Ce document porte sur le développement d’un nouveau banc de mesure pour la caractérisation de l’impédance thermique des HEMTs GaN. Le banc développé repose sur la méthode dite « 3ω » qui consiste à mesurer l’harmonique 3 d’un signal électrique véritable image des variations thermiques du composant. Un balayage en fonction de la fréquence d’excitation conduit à l’extraction de l’impédance thermique. Les résultats de mesures ont été validés par les simulations électriques. Des études complémentaires ont été réalisées pour l’identification des effets de pièges en utilisant différentes méthodes permettant l’extraction de la signature des pièges. La réalisation des modèles non-linéaires est présentée pour les transistors HEMT AlGaN/GaN et InAIN/GaN pour des applications d’amplificateur de puissance dans les bandes de fréquences X et K. / This report is devoted to the development of a new measurement bench for thermal impedance characterization of GaN HEMTs. This measurement test set uses the so-called « 3ω » technique, which consists to measure the electrical signal at third harmonic real image of the thermal magnitude variations of the device. A sweep in function of the excitation frequency allows extracting of the thermal impedance. The measurement results have been validated by electrical simulation. Other complementary studies were performed to identify the trapping effects using different methods to extract the traps signature. The realization of nonlinear models is presented for AlGaN HEMT / GaN and InAIN / GaN to the power amplification applications in frequency bands X and K.

AlGaN/GaN and InAlN/GaN-based heterojunction field effect transistors (HFETs) have demonstrated great high power and high frequency performance. Although AlGaN/GaN HFETs are commercially available, there still remain issues regarding long-term reliability, particularly degradation and ultimately device failure due to the gate-drain region where the electric field peaks. One of the proposed degradation mechanisms is the inverse-piezoelectric effect that results from the vertical electric field and increases the tensile strain. Other proposed mechanisms include hot-electron-induced trap generation, impurity diffusion, surface oxidation, and hot-electron/phonon effects. To investigate the degradation mechanism and its impact on DC, microwave, and noise performance, comprehensive stress experiments were conducted in both un-passivated and passivated AlGaN/GaN HFETs. It was found that degradation of AlGaN/GaN HFETs under reverse-gate-bias stress is dominated by inverse-piezoelectric effect and/or hot-electron injection due to gate leakage. Degradation under on-state-high-field stress is dominated by hot-electron/phonon effects, especially at high drain bias. Both effects are induced by the high electric field present during stress, where the inverse-piezoelectric effect only relates to the vertical electric field and the hot-electron effect relates to the total electric field. InAlN/GaN-based HFETs are expected to have even better performance as power amplifiers due to the large 2DEG density at the InAlN/GaN interface and better lattice-matching. Electrical stress experiments were therefore conducted on InAlN/GaN HFETs with indium compositions ranging from 15.7% to 20.0%. Devices with indium composition of 18.5% were found to give the best compromise between reliability and device performance. For indium compositions of 15.7% and 17.5%, the HFET devices degraded very fast (25 h) under on-state-high-field stress, while the HFET devices with 20.0% indium composition showed very small drain. It was also demonstrated that hot-electron/phonon effects are the major degradation mechanism for InAlN/GaN HFETs due to a large 2DEG density under on-state operations, whereas the inverse-piezoelectric effect is very small due to the small strain for the near lattice-matched InAlN barrier. Compared to lattice-matched InAlN/GaN HFETs, AlGaN/GaN HFETs have much larger strain in the barrier and about half of the drain current level; however, the hot electron/hot phonon effects are still important, especially at high drain bias.