Transcript Slide 1

NIRT: "Surface State Engineering"
Charge Storage and Conduction in Organo-Silicon Heterostructures as a Basis for
Nanoscale Devices
John C. Bean (PI)1, Avik Ghosh1, Lloyd R. Harriott1, Lin Pu2, Keith Williams3
1Department
2Department
of Electrical and Computer Engineering,
of Chemistry,
University of Virginia, Charlottesville Virginia
Basic Idea:
Create highly-pure, highly-ordered bound organo-silicon hybrids
Bound so intimately that electron waves pass easily between components
Allowing for: 1) Precise charge transfer into and out of Si surfaces
2) Conduction based on quantum mechanical resonance
3Department
of Physics
Our background:
NIRT Building Block #1) Models of Organo-Si Charge Conduction & Storage
UVA investigated Moletronics through earlier NIRT & DARPA "MOLEapps"
Formal Challenge: Coupling weak and strong quantum correlation (wires vs. dots):
But unlike others, OUR goal was to transform hero results into technology
Semiconductors normally treated via macroscopic quasi-continuum models
Molecules dominated by QM and Many Body Effects
Led us into use develop:
Extremely pure vapor phase molecular
deposition techniques:
Si-based planar devices:
Very different modeling approaches!
Deposition Chamber 1:
Original semiconductor process
Deposition Chamber 2:
Converted to Organics
Very different computational techniques!
In future nanoscale MOSFETs this could:
200 nm Au
1) Replace conventional trace donor/acceptor charge creation
100 nm SiO2
Focused Ion
Beam milled hole
(approx. 50nm)
5 nm Ti
(U=Coulomb energy, G = level broadening)
Self Assembling
Monolayer of
molecules
Silicon
2) Enhance performance by minimizing ionized impurity scattering
3) Open door to devices based on quantum interference phenomenon
NIRT Building Block #2) Vapor Phase Synthesis of Organo-Si Heterostructures
Goals: Electrically activate desired silicon sites, passivate (neutralize) all others
Organo-Si hybrids straddle this boundary. Team will model by combining:
Center Loading & Processing Chamber
Resulting in:
TRUE self-assembled monolayers: single step, self-limiting
Density Functional Theory (for Si) and Extended Hückel Theory (for molecules)
5X increase in device yields over liquid phase standard
Within framework of Non-Equilibrium Green's Functions for Si FETs, coupled with
multi-electron rate equation for molecular SETs
Or other chemical options on bare reconstructed Silicon surfaces:
Cyclo-addition
Diels-Alder Reactions
NIRT Building Block #3) Device Evaluation of Quantum Surface States
Or more complex reactions:
Use "Random Telegraph Signals" in nanoFETs for molecule-Si spectroscopy
Analogous to role served by DLTS in bulk semiconductors
(2x1) reconstruction of
Silicon (100) surface
Using basic nanoFET geometries:
Acetylene → Si
Butadiene → Si
Or more exotic FIN-FETs:
Cyclooctatetracene → Si
On hydrogen covered surfaces, we will use our proven tool of hydrosilylation:
Base molecules = Surface passivating units
Altered to produce electrical activity / transport by adding:
Electron withdrawing or electron contributing groups
Alkene/Alkyne
terminated organic
approaching Si-H
Surface hydrogen
eliminated by UV or heat
leaving Si surface radical
C=C / C≡C bond breaks,
C1 attaches to Si, C2
becomes radical
C2 radical grabs
neighboring H, creating
new Si surface radical
Analyzing with NIRT partners: SOITEC (leading manufacturer of SOI for ICs)
National Institute of Standards and Technology
Fallback option (if unsatisfactory passivation of bare Si) =
Attachment of molecules to electron transparent thin SiO2 on Si
To evaluate utility in nanoFETs & explore new modes of quantum conduction
Preliminary Results:
Education and Outreach building on two earlier NSF Grants:
2) 2005 Nanoscience Undergraduate Education (NUE) Grant
- Model of Random Telegraph Signal in nanoFET:
1) 1999 Course Curriculum & Laboratory Improvement (CCLI) Grant
To develop freshman/sophomore "Hands on Intro to Nanoscience"
Using miniature AFMs and STMs (fully explained on website in virtual reality)
Led to creation of UVA Virtual Lab Science Education Website
50+ intuitive 3D-animated presentations focusing on micro and nano technology
Our VR recreation of class's AFMs
4Xiao,
Our VR recreation of class's STMs
Yablonovitch et al., Nature 430, p. 435 (2004)
To now partner with multi-site Science Museum of Virginia
- Successful measurement of RTS in nanotube FETs
- Design of UVA SOI nanoFET
device test structure:
Semiconductor
Crystals
How transistors
work
How IC's are
made
Nanocarbon
DNA selfassembly
- Help develop new exhibits, as well as new museum in DC suburbs
- Incorporate "Intro to Nanoscience" into their K-12 teacher training programs
Over 3.5 million hits to website since early 2005
Including visitors from over 1000 Universities and 300 K-12 schools & districts
www.virlab.virginia.edu
And to spin off "Hands on Nanoscience" class to other schools:
- E.G. Danville VA's new C.C. class in support of their Nanotech Incubator