Microwave performance of 0.25-µm gate length high electron mobility transistors

The performance of 0.25-µm gate length high electron mobility transistors (HEMT's) is reported. Devices were fabricated on layers grown by MBE. One of the heterostructures had no undoped AlGaAS spacer layer (wafer A), whereas the other had a 40-A spacer layer (wafer B). The maximum stable gain on both wafers was ∼ 12 dB at 18 GHz. The minimum noise figure measured was 0.60 dB at 8 GHz and 1.3 dB at 18 GHz. Wafer A yielded devices with a unity current gain cutoff frequency f t of 65 GHz whereas wafer B gave an f t of 70 GHz. These results can be attributed primarily to the high quality material, low parasitic resistance, and short gate length.