31 W/mm at 8 GHz in InAlGaN/GaN HEMT With Thermal CVD SiN<sub>x</sub> Passivation
Atsushi Yamada, Yuichi Minoura, N. Kurahashi, Yoichi Kamada, Toshihiro Ohki, Masaru Sato, Norikazu Nakamura
Abstract
The study reports the findings on a quaternary InAlGaN/GaN high electron mobility transistor (HEMT) employing a thermal chemical vapor deposition (TCVD) silicon nitride (SiNx passivation with a record high output power density of 31.0 W/mm in the X-band. We compared the two different SiNx passivation methods, namely, TCVD deposition, and plasma-enhanced CVD (PECVD) deposition, for InAlGaN/GaN HEMTs and investigated the effects on device performance. PECVD SiNx passivation caused a considerable degradation of the two-dimensional electron gas (2DEG) mobility. However, TCVD SiNx could suppress the degradation of 2DEG mobility, resulting in a low sheet resistance of 293 ohm/sq. with a high 2DEG mobility of 2048 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}}\text{V}^{-{1}}\text{s}^{-{1}}$ </tex-math></inline-formula> . Furthermore, InAlGaN/GaN HEMT with TCVD SiNx passivation exhibited a high-drain current of 1230 mA/mm even after off-state stress due to the reduced current collapse and low sheet resistance. The off-state breakdown voltage increased from 169 to 227 V on using TCVD SiNx despite an increase in the maximum drain current, resulting in a high voltage of 90 V at radiofrequency. We successfully demonstrated the state-of-the-art high output power density GaN-based HEMTs with an InAlGaN barrier and TCVD SiNx passivation. Our results revealed that TCVD SiNx passivation can facilitate the application of InAlGaN/GaN HEMTs for high-power amplifiers.