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ScAlN/GaN Heterostructure Field Effect Transistors for Ultra-High-Power and Wide-Band MMICs
The strong polarization (spontaneous and piezoelectric) polarization of ScAlN combined with its ultra-wide bandgap (>5.0 eV) has enabled ScAlN/GaN heterostructure based transistors to achieve at microwave and mm-wave frequencies, ultra-high output power densities at least 2× larger than today’s Al(Ga)N/GaN based transistors. Moreover, the combined voltage and enhanced current scaling with ScAlN/GaN transistors facilitates design and realization of ultra-wide-bandwidth circuits. Typical carrier densities and mobilities of >2–3×10E13/cm² and >1500 cm²/(Vs) allowed fabricated transistors to achieve maximum current densities of >2 A/mm and maximum transconductance of >0.5 S/mm. However, undesired levels of high off-state leakage and DC/RF dispersion along with proven reliability needs to be addressed and demonstrated before the technology can be adopted for future RF applications. We will present approaches in transistor design and fabrication developed in part under the DARPA DREaM program aimed at addressing these challenges.