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This paper presents performances achieved with InAlGaN/GaN HEMTs with 0.15 µm gate length on SiC substrate. Technology Computer Aided Design simulations were used to optimize the heterostructure. Special attention was paid to the design of the buffer structure. I-V measurements with DC and pulsed bias voltages were performed. CW measurements at millimeter waves were also carried out and are detailed in the following sections. The technology, optimized for power applications up to 45 GHz, demonstrates a current gain cut-off frequency FT of 70 GHz and a maximum available gain cut-off frequency FMAG of 140 GHz. CW Load-pull power measurements at 30 GHz enable to achieve a maximum PAE of 41% associated with an output power density of 3.5 W/mm when biased at VDS = 20 V. These devices, with an improved buffer structure show, reduced recovery time in pulsed operating conditions. These improved characteristics should have a positive impact for pulsed or modulated signal applications.
This paper presents an original characterization method of trapping phenomena in gallium nitride high electron mobility transistors (GaN HEMTs). This method is based on the frequency dispersion of the output-admittance that is characterized by low-frequency S-parameter measurements. As microwave performances of GaN HEMTs are significantly affected by trapping effects, trap characterization is essential for this power technology. The proposed measurement setup and the trap characterization method allow us to determine the activation energy Ea and the capture cross-section σn of the identified traps. Three original characterizations are presented here to investigate the particular effects of bias, ageing, and light, respectively. These measurements are illustrated through different technologies such as AlGaN/GaN and InAlN/GaN HEMTs with non-intentionally doped or carbon doped GaN buffer layers. The extracted trap signatures are intended to provide an efficient feedback to the technology developments
This paper presents power results of L-band packaged hybrid amplifiers using InAlN/GaN/SiC HEMT power dies. The high-power densities achieved both in pulsed and continuous wave (cw) modes confirm the interest of such technology for high-frequency, high-power, and high-temperature operation. We present here record RF power measurements for different versions of amplifiers. Up to 260 W, i.e. 3.6 W/mm, in pulsed (10 µs/10%) conditions, and 105 W, i.e. 2.9 W/mm, in cw conditions were achieved. Such results are made possible thanks to the impressive performances of InAlN/GaN transistors, even when operating at high temperatures. Unit cell transistors deliver output powers of 4.3 W/mm at Vds = 40 V in the cw mode of operation at the frequency of 2 GHz. The transistor process is described here, as well as the amplifiers design and measurements, with a particular focus to the thermal management aspects.
A study of the electrical performances of AlInN/GaN High Electron Mobility Transistors (HEMTs) on SiC substrates is presented in this paper. Four different wafers with different technological and epitaxial processes were characterized. Thanks to intensive characterizations as pulsed-IV, [S]-parameters, and load-pull measurements from S to Ku bands, it is demonstrated here that AlInN/GaN HEMTs show excellent power performances and constitute a particularly interesting alternative to AlGaN/GaN HEMTs, especially for high-frequency applications beyond the X band. The measured transistors with 250 nm gate lengths from different wafers delivered in continuous wave (cw): 10.8 W/mm with 60% associated power added efficiency (PAE) at 3,5 GHz, 6.6 W/mm with 39% associated PAE at 10.24 GHz, and 4.2 W/mm with 43% associated PAE at 18 GHz.
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.
The fabrication of high-resistivity ZnO-based thin films lattice-matched to AlGaN/GaN structures has been developed. It relies on low-temperature reactive sputter deposition of ZnO:Sb from ZnSb target. Taking into account the hygroscopic nature of ZnO surface, an additional coating by Si3N4 films is applied to ensure the humidity protecition. The developped passivation suppresses leakage currents in Schottky diods, and substantially improves output characteristics of AlGaN/GaN HEMT.
A series of isothermal annealing experiments have been performed in the range 790–920°C under N2 flow in order to study the deuterium out-diffusion kinetics of Mg-doped GaN grown on sapphire under deuterated ammonia. The deuterium concentration was measured by SIMS analysis before and after each annealing step. The kinetics closely follow a first-order law. The activation energy related to the deuterium out-diffusion process is 3.1 eV. In addition, deuterium effusion measurements were performed measuring the molecular HD flux while the specimens were annealed in ultra high vacuum with a linear heating rate. In contrast to SIMS, this method detects the species that migrated out of the sample. Effusion peaks of the HD flux at 360 and 490°C are attributed to the fragmentation of adsorbed CHxDy complexes. The molecular HD flux starts increasing at 800°C which is the onset of the GaN decomposition and has its maximum at 920°C. This HD flux is accompanied by the desorption of H and D containing radicals and molecules desorbing above 900°C.
We have studied the influence of a deuterium diffusion on the electrical characteristics of the 2D gas present in AlGaN/GaN heterostructures. The deuterium diffusion is performed by exposing the structures to a rf remote deuterium plasma. We find that both the sheet carrier concentration and the electron mobility decrease and that these effects are partly reversible under thermal annealing. These results suggest that deuterium behave as acceptors in the 2D gas region. The negatively charged deuterium act as additional scattering centers for electrons.
Inspecting and understanding the thermal stability of metal contacts in the context of reliability testing on high power transistors (especially in the GaAs technology) often necessitates to view atomic concentration profiles at deep interfaces. One common method for this purpose is the combined Auger spectroscopy/ion etching technique, where the region to be investigated is etched sequentially (with a “low” etch rate, typically in the Å/second regime) and Auger electron spectra (AES) are recorded at each step of the etching process. The 3 major resolution drawbacks of this approach are first that it is time-consuming, second that the spatial resolution is limited (atomic profiles on contact regions with lateral dimensions smaller that I R~m are difficult to obtain) and third that the interface of interest is “smoothed” during the etch process. The third point yields atomic concentration profiles with an apparent inter-mixing, which sometimes hinders observation of the details of interest for the interface under investigation.
We have used a different approach for this aspect of metal contact testing, in which the interface to be studied is first “revealed” by focused ion beam (FIB) micro-sectioning. After this preparation step, chemical images of the interface are directly obtained by high resolution Auger electron spectra mapping. The different operating conditions for the FIB process (orientation of the cross-section with respect to the transistor surface, preliminary procedures to eliminate residual roughness as well as surface contamination) have been optimized in order to produce Auger spectra free of any artifact. The approach is demonstrated on Au/GeNiAu ohmics contacts to the emitter electrode of GaAs-based hererostructure bipolar transistor, designed for high power amplification in the microwave regime. Ultimate spatial resolution of 20 to 30 nm on the Ayuger chemical images is demonstrated on an Auger microscope equipped with a Schottky field emitting tip.
The structural and electrical properties have been investigated of antimony doped polycrystalline silicon films obtained by molecular beam deposition on oxidized silicon substrates. We show that low resistivity films with smooth morphology are obtained by Solid Phase Crystallization of antimony doped amorphous silicon layers deposited at 250°C. A resistivity of 4.3 mΩ cm is obtained by crystallizing the films at temperatures as low as 650°C for 15 minutes. Similar resistivities are typically obtained by Chemical Vapor Deposition at temperature of at least 850 °C. In-situ crystallization of the amorphous silicon is needed to obtain low resistivity polysilicon. We also show that direct deposition above 650 ° C gives rise to polycrystalline silicon with much higher resistivities.
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