Introduction to Molecular Devices

1
Introduction to Molecular Devices

• Geng-Chiau Liang

2
Outline

• Fundamental Concept
• Review of basic formulas
• 2-state toy model
• Molecular Devices
• Switches
• Resonant Tunneling Structures
• SAMFETs
• Summation

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Moores Law

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Limitations

• Ultra-thin gate oxides
• Short channel effect
• Doping fluctuations
• Difficult and expensive lithography

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Approaches for designing new generation devices

• Nanotube devices
• Molecular electronics
• Benefits
• Smaller ( 1-2 A)
• Self-assembled monolayer( Cheaper for
  fabrication)

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Fundamental Concept
e
Homo
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Review of Basic Formulas
Ref Datta, S. Electronic Transport in Mesoscopic
System Cambridge University Press, 1997
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Two-state Toy Model

• assumptions
• Two energy states of devices E0, E1
• Broadening gamma1, gamma2
• Eta theory eta0 or eta0.5
• Charging energy U0 or U2
• Restricted method
• Room temperature T300
• Orthogonal basis (only diagonal terms exist)

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Results (I)
Eta0.5
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Results (II)

• Eta1

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Results (III)
Eta.5
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Switches (Molecular Junction)
Ref Reed etc al., Science 278, pp. 252, 1997
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Switches (II)
PN Junction
Model 1
Model 2
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Switches (III)

• Reference
• PN junction Ellenbogen, et al., Proc. IEEE, Vol.
  88, No. 3, pp.386, 2000
• Model 1 Metzger, et al., J. Amer. Chem. Soc.
  Vol.119, pp.10455-10466, 1997
• Model 2 Zhao, et al., Appl. Phys. Lett. Vol. 71,
  pp. 611-613, 1997

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Resonant Tunneling Structure
1.31 on-off peak-to valley ration
Ref Reed, et al, Proc. IEEE Vol. 87,
pp.652-658 Apr. 1999
Ellenbogen, et al., Proc. IEEE, Vol. 88, No. 3,
pp.386, 2000
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Energy states
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Resonant Tunneling Structure (II)
Explanation 1 Seminario, et al, J. Am Chem.
Soc., Vol. 122, pp. 3015- 3020 2000
10001 on-off peak-to-valley ration
Explanation 2 Lang, et al, Phys. Rev. Lett. Vol.
86, pp.288 2001
Ref Chen, et al., Science, 286, pp. 1550 1999
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SAMFET
Ref Schon, et al., nature Vol. 413, pp. 713 2001
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Memory
Ref Reed, et al., Appl. Phys. Lett. 78, pp. 3735
2001
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Summary

• Using two-state toy model to explain how the
  device conduct
• Introduction to the simple ideas of molecular
  device designing