Molecular switches

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Molecular switches molecular electronics

• Lin Zhong
• ELE580B, 2002

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Outline

• Why molecular electronics?
• Molecular electronic devices
• Fabrication
• Fabrication with DNA

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Why molecular electronics
Moores law
Nair, 2002
of transistors on various types of chip (400
mm2) as projected by SIA roadmap
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Why molecular electronics?
ITRS 2001 Prediction
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Whats the problem?

• Things work differently at nanoscale
• Quantum effect
• Interconnect delay
• Power consumption
• Fabrication cost
• The cost to set up a wafer fab
• The cost to fabricate a wafer

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Whats the problem?
Bollinger Chynoweth, 1999
http//www.sematech.org/public/resources/econmodl/
general/05_symp.pdf
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CMOS legacy
Software

• Legacy disciplines
• Legacy software

Architecture
People tend to use what they are familiar
with Changes are usually minimized
Devices
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Solutions nano electronic devices
Ellenbogen 2000
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molecular electronic circuitry

• Input?
• Interconnecting?
• What molecules?

1-bit full adder Ellenbogen Love,
2000 Designed, not implemented
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Molecular electronic devices

• Two terminal devices
• Diode based design
• Nanowire
• Harvard, Lieber group
• Technion, Braun group
• Nanotube
• IBM T.J. Watson, Avouris group
• Deft Univ. Of Tech., Dekker group

• Aromatic molecules
• Yale, Reed group, Rice, Tour
• Rotaxane molecule
• UCLA, Heath group
• Biomolecules
• Porphyrin
• DNA

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Two terminal devices

• Diode

Ellenbogen Love 2000
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Diode-based gates

• AND
• OR

Ellenbogen Love 2000
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Nanowire

• Silicon nanowire
• Harvard, Lieber group
• Physically wire, electrically semconductor
• Metal nanowire
• We will talk about this later

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Silicon nanowire

• Harvard, Lieber group
• Devices
• Length and doping controlled
• Diameter about 5nm
• Most similar to CMOS
• Rudimentary circuitry
• Transistors
• Gates
• Array

Junction
NPN transistor
Feb, 2001
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Silicon nanowires
Directed assembly of SiNW arrays
Jan., 2001
Scale bars 500nm in A, B, C 2um in D
The device is small. Is the density high?
1012/cm2 claimed Meaning junction-junction
distance should be 20nm
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Nanotubes

• 1991 discovery of multi-wall carbon nanotubes
• 1993 synthesis of single-wall nanotubes
• 2001 integration of carbon nanotubes for logic
  circuits
• 60/g http//carbolex.com/

http//www.pa.msu.edu/

• 1nm cross, micro meters long
• Either metallic or semi-conducting
• Still difficult to fabricate semi-conducting only
  nanotubes

http//www.labs.nec.co.jp/
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IBM Avouris group

• Multi-wall nanotube(MWNT) and Single-wall
  nanotube (SWNT)
• Selectively break down NT ropes

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IBM Avouris group

• SWNT FET array
• Construct FETs
• Remove unwanted connections

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Delft Dekker group

• Transistor
• Room temperature
• 1998
• 2001 July

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Delft Dekker group

• Inverter, NOR gate, SRAM cell, ring occilator

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Aromatic molecules

• Aromatic molecules
• Rectifier (omit)
• Reed-Tour RTD
• Benzene ring RTD
• Memory cell (Omit)

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Aromatic molecules

• Conductive
• Benzene
• Polyphenylene
• Tour wire
• Semiconductive
• Substituted polyphenylene

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Reed-tour RTD

• About 1000 molecules
• Resonant tunneling effect
• Negative differential resistance
• We will talk about fab later on

Nov. 1999
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Benzene RT transistor

• IBM T.J. Watson and Univ of Tennessee
• June, 2000
• Transistor not diode

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Rotaxane molecule
cyclophane
July, 1999 R(1)
August, 2000 2catenane
UCLA, Heath group
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Rotaxane molecule
2Catenane-based
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Rotaxane molecule
Coulomb repulsion
Switch close
Switch open
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Rotaxane molecule
A lot of molecules
We will talk about fabrication later on
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Rotaxane molecule
Diode
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Rotaxane molecules
This figure by Science magazine is
misleading There are much more than one molecule
per contact!!!
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Biomolecules

