3-watt AlGaN-GaN HEMTs on sapphire substrates with thermal management by flip-chip bonding

GaN based HEMTs take advantage of the high bandgap, high saturation velocity and enhanced mobility in nitride semiconductor heterostructures. They are therefore a potential choice for high-power applications at microwave frequencies. Very high power densities >3 W/mm at 18 GHz have been demonstrated through 75-100 μm gate-width HEMTs grown on sapphire substrates, using high Al-content AlGaN as the barrier/donor layers. For practical applications, the gate-width must be scaled up, and thermal management becomes an important issue. For this reason, significant research effort has been directed to GaN growth on SiC substrates, due to the higher order thermal conductivity of SiC compared to sapphire. However, judicious thermal management with devices grown on sapphire substrates is deemed as a more cost-effective approach. Al/sub 0.25/Ga/sub 0.75/N/sapphire HEMTs with a total power of 1.4 W have been achieved through flip-chip bonding on AlN carriers, which also have a high thermal conductivity (Thibeault et al., 1997). Here, we report performance improvements with Al/sub 0.5/Ga/sub 0.5/N/sapphire HEMTs.