Physical Modelling of Dynamic Effects of GaN-on-Si Transistors in Sub-µs High-Power Events

Gallium nitride high electron mobility transistors (GaN HEMTs) are utilized in power amplifier (PA) design with their high-frequency operation and power handling capability. The properties make the device the preferred choice for high-power PA design in consideration of performance, power, area, and cost. Using cost-effective and sustainable integration of GaN HEMT on silicon (Si) substrate, imec is developing GaN-on-Si RF HEMTs relevant for 6G-and-beyond wireless communication.

GaN-on-Si PA HEMTs may encounter both regular and irregular short-duration (sub-µs) but high-power stress events: due to a distribution of output power, GaN PA HEMTs operate frequently with relative high-power RF stress voltages; they also encounter occasionally electrostatic discharge (ESD) events. The reliability of the GaN RF transistors against those sub-µs high-power events is critical. The high-power events can trigger both self-heating and trapping effects in the GaN PA HEMTs and eventually lead to device degradation and failures. The goal of this PhD is to explore TCAD electro-thermal modelling to describe the device degradation caused by sub-µs pulses with a focus on ESD events.

The candidate is expected to understand the device physics of GaN HEMTs, to identify the present challenges of co-existence between the trapping mechanism and self-heating effect in one pulse response, and finally to extract the thermal effects from the measurement data and propose simulation strategies to develop the model. The correlation between electrical characterization and physical modelling is critical for this topic. The PhD candidate will get familiar with TCAD simulations of self-heating effects of GaN RF HEMTs. Based on that, the PhD candidate will further develop transport and dynamic trapping models that describe accurately the GaN HEMT behaviour in a sub-µs high-power event. The knowledge of physical mechanisms gained from the TCAD modelling will eventually feed 5G/6G GaN-on-Si RF HEMT technology that is under development at imec.