# 2.3.1 Normal Conductors

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$ $$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$$$\newcommand{\AA}{\unicode[.8,0]{x212B}}$$

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; 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.
• 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.