Fabrication and Characterization of Gate-Last Self-Aligned AlN/GaN MISHEMTs With In Situ SiNx Gate Dielectric

This paper reports on the fabrication and characterization of gate-last self-aligned in situ SiN_x/AlN/GaN MISHEMTs. The devices featured in situ grown SiN_x by metal–organic chemical vapor deposition as a gate dielectric and for surface passivation. Selective source/drain regrowth was incorporated to reduce contact resistance. SiN_x sidewall spacers and low- $\kappa $ benzocyclobutene polymer ( $\kappa =2.65$ ) supporting layers were employed under the gate head to minimize the parasitic capacitance for high-frequency operation. The device with a gate length ( $L_{G})$ of $0.23~\mu \text{m}$ exhibited a maximum drain current density ( $I_{\rm DS})$ exceeding 1600 mA/mm with a high ON/OFF ratio ( $I_{\mathrm{{\scriptscriptstyle ON}}}/I_{\mathrm{{\scriptscriptstyle OFF}}})$ of over $10^{7}$ . The current gain cutoff frequency ( $f_{T})$ and maximum oscillation frequency ( $f_{\max })$ were 55 and 86 GHz, respectively. In addition, the effect of temperature, from room temperature up to 550 K, on the dc and RF performances of the gate-last self-aligned MISHEMTs was studied.