In this work, the off-state characteristics of AlScN/GaN high electron mobility transistors (HEMTs) grown by metalorganic chemical vapor deposition (MOCVD) were studied and directly compared to an AlGaN- and an AlN-HEMT grown in the same MOCVD. Pinch-off instability and leaky capacitive measurements were observed for AlScN-based HEMTs, which was correlated with a higher ideality factor and lower effective potential barrier height than the AlGaN and AlN-HEMTs. However, the reverse bias characteristics exhibited a sudden drain-current increase without a significant increase in gate-leakage current. The drain-leakage current is assumed to be related to a parasitic channel across the AlScN-barrier as a result of trap-assisted carrier transport with a Poole–Frenkel characteristic. The demonstrated pinch-off instability led to significant gain expansion in load-pull measurements and early soft-breakdown, which, in turn, limits the achievable voltage-margin. The results demonstrate a key issue to reveal the full potential of AlScN-based HEMTs for mm-wave applications.

This paper presents GaN-based power amplifier integrated circuits targeting D-band frequencies. Two chips have been realized, using transistors with a gate length of 100 nm and 70 nm. On-wafer S-Parameter measurements of the designed GaN MMICs yields a high linear-gain of more than 20 dB and 25 dB at 130 GHz, respectively. Performed large-signal measurements of assembled samples demonstrated a saturated output power of 21.9 dBm (150 mW) for the 100 nm MMIC, along with a maximum PAE of 8.8 % at 140 GHz. Assembled 70 nm MMICs yield an improved large-signal performance of 23.1 dBm (200 mW) and more than 11.2 % PAE. Based on the power amplifier integrated circuits with the longer gate-length, a compact split-block module with waveguide flanges has been fabricated. The assembled module has been characterized between 130-150 GHz, demonstrating a typical linear-gain of 19 dB (±3 dB within the frequency band), along with more than 18 dBm (60 mW).

HVPE grown layers typically show a high density of pyramidal structures on the surface. We found that a slight off-orientation of the substrate totally suppresses the development of these structures. Further we found that a misorientation toward the m-plane of GaN features a smoother surface morphology, compared to an off-orientation towards the a-plane. After the improvement of the surface morphology and other properties of the HVPE grown layers, we studied self-separation processes. Our approaches to remove the thick GaN-layer from the substrate were a low-temperature interlayer and a structured dielectric mask.

The paper investigates experimentally the effect of harmonic terminations on AlGaN/GaN power amplifiers (PA) performance at K-/Ka-band. Two technologies are compared, a 0.25 μm and 0.1 μm process. In both cases, a harmonic termination increases the achievable output power by about 10 % at the expense of bandwidth, whereas the efficiency is improved only in the first one.

This paper gives the state-of-the-art (SOA) of the technological development and the reliability status of deep-submicron Gallium Nitride (GaN) high-electron mobility transistors (HEMTs) with gate lengths of 100 nm or below. Several process technologies are discussed and epitaxial, process options, and reliability are compared. Promising GaN MMIC device results are also provided leading to improved GaN G-band operation at frequencies near 200 GHz.

In this paper we report on the development of a 0.50 μm AlGaN/GaN on SiC technology optimized for 100-V operation. Load pull measurements reveal a power density of more than 17 W/mm and a power-added efficiency of 77.3 % at a frequency of 1.0 GHz and a drain supply voltage of 100 V. Experimental data at 125 V even shows a power density in excess of 20 W/mm. To the authors' knowledge, the demonstrated PAE of 77.3 % is the highest ever reported in L-band for 100-V operation.

This work presents a balanced GaN-based power amplifier targeting the entire V-band frequency range. The fabricated chip was packaged in a split block WR-15 waveguide environment to make it applicable for high-power measurement applications. The designed GaN MMIC provides a high small-signal gain of more than 20 dB within a frequency range of 49 GHz up to 83 GHz. On-wafer large-signal measurements of the MMIC at 75 GHz demonstrate a linear gain of 26.3 dB, along with a saturated output power of 29.3 dBm (850 mW) and a maximum power added efficiency of 13.5 % For the assembled module, an average saturated output power of 28.1 dBm (645 mW) within a variance of ±0.4 dB has been measured for the entire V-band (50–75 GHz).

