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Nanotechnology on our Desktops
Hard Disk
Sensor Medium
Transistor
Gate
Source Drain
Switching layer5 nm
Magnetic grain10 nm
Gate oxide4 nmWell
6 nm
Alferov KroemerNobel Prize in Physics 2000
Electrons in the Conduction Band
Holes in the Valence Band
n-typep-type
Benefits of a quantum well:
1) Trap electrons and holes in the same quantum well and thereby keep them together longer.
2) Electrons and holes have well-defined, quantized energies, such that most of them contribute to the same laser line.
The electron flow from source to drain
is controlled by the gate voltage.
Electrons
MOS = Metal-Oxide-Semiconductor FET = Field Effect Transistor
The (MOSFET) Transistor
Moore’s Law of Silicon Electronics
The performance of silicon devices increases exponentially.
Corollaries:
The storage density doubles every 2 years, linear dimensions x½ every 4
years.
The cost per megabyte decreases exponentially.
The cost of a factory (“fab”) increases exponentially (now a few billion $).
Gate oxide has shrunk to <
2nm, < 10 atom layers.
Electrons can tunnel through when applying a gate voltage.
Uses up to 1/3 of the power.
Power consumption by a leaky gate oxide: A show-stopper for
Moore’s Law ?
Semiconductor-Insulator Interfaces :
From the MOSFET to Molecular Electronics
Mismatch of the bond density at the Si/SiO2 interface
The Si/SiO2 Interface
Intermediate oxidation states at the interfaceprovide a gradual transition from Si to SiO2 .
STEM + electron energy loss measurement across the Si/SiO2 interface (see Lect. 5, Slides 16,17)
0.7 nm Limit Predicted for the Gate Oxide Thickness
Intermediate oxides insulate poorly
Si2p
CBM
Intel is already at the limit:
0.8 nm oxide reached in demos
Need gate insulator with high dielectric constant :
HfO2
Thicker oxide with same capacitance and less leakage
Atomic Layer Epitaxy (ALE) for Monolayer Control
“Digital Growth”
General concept of ALE:
Adsorb fairly inert pre-cursor molecules onto a reactive sbstrate, such that only one monolayer sticks.
Reactivate the surface by chemical treatment.
Repeat this cycle.
ALE growth of Al2O3 (alumina) from an organo-metallic precursor with
reactivation by H2O.
Molecular Field Effect Transistors
Molecular Control of Gate Dielectric and its
Interface
Review: Malliaras and Friend, Physics Today, May 2005, p. 5
Halik et al., Nature 431, 963 (2004)
Si-Molecule Interfaces
Peters et al., Langmuir 18, 1250 (2002)
Attaching Alkanes to Silicon via Siloxane Chemistry
Moist
Ordered
Dry
Disordered Silicon
Alkane
ClHO
C-H
C-C OTS
In Pursuit of the Ultimate Storage Medium
1 bit = 1 atom
10 m
10 nm
CD-ROM
Silicon Surface
Density x106
Track spacing 5 atom rows
Bennewitz et al. Nanotechnology 13, 499 (2002)
CCD (Charge Coupled Device)
Physics Nobel Prize 2009: Boyle and Smith
The CCD detectors in digital cameras wiped out photographic film.
Operation of a CCDCCD detectors are based on silicon MOS technology (compare Slides 4,
5).
Each pixel consists of a MOS capacitor with positive gate voltage. Contrary to a MOSFET, electrons cannot flow directly into the channel. Only those excited by photons are able to charge the capacitor, building up a charge bucket.
Readout: Charge buckets are shifted along a row of pixels (“bucket brigade”) .
Gate Channel
VB
CB