Class Notes WW10
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Class Notes WW10 Presentation Transcript

  • 1. The Applications of Nano Materials Department of Chemical and Materials Engineering San Jose State University Zhen Guo, Ph. D.
  • 2. How to study Nanomaterials Microstructure Properties Materials Applications Processing Basic Materials Science Principles Part I -- Done Part II – Done Part III – This one
  • 3. The Applications of Nano Materials Nano Materials Applications Electronics Magnetic Device Optics MEMS Bio Device Structure Daily Life consumable Renewable Energy
  • 4. Applications of Nano Materials Dr. Danielle Chamberlin, Agilent Corp (Term paper due) Application ( VI I) – Nano Materials and Optical Device Week 15 05/11 Dr. Sun Lei Digital Health, Intel Corp. Applications (V I ) -- Biochemical Properties of Nano Materials Week 14 05/04 Dr. Geetha Dholakia NASA AMES Research Center Application (V) – Nano materials applications on Aerospace Week 13 04/27 Prof. Jiangyu Li University of Washington Application ( I V) – Nano Magnetic Materials Week 12 04/20 Prof. David Mitlin University of Alberta Application ( III ) – Nano Materials and Renewable Energy source Week 11 04/13 Blue Sheet #4 Peer review comment Due Application (I I ) – Nano Electric Materials: Quantum Computing Logic Device and memory Week 10 04/06 Quiz #4 1st Draft Due (3 copies) Application (I) – Nano grained structural materials and Nano Composite Week 9 03/22
  • 5. Session X – Nano Electric Materials -- Single Electron Transistor -- Other Novel Transistor -- Nano Crystal Memory -- Phase Change Memory
  • 6. MOSFET Principles
    • Review MOSFET principles – accumulations, depletion, and inversion. Vt, Vg, Ids, Idsat, etc.
    • Just remember that Electrons are like water, source / drain like two bottles, channel is a pipe in between and gate is like a valve to open / close the pipe...
  • 7. Single Electron Box
    • Single Electron Box
      • One Quantum Dot
      • Two Electrodes
      • Tunneling Junction
      • Control Gate Capacitor
    • Electrons are injected/ejected into / from quantum dots thru tunneling junctions.
    • Extra electrons injected into quantum dots will lead to excessive charging energy
    Courtesy from Rainer Waser: Nano-electronics and Information technology PP427-445
  • 8. Coulomb Blockade
    • Coulomb Blockade is caused by excessive charging energy Wc which increase as the size of quantum dot decrease
    With adding extra electron into QD http://www.plus2physics.com/capacitors/study_material.asp W c =e 2 /2C sp r  => C sp  => W c  When Wc >> kT, thermal energy is no longer sufficient to overcome excessive charging energy => Coulomb Blockade
    • Quantum Effect of Coulomb Blockade – Quantum confinement cause energy level split => next electrons may need to occupy higher energy level
    W c = e 2 /2C sp +  E (n)
  • 9. Bias Condition for Coulomb Blockade
    • When gate voltage is zero, the charge at quantum dot is zero.
    • As gate voltage increases to a certain value, electrons are attracted to quantum dot, making 1e net charge of dot
    • Further increase gate voltage will increase electron number.
  • 10. Bias Condition for Coulomb Blockade
    • To maintain the electron number in quantum dots, we have
    Courtesy from Rainer Waser: Nano-electronics and Information technology
    • To substitute the equations in previous slide, we obtained
    When Consider both sides, we have or
  • 11. Single Electron Transistor (SET)
    • SET – three terminal switching device that can transfer electron one by one from source to drain
    Courtesy from Rainer Waser: Nano-electronics and Information technology -- can be considered as two independent tunneling junctions -- Each will have to satisfy Coulomb Blockade conditions
  • 12. Single Electron Transistor (SET) Con’d: Two Equations can be reduced to Source Blue Line Drain Red Line
    • In grey area, both source and drain satisfy coulomb blockade condition for same n value=>Fixed # electrons.
