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.

6 nm : Optimum Thickness

Quantum Well Laser Optimization

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

Transistor

DRAM (Dynamic Random Access

Memory)

Transistor + Capacitor

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)

250 Terabit/inch2

Year 2038

When will we be down to atoms ?

Using Moore's Law ...

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