K. Nakano, H. Hanawa, K. Horio
Shibaura institute of Technology,
Keywords: GaN, HEMT, breakdown voltage, double passivation layers, high-k dielectric, two-dimensional analysis
Summary:It is well known that the introduction of field plate increases the breakdown voltage of AlGaN/GaN HEMTs. However, it increases the parasitic capacitance, leading to the degradation of high-frequency performance. As another way to improve the breakdown voltage, using a high-k passivation layer is proposed and analyzed. But, it should have high interface-state densities, degrading the device performance. Therefore, in this study, we propose a structure with double passivation layers where the first passivation layer is a SiN layer having low interface-state densities and the second passivation layer is a high-k dielectric, and study how the breakdown voltage is enhanced. As a result, it is shown that as the thickness of second passivation layer becomes thicker, the breakdown voltage becomes higher because the electric field at the drain edge of the gate is reduced. However, the existence of low-k passivation layer between AlGaN and high-k layers lowers the breakdown voltage significantly. And hence it is concluded that the thickness of first passivation layer should be as thin as possible to achieve the high breakdown voltage of the AlGaN/GaN HEMTs.