1. Conductors
Conductors are, in general, substances that have the property of transmitting different forms of energy. In the following, the focus is on electrical conductivity.
Metals
The conductivity of metals is based on the free electrons that exist as an electron gas within the metallic bond. Even a small amount of energy is enough to detach sufficient electrons from the atoms to achieve conductivity.
Metallic bond: fixed atomic cores and free valence electrons (electron gas)
Conductivity depends, among other things, on temperature. As temperature rises, the atomic cores vibrate more strongly, hindering the movement of the electrons and consequently increasing resistance. The best conductor is silver, closely followed by copper; gold, despite its reputation, ranks noticeably behind. Silver and gold are used relatively rarely because of their cost – gold mainly where corrosion resistance and good bondability matter, such as contacting finished chips. The alternatives used in semiconductor technology for wiring the individual components of a chip are aluminium and copper.
Salts
In addition to metals, salts can also conduct electric current. Here, however, there are no free electrons. Conductivity is instead based on ions, which detach from the lattice structure and become freely mobile when a salt melts or dissolves (see the chapter on bonds).