## 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.
|  | 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.

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