DEVELOPMENT OF SETUP FOR ON-WAFER PULSE-TO-PULSE STABILITY CHARACTERIZATION OF GAN HEMT TRANSISTOR IN KU-BAND

International audienceWe report on the development of a test bench to extract pulse-to-pulse (P2P) stability On-Wafer in Ku-band. The P2P stability is crucial for RADAR performances. GaN HEMT transistors are a promising candidate for RADAR application. However, they typically generate trapping effects, which can strongly affect the P2P stability. Two methods RMS and Standard Deviation based on temporal analysis are employed to extract the stability indicators. The main idea of the P2P test bench is the use of a homodyne demodulation to recover the envelop of the RF. This setup is also combined to an active load pull towards P2P stability test bench dedicated to the new generation of GaN HEMT transistors in large signal condition close to their operational mode

Circuit design and characterization of devices based on AlN/GaN double heterostructure for millimeter-wave power applications

La technologie Nitrure de Gallium s’impose actuellement comme le candidat idéal pour les applications de forte Puissance en gamme d’ondes millimétriques. Les caractéristiques de ce matériau le prédisposent à un fonctionnement à haute tension sans sacrifier la montée en fréquence, illustrées par son champ de claquage et sa vitesse de saturation des électrons élevés. Ces travaux de recherche s’inscrivent, dans un premier temps, dans le développement d’un banc de mesures permettant la caractérisation « grand signal », dite LoadPull dans la bande Ka et Q, en mode continu et impulsionnel de cette technologie émergente. En effet, la forte densité de puissance qu’est capable de générer la technologie GaN a rendu le développement de ce banc indispensable et relativement unique. Par ailleurs, cette étude s’est focalisée, dans la caractérisation de plusieurs filières innovantes qui ont mis en évidence des performances à l’état de l’art, avec un rendement en puissance ajoutée PAE de 46.3% associée à une densité de puissance de 4.5W/mm obtenue pour une fréquence d’opération de 40 GHz en mode continu. Enfin, ces travaux de thèse ont permis de générer la conception et la réalisation de deux amplificateurs de puissance en technologie GaN sur substrat silicium (basée sur la filière industrielle OMMIC) en bande Ka, représentant la finalité d’une démarche cohérente de l’étude de transistors en technologie GaN à la réalisation de circuits de type MMIC. Ces deux amplificateurs ont été conçus pour des objectifs biens précis : combiner puissance élevée et rendement PAE élevé et repousser les limites en termes de largeur de bande.Gallium Nitride (GaN) technology is now the ideal candidate for high power applications in the millimeter wave range. The characteristics of this material enable high voltage operation at high frequency, as illustrated by its breakdown field and high electron saturation velocity. This research work has initially allowed the development of a test bench capable of "Large Signal" characterization, called LoadPull up to Q band, in continuous-wave and pulsed mode of this emerging technology. Indeed, the high power density generated by the GaN technology has made the development of this bench unavoidable and relatively unique. In addition, this study has focused on the characterization of several innovative types of devices that have demonstrated state-of-the-art performance, with a power added efficiency (PAE) above 46% associated to a power density of 4.5 W/mm obtained for an operating frequency of 40 GHz in continuous-wave. Finally, this work aimed the design and fabrication of two power amplifiers on silicon substrate (based on the industrial OMMIC technology) in the Ka-band, showing the possibility of achieving MMIC type circuits from advanced GaN transistors technology. These two amplifiers were designed for specific purposes: combining high power and high PAE performance and pushing bandwidth limits

Next generation of GaN-on-Silicon power devices

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Novel heterostructures for millimeter-wave GaN devices

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High Power AlN/GaN HEMTs with record power-added-efficiency >70% at 40 GHz

International audienceWe report on breakthrough power-added-efficiency (PAE) Q-band performances using a vertically scaled AlN/GaN HEMT technology. The comparison between a 3 nm and 4 nm barrier thickness shows both superior performance and robustness for the thinner barrier layer attributed to the reduced mechanical strain into the heterostructure. Large signal characteristics at 40 GHz revealed an outstanding PAE of 73% at VDS = 30V associated to an output power density > 5 W/mm in pulsed mode. Also, the load-pull measurements mapping across the 4-inch wafer demonstrates a high uniformity and reproducibility of the results. Consequently, significantly improved PAE can be expected for next generation of high power MMICs operating in the millimeter-wave range

High Electron Confinement under High Electric Field in RF GaN-on-Silicon HEMTs

We report on AlN/GaN high electron mobility transistors grown on silicon substrate with highly optimized electron confinement under a high electric field. The fabricated short devices (sub-10-nm barrier thickness with a gate length of 120 nm) using gate-to-drain distances below 2 µm deliver a unique breakdown field close to 100 V/µm while offering high frequency performance. The low leakage current well below 1 µA/mm is achieved without using any gate dielectrics which typically degrade both the frequency performance and the device reliability. This achievement is mainly attributed to the optimization of material design and processing quality and paves the way for millimeter-wave devices operating at drain biases above 40 V, which would be only limited by the thermal dissipation

First demonstration of RF GaN-based transistors using buffer-free heterostructures with low trapping effects

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Low RF losses up to 110 GHz in GaN-on-silicon HEMTs

International audienceWe report on low RF losses at the interface between the epitaxial structure and the silicon substrate (less than 0.8 dB/mm up to 110GHz) of AlN/GaN high electron mobility transistors (HEMTs) grown on silicon substrate. This stateof-the-art performance makes GaN-on-Silicon HEMTs competitive with GaN-on-SiC in terms of parasitic RF losses. Furthermore, a maximum dc output current close to 1 A/mm together with low leakage current of 1 μA/mm and low trapping effects are achieved while using a short gate length of 0.2 μm. The large signal measurements confirmed the high quality of the epitaxy and the device processing as well as the low parasitic RF losses. This is reflected by a high output power density of 4.5 W/mm achieved at 18 GHz

GaN-based transistors using buffer-free heterostructures for next generation RF devices

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High Lateral Breakdown Voltage in Thin Channel AlGaN/GaN High Electron Mobility Transistors on AlN/Sapphire Templates

International audienceIn this paper, we present the fabrication and Direct Current/high voltage characterizations of AlN-based thin and thick channel AlGaN/GaN heterostructures that are regrown by molecular beam epitaxy on AlN/sapphire. A very high lateral breakdown voltage above 10 kV was observed on the thin channel structure for large contact distances. Also, the buffer assessment revealed a remarkable breakdown field of 5 MV/cm for short contact distances, which is far beyond the theoretical limit of the GaN-based material system. The potential interest of the thin channel configuration in AlN-based high electron mobility transistors is confirmed by the much lower breakdown field that is obtained on the thick channel structure. Furthermore, fabricated transistors are fully functional on both structures with low leakage current, low on-resistance, and reduced temperature dependence as measured up to 300 • C. This is attributed to the ultra-wide bandgap AlN buffer, which is extremely promising for high power, high temperature future applications