This paper presents recent device and MMIC results of a 70 nm AlN/GaN-HEMT technology. Based on DC-transfer characteristics, a high saturated drain current of more than 1700 mA/mm, and a maximum transconductance of 470 mS/mm were measured for this technology. A transit frequency of f t = 110 GHz along with a maximum oscillation frequency f max = 300 GHz has been extracted. A maximum PAE of 60 %, and a maximum output power density of more than 2.6 W/mm have been demonstrated on single-device level by performing load-pull measurements. The achieved device performance is further verified based on circuit level by the realization of two power amplifiers. MMIC 1 demonstrates a high saturated output power of more than 30 dBm (1 W) between 70-86 GHz. A maximum output power of P out = 28.5 dBm (700 mW) was determined at 94 GHz for MMIC 2.

This work presents the design and analysis of a 5 W power amplifier (PA) MMIC operating between 25 and 27 GHz. The technology used is the 0.1 µm AlGaN/GaN HEMT process of Fraunhofer IAF. To benchmark its performance around 26 GHz two preliminary designs are synthesized and analyzed. The measured results demonstrate for the final MMIC up to 5.2 W of output power associated with 32 % of power added efficiency (PAE). A peak PAE of 35 % was observed in continuous-wave (CW) operation at a drain supply voltage of 15 V.

The effect of gate technology and semiconductor passivation on the switching speed and device reliability has been investigated. By reducing the parasitic capacitances and reducing the passivation induced surface charge density a median lifetime of around 10(6) h at a channel temperature of 125 degrees C and a current-gain cut-off frequency of 74 GHz for a T-gate technology has been achieved. By electroluminescence and TEM cross-sectioning of a stressed device a local inhomogeneous pit formation process was found as the major degradation mechanism for the decrease of the saturation current.

First-ever realization of a W-band power amplifier (PA) millimeter-wave monolithic integrated circuit (MMIC) utilizing GaN-based Tri-gate high-electron-mobility transistors (HEMTs) is presented in this paper. Superior device- and circuit-level performances over conventional GaN HEMTs are proven to be empowered through implementation of the novel Tri-gate topology which exhibits a 3-dimensional gate profile. The measurements of the fabricated MMIC yield up to 30.6 dBm (1.15 W) of output power in the frequency range of 86-94 GHz with 8% of power-added-efficiency (PAE) and more than 12 dB of transducer power gain. The achieved results demonstrate the promising potential of Tri-gate GaN technology towards high-performance millimeter-wave PA designs.

The effect of gate metallization and gate shape on the reliability and RF performance of 100nm AlGaN/GaN HEMTs on SiC substrate for mm-wave applications has been investigated under on-state DC-stress tests. By replacing the gate metallization from NiPtAu to PtAu the median time to failure at Tch=209°C can be improved from 10h to more than 1000h. Replacing the PtAu T-gate by a spacer gate further reduces the degradation rate under on-state stress, but decreases the current-gain cut-off frequency from 75GHz to 50GHz. Physical failure analysis using electroluminescence and TEM cross-section revealed pit and Ni void formation at the gate foot as the main degradation mechanisms of devices with NiPtAu T-gate. High resolution EDX mapping of stressed devices indicates that the formation of pits is caused by a local aluminium oxidation process. Simulation of the stress induced changes of the input characteristics of devices with NiPtAu gate further proves the formation of pits and Ni voids.

This paper gives AlGaN/GaN power amplifier integrated circuits for frequencies to 100 GHz including the potential of their efficient hetero-integration. Representative mm-wave RF-MMIC designs operating from Ka-band all through W-band are being discussed for operation between 28 and 94 GHz based on this technology. At the same time significant advances in the cost-effective hetero-integration concepts offer a lot of progress on packaged-MMIC- and sub-system-level for new applications.

This paper reports on the design and fabrication of enhancement-mode high-electron mobility transistors (HEMTs) in AlGaN/GaN FinFET technology with 100 nm of gate length (L g = 100 nm). Provided by the lateral as well as the vertical modulation of the fin-shaped channels, the threshold voltages of the designed transistors are made possible to be shifted toward the positive direction, enabling the enhancement-mode (E-mode) of operation. The fabricated FinFETs also exhibit highly-improved off-state performance with minimised short-channel effects (SCE) as a result of the enhanced gate control. A very high on/off current ratio of 10 8 and a sub-threshold swing of 75 mV/decade are recorded by the E-mode devices with a threshold voltage of +0.2 V, showing substantial potential for high speed logic, mixed-signal and power electronics applications.

