(Invited) Reliability Study of RF Power Amplifiers with GaN-on-SiC HEMTs

Abstract

In total 50 RF amplifier demonstrators consisting each of a PCB board containing one GaN-on-SiC, HEMT, CHZ015A-QEG, from UMS in SMD quad-flat no-leads package (QFN) were assembled for the study. Two types of solders, one of which is lead-free, (Sn63Pb36Ag2 and SAC305) and two types of TIM materials (NanoTIM and TgonTM805) for PCB attachment to liquid cold plate were tested for thermo-mechanical reliability. Out of the total number of the demonstrators 24 were subjected to thermal stress by 2300 thermal cycles (TC) between -20°C and 80°C and remaining 26 were subjected to the electrical stress by power cycling (PC) with drain current of 100 mA at drain voltage of 45 V and cycle time of 2 min. HF characterization of all the boards was done before subjecting them to the thermal and electrical stresses. All the devices were also subjected to static electrical characterization by measuring threshold voltage and output and voltage blocking characteristics. The static electrical and HF characterization was performed again after 2300 cycles of TC stress and after 1100, 4700 and 14500 cycles of PC stress. In addition failure analysis was performed on the TC and PC stressed demonstrators by using optical microscopy and 2D X-ray microscopy. The results of electrical and HF characterization show clearly changes and degradation in device performance as a function of the number of the PC cycles and accumulated current stress time. No significant differences between the boards equipped with different solder or TIM materials are observed which means that the observed changes in performance are due to the degradation of the HEMT devices. A reduction in value of saturation current (VDS=10 V, VGS=0.8 V) of about 5, 12 and 16 % is observed after 1100, 4700 and 14500 cycles of PC stress, respectively. There is a clear tendency of the threshold voltage shift (measured at 10 mA) towards more negative values showed by devices from different groups. The shift is by -0.1 to -0.15 V from typical value of about -2.25 V. The leakage current is less well behaved. There are devices with no significant change in leakage current but also devices which show an increase in leakage current by a factor larger than 2, as a result of the PC stress. Results of HF measurements show a decrease in S11 and S21 parameters from -10.91±0.23 to -10.0±0.21 and from 16.04±0.24 to 15.51±0.28 after PC stress (measurement conditions VDS=45 V, IDS=100 mA, power level 5 dBm, 1.3 GHz). The support of Sweden´s innovation agency, Vinnova, and Sweden Energy Authority is acknowledged. Figure 1