Fabrication and Characterization of Gate-Last Self-Aligned AlN/GaN MISHEMTs With <italic>In Situ</italic> SiN<sub><italic>x</italic></sub> Gate Dielectric

Abstract

This paper reports on the fabrication and characterization of gate-last self-aligned <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /AlN/GaN MISHEMTs. The devices featured <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> grown SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> sidewall spacers and low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $ </tex-math></inline-formula> benzocyclobutene polymer ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa =2.65$ </tex-math></inline-formula> ) supporting layers were employed under the gate head to minimize the parasitic capacitance for high-frequency operation. The device with a gate length ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{G})$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.23~\mu \text{m}$ </tex-math></inline-formula> exhibited a maximum drain current density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\rm DS})$ </tex-math></inline-formula> exceeding 1600 mA/mm with a high ON/OFF ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\mathrm{{\scriptscriptstyle ON}}}/I_{\mathrm{{\scriptscriptstyle OFF}}})$ </tex-math></inline-formula> of over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{7}$ </tex-math></inline-formula> . The current gain cutoff frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{T})$ </tex-math></inline-formula> and maximum oscillation frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{\max })$ </tex-math></inline-formula> 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.