Nanoelectronics Jan Voves Department of Microelectronics, Faculty of Electrical Engineering, Czech Technical University in Prague voves@fel.cvut.cz
Nanoscale - Microscale nanotubes tranzistors quantum dots MEMS atoms molecules virus blood cels 0.1 1 10 100 1000 nm
Nanoelectronics Structure dimensions comparable to electron wavelength: De Broglie: = h / p (cca 10nm) h... Planck constant quantum effects: discrete energetic levels (in quantum well...) tunneling through the barrier (band-to-band...) interference of wavefunctions (reflection, difraction...)
Emerging Nanodevices Solid State Devices Molecular Devices CMOS Devices Quantum Devices Nano CMOS CNFETs Quantum Dots RTDs SETs Quantum Electromechanical Photoactive Electrochemical Tezaswi Raja, Vishwani Agrawal, Michael Bushnell: Emerging Nanotechnology Devices
Electron Device Scaling
techology node (μm) MOS IO Scaling 10 0.1 0.01 1 3.0um 2.0um 1.5um 1.0um 0.8um L GATE 0.5um 0.35um 0.25um 180nm 130nm 90nm 65nm 50nm 35nm 22nm 13nm 1970 1980 1990 2000 2010 2020 year
Low Dimensional Systems 3D 2D 1D 0D bulk quantum well quantum wire quantum dot g(e) g(e) g(e) g(e) E E E E
heterostructures epitaxy of nanolayers no need of nanolithography 2D system HEMT Quantum Well Lasers QW IR Detectors I I P GaAs E n + GaAs AlAs AlAs n + GaAs I V V E 1 V 1 V 2 emiter E 0 E F collector x Resonant tunneling of electrons RTD, multilevel logic, HF
Resonant Tunneling Double Barrier Quantum Well (DBQW) Structure V = 0 V = V 1 = V P V = V 2 E 0 E F E 1 E F qv 1 E F qv 2 I I P I V V 1 V 2 V
Homostructure Bipolar Transistor n+ n p n+ - - - - n Emitter + p Base Collector
Heterostructure Bipolar Transistor (HBT) n n Broad bandgap emitter p+ n - - - - n Collector + p+ Emitter Base
Heterojunction Bipolar Transistor (HBT) n n p+ graded base n - - - - - - - + p+ n Emitter Base Collector
conductance (2e 2 /ħ) 0 1 2 3 1D system Si nanowires Carbon nanotubes (CNT) Graphene nanoribbons Quantum Wire Quantum Point Contact L 2D d 2D Field effect transistors Thermoelectric materials Light emitting diodes Detectors Sensors Nanolasers Spintronics (GMR, TMR) V g Conductance quantization
Nanowires Solid, one dimensional Can be conducting, semiconducting, insulating Can be crystalline, low defects Can exhibit quantum confinement effects (electron, phonon) Si Nanowire Array Si/SiGe Nanowires
Nanowires Applications Field effect transistors Thermoelectric materials Light emitting diodes Detectors Sensors Nanolasers Superlattice nanowires in applications requiring superlattices Cui et al, Nanoletters, Vol. 3, 149 152 (2003). 5 nm Si nanowire FET
OD system Gate C g Source Self I Assembled Quantum Dots Coulomb blockade - single electron tunneling dot N-1 N N+1 Drain Total energy E(N,V g ) N electrons V g V g gate Single Electron Transistors (SET) Quantum Dot Laser Quantum Cell Array
source: Intel MOS Physical Gate Length
Advanced MOSFET 10 nm gate length high permitivity insulator silicon on insulator (SOI)
Nanotransistors Silicon transistors: L ~ 10 nm Carbon nanotube transistors: L ~ 1 nm Organic nanotransistors: L ~ 0.2 nm Bachtold, et al.,science, Nov. 2001 Schön, et al., Nature,413, 713,2001
FinFET Gate SiO 2 wafer fab compatible technology FET for 32 nm node SiO 2 22 SiO 22 Source Drain BOX Substrate Silicon Fin Fin Source Drain Poly Gate
Carbon Based Nanostructures Carbon-based nanostructures occur naturally and have been found in interstellar dust and geological formations Forms: Carbon nanotubes Carbon onions Buckyballs (C 60 ) http://www.ruf.rice.edu/~smalleyg/index.htm
Carbon Nanotubes
Buckyballs Properties of buckyballs: One molecule = 60 C atoms 7 15 Å in diameter Chemically stable Thermally stable requires > 1000 C to break bonds Adding specific atoms gives unique properties such as superconductivity Photosensitive (polymerizes in UV light) Buckyball caged carbon Potential applications: Tribology Drug delivery Solar cells http://www.mindspring.com/~kimall/fuller/
Carbon Nanotubes Carbon nanotube properties: One dimensional sheets of hexagonal network of carbon rolled to form tubes Approximately 1 nm in diameter Can be microns long Essentially free of defects http://physicsweb.org/article/world/11/1/9/1
Quantum wire MOSFET
