GaN high electron mobility transistors (HEMTs) are becoming the mainstream for microwave power applications. Devices and circuits based on these emerging materials are more suited to operate at higher
voltages and temperatures owing to their superior physical properties. The emergence of 5G cellular has created new interest in the millimeter-wave spectrum (30 to 300 GHz). There is simply not enough
bandwidth at lower frequencies to satisfy future system requirements for speed and capacity. GaN-based MMICs can offer a factor of 10 improvement in the power density compared with older technologies such as GaAs and InP.

In this context, the power-added-efficiency (PAE) becomes a key parameter in order to support complex waveforms with high peak-to-average ratio and large instantaneous bandwidth required for 5G
applications for instance. Overall, a high PAE is mandatory in order to reduce the power dissipation, which is a major issue for next generation of compact solid-state power amplifiers. State-of-the-art GaN
HEMT PAE performances are typically limited to 50% or below in the Ka-band and above, especially for high power densities > 2 W/mm. This is mainly due to the lack of power gain, the enhanced trapping
effects and reduced electron confinement when down scaling the device size or the self-heating. In this presentation, I will show the current status of III-Nitride based technology for RF applications that
has been developed in our group through partnerships with industry. In particular, the evolution of the promising approach based on highly scaled GaN HEMTs with Al-rich ultra thin barriers for future
millimeter-wave applications will be described.