Passivation-layer thickness and field-plate optimization to obtain high breakdown voltage in AlGaN/GaN HEMTs with short gate-to-drain distance

摘要

A two-dimensional analysis of the off-state breakdown characteristics in field-plate AlGaN/GaN HEMTs is performed. The gate-to-drain distance is 1.5 mu m, and the parameters are the SiN passivation-layer thickness d and the field-plate length L-FP. For a moderate d of 0.1 mu m, the breakdown voltage V-br increases with L-FP, and takes an maximum value (similar to 400 V) around LFP = 0.3 mu m, and decreases when L-FP becomes even longer. This decrease is attributed to the fact that the drain voltage is almost applied along the region between the field plate and the drain. For thin d = 0.03 mu m, V-br becomes relatively low (= 150 V) when L-FP becomes long (0.6 mu m). This is attributed to the fact that when d is very thin, the field plate acts like a gate electrode. When d is relatively thick (= 0.3 mu m), V-br decreases at L-FP = 0.3 mu m as compared to the case of d = 0.1 mu m, and it decreases to 250 V at d = 0.5 mu m. This is because the field-plate effects become weak for thick d. The optimum thickness of the SiN passivation layer is approximately 0.1-0.2 mu m and V-br peaks at approximately 400 V when L-FP = 0.3 mu m. The novelty of this paper is to show the dependence of V-br on the passivation-layer thickness d and the field-plate length L-FP when the gate-drain distance is short.