Ultra-Low Noise InP HEMTs for Cryogenic Amplification

Licentiate thesis, 2012

InGaAs/InAlAs/InP High Electron Mobility Transistors (InP HEMTs), are today the best devices to design cryogenic low noise amplifiers. However, reported progress in reducing the noise has been slow in the last decade. In this thesis the fabrication, optimization and characterization of 130 nm gate length InP HEMTs for cryogenic amplification at very low power dissipation is presented. By investigating device passivation, metallization, gate recess etch, and circuit integration, low-noise performance was optimized for the HEMT at low temperature around 10 K. The effect of Al2O3 atomic layer deposition (ALD) for InP HEMTs was investigated. In comparison to standard plasma enhanced chemical vapor deposition passivated InP HEMTs, ALD passivated devices demonstrated much less kink effects associated with surface traps in the output drain current characteristics at room temperature. An InP HEMT designed for ultra-low noise cryogenic amplification was fabricated. When 4x50 um devices were integrated in a 4-8 GHz 3-stage hybrid low noise amplifier (LNA), a noise temperature of 1.2 K was measured at 5.2 GHz and 10 K operating temperature. The gain of the amplifier was 44 dB across the band, consuming only 4.2 mW of DC power. The extracted minimum noise temperature of the InP HEMT was 1 K at 6 GHz. This noise temperature represents a new state-of-the-art for InP HEMT technology. The relation between DC, S-parameter, and noise performance of the InP HEMTs has been investigated at room as well as at cryogenic temperatures. As the main noise contribution in the InP HEMT is observed to be linearly dependent on drain current Id, excellent device performance at low Id is a prerequisite for ultra-low noise operation. Transconductance gm and cut-off frequency fT of the InP HEMT at optimum low noise bias at 4 K was observed to increase with 100 % and 60 %, respectively, when cooled down from room temperature to 4 K. To demonstrate the excellent low noise performance of the InP HEMT technology developed in this work, a 0.5-13 GHz cryogenic monolithic microwave integrated circuit (MMIC) LNA was designed and fabricated. At 15 K, the measured noise temperature within the entire band was below 7 K with a minimum of 3 K at 7 GHz. The gain was more than 38 dB and the power dissipation was 16.5 mW.