Novel double deck gate field plate structure on a normally-off AlGaN/GaN HEMT- An extensive analysis

A novel double deck gate field plate structure on a normally-off AlGaN/GaN HEMT is proposed and compared with the conventional no field plate structure. Several passivation materials with relative permittivity (ε_r) ranging from 3.9 to 22 is taken into consideration to study the breakdown and DC characteristics. The implementation of field plate along with a higher ε_r material helps in improving breakdown voltage (V_Br) as they both decrease the electric field at the gate's drain edge. Aiming device optimization several field plate configurations are studied including tri field plate structure, dual field plate structures and single gate FP structure. Extensive analysis in these structures are done with different lengths of the field plates and distance between source and drain. Distance between source and drain (L_SD) is varied from 8.4 to 13.4 μm, source FP lengths (L_{S_FP}) varies from 1 to 7 μm, gate FP lengths (L_{G_FP}) varies from 0.9 to 2.3 μm and drain FP lengths (L_{D_FP}) varies from 0.2 to 4.9 μm. In all scenarios with varying L_SD, V_Br rises with increasing L_SD. For source, gate and drain FP lengths variation, V_Br decreases as it gets longer because the electric field becomes very high. As the distance between the FP edge and the drain becomes narrower with increase in FP lengths, the breakdown occurs at lower voltage. At L_SD 13.4 μm, this novel double deck gate FP structure with conventional drain field plate structure gives highest V_Br of 1660 V and a small R_on of 2.39 Ω mm as compared to other structures. It also outperforms the other three structures in F_T (9.84 GHz) at this particular L_SD. Analysis of the simulated structures shows that the union of gate-drain field plate boosts the V_Br while decreasing the R_on, resulting in improved electrical performance and a wider application range.