These findings, presented at the IEEE International Reliability Physics Symposium (IRPS) 2025, show that it is possible to design reliable GaN-based power amplifiers to avoid positive bias instability and enable handset applications for 6G communication.
GaN MISHEMTs are being explored for use in 5G+/6G RF systems due to their combination of efficiency and power-handling capabilities. However, there are challenges, particularly with positive gate bias instability (ΔVth), where shifts in the threshold voltage under certain conditions and can affect the performance and long-term reliability of the power amplifier.
Gate bias instability in GaN MISHEMTs is a complex and largely unexplored phenomenon that can occur in the different operational states —off, semi-on, and on state— each exhibiting distinct instability mechanisms.
In addition, its role in the power amplifier operation has not been widely studied, partly because traditional RF power amplifiers typically use GaAs) HBT or HEMTs without a dielectric gate.
To bridge this gap, imec researchers have introduced a pragmatic analytical approach that directly compares a stable range of gate voltages in DC conditions with the actual gate modulation range in the RF power amplifier operation. Their analysis revealed a strong overlap between these two ranges, confirming that GaN MISHEMTs remain stable within the typical voltage swing of RF power amplifiers. This allows linearly operating power amplifiers to be designed that avoid a ΔVth concern.
“Our research offers practical solutions, demonstrating that GaN MISHEMTs can be reliably used in power amplifier applications for 5G+/6G technology. By integrating fundamental device reliability research with real-world RF system assessments, our team has been able to bridge the gap between theoretical studies and practical applications, ensuring that GaN technology can meet the demands of next-generation communication systems,” said Hao Yu, Principal member of the technical staff at imec.
The researchers were also able to show that the presence of naturally occurring positive interfacial polarisation charges at the material interface plays a key role in preventing unwanted shifts in operating voltage over time.
This finding is significant because it highlights a unique feature of GaN MISHEMTs that makes them more immune to on-state threshold voltage (Vth) instability compared to other gate dielectric contained devices, such as MISFETs. Simulations further demonstrate that even under real-world RF input signals, the on-state Vth instability is mitigated. These combined insights provide crucial guidance for designing robust, high-performance power amplifiers.
The research was presented alongside three complementary papers from imec's advanced RF program in collaboration with Prof. Tian-Li Wu’s team in National Yang Ming Chiao Tung University (NYCU) in Taiwan.
(Top left) Schematic of the MISHEMTdevice, and (Top right) critical stress states during power amplifier operation. (Bottom) Comparison of the papers presented at the 2025 IEEE IRPS conference from imec's advanced RF program in collaboration with Prof. Tian-Li Wu’s team in National Yang Ming Chiao Tung University (NYCU) in Taiwan.
