Substrate effects in advanced GaN RF technologies

Ushering in the era of advanced communication systems (5G, 6G) requires enabling increasingly complex circuits which are composed of several chips, each implemented in different technologies tailored for a specific function. Downscaling of CMOS technology has allowed the integration of radio-frequency (RF) transceivers on Silicon chips, but power amplifiers using III-V (InP, GaAs) and III-N (GaN) technologies, and high-performance switches fabricated on SOI substrates remain the preferred choice for RF Front-End circuits.

In order to develop sustainable, cost and power efficient RF systems, the current research at imec for RF front-end module technologies addresses: (i) the integration of high-speed GaN and III-V devices on a Si platform; and (ii) the co-integration of these device architectures with standard Si CMOS.

The integration of devices such as GaN HEMTs on Si substrates can degrade HEMT performance from both electrical (e.g. RF losses and distortion) and thermal perspectives, necessitating continued research on enhanced device and system performance solutions.

In this PhD, you will contribute to solve these challenges of GaN on Si technology by:

• Studying the effect of various substrate technologies on RF figures of merit (loss, crosstalk, distortion, ...). Various non-ideal material interfaces created during advanced device integration are expected to present fixed charges and traps in layer stack causing RF losses and non-linearities as well as frequency dependent phenomena;
• Characterizing the material properties of various substrates and thin films, for instance, extraction of dielectric constant and losses from advanced on-wafer measurements in millimeter-wave domain, as well as analyze their thermal properties;
• Studying the impact of these material stacks on the transistor and circuit electrothermal performances through advanced GaN HEMT characterization (DC, pulsed, small and large signal RF) and physics-based modeling;
• Process optimization towards high performance sustainable solutions.