In this paper, two high efficiency monolithic microwave integrated circuits (MMICs) are demonstrated using NANOTAM's in-house Ka-band fabrication technology. AlGaN/GaN HEMTs with 0.2 ${\rm \mu}$m gate lengths are characterized, and an output power density of 2.9 W/mm is achieved at 35 GHz. A three-stage driver amplifier MMIC is designed, which has a measured gain higher than 19.3 dB across the frequency band of 33–36 GHz. The driver amplifier exhibits 31.9 dB output power and 26.5% power-added efficiency (PAE) at 35 GHz using 20 V supply voltage with 30% duty cycle. Another two-stage MMIC is realized as a power amplifier with a total output gate periphery of 1.8 mm. The output power and PAE of the power amplifier are measured as 3.91 W and 26.3%, respectively, at 35 GHz using 20 V supply voltage with 30% duty cycle. The high efficiency MMICs presented in this paper exhibit the capabilities of NANOTAM's 0.2 $\rm\mu$m AlGaN/GaN on SiC technology.

In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the InxGa1−xAs channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the InxGa1−xAs layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the InxGa1−xAs channel layer was pseudomorphically grown leading to tetragonal strain along the [001] growth direction and that the average indium content (x) in the epilayer is ~0.12. We found consistency in the results obtained using various methods of analysis.

This paper presents a design method of internally-matched packaged GaN high electron mobility transistors (HEMTs) for achieving not only high-efficiency and high-power performances but also a wide bandwidth and insensitivity to harmonic terminations in the S-band. The package and its internal matching networks are synthesized to confine the second harmonic impedances seen by the GaN die to high-efficiency regions whatever the harmonic impedances presented outside the package. This paper reports the design of a packaged GaN HEMT achieving 78% of power-added-efficiency (PAE) and 25 W of output power at 2.5 GHz. A packaged GaN power bar is also reported with the addition of fundamental matching networks inside the package. In 50 Ω environment, the packaged GaN power bar provided more than 56% of PAE from 2.5 to 3.1 GHz and was desensitized to harmonic load variations with less than two points of PAE variation when a load-pull is performed at second harmonic frequencies outside the package.

We report cryogenic noise temperature and gain measurements of a prototype heterodyne receiver module designed to operate in the atmospheric window centered on 150 GHz. The module utilizes monolithic microwave integrated circuit (MMIC) InP high electron mobility transistor (HEMT) amplifiers, a second harmonic mixer, and bandpass filters. Swept local oscillator (LO) measurements show an average gain of 22 dB and an average noise temperature of 87 K over a 40 GHz band from 140 to 180 GHz when the module is cooled to 22 K. A spot noise temperature of 58 K was measured at 166 GHz and is a record for cryogenic noise from HEMT amplifiers at this frequency. Intermediate frequency (IF) sweep measurements show a 20 GHz IF band with less than 94 K receiver noise temperature for a fixed LO of 83 GHz. The compact housing features a split-block design that facilitates quick assembly and a condensed arrangement of the MMIC components and bias circuitry. DC feedthroughs and nano-miniature connectors also contribute to the compact design, so that the dimensions of the moduleare approximately 2.5 cm per side.

This paper reports on a novel voltage-mode class-S power amplifier for the 450 MHz band, based on GaN–HEMT monolithic microwave integrated circuits (MMICs). It achieves a peak output power of 3.4 W for a single tone at 400 MHz, encoded in standard band-pass delta-sigma modulation with 1.6 Gbps sampling frequency. The corresponding efficiency is 38%, peaking at 52% for 0.5 W output power. In order to demonstrate the influence of coding efficiency, additional measurements using a periodic square-wave signal were performed (class-D operation), which yield a maximum output power of 7 W with 64% efficiency. To the author's knowledge, these are the best results in this frequency range achieved so far with the voltage-mode class-S configuration. The paper discusses behavior at power back-off and the influence of the loss mechanisms.

We review the AlGaN/GaN high electron mobility transistor (HEMT) activities in the Millimeter-Wave Electronics Group at ETH-Zürich. Our group's main thrust in the AlGaN/GaN arena is the extension of device bandwidth to higher frequency bands. We demonstrated surprising performances for AlGaN/GaN HEMTs grown on high-resistivity (HR) silicon (111) substrates, and extended cutoff frequencies of 100 nm gate devices well into the millimeter (mm)-wave domain. Our results narrow the performance gap between GaN-on-SiC (or sapphire) and GaN-on-silicon and establish GaN-on-Si as a viable technology for low-cost mm-wave electronics. We here contrast the difference in behaviors observed in our laboratory between nominally identical devices built on high-resistivity silicon (HR-Si) and on sapphire substrates; we show high-speed devices with high-cutoff frequencies and breakdown voltages which combine fT,MAX × BV products as high as 5–10 THz V, and show AlGaN/GaN HEMTs with fT values exceeding 100 GHz on HR-Si. Although the bulk of our activities have so far focused on AlGaN/GaN HEMTs on HR-Si, our process produces excellent device performances when applied to GaN HEMTs on SiC as well: 100 nm gate transistors with fT > 125 GHz have been realized at ETH-Zürich.

The present paper presents an overview of the AlGaN/GaN-based circuits realized over the years. Two technological processes with 0.25 and 0.7 μm gate length allowed one to address applications from L- to Ku-bands. Depending on the process development and frequency of the operation, results on hybrid or MMIC technology are presented. GaN technology is evaluated through the realization of high-power amplifiers, robust low-noise amplifiers, or power switches to prepare the next generation of Tx-Rx modules.

We present an overview on epitaxial growth, processing technology, device performance, and reliability of our GaN high electron mobility transistors (HEMTs) manufactured on 3- and 4-in. SiC substrates. Epitaxy and processing are optimized for both performance and reliability. We use three different gate lengths, namely 500 nm for 1–6 GHz applications, 250 nm for devices between 6 and 18 GHz, and 150 nm for higher frequencies. The developed HEMTs demonstrate excellent high-voltage stability, high power performance, and large DC to RF conversion efficiencies for all gate lengths. On large gate width devices for base station applications, an output power beyond 125 W is achieved with a power added efficiency around 60% and a linear gain around 16 dB. Reliability is tested both under DC and RF conditions with supply voltage of 50 and 30 V for 500 and 250 nm gates, respectively. DC tests on HEMT devices return a drain current change of just about 10% under IDQ conditions. Under RF stress the observed change in output power density is below 0.2 dB after more than 1000 h for both gate length technologies.

Piezoelectric AlGaN/GaN FETs on SiC with high carrier mobility have been fabricated yielding IDS=450 mA/mm and gm=200 mS/mm. In the on-state, under UV-illumination, the devices sustain a drain voltage of VDS=49 V, corresponding to a power dissipation of 26.5 W/mm. On turn-on of the device from the pinch-off state, a significant delay in the drain current build-up is observed. This effect depends on the pinch-off time and the pinch-off voltage and can be removed by either a brief UV-illumination or a VDS>25 V applied in the on-state. The drain current transients are characterized by a relaxation time τ, which is in the order of several hundred seconds. From the temperature dependence of τ, an activation energy of about 280 meV and a capture cross section of 4.4·10−18cm2 were determined. The devices show pronounced persistent photoconductivity (PPC) and the drain current ID is sensitive to illumination.