InAl(Ga)N/GaN HEMTs on SiC Technology for Ka and Q band Applications
III–N semiconductors are expected to be the best candidates in the field of high-power electronics for high frequency operations. Nevertheless, they still have some limitations in their RF performances, especially at microwave and millimeter wave frequencies when it becomes necessary to reduce short channel effects and achieve high transconductance to save microwave gain. Under high drain voltages, these conditions lead to a high field region at the gate edge near the drain, and are responsible of trapping effects that degrade the transistor performances denoted by current collapse, power slump, or even bias current variations. Preliminary studies done in our laboratory on InAlN-based lattice matched on GaN heterostructures showed promising results up to 18 GHz, reaching 12.5 W/mm. Moving the technology from a horizontal MOCVD 2’’ reactor to 4’’ multi-wafers CCS vertical one, new heterostructures and associated process are currently developed to build devices able to address Ka to Q band applications. Despite a better crystalline quality of the HEMT structure, one of the main differences is the non intentional incorporation of Ga atoms in the barrier layer giving a quaternary barrier composition. Quaternary barrier InAlGaN/GaN HEMTs introduce some strain in comparison to In17Al83N but show higher mobilities than ternary In17Al83N, while keeping similar electron gas density. Thus, In-containing HEMTs should achieve higher current densities and thus better power performance than more conventional AlGaN/GaN HEMTs. In this work, we present the interest in high-frequency and high-power operations of InAlGaN/AlN/GaN HEMTs structure based on quaternary barrier layer. With a dedicated epitaxial heterostructure including a patented AlGaN back-barrier buffer layer associated with an optimized process especially on the passivation step, we present here an overview of the achieved performances on 0.15µm gate length devices covering the full chain of fabrication from the epitaxy to robustness assessment, confirming that InAlGaN-based technology can be very attractive for millimetre waves applications.