Nanoelectronics: Solid-State Quantum-Effect, Molecular Electronic Devices
6. Nanoelectronics
Nanoelectronics encompasses nanoscale circuits and devices including (but not limited to) ultra-scaled FETs, spin devices, superlattice arrays, quantum coherent devices, molecular electronic devices, and carbon nanotubes.
Over the past four decades, electronic components have grown more powerful as the transistor, has shrunk in dimensions by several factors. However, the laws of quantum mechanics, and the limitations of materials and fabrication techniques are making it very difficult for further reduction in the minimum size of today's semiconductor transistors. Researchers have projected that as the overall size of the bulk-effect, semiconductor transistor is aggressively miniaturized to approximately 0.1 micron (i.e., 100 nanometers) and beyond the devices may no longer function as well.
Thus, in order to continue the miniaturization of integrated circuits well into the next century, it is likely that present day, micron-scale microelectronic device designs will be replaced with new designs for devices that take advantage of the quantum mechanical effects that dominate on the much smaller, nanometer scale. (Note that 1 nanometer, abbreviated nm, is one billionth of a meter or 10 atomic diameters.)
The nanoelectronic devices are subdivides into two broad areas, as follows:
i. Solid-state quantum-effect nanoelectronic devices
ii. Molecular electronic devices
6.a Solid-state quantum-effect nanoelectronic devices
Solid-state quantum-effect nanoelectronic devices are used to continually increase the density and speed of information processing. This technology, which changes the operating principles, but not the fabrication medium for integrated circuits, might extend Moore's Law of electronics miniaturization to produce devices down to a few tens of nanometers. Present-day field effect transistors (FETs) on commercial integrated circuits are approximately 1 micron or 1000 nm across, and it is believed that bulk-effect FETs will cease to function effectively when their gate lengths dip below 25 nm, which corresponds to an overall device length of approximately 100 nm.
On the other hand, quantum-effect switching devices tend to function better when they are made smaller. Solid state quantum-effect nanoelectronic devices might be made as small as approximately 12 to 25 nanometers across and still expected function effectively.
A number of solid-state nanoelectronic switching devices have reportedly been fabricated, and prototype solid-state nanoelectronic processors are demonstrated. As a result of nanometric scale, significant reduction could result in ultra-fast, low power integrated circuits with billions of transistors on a single CPU chip, and Terabyte memories on a chip.
Such advances would require, reliable fabrication of devices and circuits with only 5 to 10 nanometers wide. This is about 10-20 smaller than that achievable using UV lithography.
6.b Molecular electronic devices
Molecular electronics, using individual covalently bonded molecules to act as wires and switching devices, is expected to bring the Moore's Law down to nanometer scale. Individual molecular switching devices could be as small as a few nanometers. This decrease in size could result in Terabyte memories on a chip and in excess of one trillion switching-devices on a single CPU chip. A primary advantage of molecular electronics is that molecules are natural nanometer-scale structures that can be made absolutely identical in vast quantities. Also, synthetic organic chemistry offers more options for designing and fabricating these intrinsically nanometer-scale devices than the technology presently available for producing solid-state chips with nanometerscale features.
Molecular wires
The subject of molecular wires is of primary significance, even in an overview of nanoelectronics switching devices. Molecular wires are used to demonstrate conductance in a single molecule.
Quantum-effect Molecular electronic devices
Using molecular structures for quantum confinement might make it possible to manufacture fast, quantum-effect switching devices on a large scale more uniformly and cheaply than has thus far been feasible with solid semiconductors.
Electromechanical Molecular electronic devices
Electromechanical molecular switching devices are not so closely analogous to microelectronic transistors as are the molecular devices. Deforming or re-orienting molecular structures is the underlying principle in of an Electromechanical molecular electronic. An Electromechanical molecular switch does not use electron charges like microelectronic switch. The input is also normally mechnical. However, just like all those other switches, they can turn on or off a current between two wires, which makes them interesting for nanocomputing.
