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

Abstract

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 (V_br) 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 ( f_T), 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 (I_dss), transconductance (g_m), and V_br, 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 V_br (~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 f_T 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, V_EA, A_V), Type-B achieves superior overall RF performance.