The new Inverse Class F operation mode for high-efficiency power amplifiers is analyzed. Unlike regular Class F, it requires an open circuit termination at the second harmonic and a small impedance termination at the third harmonic. The Inverse Class F features higher PAE than Class F but requires transistors with higher breakdown voltages. A study performed using the waveform measurement technique in conjunction with the activdpassive load-pull system showed PAE=83% for the Inverse Class F compared to PAE=64% for the Class F. The measured results are in good agreement with the analytical prediction.

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Hot-electron trapping in the SiN passivation was found to be a cause for gradual degradation during RF operation of metal-semiconductor field-effect transistors. The time dependence and threshold energy for trap formation was determined by dc and electroluminescence tests. The spatial distribution of trapped electrons was directly observed by a novel high-voltage electron-beam-induced-current imaging technique. Argument was also made for trapping in the SiN instead of at the GaAs/SiN interface.

An enhancement mode power PHEMT technology is demonstrated as a viable alternative to an HBT for single supply high efficiency power amplifiers. The newly developed E-PHEMT has Idss=0.5 pA/mm, Imax=190 mA/mm, Vp=+0.3 V, Gm=340 mS/mm and Vbdg=20 V. Various on-wafer loadpull results at 900 and 1800 MHz are presented. A 315 mW/mm output power with PAE=76.4% is demonstrated at 1800 MHz and 4V, while 37 mW/mm and PAE=71% is achieved at 900 MHz and 1.5V. These state of the art results for any single-supply technology were achieved by utilizing systematic harmonic loadpull measurements in conjunction with accurate large-signal modeling.