MMICs are dimensionally small (from around 1 mm² to 10 mm²) and can be mass produced, which has allowed the proliferation of high frequency devices such as cellular phones. MMICs were originally fabricated using gallium arsenide (GaAs), a III-V compound semiconductor. It has two fundamental advantages over Silicon (Si), the traditional material for IC realisation: device (transistor) speed and a semi-insulating substrate. Both factors help with the design of high frequency circuit functions. However, the speed of Si-based technologies has gradually increased as transistor feature sizes have reduced and MMICs can now also be fabricated in Si technology. The primary advantage of Si technology is cost. The wafer diameters are larger (typically 8" or 12" compared with 4" or 6" for GaAs) and the wafer costs are lower. This leads to much lower cost ICs.
Other III-V technologies, such as Indium Phosphide (InP), have been shown to offer superior performance to GaAs in terms of gain, higher cutoff frequency, and low noise. However they also tend to be more expensive due to smaller wafer sizes and increased material fragility.
Silicon Germanium (SiGe) is a Si-based compound semiconductor technology offering higher speed transistors than conventional Si devices but with similar cost advantages.
Author S. P. Marsh
Editors I. D. Robertson and S. Lucyszyn