Performance Trade-Offs and Optimization of Single and Dual-Layer Passivation AlGaN/GaN HEMTs with Double-Deck Gate Field Plate

This study presents a comprehensive evaluation of AlGaN/GaN-based high electron mobility transistors (HEMTs) with various passivation schemes, providing critical insights for device optimization. HfO2-passivated devices exhibit superior breakdown characteristics, achieving a remarkable breakdown voltage (Vbr) of 788 V, which confirms the advantage of high-k dielectrics in enhancing voltage withstand capability. In contrast, SiO2-passivated HEMTs exhibit optimal radio frequency (RF) performance, including the highest cut-off frequency ( fT), which is attributed to their lower parasitic capacitance, making them ideal for high-frequency applications. This reflects a fundamental trade-off between breakdown strength and frequency response in HEMT devices. To overcome this limitation, a dual-passivation approach is investigated. Type-A exhibits superior DC performance, with higher drain saturation current (Idss), transconductance (gm), and Vbr, owing to the stronger gate control and electric field modulation provided by the high-k HfO2 top layer. Both dual-layer passivation schemes significantly enhance Vbr (~798 V for Type-A, ~797 V for Type-B) compared to single-layer passivation. In RF analysis, Type-B (Si3N4 on top, HfO2 below) outperforms Type-A. Although Type-A exhibits higher fT up to 0.4 µm, thicker HfO2 increases parasitic capacitances, degrading GFP, TFP, and GTFP. In contrast, Type-B improves with thicker Si3N4, validating the advantage of placing a low-k on top of a high-k dielectric. Considering composite FOMs (TFP, GFP, GTFP, VEA, AV), Type-B achieves superior overall RF performance.