The Study of Gold-free Metallization for AlGaN/GaN High Electron Mobility Transistors
Chang, Edward Yi
GaN has drawn much attention for high power and high frequency applications. Au is usually used as Ohmic and gate metal in conventional GaN HEMT. However, as the price of Au getting higher and higher, the processing costs of GaN HEMTs were increased massively. Besides, long-term Au diffusion has been proposed as a serious problem. The penetration of Au into semiconductor subtract would cause device failure. To replace traditional gold metallization on GaN, the Au-free metallization was studied for lower costs and better reliability. Instead of the traditional Ti/Al/Ni/Au, Ti/Al/W was used for ohmic contacts in this study, and the bias stress test has been done for the Ohmic structure. The result shows that the drain-source currents remain at about 62mA/mm even stressed under 100 V after 15 hours. However, the conventional Ti/Al/Ni/Au Ohmic structure devices crashed after 44 minutes stressing. This result indicates that the Ti/Al/W Ohmic structure shows better resistance to high voltage. Instead of Ni/Au, WNx was used for Schottky contact metal. The WNx Schottky contact shows good thermal stability. The devices have low leakage current even after annealing at 700℃ for 5 minutes. These results indicate that Au-free metallization process can be used on GaN HEMT and show good reliability performance.
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