Design, Characterization and Modeling of GaN-based HEMTs for Low-Noise and Cryogenic Applications
Doktorsavhandling, 2025
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.
Författare
Mohamed Aniss Mebarki
Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium
Low-noise amplifiers (LNAs) are essential components in highly sensitive electronic systems,
enabling the amplification of weak signals with minimal added noise. In radio astronomy, they
play a crucial role in detecting cosmic signals—faint traces of distant galaxies, pulsars, and other
celestial phenomena. To achieve the highest sensitivity, LNAs are cooled to cryogenic
temperatures for ultimate noise reduction.
Like most modern electronics, LNAs rely on semiconductor materials. While widely used
semiconductor technologies have enabled significant advancements, they also come with
limitations: they are vulnerable to interference from unwanted radio signals and have limited
power-handling capabilities, posing risks of failure and reliability issues in extreme environments.
At room temperature, GaN-based LNAs are valued for their robustness and high survivability, but
their performance at cryogenic temperatures remains largely unexplored.
This research investigates the behavior of GaN-based high-electron-mobility transistors (HEMTs)
at cryogenic temperatures and explores strategies to optimize them for ultra-low-noise
applications. The impact of various design choices was analyzed, including the incorporation of
field plates and insulation layers, revealing trade-offs between improved reliability and noise
performance. Innovative solutions for noise reduction were also examined, such as the
integration of superconducting materials. These findings provide valuable insights into enhancing
both the reliability and low-noise performance in cryogenic environments using GaN-based
HEMTs.
Beyond radio astronomy, this work contributes to the broader evolution of GaN-based HEMTs
technology. As the demand for ultra-low-noise electronics grows—particularly in fields such as
quantum computing, where cryogenic conditions are essential—these advancements have
implications not only for radio astronomy but also for next-generation computing and
communication technologies.
enabling the amplification of weak signals with minimal added noise. In radio astronomy, they
play a crucial role in detecting cosmic signals—faint traces of distant galaxies, pulsars, and other
celestial phenomena. To achieve the highest sensitivity, LNAs are cooled to cryogenic
temperatures for ultimate noise reduction.
Like most modern electronics, LNAs rely on semiconductor materials. While widely used
semiconductor technologies have enabled significant advancements, they also come with
limitations: they are vulnerable to interference from unwanted radio signals and have limited
power-handling capabilities, posing risks of failure and reliability issues in extreme environments.
At room temperature, GaN-based LNAs are valued for their robustness and high survivability, but
their performance at cryogenic temperatures remains largely unexplored.
This research investigates the behavior of GaN-based high-electron-mobility transistors (HEMTs)
at cryogenic temperatures and explores strategies to optimize them for ultra-low-noise
applications. The impact of various design choices was analyzed, including the incorporation of
field plates and insulation layers, revealing trade-offs between improved reliability and noise
performance. Innovative solutions for noise reduction were also examined, such as the
integration of superconducting materials. These findings provide valuable insights into enhancing
both the reliability and low-noise performance in cryogenic environments using GaN-based
HEMTs.
Beyond radio astronomy, this work contributes to the broader evolution of GaN-based HEMTs
technology. As the demand for ultra-low-noise electronics grows—particularly in fields such as
quantum computing, where cryogenic conditions are essential—these advancements have
implications not only for radio astronomy but also for next-generation computing and
communication technologies.
Ämneskategorier (SSIF 2025)
Nanoteknik
Elektroteknik och elektronik
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie
Utgivare
Chalmers