AN INTRODUCTION TO NANOCOMPUTING - Bio-Inspired and Nanoscale Integrated Computing - page 5

Analog circuits

Modern CMOS
circuits

Wave-based
communication
and logic

Switch-based logic

Cellular and neural logic

DNA and protein computing

Quantum Computing

Estimated computational power

Figure 1.2. Visualization of how future paradigms in nanocomputing may com-
pare to today's CMOS technology.

1.3. THE MICROCOMPUTING ERA: THE TRANSISTOR AS A SWITCH

Traditionally, the most common way to use physics for computation is to cleverly
control electricity. Figure 1.3 shows a simplified transistor. We can add or remove
electrons from the gate. When there is no charge in the gate, the wire can easily
transmit its own electrons. If there are electrons in the gate, an electric field of
negative charge is created, and this repelling force makes it difficult for electrons to
flow through the wire. In a sense, we can control how much current flows through
the wire by controlling how much charge we put into the gate.
With this physical device, an abstract 0 or 1 is represented as a low or high
current on the wire. This is known as the digital abstraction. The transistor's

Gate Gate

−

Insulating barrier − −

−

−
−

−

−

−

−

−

− −

−

− −

− − − − − −

− −

−

− −

−

−

−

− −

− − − − − −

− − − −

−

Current flowing through channel Channel blocked

Figure 1.3. A simplified field-effect transistor. Ideally, the gate can ''switch''

current on or off.