    • In green area, source and drain satisfy different value.
      • -- In Area A, for source junction, it satisfy n=1 so one electron will tunnel from source to QD
      • -- Once electron at QD, it found that drain junction is favor n=0 so this electron will further tunnel to drain
      • -- Current Flow from source to drain
      • -- Giving a small Vds, Ids will vary with Vg periodically
      • -- Vg can behave as a switch. Vg=0, need Vds greater than threshold, Vg=e/2Cg, linear Ids verse Vds
  • 13. Fabrication of SET (I)
    • PADOX – Pattern Dependent Oxidization
      • -- 1-D Si Nano Wire connected with 2-D Si layers at both ends
      • -- Oxidization process forms tunneling barriers at both ends.
      • -- Can be either width or thickness modulated.
      • -- For Vertical PADOX, it is possible to form 2 tiny islands
  • 14. Fabrication of SET (II)
    • Surface-Treated SOI Channel
      • -- 1-D SOI channel intentionally undulated with alkaline based solutions
      • -- The nano scaled undulation results in potential fluctuation due to the difference of quantum confinement effect from one part to another.
      • -- The channel effectively splits into several quantum dots.
      • -- Process is completely compatible with current CMOS fabrications
  • 15. Advantage and Disadvantages
    • Advantages:
      • Lower power assumption
      • Good scalability
    • Disadvantages
      • Operated usually at low temperature
      • High output impedance due to tunneling
      • Vds has to be less than Vg to have gate fully control the switch.
  • 16. Other Novel Logic Transistor
    • Ferro-Electric Field Effect Transistor (FeFET)
    Courtesy from Rainer Waser: Nano-electronics and Information technology -- On state: for positive gate voltage, the polarization vector P is directed towards Channel. -- Cohesive voltage Vc keep remanent polarization Pr large enough to invert channel and keep current flow even when Vg=0 (non-volatile operation) -- Off State: negative gate voltage will bring Pr direct opposite to channel and + charge are accumulated in the channel region. Channel resistance is high and no current flow
  • 17. Other Novel Logic Transistor
    • Spintronic transistor – based on the effect of spin orientation on electron’s transportation properties
    -- Source and drain are both ferro-magnetic materials with identical magnetization direction -- Channel is a hetero-junction of semiconductor compound with a highly mobile 2-D electron gas. -- Source will inject a spin-polarized current into channel. Without gate voltage, spin will remain unchanged so electron travel to drain on a very high velocity (1% of speed of light) -- When applied gate voltage, spin direction will be rotated by magnetic field so the spin is no longer aligned with drain side => More scattering, higher resistance, lower velocity.
  • 18. Other Novel Logic Transistor
    • Molecular transistor – Single Molecular acting as electronic switch and storage elements
  • 19. Nano Crystal Memory
    • Introduction
    • Why Nano Crystal Memory
    • New Development on Nano Crystal Memory
    Nano Crystal Flash Memory Traditional Floating Gate Memory Floating Gate Usually Poly Si
  • 20.  
  • 21. Recent Trend in Non-volatile Memory
    • Current flash memory is continuing to follow Moore’s Law at 90 / 65 / 45nm Nodes
        • -- 18 years for 9 generations
    • ETOX and NAND will still be the mainstream flash memory in next 5 years.
    • There is no clear roadmap to continuously scale flash memory beyond 32nm node.
  • 22. ITRS Roadmap for Emerging Memory Device (2003) 63
  • 23. Nano-crystal Memory for Technology Gap S. J. Baik et al, IDEM, 2003
  • 24. Principle of Nano Crystal Memory Improvement of Data Retention and SILT. Nano Crystal Flash Memory Traditional Floating Gate Memory Floating Gate Usually Poly Si
  • 25. Nano Crystal as Storing Bit
    • Nano Crystal Technology has been studied extensively to replace traditional floating gate as charge storage media .
