Advanced GaN/Si transistors for Ka band amplification: Gate stack optimization

Published : 27 February 2019

Today, Ka band amplifiers based on GaN mainly use GaN/SiC technology due to the quality of epilayers and the good thermal conductivity and electrical resistivity of SiC substrate. GaN/Si technology is available for low frequency bands [1] with performances around 3 GHz close to GaN/SiC. GaN/Si is targeting higher frequency band like Ka band to address 5G base station applications[1-2].

One of the most critical brick to make Ka-band GaN/Si transistors is the gate module. Higher frequency require shorter gate length (~100nm) and thinner channels (< 10nm). Schottky gate, which is widely used at lower frequency on GaN/SiC show some weakness in terms of gate leakage and reliability, especially on GaN/Si due to the higher concentration of native defects. This gate must be improved or replaced by a MIS gate.

At CEA-Leti, in the Framework of 5G-GaN2 and III-Vlab projects, we are developping a 200mm GaN/Si CMOS compatible technology. This technology is based on GaN/SiC background but also on CMOS and III-V/Si technologies that will be adapted to GaN/Si Ka-band transistor requirements. The work of this thesis will consist in optimizing the Schottky gate in terms of static and RF performances and also to study and evaluate a new MIS-gate technology. The ultimate objective is to integrate this new gate module into the GaN/Si 200mm flow in order to evaluate the potential of this approach.

[1] GaN-on-Silicon Present Challenges and Future Opportunities, Timothy Boles, MACOM Technology Solutions, 12th European Microwave Integrated Circuits Conference Oct 2017.

[2] 100nm and 60nm GaN/Si MMICs for 5G Mobile Telecommunications. Marc Rocchi, OMMIC, IMS 2018

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