High-voltage AlGaN/GaN heterostructure field-effect transistors (HFETs) with graded gate field-plate (FP) structures were fabricated to investigate the effectiveness of a linearly graded FP structure on current collapse. To improve the reproducibility of the FP structure manufacturing process, a simple process for a linearly graded SiO 2 profile formation was developed. A HFET with a 238-angle FP exhibited a significantly decreased on-resistance increase ratio of 1.16 after application of a drain bias of 600 V.Introduction: AlGaN/GaN heterostructure field-effect transistors (HFETs) are promising switching power devices since they can allow for extremely low switching and static losses even at very high frequency operation. To realise the high-voltage operation of HFETs, solving the problem of the increase in on-resistance (R on ) due to a phenomenon known as 'current collapse' is critical. Field-plate (FP) structures effectively suppress current collapse [1,2]. The effects of these conventional FP structures are, however, insufficient because an electric field still concentrates at the gate edge and the FP electrode edge. Therefore, a linearly graded FP structure is appropriate for HFETs because it disperses electric field concentration and minimises peak electric field strength [3]. However, there are few reports of HFETs with these structures because of difficulties in the manufacturing process [4].In this Letter, to investigate the effectiveness of a linearly graded gate FP structure, we report having developed simple and reproducible linearly graded FP manufacturing processes and having applied them to the fabrication of AlGaN/GaN HFETs.
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