Monolithic Microwave Integrated Circuits (MMICs): Materials, Design, and Applications

Modern technology integrates multiple circuit functions onto a single semiconductor substrate, providing improvements over traditional discrete component approaches via Monolithic Microwave Integrated Circuits (MMICs).

What are monolithic microwave integrated circuits?

MMICs are specialized integrated circuits for ultra-high frequency and high-power electronic applications, commonly functioning within the 300 MHz to 300 GHz frequency range. They offer distinct advantages in applications demanding compact, cost-effective circuit solutions, particularly within upper microwave and millimeter-wave frequencies.

The manufacturing process involves direct fabrication on semiconductor substrates, where passive components, active devices, and interconnection networks are integrated using deposition technologies such as diffusion, evaporation, and epitaxial growth.

Key Components

Individual MMICs can execute fundamental operations including microwave signal mixing, power amplification, and low-noise amplification. Essential circuit elements for microwave systems for both receivers and transmitters include low-noise amplifiers (LNAs), band-pass filters, mixers, oscillators, phase shifters, and power amplifiers, as shown in Fig. 1.

Phase shifters can be strategically positioned within the local oscillator (LO), radio frequency (RF), or intermediate frequency (IF) sections of a system, and may be avoided entirely in non-phased-array applications.

Fig. 1 Block diagram of a monolithic microwave integrated circuit image-reject mixer receiver. Source: MDPI

This architecture integrates a low-noise amplifier, quadrature mixer, local oscillator chain with frequency quadrupler, phase shifter, and band-pass filters on a single chip. Key error sources, including mixer phase imbalance (α), LNA gain mismatch (β), and quadrature imbalance (γ), are indicated in red. It enables high-frequency RF signal processing with minimized image interference, suitable for advanced microwave and millimeter-wave applications.

Materials

MMICs are built using materials chosen for their electronic, thermal, and frequency characteristics. The main categories and examples are:

● Substrate materials: These form the base on which the entire MMIC is built. The most common substrate materials are gallium arsenide, gallium nitride, silicon, silicon-germanium, and silicon carbide.

● Conductor materials: The materials include gold, aluminum, copper, and silver, which are selected for excellent conductivity and process compatibility.

● Dielectric films: They are composed of silicon dioxide, silicon nitride, tantalum pentoxide, and titanium dioxide, used for insulation, capacitors, and passivation.

● Resistive films: Made up of chromium, nickel-chromium, tantalum, and titanium, used to form integrated resistors.

● Other substrate materials: Made up of alumina, beryllia, sapphire, rutile, are used for specific high-performance or specialized applications.

Advantages

Miniaturization and Integration: MMICs enable significant size reduction of microwave functions into compact packages. These circuits occupy areas ranging from 1 mm² to 10 mm², and the high degree of integration reduces both packaging and interconnection expenses to optimize material properties and device performance.

Cost-Effectiveness: MMICs achieve cost reduction through efficient batch manufacturing processes. While early fabrication predominantly utilized GaAs substrates, which provided superior transistor switching speeds. Silicon MMIC technology has increasingly gained market acceptance due to its economic advantages and availability in larger wafer formats.

Reliability and Reproducibility: They have enhanced reliability and consistency compared to alternative circuit approaches. System-level reliability depends on the uninterrupted operation of each individual MMIC component within the overall architecture.

Applications

Satellite Communication Systems: They are ideal for satellite applications where size, weight, and power constraints are important. They enable reliable signal amplification, frequency conversion, and filtering essential for maintaining communication across vast distances in the challenging space environment.

Phased-Array Antenna Systems: MMICs deliver the consistent electrical characteristics and compact packaging necessary for dense antenna arrays, enabling advanced beamforming, electronic steering, and multi-beam capabilities in both military and commercial radar systems.

Sensor and Radar Applications: These circuits enable the development of sensor systems for automotive collision avoidance, weather monitoring, air traffic control, and surveillance applications. Modern radar systems depend on MMIC for important functions, including low-noise signal reception, high-power transmission, and precise frequency synthesis. The broadband capabilities of MMICs support advanced radar techniques such as frequency-modulated continuous wave and ultra-wideband sensing.

Electronic Warfare Systems: These circuits enable signal intelligence gathering, jamming systems, and countermeasure equipment that form the core of modern defense electronics.

