T. Kabemura, H. Hanawa, K. Horio
Shibaura institute of Technology,
Keywords: GaN, HEMT, field plate, high-k passivation layer, breakdown voltage
Summary:It is well known that the introduction of field plate increases the breakdown voltage of AlGaN/GaN HEMTs. This is because the electric field at the drain edge of the gate is reduced. As another way to improve the breakdown voltage, using a high-k passivation layer is proposed and analyzed. So, in this study, we combine the two structures and analyzed the breakdown characteristics of field-plate AlGaN/GaN HEMTs with a high-k passivation layer, and study how the breakdown voltage is enhanced. It is shown that the breakdown voltage is higher when the relative permittivity of the passivation layer is higher, particularly in the region where the field-plate length is relatively short. The breakdown voltage becomes low when the field-plate length becomes relatively long, because the distance between the field-plate edge and the drain becomes short and the electric field in this region becomes very high. Hence, there is an optimum field-plate length to obtain the high breakdown voltage, and it is around 0.2 and 0.3 m in the case where the gate-to-drain distance is 1.5 m. When the relative permittivity of the passivation layer becomes high of 50, the electric field between the field-plate edge and the drain becomes rather uniform, and the breakdown voltage becomes about 400 V which corresponds to an effective electric field of 2.7 MV/cm between the gate and the drain.