TECHNICAL SEMINAR

ON

TECHNOLOGIES ANDDESIGNS FOR

ELECTRONIC NANOCOMPUTERS

PRESENTED BY : BIJAY KUMAR XESS ADMN NO : 4 I&E/2K

Genesis of Nanotechnology. A timeline of selected key events plotted versus time with Moore’s Law trend line.

FUTURE TECHNOLOGIES : LIKELY APPROACHES TO NANOELECTRONIC TWO STATE DEVICES

1. RESONANT TUNNELING TRANSISTOR

2. SINGLE-ELECTRON TRANSISTOR

3. ELECTROSTATIC QUANTUM DOT CELLS

4. MOLECULAR SHUTTLE SWITCH

5. ATOM RELAY

6. REFINED MOLECULAR RELAY

DEVICE OPERATING PRINCIPLE

STATUS ADVANTAGES DISADVANTAGES

Resonant Tunneling Transistor

Quantum resonance in double barrier potential walls

Capable of large scale fabrication

Logic compression semiconductor based

Limits in scaling similar to microelectronics

Single Electron Transistor

Coulomb blockade Experimental, only operates at very low

temp.

High gain operation principles similar to MOSFET

Low temp. difficult to control

Quantum Dot Cell Single electron confinement in arrays of quantum dots

Quantum dots can be fabricated, quantum

dot cells are still theoretical

Wireless low energy dissipation

Difficult design rules susceptible to noise

Molecular Shuttle Switch

Movement of a molecular “bead” between two stations on a molecule

Experimental, can only be switched

chemically

Small but robust assembled chemically

Slow switching speed

How to interconnect?

Atom Relay Vibrational movement of a single atom in and out of an atom wire

Theoretical Very high speed subnanometer size

Low temp. very unreliable

Refined Molecular Relay

Rotational movement of a group in and out of an atom wire

Theoretical Subnanometer size more reliable than atom relay

How to fabricate?

How to interconnect?

CONDUCTANCE PEAK OF AN RTD

RESONANT TUNNELING TRANSISTOR

SCHEMATIC OF A RESONANT-TUNNELING

DIODE (RTD)

Single Electron Transistor

Concept of a Quantum Dot

DESIGN OPERATIONAL PRINCIPLE

STATUS ADVANTAGES DISADVANTAGES

Traditional wired design

Switching devices are connected with metal or doped polysilicon wires

Design has been used in microelectronic computers since invention of the IC

Fabrication tolerances do not have to be automatically precise. Not as susceptible to noise

Submicron wires have short lifetimes (<100 hrs). Submicron wires have high resistance so they are slow.

Wireless ground state computing (QCAs)

Insulated quantum dots influence each other with electrostatic fields. The computer is driven towards the ground state of the system of electrons.

Theoretical Interconnection speed is extremely fast and can work on the nanometer-scale. Very low power dissipation

Total system relaxation time is slow. Design rules are complicated.

Wireless dissipative computing

Insulated quantum dots influence each other with electrostatic fields. Computation is done with metastable states.

Theoretical Fast interconnects Simple design rules

Sensitive to background charge. Can all circuits be implemented?

Nanometer-scale non-linear networks (NNNs)

Array of interconnected devices. Analog computing with synaptic laws.

Theoretical Primarily local interconnections. Use non-linearities in charge transport.

Sensitive to stray charges

Emerging technologies for the implementation of Nanoelectronics

a. Molecular electronics

# Uses primarily covalently bonded molecular structures# Molecules are nanometer-scale structures# Three obstacles must be overcome to realize molecular electronics# Potential increase in device density by a factor of as much as 10^7 i.e. 10 million# Challenges that remain on the path to creating molecular electronic computational devices# Potential advantages from a pursuit of molecular electronics# Ultimate solution to the problem of economical fabrication of ultra dense, nanometer-scale computer electronics

b. Silicon Nanoelectronics

# Si has a lower thermal conduction limit# Electrons move faster in GaAs than in Si in low electric fields# More reliability and uniformity in the processing of Si substrates# More economical over time and ecologically safer for the environment# A heterojunction is necessary to create a potential well or barrier , the basis for constructing a solid state quantum effect device# Tunnel barriers or heterolayers will also be needed to control leakage current in a nanometer-scale Si based device

FABRICATION

1. LITHOGRAPHY

2. MOLECULAR BEAM EPITAXY (MBE)

3. MECHANOSYNTHESIS WITH NANOPROBES

4. CHEMOSYNTHESIS

REMAINING CHALLENGES FOR NANOELECTRONICS

1. Build logic structures or computers from nanometer-scale components

2. Devising and putting in place the infrastructure for manufacturing thousands or millions of ULSI computers

3. Raise operational temperatures close to room temperature

4. Reliable, precision manufacture of such devices

5. Functioning logic structure must be demonstrated

6. Devices must be arranged and connected densely in units

7. Processes for error correction must be invented

8. Conversion of research on small numbers of prototype nanodevices and nanocomputers to practical and reliable mass produced systems

CONCLUSION

-- New approaches to building computers are necessary to ensure technical progress at the current rate

-- RTDs, Quantum dots or SETs should be attainable with next generation technology

-- Smaller molecular electronic devices are likely to require further research

-- Factors governing choice of technologies and designs – Device speed, power dissipation, Reliability, ease of fabrication

-- Developments in molecular electronics may even race ahead of those in solid-state nanoelectronics

END OF THE SEMINAR

THANK YOU