Monolithic Microwave Integrated Circuit

Monolithic microwave integrated circuit (MMIC) is a semiconductor chip that contains multiple active and passive devices. These devices are bonded on an insulating substrate.

MMICs can perform a variety of functions such as frequency mixing, power amplification and high-frequency switching. They are often matched to a 50-ohm characteristic impedance, which simplifies circuit design and test equipment operation.

Basics

Before MMICs were available, RF circuits were constructed from discrete components and passives in a PCB layout. This approach can become problematic at high frequencies, where parasitic effects (interconnect resistance and crosstalk) degrade circuit performance. MMICs and hybrid microwave integrated circuits (HMICs) reduce these effects by making component and circuit blocks smaller in size.

Unlike discrete semiconductor devices that consist of multiple transistors, resistors, diodes, and capacitors connected by bond wires, monolithic MMICs contain all these components formed together on the surface of a sliver or chip of pure silicon. This is accomplished through one of the most exacting production processes ever developed.

An example of an MMIC is the instrumentation amplifier (INA) shown in Figure 3-38 and Figure 3-39. INAs are often used to amplify small differential signals in systems such as microwave receivers and transmitters and phased-array antennas. Compared to a discrete INA, the monolithic version has lower cost and is much smaller. In addition, the input and output ports on an INA are typically matched to characteristic impedances of 50 ohms, which simplifies their use.

Applications

A monolithic microwave integrated circuit can perform functions such as microwave mixing, power amplification, and low noise amplification on low dropout regulator a single semiconductor substrate. Unlike a conventional IC which uses discrete components, MMICs have inputs and outputs that are often matched to a characteristic impedance of 50 ohms. This simplifies their use because external matching networks are not needed.

MMICs can be made in a variety of shapes and sizes, making them useful for many applications, such as mobile device antennas, satellite transmission systems, and radio frequency (RF) amplifiers. Compared to traditional RF circuits constructed from discrete components and passives, MMICs offer lower component count and size, better performance, and the ability to integrate exotic semiconductor materials.

Input devices such as phase shifters are often integrated into MMICs. Using a monolithic phase shifter can eliminate the need for multiple phase shifters and amplifiers to achieve a given scan angle, which reduces power consumption and increases mechanical steering efficiency over a traditional mechanical steering antenna.

Design

A functional electronic circuit requires transistors, resistors and diodes as well as the connections between them. A monolithic integrated circuit has all these components formed on the surface layer of a single sliver, or chip, of a semiconductor. The most common semiconductor material used for ICs is silicon. Monolithic ICs can be found in many commercial products such as music synthesizers, radios and TVs, function generators, FM and AM transmitters and receivers, and programmable filters.

MMIC devices are designed to perform functions such as microwave mixing and power amplification, while maintaining a low characteristic impedance for easy connection to other devices. Inputs and outputs of MMIC devices are often matched to a 50 ohm characteristic impedance, eliminating the need for external matching networks.

MMIC technology has advanced by means of improvements in fabrication processes, metallurgy and circuit design and configuration. These advances include new analytical and computer-aided modelers of GaAs MESFETs, HEMTs or MODFETs; nonlinear CAD programs for MOSFET-based distributed amplifiers; and the development of techniques for designing complex RF active and passive elements in unconventional arrangements.

Fabrication

Until recently, most RF circuits were built from discrete components and passives in a PCB layout. These designs become difficult to work with at dynamic power management high frequencies because of parasitic effects that result in undesired signal behavior and crosstalk among various circuit blocks in the PCB layout. HMICs and MMICs reduce parasitics and overall component count/size by integrating various circuit blocks on a single semiconductor substrate.

An example is an MMIC that combines an RF amplifier and mixer on the same substrate with a phased array antenna. Such a monolithic integrated circuit allows for smaller, lighter, and more cost effective systems that can perform the same functions as older technologies.

Developing these monolithic microwave integrated circuits requires processes and metallurgies that allow the fabrication of active devices and circuit elements whose dimensions and properties are suitable for use with signals at microwave and millimeter wave wavelengths. For example, a new type of MOSFET can produce nonalloyed ohmic contacts on a silicon substrate at room ambient temperature to avoid the need for separate bias systems and emitter circuit swamping resistors and to enable circuit fabrication largely in situ.

Measurement

The manufacture of monolithic microwave integrated circuits (MMICs) involves one of the most exacting production processes ever developed. It begins with the growth of a crystal of pure semiconductor material, commonly called a silicon chip. This is then cut into small pieces that are then placed on a board and exposed to ultra-violet radiation.

The resistors, diodes and transistors that make up a functional electronic circuit are formed on the surface of these chips. The monolithic manufacturing process allows the resulting chip to have virtually identical transistor characteristics, which can then be paralleled during manufacture to give a highly efficient low impedance and low noise matched pair.

This level of circuit integration increases the performance of a given system while decreasing component count, assembly time and overall cost. MMICs are often used in high frequency systems such as receivers and transmitters for communications, phased-array antennas that require small size and uniform circuit performance, and sensors and radars that operate at very high frequencies. The MMIC market is driven by factors such as 5G technology, increased usage of smartphones and digital data generation, technological advances in defense equipment, and increase in global space programs.