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IEEE Microwave and Guided Wave Letters
Volume 10 Number 8, August 2000

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Cascode Connected AlGaN/GaN HEMT's on SiC Substrates

Bruce M. Green, Student Member IEEE Kenneth K. Chu, Joseph A. Smart, Vinayak Tilak, Hyungtak Kim, Student Member, IEEE James R. Shealy and Lester F. Eastman Life Fellow, IEEE

Page 316.

Abstract:

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 0.25µm cascode connected to a 0.35 µm common gate device. The gate width of each device is 250µm. The fabricated circuit exhibited a current density of 800 mA/mm and yielded an fT and fmaxof 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 × 0.35 µm2 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.

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