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

Abstract

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 μm, and the parameters are the SiN passivation-layer thickness d and the field-plate length LFP. For a moderate d of 0.1 μm, the breakdown voltage Vbr increases with LFP, and takes an maximum value (~400 V) around LFP = 0.3 μm, and decreases when LFP 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 μm, Vbr becomes relatively low (≤150 V) when LFP becomes long (≥ 0.6 μm). 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 μm), Vbr decreases at LFP = 0.3 μm as compared to the case of d = 0.1 μm, and it decreases to 250 V at d = 0.5 μm. 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 μm and Vbr peaks at approximately 400 V when LFP = 0.3 μm. The novelty of this paper is to show the dependence of Vbr on the passivation-layer thickness d and the field-plate length LFP when the gate-drain distance is short.