Microwave Integrated Circuits on GaAs

A review of the present status of MMIC´s is given with special reference to the specific advantages and problems of monolithic microwave circuits as opposed to hybrid circuits. Some applications will also be discussed together with perspectives of future progress in the field. GaAs integrated circuits are nearly 10 years old. The first circuits were, rather surprisingly, ligic circuits. Surprisingly since the GaAs field effect transistor had already shown success with microwave analogue hybridcircuits to the extent of pushing all other devices either towards higher frequences (for Gunn and Avalanche diodes) or higher powers (for tubes) where the FET´s are no longer operational. Microwave integrated circuits soon made their appearance however when Ray Pengelly prresented his first amplifier in 1976. The problem that was immediately apparent was that the surface required for microwave circuits was comparatively big for an integrated circuit although much smaller than a hybrid circuit. The real advantages of the monolithic concept, control of parasitic reactances, reproducability, reliability, were offset by the cost of the basic GaAs material since the passive elements occupied a very large proporation of the surface (> 90 %) and as a dielectric substrate GaAs is greater than 50 times more expensive than Al2 02.