Nanotechnology on our Desktops Hard Disk Sensor Medium Transistor Gate SourceDrain Switching layer 5...
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Transcript of Nanotechnology on our Desktops Hard Disk Sensor Medium Transistor Gate SourceDrain Switching layer 5...
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