Cascode connected AlGaN/GaN HEMT's on SiC substrates

We report on the fabrication and characteristics of cascode-connected AlGaN/GaN HEMT's, The HEMT's were realized using Al0.3Ga0.7N/GaN heterostructures grown on 6-H semi-insulating SiC substrates, The circuit reported here employs a common source device having a gate length of 0.25 mu m cascode connected to a 0.35 mu m common gate device. The gate width of each device is 250 mu m The fabricated circuit exhibited a current density of 800 mA/mm and yielded an f(T) and f(max) of 24.5 and 56 (extrapolated) GHz, respectively. Large signal measurements taken at 4 GHz produced 4 W/mm saturated output power at 36% power-added efficiency. Comparisons to the performance of a 250 x 0.35 mu m(2) common source device taken from the same wafer show that the cascode configuration has 7 dB more linear gain and 3 dB more compressed gain than the common source device at 4 GHz.