Ohm,  ~ 10-12s)
h: 1um – 10nm Ref.1
Number of functions without restoration (amplification)
Spin wave coherence length /wavelength
(L ~ : 100nm-10nm
Signal restoration energy
Electromagnetic coupling
102kT-105kT
 - magnetoelectric coupling
range from 10 to 1000 mV/(cm Oe) Ref.2
Signal propagation speed
Spin wave group velocity
106 cm/s - 107cm/s
(function of film thickness)
Time delay
Propagation length/Spin wave velocity
0.05ns-1ns
d range from 1um to 100nm
Scaling factor and Defect Tolerance
Spin wavelength 
10nm - 100nm
(insensitive to defects with size << )
Operation frequency
Spin wave frequency 
1GHz - 200GHz (NiFe, CoFe) Ref.3,4
(depends on the material structure)
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 , 2007.
2) Eerenstein, W., N.D. Mathur, and J.F. Scott, Multiferroic and magnetoelectric materials. Nature, (17): p
3) 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
4) 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).

29. 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 , 2005.
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, , 2006.
Spin wave modulation using multiferroics:
None

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

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

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

33. Vertical Lines
The Problem – stray fields cause vertical bits to flip first
The Solution – Add stabilizing bits to left and right

34. The B-gate (NAND function)00 10 01 11
D. Carlton, UCB

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

36. Nano magnet Switching speed
Direct observation of spin transfer switching by
x-ray microscopy.
d) 8.6 ns
e) 9.0 ns
f) 9.6 ns
g) 12.0 ns
h) 12.2 ns
i) 13.2 ns
a) 0 ns
b) 0.15 ns
c) 0.6 ns a b c d e f i h g
20 nm CoPt free layer
5 nm Cu as a tunneling layer
Fe as Fixed layer
20 nm CoPt free layer: 5 nm Cu as a tunneling layer and the Fe as Fixed layer.
The circularly polarized x-ray beam from an undulator
on beam line at the Advanced Light Source
(ALS) is incident 30 from the surface normal. It is focused
to 30 nm by a zone plate. The transmission of the
x rays through the whole pillar is monitored by a fast
avalanche detector as a function of the position x; y while
the pillar is scanned in steps of 10 nm across the x-ray
focus. Tuning the photon energy to the characteristic Co L3
resonance provides magnetic contrast through the x-ray
magnetic circular dichroism (XMCD) effect [19].
Y. Acremann et al., PRL 96, /1-4 (2006)
Joachim Stöhr – SLAC
with Yves Acremann

37. Field Effect in DMS Confirmed Transistor with Memory
Spin FET
Field Effect in DMS Confirmed Ge
MnGe
Al2O3 Al
Schematic Spin gain FET structure with a MnGe/SiGe quantum well.
Transistor with Memory
Bohr magneton: e*hbar/2m
μB = (80) × J·T-1
JingJing Chen and KL Wang et al., App. Phys. Letts. 90,

38. Molecular Building Blocks
Physical Molecular Change
Molecular Motion
Rotational Conformation
Phase Change
Put mems materials to this.
MEMORY applications
LOGIC applications

39. Molecular Rotation - metallacarboranes
Metal carborane molecules
“electronic switching”
Atomic Scale: 90 rotation Cu(II)   Cu(I)
Rotor
Stator
Tetrahedral
Square planar
“ON”
“OFF”
LUMO
HOMO EF
Metal Ec Ev
P+ Si
5.2eV
4.6eV
4.1eV
Cu Carborane has 90 degree switching ability. (Phen), Switching voltage may be ~ 1V.
As part of the FENA center, we are in the process of taking these molecules to the solid state
Similarly, these nickel carborane molecules Ni (iii) to (IV) are based on a redox process, which rotates the ligands by 180 degrees changing the tunneling current and alterning the conductivity through the structure
I-V characteristics
Negative differential resistance due to tunneling through molecular rotor
Hysteresis due to rotation

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