Design variations of HVVFET™ transistors for high-efficiency class-AB L-band power amplifiers

HVVFET™, with its proven RF performances, such as high power gain, high peak power density and superior ruggedness, represents a major step forward in realizing compact high-power modules for ground-based and airborne radars. In this paper, the dependence of the HVVFET´s RF performances on process-related parameters-including Si epilayer thickness and top-surface gold-bump thickness (H_bump) - is examined. The packaged device with a 2mil-thick bump results in a total C_gd of 0.49pF and 0.38pF at V_ds=10V and 30V respectively, from which an extrinsic component (C_gd, _ext) of 0.29 pF is extracted. Independently, on a 1mil-bump sample, a C_gd, _ext of 0.58 pF is obtained, doubling the value of the 2mil sample. The C_gd, _ext-to-H_bump proportionality suggests that C_gd, _ext predominantly arises from the parallel-plate, air-dielectric capacitor between the gate metal trace on the package and the exposed Si bulk. When operated at 1.03GHz with V_dq=36V in class-AB mode, the 2mil and 1mil samples exhibit an output power of 41.2W and 42.4W at 1dB compression, with a peak power gain of 20.1dB and 19.4dB, respectively.