Other Integrated Circuit Technologies

Abstract

Thus far, this book has dealt exclusively with silicon MOS integrated circuits as this represents the majority of Application-Specific Integrated Circuits. However, the first semiconductor amplifier was a bipolar transistor and this device has not become significantly less important with the passing of the years. There is also considerable investment in a relatively recent technology known as’ silicon-on-Insulator’ (SOI). This is fundamentally an MOS process but the substrate is a wafer made of some insulating material. There are a number of materials which can be used for the substrate but the most promising to date is sapphire and, not unreasonably, this variant of SOI is known as Silicon-on-Sapphire (SOS). Silicon is not the only semiconductor known to science. There has always been germanium and, holding great promise for the future, there are the so-called III–V compounds such as gallium arsenide. These have some advantages over silicon.