Computer Engineering and Nanotechnology - Molecular Computing: Origins and Promises - page 34

different countries. However, thousands of electron tubes in a single device con-
sumed a lot of energy and required labor-intensive maintenance by skilled personnel.
Electron tube-based computing systems were capricious in operation. In order to
achieve stable operation, days had to be spent on debugging the system. The
temperature in the computer room was sometimes 10-15 C. Therefore, the appear-
ance of semiconductors dramatically increased the reliability of computers and paved
the way for their further improvement.
It is not by accident that semiconductors won a strong position in computer
engineering. As is known, in contrast to the quantum objects like atoms and
molecules, solids have electronic band structure.
In order to understand the underlying reasons for the formation of the band
structure, let us consider a simple model—a one-dimensional chain of atoms
(Fig. 2.6 ). If there were two atoms, the electronic levels of such a system would
be split into two components—a bonding and an antibonding orbital (see Chap. 3 ) .
Fig. 2.6 Scheme of the formation of bands in a chain of Li atoms (a) and band structure of a
conductor insulator and semiconductor (b)