Demonstration of $>$ 8-kV GaN HEMTs With CMOS-Compatible Manufacturing on 6-in Sapphire Substrates for Medium-Voltage Applications

Traditional GaN HEMTs on silicon suffer relatively low lateral and vertical blocking voltages and thick buffers, which impede their use in $\bm{\ge} $ 1.2-kV applications. In this work, the prototypes of 8-kV GaN HEMTs on 6-in sapphire are successfully fabricated using CMOS-compatible processing. An etch-stop nitride layer AlN in the in situ SiN cap precisely defines the gate dielectric thickness. Au-free low-temperature ohmic contact and metal I are achieved by Ti/AlCu/Ti/TiN, and gate metal is achieved by TiN/Ti/AlCu/Ti/TiN, which significantly reduces the material cost. The high mechanical strength of sapphire results in low nonuniformity and well-controlled warpage, enabling the use of a 1.5- $\bm{\mu} $ m buffer. The fabricated HEMTs with an $\textit{L}_{\text{GD}}$ of 100 $\bm{\mu} $ m exhibit a low $\textit{R}_{\text{ON}}$ of 52 $\bm\Omega \cdot$ mm and a stable $\textit{V}_{\text{TH}}$ of $-$ 20 V. Benefiting from high-quality in situ SiN passivation, the dynamic $\textit{R}_{\text{ON}}$ and $\textit{V}_{\text{TH}}$ shift are maintained within 2.5% and 10%, respectively. The OFF-state breakdown voltage (BV) is increased beyond 8 kV using a simple device structure with only two field plates. The proposed low-cost and CMOS-compatible 8-kV GaN HEMTs fabricated on 6-in sapphire highlight an extremely simple epitaxy process, lateral device structure, and processing flow. Therefore, they offer great potential for serving future medium-voltage applications.