• Porphyrins
• DNA

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Porphyrin

• NCSU, Lindsey and colleagues Sep/Oct 2000
• Self-assembled monolayer (SAM) on Au substrates
• Memory cell
• Information stored in the multiple oxidation
  states
• Neutral, monocation, dication

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DNA as devices

• Dekker group, Feb, 2000
• 10.4-nm-long, ds-DNA
• Non-linear behavior
• Like a threshold gate
• Threshold increases with temperature

Single molecule measurement
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Outline

• Why molecular electronics?
• Molecular electronic devices
• Fabrication
• Fabrication with DNA

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Fabrication

• Everyone agrees with Bottom-up
• How did they fabricate?
• Not really single molecule device
• Contacts matter

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Bottom-up vs. Top-down

• CMOS Lithography
• Financially
• Technically
• Impossible
• Nano Chemical assembly
• Self assembly

http//www.talkabouttheworld.com/edition_45/
http//www.wisconsinhistory.org/
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Self-assembly
Assembly of ice crystals around a particle
snowcrystals.net
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How did they fab?

• Nanowire
• Reed-tour RTD
• Rotaxane Diode

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Silicon Nanowire

• Use laser to produces gold nanocluster catalyst
  particles
• Grow SiWNs in a flow of SiH4
• SiNWs are doped with boron or phosphorus
• Add electrical contacts using e-beam lithography

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Fab Reed-Tour RTD

• E-beam lithography and reactive ion etching to
  form the hole
• 30-50nm
• Evaporate a Au contact onto the top side
• Thickness 200nm
• Self assembly of molecules onto the gold
  substrate
• It takes 48 hours.
• Evaporate another layer of Au

The Au-SAM-Au junction contains about 1000
molecules
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Rotaxane device fab

• Lithographically pattern 6-um-diameter Al wire
  onto silica substrate
• Deposit a single monolayer of the rotaxane
  molecules over the entire substrate
• Evaporate a second set of 11-um-duameter wires
  (Ti and Al) through a contact shadow mask
  (electron beam deposition)
• Not a single molecule!

Painfully slow and impractical for large scale
manufacturing---Science
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How did they fab?

• Someone did not even fab.

Not real
Science, Dec. 2001
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Problems!!!

• We are still unable to assemble the building
  using different kinds of bricks
• Same kind of bricks
• Random instead of controlled
• Only nanotube and nanowire are used molecularly
• Others used a group of same molecules instead of
  a single molecules
• No interconnect is molecular
• Conventional metal wire is still used
• Lieber group claimed nanowires can be used as
  interconnect as well. That is not verified.
  Pessimistic in view of SiNWs conducting
  properties

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Outline

• Why molecular electronics?
• Molecular electronic devices
• Fabrication
• Fabrication with DNA

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Fabrication with DNA

• DNA as movers
• Nanoparticles
• PSU, Mallouk group
• DNA directed small molecule synthesis
• Harvard, Liu group
• DNA as template
• DNA-Template Nanowire
• UIUC
• Technion, Braun group
• DNA Metalization
• There is a workshop!!!
• DNA-based molecular construction, Jena, Germany,
  May 23-25, 2002

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Nanoparticles
polycarbonate membrane
Thiol tagged DNA
Diameter 200nm Length 3um
Mallouk group 2001
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Nanoparticles
Complementary oligonucleotides tagged on Au film
Noncomplementary oligonucleotides tagged on Au
film
Complementary oligonucleotides tagged on Au
patterns
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Nanoparticles
Science, 2001
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DNA catalyzing

• Liu group
• Small molecule synthesis
• Sheppard group

2001
Maybe useful for molecularly interconnecting
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DNA as template nanowire I
Diameter 5-10nm Length 1um
UIUC, Murphey and Bezryadin 2002
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DNA as template nanowire II

• Technion, Braun group
• Silver nanowire

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DNA as template nanowire III

• Molecular lithography

Binding specificity is decided by the probe
sequence
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DNA as template nanowire III
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Conclusions

• Many molecular devices are not molecular
• Although they used molecules
• Interconnecting device molecules is challenging
• May change molecules electronic properties
• Interface between conventional circuitry and
  molecular circuitry
• Almost all proposed molecular devices are not
  fabrication-friendly
• CMOS techniques, fled of randomness
• What can DNA do?
• What can cells do?