1.5 Machines and Computers on the Microscale and Nanoscale

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Figure 1.42: Logic gates, including their symbols and truth table.

tance can be defined as voltage per unit of current. The resistor heats up in the process

of hindering the electrical flow; this has led to the resistor’s use in heaters as well as

light bulbs, in addition to their regulation of current flow.

Diodes are made from a p-n-junction, or the interface between a p-type and an

n-type semiconductor, and can transmit electricity only in one direction (Figure 1.44).

If the recombination of an electron and hole at the interface results in light emission

instead of voltage, the diode is called a “light-emitting diode” or LED.

Capacitors can store charges (Figure 1.45). A capacitor is made up of two metal-

lic plates with a dielectric material in between the plates. A dielectric is an insulator

that can be polarized by an electric field to hold charges (air is a common example).

When you apply a voltage over the two plates, an electric field is created. A positive

charge will collect on one plate and a negative charge on the other, thus separating the

charges.

If you integrate several components into one discrete circuit it is called an “inte-

grated circuit” (IC), or “(micro-)chip”. If the system involves a micro-sized or nano-sized

moving part, the chips are called micro-electrical-mechanical systems (MEMS) or nano-

electrical-mechanical systems (NEMS), respectively. One common moving, or mechani-

cal, device often incorporated in a circuit is a piezo-electric material, i. e., a material that

generates a current when mechanically stressed.

Besides LEDs, there are also phototransistors, photodiodes, and photoresistors. All

work the same way as their electronic counterparts, but they are initiated by light in-

stead of voltage. All can be incorporated into ICs.

Other possible components of ICs are optoelectronic devices, display technologies,

magnetic (inductive) devices, or, if you are talking about sensors, sensing or detection

elements, transducers, and detectors. In other words, an IC could contain a complete

sensor. We are going to talk about sensing or detection elements, transducers, and de-

tectors further below (Section 1.7).