TECHNICAL SEMINAR ON TECHNOLOGIES AND DESIGNS 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

DEVICEOPERATING PRINCIPLE STATUSADVANTAGESDISADVANTAGES 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 blockadeExperimental, only operates at very low temp. High gain operation principles similar to MOSFET Low temp. difficult to control Quantum Dot CellSingle 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 RelayVibrational movement of a single atom in and out of an atom wire TheoreticalVery high speed subnanometer size Low temp. very unreliable Refined Molecular Relay Rotational movement of a group in and out of an atom wire TheoreticalSubnanometer 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

DESIGNOPERATIONAL PRINCIPLE STATUSADVANTAGESDISADVANTAGES 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. TheoreticalInterconnection 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. TheoreticalFast 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. TheoreticalPrimarily 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