    • Advantages:
      • Scalability with Channel Tunneling and Erase
      • Compatible with Traditional CMOS Platform
      • Improved Charge Retention and Endurance
      • Potential Multi Bit usage
    • Challenges:
      • Strictly control the size and distribution of nano crystals
      • Still Litho node limited
      • Much work to be done for a integrated reliable and high yield process
  • 26. Silicon Nano Crystal as Storing Media R. Muralidhar et al. IDEM, 2003
    • Reduce SILC and thus improve data retention and endurance
    • Decrease gate coupling and thus improve leakage and erase saturation
    • Possible multi-bit storage as particle size goes down to discrete energy state of electrons
  • 27. Metal Dots as Storage Media
    • Metal dots can be Co, W or Au
    • Suppose to be better than Si as work function is higher (more attractive to electrons)
    • Multilayer can improve retention and endurance
    C. Lee, et al, IDEM, 2003 M. Takata, et al, IDEM, 2003
  • 28. Silicon Nano Crystals Produced by CVD Methods (I)
    • A Si-rich SiOx thin film is deposited on Si surface by PECVD method. The non-stoichemetry are controlled by gas flow ratios.
    • An furnace annealing were performed on this film at 1000C in N2 atmosphere to precipitate Si Nano crystals out of supersaturated film.
    -- U.S. Pattern Pending
  • 29. Si – SiO 2 Binary Phase Diagram -- Si has no solubility in SiO2 at equilibrium state
  • 30. Silicon Nano Crystals Produced by CVD Methods (II) -- U.S. Pattern Pending
    • Thermal Decomposition of SiH 4 precursor on Silicon surface for Si Nano crystals .
    • No Anneal Step is required.
    • Most compatible with current CMOS technology.
    • Challenge is how to control location and size distribution.
  • 31. Other Ideas of Synthesis Nano Crystals
    • Controllable Nucleation and Growth
    • Volmer -Weber Growth (3-D Island Growth) on Thin Film
    • In-Situ Phase Segregation ( Spinodal Decomposition )
    • Pre-patterned Growth ( Polymer Precursor Self-assembly )
  • 32. Summary
    • Nano storing bit can and must meet Si technology in 5 years.
    • Nano crystal memory is the most promising one to be compatible with CMOS platform
    • Many challenges still exist ranging from manufacturing nano particles to integration into traditional process flow
    • Materials scientist can definitely help!
  • 33. Phase Transformation Memory
    • Same principle as DVD
    • Using transformation between amorphous and crystalline phase based on cooling speed.
    • Different phases has different optical and electrical properties.
    • Easy to be integrated and scalable.
    Phase Transformation Memory
  • 34. Stephen Lai, Intel, December 2003.
  • 35. Basic Architecture of Nano Crystal Memory Floating nano crystals can be -- Silicon nano crystals (multiple or single) -- Silicon nano wires -- Metal nano dots (single or Multi layers) S. Tiwari et al. Appl, Phy lett, 1996 R. Muralidhar et al. IDEM, 2003
  • 36. Nucleation and Growth Control
    • Nano particles need strong nucleation and slow growth
    • Low temperature (high  T) promote nucleation and slow down growth
    • The distance among nucleation sites has to be bigger than diffusion length
    • Nucleus size should be controlled around critical radius
  • 37. Volmer-Weber Growth
    • 3-D island growth
    • Neither complete wetting nor complete non-wetting surface
    • Island size and distribution controlled by heterogeneous nucleation sites
  • 38. Spinodal Decomposition
    • Spontaneous transformation due to instability
    • No nucleation barriers-only require local compositional fluctuations
    • Wave length (or particle size) is a function of undercooling
    • Misfit strain will also play a key role in particle size (barriers for growth)
  • 39. Self-Assembly Patterning K. W. Guarini et. al. IDEM, 2003