TCAD study of high breakdown voltage AlGaN/GaN HEMTs with embedded passivation layer

The breakdown characteristics of AlGaN/GaN high-electron-mobility transistors are one of the most important parameters for practical applications when used as power devices. In this study, the relationship between the relative permittivity of the passivation layers and the breakdown voltages in the off state was investigated in detail using TCAD simulations. An embedded double-passivation layer was proposed to enhance the breakdown voltage of the devices. This device structure was realized using an additional step of etching and opening holes on the edge of the gate metal, followed by the deposition of the embedded passivation films. The extracted electric field shows that this embedded passivation layer not only can improve the breakdown characteristics of the device like using a single high-k passivation film but also presents as the function of the 'Metal Field Plate', additionally resulting in the enlarged breakdown voltage. Further theoretical simulations indicated that the greater the difference between the dielectric constants of the high/low passivation materials, the higher the breakdown voltage can be obtained.