04/06/2004 DENikonov, Talk at Texas A&M PAGE 1Overview of Spintronicsand Its place in the Semiconductor Industry RoadmapDmitri NikonovCollaborators: George Bourianoff (Intel)David Awschalom, Wayne Lau (UCSB)04/06/2004 DENikonov, Talk at Texas A&M PAGE 2IntroductionGood to be home !!!04/06/2004 DENikonov, Talk at Texas A&M PAGE 3Questions• What is scaling of transistors and why beyond CMOS devices are required ?• What is the field of spintronics ?• How to manipulate spins ?• How to inject and detect spins ?• Road to the future ?* Disclaimer: no original material, subjective review of publications, very superficial, incomplete, not always quoted the pioneering publication04/06/2004 DENikonov, Talk at Texas A&M PAGE 4Moore’s LawNo exponential is forever, but we can delay “Forever”1,000,000100,00010,0001,000101001’75 ’80 ’85 ’90 ’95 ’00 ’05 ’10’151 1 Billion Billion TransistorsTransistors808680286i386™ Processori486™ ProcessorPentium®ProcessorPentium®Pro ProcessorK TransistorsPentium®II ProcessorPentium®III ProcessorPentium®4 Processor04/06/2004 DENikonov, Talk at Texas A&M PAGE 5Scaling into Nanotechnology10000100001000100010010010101010110.10.10.010.01MicronMicronNanoNano--metermeterNominal feature sizeNanotechnologyNanotechnology130nm130nm90nm90nm70nm70nm50nm50nmGate Width19701970198019801990199020002000201020102020202004/06/2004 DENikonov, Talk at Texas A&M PAGE 6Fundamental Limits Are NearaEbaEbwwZhirnov et al., Proc. IEEE 91, 1934 (2003).222biteEmw=ln 2bit BEkT≥minbitEτ=1.5nmw =min40fsτ=212.8 10 J 17meVbitE−=× =04/06/2004 DENikonov, Talk at Texas A&M PAGE 7Power Grows ExponentiallyPresently computing scaling is mostly limited by power dissipation100W/cm2Like a hotplate!!!04/06/2004 DENikonov, Talk at Texas A&M PAGE 8Future Integrated Circuit* European Technology Roadmap for Nanoelectronics04/06/2004 DENikonov, Talk at Texas A&M PAGE 9Requirements to Devices• Performance (esp. gain)• CMOS architectural compatibility• Operational reliability • CMOS process compatibility• Room temperature operation• Energy efficiency• Low sensitivity to parameters• Scalability04/06/2004 DENikonov, Talk at Texas A&M PAGE 10International Technology Roadmap for SemiconductorsTwo numbers: Performance potential Risk3 = better than CMOS 3 = solutions known2 = comparable to CMOS 2 = concept feasible1 = worse than CMOS 1 = no known solution04/06/2004 DENikonov, Talk at Texas A&M PAGE 11My Definition of Spintronics• Spintronics IS• Science and technology of• manipulation of particle spins• in coherent quantum states• in non-equilibrium• IS NOT• (Collection of phenomena)• (Spectroscopy)• (Optical pumping)• (Traditional magnetics)04/06/2004 DENikonov, Talk at Texas A&M PAGE 12Atomic Spintronics=Orbital I=1Spin S=1/2Electron J=1/2NaElectron J=1/2=Nuclear i=3/2Total F=2Laser λ1Laser λ2Good example of spin manipulation in atoms. Coherent state created. Electromagnetically-induced transparency and Lasing without inversion is observed.E.S.Fry, X.Li, D.Nikonov, G.G.Padmabandu, M.O.Scully, A.V.Smith, F.K.Tittel, C.Wang, S.R.Wilkinson, S.