11-04-2011, 10:16 AM
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Moore’s Law
• The number of transistors that can be fabricated on a silicon integrated circuit--and therefore the computing speed of such a circuit--is doubling every 18 to 24 months.
• After four decades, solid-state microelectronics has advanced to the point at which 100 million transistors, with feature size measuring 180 nm can be put onto a few square centimeters of silicon
Silicon and Moore’s Law
• Heat dissipation.
– At present, a state-of-the-art 500 MHz microprocessor with 10 million transistors emits almost 100 watts--more heat than a stove-top cooking surface.
• Leakage from one device to another.
– The band structure in silicon provides a wide range of allowable electron energies. Some electrons can gain sufficient energy to hop from one device to another, especially when they are closely packed.
• Capacitive coupling between components.
• Fabrication methods (Photolithography).
– Device size is limited by diffraction to about one half the wavelength of the light used in the lithographic process.
• ‘Silicon Wall.’
– At 50 nm and smaller it is not possible to dope silicon uniformly. (This is the end of the line for bulk behavior.)
Silicon and Moore’s Law
• Moore’s second law.
– Continued exponential decrease in silicon device size is achieved by exponential increase in financial investment. $200 billion for a fabrication facility by 2015.
• Transistor densities achievable under the present and foreseeable silicon format are not sufficient to allow microprocessors to do the things imagined for them.
Electronics Development Strategies
• Top-Down.
– Continued reduction in size of bulk semiconductor devices.
• Bottom-up (Molecular Scale Electronics).
– Design of molecules with specific electronic function.
– Design of molecules for self assembly into supramolecular structures with specific electronic function.
Connecting molecules to the macroscopic world
Bottom-Up (Why Molecules?)
• Molecules are small.
– With transistor size at 180 nm on a side, molecules are some 30,000 times smaller.
• Electrons are confined in molecules.
– Whereas electrons moving in silicon have many possible energies that will facilitate jumping from device to device, electron energies in molecules and atoms are quantized - there is a discrete number of allowable energies.
• Molecules have extended pi systems.
– Provides thermodynamically favorable electron conduit - molecules act as wires.
• Molecules are flexible.
– pi conjugation and therefore conduction can be switched on and off by changing molecular conformation providing potential control over electron flow.
• Molecules are identical.
– Can be fabricated defect-free in enormous numbers.
• Some molecules can self-assemble.
– Can create large arrays of identical devices.
• 1950’s: Inorganic Semiconductors
• To make p-doped material, one dopes Group IV (14) elements (Silicon, Germanium) with electron-poor Group III elements (Aluminum, Gallium, Indium)
• To make n-doped material, one uses electron-rich dopants such as the Group V elements nitrogen, phosphorus, arsenic.
Moore’s Law
• The number of transistors that can be fabricated on a silicon integrated circuit--and therefore the computing speed of such a circuit--is doubling every 18 to 24 months.
• After four decades, solid-state microelectronics has advanced to the point at which 100 million transistors, with feature size measuring 180 nm can be put onto a few square centimeters of silicon
Silicon and Moore’s Law
• Heat dissipation.
– At present, a state-of-the-art 500 MHz microprocessor with 10 million transistors emits almost 100 watts--more heat than a stove-top cooking surface.
• Leakage from one device to another.
– The band structure in silicon provides a wide range of allowable electron energies. Some electrons can gain sufficient energy to hop from one device to another, especially when they are closely packed.
• Capacitive coupling between components.
• Fabrication methods (Photolithography).
– Device size is limited by diffraction to about one half the wavelength of the light used in the lithographic process.
• ‘Silicon Wall.’
– At 50 nm and smaller it is not possible to dope silicon uniformly. (This is the end of the line for bulk behavior.)
Silicon and Moore’s Law
• Moore’s second law.
– Continued exponential decrease in silicon device size is achieved by exponential increase in financial investment. $200 billion for a fabrication facility by 2015.
• Transistor densities achievable under the present and foreseeable silicon format are not sufficient to allow microprocessors to do the things imagined for them.
Electronics Development Strategies
• Top-Down.
– Continued reduction in size of bulk semiconductor devices.
• Bottom-up (Molecular Scale Electronics).
– Design of molecules with specific electronic function.
– Design of molecules for self assembly into supramolecular structures with specific electronic function.
Connecting molecules to the macroscopic world
Bottom-Up (Why Molecules?)
• Molecules are small.
– With transistor size at 180 nm on a side, molecules are some 30,000 times smaller.
• Electrons are confined in molecules.
– Whereas electrons moving in silicon have many possible energies that will facilitate jumping from device to device, electron energies in molecules and atoms are quantized - there is a discrete number of allowable energies.
• Molecules have extended pi systems.
– Provides thermodynamically favorable electron conduit - molecules act as wires.
• Molecules are flexible.
– pi conjugation and therefore conduction can be switched on and off by changing molecular conformation providing potential control over electron flow.
• Molecules are identical.
– Can be fabricated defect-free in enormous numbers.
• Some molecules can self-assemble.
– Can create large arrays of identical devices.
• 1950’s: Inorganic Semiconductors
• To make p-doped material, one dopes Group IV (14) elements (Silicon, Germanium) with electron-poor Group III elements (Aluminum, Gallium, Indium)
• To make n-doped material, one uses electron-rich dopants such as the Group V elements nitrogen, phosphorus, arsenic.
