CRYOGENIC 1.5-4.5 GHz ULTRA LOW NOISE AMPLIFIER

This paper describes cryogenic broadband amplifier with very low noise for the frequency band 1.5-4.5 GHz. At 15 K the twostage InP-based amplifier has a gain of 28+/-2 dB dB and a noise temperature below 5 K. For a narrower band of 2-4 GHz at 15 K the measured gain is 30.0+/-0.8 dB and noise temperature is 1.5 K. The total DC power consumption of the amplifier is 6.8 mW. A lattice matched structure on InP grown by molecular beam epitaxy was used in the fabrication of the Chalmers HEMT. The structure has a 40Å AlInAs space layer, whose purpose is to separate the 300Å thick In0.53Ga0.47As channel from the planar silicon doping. We use a 200Å thick AlInAs Schottky barrier and a cap layer consisting of 50Å undoped InGaAs. The measured transconductance at room temperature is around 550mS/mm, which gives ≈ 110 mS/200μm device. The Chalmers transistors were fabricated according to the Chalmers standard InP HEMT process. A combination of optical and electron beam lithography techniques was used [6]. Mesa isolation was obtained by means of wet chemical etching. The channel layer was selectively etched at the mesa sidewall. This procedure prevented the gate electrode from contacting the channel at the mesa edge and thereby decreased the gate leakage current. Index Terms – cryogenic low noise amplifier, HEMT, InP, noise temperature, LNA.