Polarization-Engineering of III-N mm-Wave Transistors for High Efficiency and Linearity

III-N-based transistors are leading candidates for RF and microwave applications, and are increasingly being explored for mm-wave applications. While excellent speed [1] and power performance [2] have been achieved, many applications would benefit from further improvements in performance. In particular, the limited linearity of conventional GaN HEMTs necessitates extensive digital predistortion (DPD) correction, and field plates are often used to manage the drain-side electric field. Field plates can be effective at managing the field, but they also result in parasitic capacitance that compromises performance, especially at mm-wave frequencies. These limitations can be addressed by exploiting polarization engineering and compositional grading to go beyond the limits of abrupt-heterostructure device performance. This approach has enabled improvements in mm-wave transistor linearity [3], noise figure and ft/fmax [4], and power scaling and power-added efficiency [5].