Enhancement of breakdown voltage in AlGaN/GaN high electron mobility transistors using a field plate

We investigate the breakdown (V_br) enhancement potential of the field plate (FP) technique in the context of AlGaN/GaN power HEMTs. A comprehensive account of the critical geometrical and material variables controlling the field distribution under the FP is provided. A systematic procedure is given for designing a FP device, using two-dimensional (2-D) simulation, to obtain the maximum V_br , with minimum degradation in on-resistance and frequency response. It is found that significantly higher V_br can be achieved by raising the dielectric constant (ε_i) of the insulator beneath the FP. Simulation gave the following estimates. The FP can improve the V_br by a factor of 2.8-5.1, depending on the 2-DEG concentration (n_s) and ε_i. For n _s=1×10¹³/cm², the V_br can be raised from 123 V to 630 V, using a 2.2 μm FP on a 0.8 μm silicon nitride, and 4.7 μm gate-drain separation. The methodology of this paper can be extended to the design of FP structures in other lateral FETs, such as MESFETs and LD-MOSFETs