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2.3.1 Normal Conductors

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    2763
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    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 AuAgPt etc. may be critical).
    • Chemistry (general stability and reactivity; esential excludes NaKHg 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.
    • Others

    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.