2.3. General Applications

2.3.1 Normal Conductors

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.
  • Antennas.
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; esentiall 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.
  • W.
  • TiN.
because one material simply does not meet the specific requirements for conductor on chips.

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© H. Föll (Advanced Materials B, part 1 - script)