A Novel Ring-Gate AlGaN/GaN HEMT Device and Electrode Structure Optimization

In this paper, a novel ring-gate structure AlGaN/GaN HEMT device is proposed and fabricated successfully. When the gate-source spacing Lgs = 5 μm, gate-drain spacing Lgd = 7 μm, gate length Lg = 3 μm, the maximum drain current Idmax of this ring-gate AlGaN/GaN HEMT device improved by 161.8% comparing with the conventional structure device, the threshold voltage Vth increased by 66.7% from 1.65 V to 2.5 V. In order to further improve the performance of the device, a series of electrode structure optimization designs have been carried out. Firstly, the effect of source-drain electrode alloy type and etching depth under source-drain region on the transfer and output characteristics was investigated, we fabricated devices with two alloy electrodes of multi-layer Ti/Al/Ti/Al/Ti/Al/Ni/Au and single layer Ti/Al/Ni/Au, then perform groove etching under the source and drain electrodes, the etching depth is set to 10/20 nm, after analysis and calculation, it is found that among ring-gate and conventional-gate devices, the device with multi-layer electrodes and an etched depth of 10 nm performs best. Then, the influence of device size parameters on transfer and output characteristics was explored, devices with different Lg and Lgd were prepared, after testing it is found that with the increase of Lg, the Vth of the conventional-gate and ring-gate HEMT devices both showed a positive-shift trend, in conventional device Vth increased from 1.53 V to 1.7 V, and this value increased from 1.5 V to 2.5 V in ring-gate device; the saturation drain current decreases when Lg increasing, and the decrease of the ring-gate device is more obvious, from 51.28 mA at Lg = 3 μm to 24.48 mA at Lg = 6 μm; when Lds decreases, the Vth of the two structures doesn’t change significantly, but the output current increases with the reduction of Lds, among them, the Idmax of the conventional structure device at Lgd = 19 um is 79.07% lower than that at Lgd = 7 μm; the value of the ring-gate device is reduced by 113.7%. In addition, among all the above devices, the ring-gate devices all show better output characteristics and higher Vth than conventional devices.