Silicon

Notes

Silicon dioxide, grown simply by heating the wafer in oxygen, is the quiet reason silicon beat germanium.

Overview

Silicon is the chemical element (symbol Si, atomic number 14) from which almost all chips are made, used in the form of large single crystals of extreme purity. It is a semiconductor with a band gap of about 1.12 electronvolts at room temperature, it is plentiful, and it grows a stable insulating oxide, a combination no other material has matched at industrial scale. Engineers also use "silicon" loosely to mean finished chips, as in "first silicon".

How it works

Silicon never occurs pure in nature; it comes from quartz and sand. Quartz is reduced with carbon in an arc furnace to metallurgical-grade silicon of roughly 95 to 99 per cent purity, a small share of which is refined further for electronics, typically to at least 99.9999999 per cent purity. That material is melted and grown into single-crystal ingots, which are sliced into polished wafers.

Its oxide is a large part of why silicon won. Heating silicon in oxygen or steam grows a layer of silicon dioxide, a good insulator that is stable and does not dissolve in water. For decades it formed the insulating layer under every transistor gate, and it is still used throughout chipmaking. Germanium, used in the first transistors, has no equally stable oxide.

Silicon has limits. Lasers and LEDs use compound semiconductors such as gallium arsenide instead, and wide band gap materials such as silicon carbide and gallium nitride take over where higher voltages and temperatures are needed.

Examples

Related terms

• Germanium
• Compound semiconductor
• Wafer
• Semiconductor

Where it appears on the Hub

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