Linearity Improvement with AlGaN Polarization-Graded Field Effect Transistors with Low Pressure Chemical Vapor Deposition Grown SiNx Passivation

In this letter, we discuss the application of low pressure chemical vapor deposition (LPCVD) grown SiNx passivation-first process to improve the power density and linearity performance of a metal oxide chemical vapor deposition (MOCVD) grown AlGaN channel polarization-graded field-effect transistor (PolFET). Significantly improved dispersion behavior was observed compared to plasma enhanced chemical vapor deposition (PECVD) grown SiNx passivation. The Current collapse at 30 V drain quiescent condition for pulsed I-V was reduced to 8% (LPCVD) from 25% (PECVD). 10 GHz load-pull measurement showed a maximum output power density of 3.4 W/mm with a peak power added efficiency (PAE) of 40%. Two-tone intermodulation distortion measurement at 10 GHz for devices with $150\boldsymbol {\mu }\text{m}$ width revealed an OIP3 of 39 dBm and an excellent corresponding linearity figure of merit OIP3/ $\text{P}_{{\textit {DC}}}$ of 13.3 dB. This is the best device level OIP3/ $\text{P}_{{\textit {DC}}}$ reported to date at X-band for III-Nitride microwave transistors.