Kathia Harrouche's thesis

"Design and production of GaN-based power transistors up to W-band".

Thesis defence on 16 December 10.30 a.m.
IEMN Amphitheatre - Central Laboratory - Villeneuve d'Ascq

Jury :

Nathalie MALBERT, Professor, IMS Bordeaux, Rapporteur
Olivier LATRY, Professor, GPM Rouen, Rapporteur
Chloé BOUEXIERE, Engineer, DGA, Examiner
Didier FLORIOT, Deputy CTO, UMS, Examiner
Katir ZIOUCHE, Professor, University of Lille, Examiner
Farid MEDJOUB, CNRS Researcher, Thesis Director

Summary:

Over the last few decades, remarkable progress has been made on GaN-based high electron mobility transistors (GaN HEMTs) for high-frequency power amplification and switching applications. Currently, the most mature GaN HEMTs are based on AlGaN/GaN heterostructures. More recently, Al-rich (In)(Ga)AlN/GaN heterostructures with ultra-thin (<10 nm) barriers have also shown considerable interest for applications in the millimetre-wave range. Unlike AlGaN/GaN structures, Al-rich ultrathin barriers can provide twice the electron density (2DEG) while offering a high aspect ratio (grating length/gating-to-channel distance) even with very short gratings of less than 100 nm. As a result, GaN HEMTs with ultra-thin Al-rich barriers can operate robustly at higher frequencies. In this context, several research groups have demonstrated a unique combination of higher power and wider bandwidth up to 100 GHz using GaN transistors compared to other technologies (GaAs or silicon). However, most applications require power amplifiers with very high efficiency combined with proven reliability and improved linearity. The state of the art in GaN HEMTs is currently limited to around 50% PAE (Power Added Efficiency) and little work has been reported on the reliability of GaN devices using short gates of less than 150 nm. However, one of the major limitations of modern RF components is thermal dissipation. Indeed, the power dissipation improves by 80% when the PAE efficiency increases from 50% to 80%.
The aim of this work is to optimise a leading-edge technology in this field through the development of sub-150 nm gate GaN transistors for millimetre-wave range applications. In particular, we have optimised the buffer layers and an ultra-thin AlN barrier of less than 5 nm in order to increase power gain, improve electron confinement at high electric fields and simultaneously reduce trap effects. In addition, the development of a bench for measuring power at 94 GHz has made it possible to demonstrate state-of-the-art power density at W-band with the components manufactured. This work provides a promising basis for guaranteeing the high performance (particularly PAE efficiency) and reliability of GaN HEMTs for power amplification in the millimetre-wave range for future 5G telecommunications, space and military applications.

Abstract:

Over the last decades, remarkable progress has been made on GaN-based high electron mobility transistors (GaN HEMTs) for high frequency power amplification and switching applications. Currently, the most mature GaN HEMTs are based on AlGaN/GaN heterostructures. More recently, Al-rich (In)(Ga)AlN/GaN ultra-thin barrier heterostructures (<10 nm) have also shown great interest for millimeter-wave applications. Indeed, unlike AlGaN/GaN structures, Al-rich ultrathin barriers can provide twice the electron density (2DEG) while offering a large aspect ratio (grid length/grid-channel distance) even with very short grids below 100 nm. Therefore, Al-rich ultra-thin barrier GaN HEMTs enable higher frequency operation in a robust manner. In this context, several research groups have demonstrated a unique combination of higher power and wider bandwidth up to 100 GHz by using GaN transistors compared to other technologies (GaAs or silicon). However, most applications require power amplifiers with very high efficiency combined with proven reliability and increased linearity. The state of the art of GaN HEMTs is limited today to about 50% PAE (Power Added Efficiency) and little work has been reported on the reliability of GaN devices using short gates smaller than 150 nm. Nevertheless, one of the major limitations of modern RF devices is the thermal dissipation. Indeed, the power dissipation improves by 80% when the PAE efficiency increases from 50% to 80%.
The objective of this work is to optimize a state-of-the-art technology in this field through the development of sub-150 nm GaN gate transistors for millimeter-wave applications. In particular, we have optimized the buffer layers and an ultra-thin AlN barrier of less than 5 nm in order to increase the power gain, to improve the electron confinement under high electric field and to simultaneously reduce the trapping effects. In addition, the development of a power measurement bench at 94 GHz has allowed to demonstrate a state-of-the-art power density at W-band with the fabricated components. This work provides a promising basis for ensuring high (including PAE efficiency) and reliable performance of GaN HEMTs for power amplification in the millimeter-wave range related to future 5G telecommunication, space or military applications.