Enhanced Operational Characteristics Attained by Applying HfO(2) as Passivation in AlGaN/GaN High-Electron-Mobility Transistors: A Simulation Study

This study investigates the operating characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) by applying HfO(2) as the passivation layer. Before analyzing HEMTs with various passivation structures, modeling parameters were derived from the measured data of fabricated HEMT with Si(3)N(4) passivation to ensure the reliability of the simulation. Subsequently, we proposed new structures by dividing the single Si(3)N(4) passivation into a bilayer (first and second) and applying HfO(2) to the bilayer and first passivation layer only. Ultimately, we analyzed and compared the operational characteristics of the HEMTs considering the basic Si(3)N(4), only HfO(2), and HfO(2)/Si(3)N(4) (hybrid) as passivation layers. The breakdown voltage of the AlGaN/GaN HEMT having only HfO(2) passivation was improved by up to 19%, compared to the basic Si(3)N(4) passivation structure, but the frequency characteristics deteriorated. In order to compensate for the degraded RF characteristics, we modified the second Si(3)N(4) passivation thickness of the hybrid passivation structure from 150 nm to 450 nm. We confirmed that the hybrid passivation structure with 350-nm-thick second Si(3)N(4) passivation not only improves the breakdown voltage by 15% but also secures RF performance. Consequently, Johnson’s figure-of-merit, which is commonly used to judge RF performance, was improved by up to 5% compared to the basic Si(3)N(4) passivation structure.