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Index Terms-GaN, high electron-mobility transistor (HEMT), -band, microwave noise, microwave power.

The cryogenic performance ofAlInAs/GaInAs/InP .1 pm HEMT's is reported.Collapse free d.c. operation is observed down to the ambient temperature of 18 K.The application of these devices to Q-and E-band low-noise, cryogenicallycoolable amplifiers is demonstrated. The measured record-breaking noise temperature of 15 K (noise figure of .2 dB) for a multi-stage 40-45 GHz amplifier with 33 dB of gain at the ambient of 18 K is in close agreement with the prediction of a simple noise model. A very low power consumption per stage of less than 1 mW is recorded. The noise temperature of the E-band cryogenic amplifier is less than 47 K at 70 GHz, demonstrating that the performance of HEMT receivers is now competitive with that of SIS receivers in the 3-mm wavelength atmospheric window.

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