1.1 Introduction

A monolithic microwave integrated circuit (MMIC) is a microwave circuit in which the active and passive components are fabricated on the same semiconductor substrate. The frequency of operation can range from 1 GHz to well over 100 GHz, and a number of different technologies and circuit approaches can be used. The additional term 'monolithic' is necessary to distinguish them from the established microwave integrated circuit (MIC), which is a hybrid comprising a number of discrete active devices and passive components integrated onto a common substrate using solder or conductive epoxy adhesive. These became known as integrated circuits because the alternative is to employ hollow metal waveguides, where the inclusion of active devices is a matter requiring considerable mechanical design and workshop machining.

Strictly speaking, monolithic circuits operating above 30 GHz should perhaps be called monolithic millimetre-wave integrated circuits, but a number of alternative abbreviations have been used (such as MMWIC or M ³IC), and there doesn't seem to be general agreement as yet. Further confusion arises with the term 'RFIC', which is used by some to mean circuits operating in the low GHz range (most often using silicon technology), and by others as a vague general term for RF, microwave or millimetre-wave monolithic circuits. In this book the abbreviation MMIC is used almost exclusively, and it should be understood to include millimetre-wave circuits as well. All these terms may become redundant as the current trend is towards systems-on-a-chip, where the goal is an...