材料物理课件学习PPT文档

1、会计学1材料物理课件学习材料物理课件学习PPT文档文档Nanoscale devices Electronic Nanocomputers Quantum mechanical tunneling effect Chemical Nanocomputers Stores information in the chemical bonds: DNA etc. Mechanical Nanocomputers Moving molecular scale parts: how to assemble ? Quantum computer Each bit of information as a q

2、uantum state: spins etc Solid state nanoelectronic devicesQuantum dots “artificial atoms” (QD): 0-DResonant Tunneling Devices (RTD, RTT): 1- or 2-DSingle Electron Transistor (SET): 3-DQuantum Cellular Automata (QCA)Magnetic Random Access Memory (MRAM)Islands confineelectronsFunction of transistor -

3、Two state device or switch - Amplificationp-typeB dopedHole carriern-typeP, As dopedElectron carrierBP- +- +- +-EF p nSome of the free electrons in the n-region diffuse across the junction and combine with holes to form negative ions. In so doing they leave behind positive ions at the donor impurity

4、 sites. VGate = 5V 4 V 3 V 2 V High electric field due to bias voltage to short distance - avalanche break down due to high kinetic energy electrons - tunneling through insulating layers Heat Dissipation of transistors due to limited thermodynamic efficiency - molecular scaled device: as much heat a

5、s gunpowder Vanishing bulk properties and nonuniform dopant concentration - few dopant atoms in nano scale: functioning as transistor? - quantum mechanical effect Shrinkage of depletion regions( kT DE = eV Ec R1) - Current steps at e/2C2 + n(e/C2)esourcedraingateIslandN= 2 1 0 N= 2 1 vIVonoffR1 R2C1

6、 C2R2/R1 =1000R2/R1 =1S.Y. Chou et al, Appl. Phys. Lett 67, 938 (1995)Si dot with 20nm diameter : energy spacing = 40meV Current oscillation due to the interference between different modes of quantum waves in a cavityUnclear coulomb staircase due to the symmetric size of the tunnel junctonCoulomb st

7、aircase with periods of 150mVeSourceDrainGateIslandStorage dotDiscrete shift in the threshold voltageStaircase relation between the charging voltage and the shiftSelf-limiting charging processP. Avouris et al ,Appl. Phys. Lett, 73, 2447 (1998)The amount of current (ISD) flowing through the nanotube

8、channel can be varied by a factor of 100,000 by changing the voltage applied to a gate (VG), I. Amlani et al, Science, 284, 289 (1999)Wireless interconnectionCommunicate by the electric fields of electrons Y. Cui and C.M. Lieber, Science 291, 851 (2001)Common base current gain: IC/IE=0.94Common emit

9、ter current gain: IC/IB=16EFE B C n p nVEBVCBValley current in RTD - not clear on and offSensitivity to input and current fluctuations - accidental on and offCryogenic operation: 30nm Si SET at 150 K - reducing size: Ec and De increase.Materials: Si is still preferred - SiO2 is still best insulator

10、- GaAs is far inferior to electric fieldsBackground charge problemsExtreme sensitivity of the tunneling current to width of potential barriers - SOI technology or nonpolarizable organic compoundsExtreme difficulty of making islands and tunnel barriers precisely and uniformlyMolecular electronic devi

11、cesVoltage pulse yieldshigh conductivityState - data bit storedBit is read as highin low voltage regionApplied perpendicular field favorszwitterionic structure which is planarBetter pi overlap, better conductivity.Nature Photonics 1, 717 - 722 (2007) Adv.Mater,2004,16,No.12,1009-1013Appl. Phys. Lett

12、. 90, 222109 2007Function of transistor - Two state device or switch - AmplificationS.Y. Chou et al, Appl. Phys. Lett 67, 938 (1995)Si dot with 20nm diameter : energy spacing = 40meV Current oscillation due to the interference between different modes of quantum waves in a cavityY. Cui and C.M. Lieber, Science 291, 851 (2001)Co