Andreas Divinyi, Microwave Electronics Laboratory

Abstract: 

GaN HEMT technology exhibits dynamic behaviour due to thermal and electrical memory effects, which reduce the performance of GaN MMICs used in compact microwave front ends. Addressing these challenges requires careful characterisation under realistic operating conditions to identify, mitigate, or compensate for these effects. This thesis investigates the thermal and electrical effects in two main ways.

The characterisation of thermal effects focuses on accurately monitoring on-chip hotspots caused by high-power operations. The surrounding thermal environment, including packaging and thermal management components, complicates this task. The proposed solution involves the use of on-chip sensors integrated into both dedicated test structures and actual circuits, enabling real-time, package-independent, and electrical measurements for thermal characterisation of device operation.

The trapping-induced effects risk unpredictable performance degradation, especially in GaN HEMT switch devices, where drift conditions are not yet fully characterised. The second part of this thesis aims to develop a method for determining the impact of trapping on the recovery time of GaN HEMT switches used in front-
end applications. This method quantifies the effects of recovery, allowing for comparing different devices and technologies.

Main supervisor: Mattias Thorsell, Docent, Saab Surveillance

Supervisor: Niklas Billström, MSc, Saab Surveillance

Examiner: Christian Fager, Professor, Microwave Electronics Laboratory

Discussion leader: Olle Axelsson, Ericsson AB