-Y.Zhu, Phys. Rev. Lett. 70, 3235 (1993).04/06/2004 DENikonov, Talk at Texas A&M PAGE 13Metal SpintronicsFeCrFeAFcurrentFeCrFeAFno currentAnti-ferromagnetic layer “pins” the magnetization of the bottom layerLow resistance if the two ferromagnetic layers are parallel, high resistance if anti-parallelUsed to be current in plane, now current perpendicular to the plane configurations04/06/2004 DENikonov, Talk at Texas A&M PAGE 14Magnetoresistance* Courtesy S. Wolf (DARPA)Low ResistanceCo Cu CoCo Cu CoHigh ResistanceMetallic energy states.In a ferromagnet a band with one spin is completely occupied and not conductingNo available states for electrons with the spin which is conductedECuCoE fEN(E)N(E)04/06/2004 DENikonov, Talk at Texas A&M PAGE 15Spintronics for Storage• When can one buy spintronics in a store? TODAY !!!• Giant magnetoresistance (many layer of interchanging magnetization) – how most of 10GB –100GB hard drives are made• 1MB Magnetic-RAM chip made on 0.5um CMOS, <35ns access, magnetoresistance >40%* Finding names of the companies left to reader as a homework04/06/2004 DENikonov, Talk at Texas A&M PAGE 16Map of Semiconductor SpintronicsSeemingly disconnected fields of researchSpin manipulationOptical, magnetic, electricalPicosecond pulsesSpin injectionTunneling barriersSwitching of magnetizationFerromagnetic semiconductorsBand structureSteady-state04/06/2004 DENikonov, Talk at Texas A&M PAGE 17Spin in Magnetic FieldPrecession in the magnetic field.g-factor depends on the materialg=2 for electron in vacuumdGdt=×SSB2egqGm=2Beemµ=G=µSHamiltonianMagnetic moment vs. spinGyromagnetic ratio vs. g-factorBohr magnetonBloch equationBmaggqHeµ=− =SBµBii04/06/2004 DENikonov, Talk at Texas A&M PAGE 18Optics is Spintronics’ Best FriendPolarized light is the most natural way to create and detect spin polarization in semiconductorE-h pair1/21/21/2-3/2 -1/2 3/21/2-1/2electronshhlhekElight holesheavy holes321321Rel. squares ofmatrix elements04/06/2004 DENikonov, Talk at Texas A&M PAGE 19Faraday Effect04/06/2004 DENikonov, Talk at Texas A&M PAGE 20Time-Resolved Faraday RotationCirc. polar. pump, linear polar. 45deg probe, dt=50 to 900 ps, 50um spotCrooker, Awschalom, Samarth, IEEE Select. Topics Quant. Electr. 1, 1082 (1995).04/06/2004 DENikonov, Talk at Texas A&M PAGE 21Faraday ResultsInteresting non-monotonic dependence of spin lifetimeKikkawa, Awschalom, Phys. Rev. Lett. 80, 4313 (1998).04/06/2004 DENikonov, Talk at Texas A&M PAGE 22Motion of Spins in a Semiconductor560 umpumpprobeDxInject spins at xDetect spins at x + dxdistancetime• Spin coherence persists for 100’s of nanoseconds over 100’s of microns• Largely insensitive to temperatureKikkawa and Awschalom, Nature 397, 139 (1999)04/06/2004 DENikonov, Talk at Texas A&M PAGE 23G-factor ModulationH = g µΒS·Bg-factor depends on material compositionAl concentration x00.1 0.2 0.3 0.4g-factor0-0.40.4Weisbuch et al., Phys. Rev. B 15, 816 (1977)g-factor in AlxGa1-xAsMagnetic fieldParabolic Quantum Well (PQW)Al composition is parabolicallygraded to allow translation of the whole wavefunction to higher Al content regionE=0E>0g-factorincrease04/06/2004 DENikonov, Talk at Texas A&M PAGE 24G-factor Modulation ResultsSI-GaAs substrateGaAs buffer/smoothing SLn-GaAs (back gate)LT-GaAsAlGaAs Barrier100nm PQW