The rapid development of the RF power electronics requires the introduction of wide bandgap material due to its potential in high output power density, high operation voltage and high input impedance GaN-based RF power devices have made substantial progresses in the last decade This paper attempts to review the latest developments of the GaN HEMT technologies, including material growth, processing technologies, device epitaxial structures and MMIC designs, to achieve the state-of-the-art microwave and millimeter-wave performance The reliability and manufacturing challenges are also discussed

GaN-Based RF Power Devices and Amplifiers

Understanding energy dissipation and transport in nanoscale structures is of great importance for the design of energy-efficient circuits and energy-conversion systems. This is also a rich domain for fundamental discoveries at the intersection of electron, lattice (phonon), and optical (photon) interactions. This review presents recent progress in understanding and manipulation of energy dissipation and transport in nanoscale solid-state structures. First, the landscape of power usage from nanoscale transistors (∼10−8 W) to massive data centers (∼109 W) is surveyed. Then, focus is given to energy dissipation in nanoscale circuits, silicon transistors, carbon nanostructures, and semiconductor nanowires. Concepts of steady-state and transient thermal transport are also reviewed in the context of nanoscale devices with sub-nanosecond switching times. Finally, recent directions regarding energy transport are reviewed, including electrical and thermal conductivity of nanostructures, thermal rectification, and the role of ubiquitous material interfaces. 
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Energy dissipation and transport in nanoscale devices

Gallium-nitride power transistor (GaN HEMT) and integrated circuit technologies have matured dramatically over the last few years, and many hundreds of thousands of devices have been manufactured and fielded in applications ranging from pulsed radars and counter-IED jammers to CATV modules and fourth-generation infrastructure base-stations. GaN HEMT devices, exhibiting high power densities coupled with high breakdown voltages, have opened up the possibilities for highly efficient power amplifiers (PAs) exploiting the principles of waveform engineered designs. This paper summarizes the unique advantages of GaN HEMTs compared to other power transistor technologies, with examples of where such features have been exploited. Since RF power densities of GaN HEMTs are many times higher than other technologies, much attention has also been given to thermal management-examples of both commercial “off-the-shelf” packaging as well as custom heat-sinks are described. The very desirable feature of having accurate large-signal models for both discrete transistors and monolithic microwave integrated circuit foundry are emphasized with a number of circuit design examples. GaN HEMT technology has been a major enabler for both very broadband high-PAs and very high-efficiency designs. This paper describes examples of broadband amplifiers, as well as several of the main areas of high-efficiency amplifier design-notably Class-D, Class-E, Class-F, and Class-J approaches, Doherty PAs, envelope-tracking techniques, and Chireix outphasing.

/pdf/a-review-of-gan-on-sic-high-electron-mobility-power-4mjzeqemry.pdf

A Review of GaN on SiC High Electron-Mobility Power Transistors and MMICs

Understanding energy dissipation and transport in nanoscale structures is of great importance for the design of energy-efficient circuits and energy-conversion systems. This is also a rich domain for fundamental discoveries at the intersection of electron, lattice (phonon), and optical (photon) interactions. This review presents recent progress in understanding and manipulation of energy dissipation and transport in nanoscale solid-state structures. First, the landscape of power usage from nanoscale transistors (~10^-8 W) to massive data centers (~10^9 W) is surveyed. Then, focus is given to energy dissipation in nanoscale circuits, silicon transistors, carbon nanostructures, and semiconductor nanowires. Concepts of steady-state and transient thermal transport are also reviewed in the context of nanoscale devices with sub-nanosecond switching times. Finally, recent directions regarding energy transport are reviewed, including electrical and thermal conductivity of nanostructures, thermal rectification, and the role of ubiquitous material interfaces.

/pdf/energy-dissipation-and-transport-in-nanoscale-devices-17sw2ubrhz.pdf

Energy Dissipation and Transport in Nanoscale Devices

Recent advances in developing nonlinear optical techniques for processing serial digital information at high speed are reviewed. The field has been transformed by the advent of semiconductor nonlinear devices capable of operation at 100 gigabits per second and higher, well beyond the current speed limits of commercial electronics. These devices are expected to become important in future high-capacity communications networks by allowing digital regeneration and other processing functions to be performed on data signals “on the fly” in the optical domain.

https://science.sciencemag.org/content/sci/286/5444/1523.full.pdf

Nonlinear Optics for High-Speed Digital Information Processing.

A CMOS digital microcircuit, utilizing sub-micron technology, was designed for the purpose of providing integrated control circuitry to an array of high-voltage micro-electromechanical systems (MEMS) switch based phase shifter devices. The grid of MEMS phase shifters is part of a phased array antenna system. The phase of each element of the array is controlled via the CMOS microcircuit. This paper presents the design, physical layout, and the measured test results for CMOS digital control circuit that has been fabricated using the MOSIS Integrated Circuit Fabrication Service. The circuit converts serial data to parallel outputs to reduce number of control lines and lower the cost of wiring the phased array. In addition, discrete digital control circuitry for loading phase shifts into each MEMS device is presented.

Integration of MEMS phase shifters with CMOS control circuitry

The ability to accurately determine the breakdown voltage of microwave transistors is critical to the design of high power microwave amplifiers The optimal bias point and output impedance should be selected to ensure that the load line of the device during peak output power does not intersect the portion of the IV curve where the device breaks down [1] A technique that has proven useful for the measuring off-state breakdown voltage for FETs was reported on by Bahl and del Alamo in 1993 [2] This procedure works well for a variety of devices including microwave GaAs MESFETs, as described in the original article, and GaAs HEMTs Fig 1 shows the circuit diagram for the gate breakdown measurement system The procedure for the measurement consists of using a current source to force a fixed current through the drain The voltage on the gate is swept from zero to a negative value, while the voltage on the drain is allowed to float to whatever value is required to force the drain current Bahl and del Alamo use a rule of thumb for the drain current of 1mA/mm [2] This has proven to be a useful standard for GaAs MESFETs and HEMTs

Investigation of breakdown behavior for AlGaN HEMTs

We report the development of an accurate closed-form model for 3D transmission line analysis and synthesis. Close agreement is observed between our model and full wave analysis. Additionally, we built and measured a number of 3D special elements. Excellent performance is obtained from a delay line, and a broadband coupler. A 3D 4-way Wilkinson divider design and measurement are presented. Transmission line losses are measured.

Ali M. Darwish

Papers

Integration of MEMS phase shifters with CMOS control circuitry

Investigation of breakdown behavior for AlGaN HEMTs

Three dimensional transmission lines and special elements design