This work discusses the fabrication of two GaN-based power amplifier modules, suitable to increase the available output power levels of E-band multi-Gigabit fixed wireless links dedicated to aeronautics and space applications. The first mounted module contains one GaN-based power amplifier MMIC, packaged in a WR-10 waveguide environment. The module shows a small-signal gain of 13.4 dB with a gain flatness of ± 1 dB, along with a saturated output power of more than 26 dBm (400 mW) for the entire intended frequency range between 71-76 GHz. The second module, parallelizing four MMICs, demonstrates a high saturated output power of more than 31.1 dBm (1290 mW), along with a small-signal gain of typically 11.2 dB and a flatness of ±1 dB within the frequency range of interest.

AlGaN/GaN high-electron mobility transistors (HEMTs) with varied Tri-gate topologies have been fabricated and influences of the fin-shaped nano-channels on device parasitics are examined. Through S-parameter measurements and modelling of the designed Fin-FETs, a detailed RF investigation on intrinsic device parameters is performed under different biasing schemes. Corresponding RF performances and transfer characteristics as well as the derived small-signal parameters of the measured devices are extracted by employing 3-D EM FET model analysis at 110 GHz. Comparisons between the designed fin-geometries and intrinsic device parameters have proven flatter gm, gds and fT responses, which are presented through experimental results in detail for the first time.

The temperature dependence of device degradation of AlGaN/GaN HEMTs on SiC substrate with a gate length of 0.25μm has been investigated. The critical surface temperature, where device degradation sets in has been determined using drain-current step-stress tests in combination with infrared microscopy. Using this fast reliability test, devices with different passivation technologies have been compared and, by optimizing the passivation technology, the critical temperature at which degradation of the threshold voltage begins has been improved from 310°C to above 330°C. Storage tests at 300°C in nitrogen atmosphere confirm the improvement in high temperature stability. Physical failure analysis using electroluminescence and TEM/EDX cross-section revealed void formation and Au-diffusion at the gate as the main degradation mechanisms of devices with the conventional passivation technology.

This letter presents the realization of a high-efficiency, high-temperature Continuous Class-E Sub-Waveform Solution power amplifier using for the first time GaN technology. The recently introduced Continuous Class-E PA mode theory has revealed new and various impedance solutions for which high efficiency switch mode PAs can be realized. The investigation carried out in this work clearly shows that very high efficiency is still delivered despite the smaller voltage waveform peak when compared to standard Class-E, leading to more reliable PAs. The Continuous Class-E Sub-Waveform Solution PA prototype shows efficiency as high as 80% while delivering output power of 4 W and gain > 10 dB at 2 GHz of frequency and ambient temperature. The PA module has also been tested at high temperature T=150 ° C revealing targeted performance with efficiency up to 71% while delivering 3.5 W of output power. Reliability measurements also show satisfactory results in the time frame up to 1500 hours.

The reliability of AlGaN/GaN HEMTs with a gate length of 100 nm suitable for applications up to W-band frequencies has been investigated by on- and off-state DC-stress tests. The extrapolated life time measured using the constant current stress test exceeds 105 h at a base plate temperature of 125°C. Very promising reliability results have also been found for the current step-stress tests even at the highest stress level of a DC power density of 12 W/mm. During off-state step-stress test the drain current exceeds the gate current indicating the onset of a buffer leakage current at drain voltages above the operation voltage.

This paper reports on two AlGaN/GaN MMIC technologies, performances of MMICs and modules, and reliability for space applications at X-band to W-band frequencies. Quarter-micron gate length HEMTs deliver 5 W/mm output power density at 30 V drain bias with >58% PAE at 10 GHz operating frequency. Dual-stage 8 W output power MMICs for telemetry applications in space have a PAE of more than 50% at 8.5 GHz with a lifetime of 106 h at a channel temperature of 200°C. Space evaluation tests indicate a stability of this technology suitable for space. For scientific missions a high-gain high power amplifier MMIC and module have been developed for 90 GHz operation with up to 16 dB of linear gain and 400 mW of output power.