It is helpful to appreciate that current MOS transistors are direct descendants of the electromechanical switches first used by Zuse to code digital information in an electronic form. Representing binary information by turning on or off a current switch has been one of the most fruitful ideas in the history of technology. This paradigm does however have serious drawbacks as device sizes are reduced. The interconnect problem is one. One needs to distribute signals over large distances, which involves charging long lines.
Remarkable complexity attends the routing of signals on multiple levels.
At the other end, as transistors become smaller, the quantization of charge both in the channel and in the doping layer become significant. When reduced to nanometer scales, current switches may not be the best way to code information. The developing technology of quantum dot fabrication may prove a key element in crafting another approach. Researchers have already demonstrated the ability to fabricate quantum dots with single charges , to make large arrays of dots and control their occupancy , and to put dots in close enough proximity to observe both tunneling and Coulomb coupling between dots. Of course, these experiments are difficult and consistent, high-yield processing techniques are not yet at hand.