Enhancement-mode power AlGaAs/InGaAs/AlGaAs pseudomorphic high electron mobility transistors

An overview of the Enhancement-mode PHEMT (E-PHEMT) process developed at Alpha Industries is presented. This E-PHEMT process is characterized by Idss=0.5 mu A/mm, Imax=190 mA/mm, Vp=+0.3 V, Gm=340 mS/mm and Vbdg=20 V. Various on-wafer power characteristics are presented, including 315 mW/mm output with associated PAE=76.4% achieved at 1800 MHz and 4 V, and 35 mW/mm with associated PAE=71% achieved at 900 MHz and 1.5 V. The E-PHEMT has high small-signal gain and high efficiency under linear and 1dB compressed gain conditions, making it attractive for high efficiency linear power amplifiers. The large-signal nonlinear model developed for E-PHEMT demonstrates good agreement with the measured power sweep and harmonic loadpull characteristics. The new "Inverted Class F" mode of operation was employed for high efficiency operation to compensate for the low Imax of E-PHEMT compared to the conventional D-PHEMT technology. It featured an open circuit termination for the 2(nd) harmonic and a short circuit termination for the 3(rd) harmonic on the output, which resulted in clamped Id current waveform and Vds voltage waveform overshoot. Under optimum harmonic loading conditions PAE=80% at 3.2 V and 900 MHz can be achieved.