Novel T-Shaped Gate With Air Gap for AlGaN/GaN HEMTs on Silicon With High Johnson's Figures of Merit

• Published in: IEEE transactions on electron devices 2024-05, Vol.71 (5), p.2943-2949
• Main Authors: Liu, Xiaoyi, Chen, Jingxiong, Jiang, Yuanxi, Bian, Kairan, Wang, Hong
• Format: Article
• Language: English
• Subjects: Air gap; Air gaps; AlGaN/GaN HEMT; Aluminum gallium nitrides; breakdown voltage; Electric fields; Figure of merit; Gallium nitrides; Hafnium oxide; HEMTs; High electron mobility transistors; Logic gates; MODFETs; Passivation; Passivity; Radio frequency; Semiconductor devices; Silicon dioxide; Silicon substrates; T shape; T-shaped gate
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2024.3381101

We present high-performance AlGaN/GaN high-electron-mobility transistors (HEMTs) fabricated on a silicon substrate featuring a novel T-shaped gate. The incorporation of the air gap between the gate and the low-k passivation layer effectively reduces the gate capacitance and thus improves the RF characteristics of the device. The prepared device with a gate length of 180 nm has a unit current gain cutoff frequency ( {f} _{{\text {T}}} ) of 55.2 GHz, a maximum oscillation frequency ( {f}_{{\text {MAX}}} ) of 73.7 GHz, and a three-terminal OFF-state breakdown voltage ( \text{B}{V} _{{\text {gd}}} ) of 143 V at the gate-drain distance of 2.2~\mu \text{m} . The estimated Johnson's figure of merit (J-FOM = \text{B}{V} _{{\text {gd}}} \times {f}_{{\text {T}}} ) is 7.9 THz \cdot \text{V} , representing a significant 30% improvement in comparison to the device with only stacked passivation layers. Besides, the J-FOM surpasses that of the single HfO2 passivation and single SiO2 passivation devices by 64.6% and 58%, respectively. These results clearly indicate that the AlGaN/GaN HEMTs with novel T-shaped gate design have great potential for radio frequency (RF) power device applications.