A world without conductors is even harder to imagine than a world without semiconductors. Examples for applications include
- High-voltage free-air power transmission lines.
- High voltage wires for trains (getting "scratched" all the time).
- In-house wiring.
- Low-voltage wiring (car systems).
- High current wiring (machines).
- System on-board wiring.
- Bond wires for IC's (diameter < 30µm).
- Metallization on chips.
- Screening electrical or magnetic fields.
- Avoidance of electrostatic charging.
- Electrodes for batteries, chemical reactors etc.
- Each use has special requirements which should be met by the conducting material.
Some examples for requirements
- Money (Use of Au, Ag, Pt etc. may be critical).
- Chemistry (general stability and reactivity; esential excludes Na, K, Hg etc. for most applications; corrosion properties, ...).
- Mechanical properties (Pure metals are often too soft, but alloys have higher resistivity).
- Thermal properties (temperature coefficient; no metal usable beyond ca. 1000 K) .
- Compatibility with other materials (contact corrosion, solderability, thermoelectric and thermomechanical properties, general chip compatibility, ...).
- Compatibility with production technologies (e.g. thin film deposition methods, wire making (try this with a brittle superconductor!)...).
Whole families of conductors, fine-tuned for a specific applications, were developed; below are some examples.
- Cu based conductors There are many precisely specified Cu-based conductors for all kind of specific applications, examples are given in the link.
- Al based conductors This family is primarily used for high-voltage free-air cables (in combination with a steel core) because of best fitting in terms of conductivity - price - mech. strength - corrosion requirements; cf. the illustration in the link.
In one IC you may find the following conductor materials:
- Poly crystalline highly doped Si.
- Silicides; i.e. Si - metal compounds like NiSi2.
- Al with ≤ 1% of Si and Cu if the chip was made before, say, 2000.
- Cu with some additions instead of Al if the chip was made after 2000.
because one material simply does not meet the specific requirements for conductor on chips.