Overview
- Date:Starts 31 March 2025, 10:00Ends 31 March 2025, 13:00
- Location:Lecture hall EA, EDIT-huset
- ThesisRead thesis (Opens in new tab)
Radio astronomy relies on detecting extremely weak signals and requires robust and rugged technologies,
capable of preventing and withstand radio frequency interference (RFI). Low-noise amplifiers (LNAs)
operating at cryogenic temperatures are key components in radio astronomy instrumentation. While
LNAs based on advanced semiconductor technologies with limited power-handling capabilities have been
widely used, gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs) offer a promising
alternative due to their high robusteness and excellent low-noise performance at room temperature.
However, their low-noise behavior at cryogenic temperatures has remained largely unexplored.
This thesis investigates the potential of GaN-based HEMTs for cryogenic low-noise operation. The
minimum noise temperature of GaN-HEMTs at 10 K was found to be in the range of 4–5 K (0.06–0.07 dB
noise figure), which is comparable to other advanced technologies in the field. This was achieved through
well-established experimental and modeling techniques, allowing for the characterization of noise
contributions in GaN-HEMTs as a function of operating frequency, dissipated power, and total device
periphery. The findings provide a foundation for designing future GaN-based LNAs that meet the
requirements of cryogenic applications.
For the first time, GaN-HEMTs with superconducting niobium (Nb) gates were demonstrated. A
comparative study with conventional gold (Au)-gated GaN-HEMTs revealed that superconducting Nb
gates suppress the gate resistance dependence on gate width and length below Nb critical temperature
(Tc < 9.2 K). However, self-heating effects were found to prevent the maintenance of Nb superconductivity
at optimal noise-bias conditions, highlighting the need for further optimization of the device's heat
dissipation capabilities.
GaN-based metal-insulator-semiconductor (MIS)-HEMTs with a silicon nitride (SiNx) gate dielectric were
also examined at 4 K, demonstrating a minimum noise temperature of 8 K—comparable to their
conventional HEMT counterparts under the same conditions. These results highlight the impact of the
gate dielectric on the cryogenic small-signal and noise parameters of the device, suggesting that further
reduction of gate leakage current through improved gate insulation could enable additional noise
reduction.
The incorporation of gate field plates (FPs) was shown to improve device reliability by mitigating high-field
and trapping effects, which become more pronounced at cryogenic temperatures. However, noise
analysis of devices with and without FPs at 4 K revealed an overall detrimental impact of FPs, leading to
at least a 35% noise degradation. This was attributed to increased parasitic capacitances, which reduced
the cutoff frequency. Nonetheless, devices with FPs exhibited improved drain-source conductance,
offering advantages for low-noise impedance matching.
capable of preventing and withstand radio frequency interference (RFI). Low-noise amplifiers (LNAs)
operating at cryogenic temperatures are key components in radio astronomy instrumentation. While
LNAs based on advanced semiconductor technologies with limited power-handling capabilities have been
widely used, gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs) offer a promising
alternative due to their high robusteness and excellent low-noise performance at room temperature.
However, their low-noise behavior at cryogenic temperatures has remained largely unexplored.
This thesis investigates the potential of GaN-based HEMTs for cryogenic low-noise operation. The
minimum noise temperature of GaN-HEMTs at 10 K was found to be in the range of 4–5 K (0.06–0.07 dB
noise figure), which is comparable to other advanced technologies in the field. This was achieved through
well-established experimental and modeling techniques, allowing for the characterization of noise
contributions in GaN-HEMTs as a function of operating frequency, dissipated power, and total device
periphery. The findings provide a foundation for designing future GaN-based LNAs that meet the
requirements of cryogenic applications.
For the first time, GaN-HEMTs with superconducting niobium (Nb) gates were demonstrated. A
comparative study with conventional gold (Au)-gated GaN-HEMTs revealed that superconducting Nb
gates suppress the gate resistance dependence on gate width and length below Nb critical temperature
(Tc < 9.2 K). However, self-heating effects were found to prevent the maintenance of Nb superconductivity
at optimal noise-bias conditions, highlighting the need for further optimization of the device's heat
dissipation capabilities.
GaN-based metal-insulator-semiconductor (MIS)-HEMTs with a silicon nitride (SiNx) gate dielectric were
also examined at 4 K, demonstrating a minimum noise temperature of 8 K—comparable to their
conventional HEMT counterparts under the same conditions. These results highlight the impact of the
gate dielectric on the cryogenic small-signal and noise parameters of the device, suggesting that further
reduction of gate leakage current through improved gate insulation could enable additional noise
reduction.
The incorporation of gate field plates (FPs) was shown to improve device reliability by mitigating high-field
and trapping effects, which become more pronounced at cryogenic temperatures. However, noise
analysis of devices with and without FPs at 4 K revealed an overall detrimental impact of FPs, leading to
at least a 35% noise degradation. This was attributed to increased parasitic capacitances, which reduced
the cutoff frequency. Nonetheless, devices with FPs exhibited improved drain-source conductance,
offering advantages for low-noise impedance matching.