Challenges

MMIC design faces challenges like RF interference, mutual coupling, skin effect, and complex electromagnetic analysis. Parametric shifts can cause system failure, reducing the reliability. Power amplifiers suffer from hot-electron trapping, electromigration, and metal diffusion. LNAs face gate metal sinking and contact diffusion. Mixers deal with harmonic distortion and noise. Oscillators are affected by phase noise and thermal issues. Phase shifters risk parametric drift and insertion loss.

An Effective MMIC To Consider

HMC951A MMIC I/Q Downconverter Features

The Analog Devices HMC951A, as shown in Fig. 2, is a compact GaAs MMIC I/Q downconverter with RF range (5.6-8.6 GHz) that covers C-band radar and satellite communication frequencies, enabling applications in weather radar, air traffic control, and satellite downlinks.

The LO range (4.5-12.1 GHz) allows the mixer to handle various IF frequencies and support multiple systems. The wide IF bandwidth (DC-3.5 GHz) accommodates both narrowband and wideband signal processing, supporting modern communication standards requiring high data rates.

Fig. 2 HMC951A MMIC I/Q Downconverter. Source: Utmel Electronics

The 13 dB conversion gain eliminates the need for additional amplification stages in many applications. The low 2 dB noise minimizes added noise for maintaining sensitivity in receiver systems. 32 dBc image rejection significantly reduces signal interference, improving overall system dynamic range. The -6 dBm P1dB and 3 dBm IP3 specifications provide handling multiple signals without generating problematic intermodulation products.

The exceptional 0.2 dB amplitude balance and -2° phase balance ensure accurate quadrature signal processing, essential for digital modulation schemes, radar coherent processing, and advanced signal analysis applications.

The 48 dB LO-to-RF isolation prevents local oscillator leakage from interfering with received signals or radiating through the antenna. The compact 4×4 mm lead frame chip scale package (LFCSP) enables dense circuit board layouts essential for phased arrays, portable equipment, and cost-sensitive applications.

The -40°C to +85°C operating range ensures reliable operation across military, aerospace, automotive, and industrial temperature extremes, eliminating the need for additional thermal management in most applications.

Summarizing the Key Points

● MMICs significantly miniaturize microwave functions, integrating passive and active components on semiconductor substrates for compact, high-performance communication and radar systems.

● They utilize advanced materials like GaAs, SiGe, and silicon to achieve high-speed switching, reliability, and cost-effectiveness in high-frequency applications across various industries.

● Key components such as LNAs, mixers, oscillators, and phase shifters enable MMICs to perform essential functions in satellite, radar, and wireless communication systems.

● MMICs enable a wide range of applications like phased-array antennas, electronic warfare, and high-data-rate satellite links, addressing challenges like RF interference and electromagnetic coupling.

Reference

Chen, X., Hu, A., Gong, J., Altaf, A., & Miao, J. (2022). Coupling effects analysis and suppression in a highly integrated Ka-Band Receiver Front-End MMIC for a passive Millimeter-Wave imager system. Sensors, 22(15), 5695. https://doi.org/10.3390/s22155695

S.S. Srikant/Turkish Journal of Engineering, Science and Technology- https://www.researchgate.net/publication/275645488_An_Overview_on_Monolithic_Microwave_Integrated_Circuits

A. N. Downey, G. E. Ponchak, and R. R. Romanofsky-Monolithic Microwave Integrated Circuits - https://parts.jpl.nasa.gov/mmic/3-IX.PDF

Ekeeda. (2022a, April 6). Introduction to Monolithic microwave Integrated circuits - Monolithic microwave integrated circuits [Video]. YouTube. https://www.youtube.com/watch?v=GEgZ4_kg2TU

Ekeeda. (2022, April 6). Materials of monolithic microwave integrated circuits - Monolithic microwave integrated circuits [Video]. YouTube. https://www.youtube.com/watch?v=7ExSvLHIqUk

Utmel. (2021, July 22). HMC951ALP4E - Datasheet PDF - RF Mixers - Analog Devices Inc. - Utmel. Utmel All Rights Reserved. https://www.utmel.com/productdetail/analogdevicesinc-hmc951alp4e-8606214