Quantum Dots and Arrays Dot occupied by Electron Dot unoccupied Inter-dot Barriers Outer Barriers 3 dimensional island barrier State determined by presence of electron and not by conduction Quantum cell array (QCA) is a lattice of these cells with 2 electrons confined Occupied electrons are furthest from each other due to repulsive forces
Quantum Cellular Automata 1 1 0 1 QCA Wire Stable 1 0 Unstable QCA Inverter 2 states 1 and 0 Electrostatic interaction of nearby cells makes the bits flip Input to the cell is by manipulating the Inter-dot barriers Logic gates can be constructed as shown
LASERS - a brief history 1666 Isaac Newton - refraction of light 1860 James Clark Maxwell - wave equations of light 1900 Max Planck : quantum nature of light 1916 Albert Einstein: stimulated emission 300 years of BASIC RESEARCH! 1953 MASER (microwave LASER) demonstrated by Charles Townes (Nobel prize, 1964) a solution looking 1958 LASER predicted by Townes and Schawlow(BTL) 1960 First working LASER (using ruby crystal) for a problem 1960 s More LASERS: HeNe, Nd:YAG, semiconductor, argon, carbon diodixe,... First applications: spectroscopy, telecoms, cutting,... 1980-90 Multi-billion dollar LASER industry surgery, telecoms, surveying, welding, printers, CD players, security,... a pervading technology
Diode Laser Structures Semiconductor Lasers Edge emitters (single-element & arrays) Surface emitters (mostly arrays) Homojunction DH SH Planar cavity Vertical cavity Stripe Broad area Gain-guided Index-guided Variety of structures
Multiple-Quantum Well Laser (MQWL) MQW using isotype SQW: P p P E C P p P p P p P p P E V hf hf hf hf mini bands
InGaAsP InGaAs Separate Confinement Heterostructure (SCH) P p N InP InP E C InGaAsP InGaAsP x hf E V 5 nm 10 nm 50 nm cladding SCH region MQW region SCH region cladding
Other Structures Vertical Cavity Vertical cavity lasers Vertical Cavity Surface Emitting Lasers (VCSEL) Resonant cavity is in plane of active layer Light resonates between top and bottom of structure Photons have a very short path length (< 1 m) in active region Need high reflectance mirrors to overcome losses Active layer could be SQW or MQW Low thresholds, symmetrical beam profiles, high temp stability Divergence angle of 7-10 Easy to fabricate into one- or two-dimensional arrays
Contact l /4n 2 l /4n 1 Dielectric mirror Active layer Dielectric mirror Substrate Contact Surface emission A simplified schematic illustration of a vertical cavity surface emitting laser (VCSEL).
Spintronics Conventional electronics: charge of electron used to achieve functionalities diodes, transistors, detectors, lasers Spintronics: manipulate electron spin (or resulting magnetism) to achieve new/improved functionalities - spin transistors, memories, higher speed, lower power, tunable detectors and lasers, bits (Q-bits) for quantum computing.
Device Applications spin-led structure - circularly polarised light emission. spin-polarised field effect transistor (spin- FET) - change properties of magnetic layer by applied gate voltage. spin resonant tunneling device (spin-rtd) Multilayers with alternating magnetic and non-magnetic semiconductors giant magnetoresistance (GMR) effect - magnetic field sensors, hard disk industry. magnetoresistive random access memory (MRAM). quantum information processing qubits using coherent spin states in quantum dots
Hard Drive Information Density 100000 Areal Density 10000 GMR Read Head MB/in 2 1000 MR Read Head 100 Inductive Read Head 10 1980 1985 1990 1995 2000 2005 Date of General Availability
Advantages of Spintronics nonvolatility, increased data processing speed, decreased electric power consumption, increased integration densities compared with conventional semiconductor devices.
Challenges in Spintronics achieving a room temperature ferromagnetism in a proper semiconductor material, optimisation of electron spin lifetimes there, detection of spin coherence in nanoscale structures, transport of spin-polarised carriers across relevant length scales and heterointerfaces, the manipulation of both electron and nuclear spins on sufficiently fast time scales.
Predicted Curie Temperatures Si Ge AlP AlAs GaN GaP GaAs GaSb InP InAs ZnO ZnSe ZnTe Room Temperature 10 100 1000 K Dietl et al., Science, (2000)
Device model levels MACROPHYSICAL HYDRODYNAMIC MICROPHYSICAL QUANTUM electron wavelength region electron free-path region local termodynamic equilibrium region 1nm 10nm 100nm 1000nm critical dimensions