Cryogenic Ultra-Low Noise InP High Electron Mobility Transistors
Abstract: Indium phosphide high electron mobility transistors (InP HEMTs), are today the best transistors for cryogenic low noise amplifiers at microwave frequencies. Record noise temperatures below 2 K using InP HEMT equipped cryogenic low noise amplifiers (LNAs) were demonstrated already a decade ago. Since then, reported progress in further reducing noise has been slow. This thesis presents new technology optimization, modeling, measurements and circuit implementation for the cryogenic InP HEMT. The findings have been used to demonstrate a new record minimum noise temperature of 1 K at 6 GHz. The thesis considers aspects all the way from material, process and device design, to hybrid and monolithic microwave integrated circuit (MMIC) LNAs. The epitaxial structure has been developed for lower access resistance and improved transport characteristics. By investigating device passivation, metallization, gate recess etch, and circuit integration, low-noise InP HEMT performance was optimized for cryogenic operation. When integrating the InP HEMT in a 4-8 GHz 3-stage hybrid LNA, a noise temperature of 1.2 K was measured at 5.2 GHz and 10 K operating temperature. The extracted minimum noise temperature of the InP HEMT was 1 K at 6 GHz. The low-frequency 1/f noise in the 1 Hz to 1 GHz range and gain fluctuations in the 1Hz to 100 kHz range have been measured for six different types of HEMTs, and compared to two different SiGe heterojunction bipolar transistors (HBTs). The results showed that radiometer chop rates in the kHz range are needed for millimeter wave radiometers with 10 GHz bandwidth. A comparative study of GaAs metamorphic HEMTs (mHEMTs) and InP HEMTs has been performed. When integrated in a 4-8 GHz 3-stage LNA, the InP HEMT LNA exhibited 1.6 K noise temperature whereas the GaAs mHEMT LNA showed 5 K. The observed superior cryogenic noise performance of the InP HEMT compared to the GaAs MHEMT was related to a difference in quality of pinch-off as observed in I-V characteristics at 300 K and 10 K. To demonstrate the low noise performance of the InP HEMT technology, a 0.5-13 GHz and a 24-40 GHz cryogenic monolithic microwave integrated circuit (MMIC) LNA was fabricated. Both designs showed state-of-the-art low noise performance, promising for future radio astronomy receivers such as the square kilometer array.
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